1!7/10/2002 12:05:00 PM!Sustainable Garden Brochure1!McPherson, E.G!1999!Sustainable Garden Demonstration!Miscellaneous!Sustainable Garden!1/cufr_1.pdf!PDF!Sustainable Garden Brochure1!sustainable garden, rainwater, roof runoff, landscape irrigation!The Sustainable Garden is an outdoor laboratory for students, faculty, home gardeners, and landscape professionals to learn more about effective multipurpose solutions to regulating the flow of water, energy, and materials through urban ecosystems!
2!7/10/2002 12:06:00 PM!Sustainable Garden Materials and Costs!McPherson, E.G!1999!Sutainable Garden Materials!Miscellaneous!Sustainable Garden!1/cufr_2.pdf!PDF!Sustainable Garden Materials and Costs!Sustainable, garden!!
3!7/10/2002 12:06:00 PM!UCD's Sustainable Garden Debuts!Weinshilboum, D!1999!The Davis Enterprise!Articles in Periodicals!Sustainable Garden!1/cufr_3.pdf!PDF!Sustainable Garden Enterprise Article!!!
5!7/10/2002 5:15:00 PM!Proceedings of the Best of the West summit; 1998; San Francisco!McPherson, E.G. and S. Mathis (eds)!1999!Davis, CA: UC Davis College of Agricultural and Environmental Sciences!Conference Proceedings!Best of the West Summit!cufr_5_EM99_24.PDF!PDF!McPherson, E.G. and S. Mathis (eds). 1999. Proceedings of the Best of the West summit; 1998; San Francisco. Davis, CA: UC Davis College of Agricultural and Environmental Sciences. 93!!!
6!7/10/2002 5:17:00 PM!Perspectives on research and development needs in urban and community forestry!Salwasser, H. and E.G. McPherson!1999!In: McPherson, E.G. and S. Mathis, (eds). Proceedings of the best of the West summit; 1998; San Francisco. Davis: UC Davis College of Agricultural and Environmental Sciences!Articles in Conference Proceedings!Best of the West Summit!cufr_6_HS99_75.PDF!PDF!Salwasser, H. and E.G. McPherson. 1999. Perspectives on research and development needs in urban and community forestry. In: McPherson, E.G. and S. Mathis, (eds). Proceedings of the best of the West summit; 1998; San Francisco. Davis: UC Davis College of Agricultural and Environmental Sciences: 66-71!!Research and development in urban and community forestry has potential to enhance the visibility and management of urban forests in the West. We explore this potential by first presenting our perspective on the value of urban and community forestry as a platform from which people connect with the land and each other. We explain the need for urban forest science to substantiate the claims we make about the benefits of trees and as a basis for sound resource management. Looking to the future, we identify social and demographic trends that will influence how we conduct research and disseminate findings and technologies. Several specific issues that are likely to require research in the West are described. Finally, we assess the availability of resources for research and development to support the growth of urban and community forestry in the West!
7!7/10/2002 5:20:00 PM!Green parking lots: can trees improve air quality?!Scott, K., J. Simpson and E.G. McPherson!1999!In: McPherson, E.G. and S. Mathis, (eds). Proceedings of the best of the West summit; 1998; San Francisco. Davis: UC Davis College of Agricultural and Environmental Sciences!Articles in Conference Proceedings!Best of the West Summit!cufr_7_KS99_76.PDF!PDF!Scott, K., J. Simpson and E.G. McPherson. 1999. Green parking lots: can trees improve air quality?. In: McPherson, E.G. and S. Mathis, (eds). Proceedings of the best of the West summit; 1998; San Francisco. Davis: UC Davis College of Agricultural and Environmental Sciences: 86-87!!Ozone is a serious air pollution problem in most large U.S. cities. In the Sacramento County metropolitan area, motor vehicles are a major source of ozone precursors, contributing approximately 59 tons per day (tpd) (68% of total) nitrogen oxides (NOx) and 59 tpd (49% of total) anthropogenic hydrocarbon (HC) emissions. While the bulk of HC emissions are from tailpipe exhaust, approximately 9.7 tpd (16%) are from evaporative emissions that occur during daytime heating of fuel delivery systems of parked vehicles. Evaporative emissions, as well as exhaust emissions during the first few minutes of engine operation (primarily NOx), are sensitive to local microclimate. Many municipalities in the West also have parking lot shade tree ordinances, which require that parking lots be designed to achieve 50% tree canopy cover within 15 years of construction. While originally viewed by ordinances as an aesthetic amenity, parking lot trees may provide important environmental benefits. In the pilot study described here, we posit a relationship between tree cover, parking lot microclimate and vehicle emissions!
8!7/10/2002 5:22:00 PM!A conceptual framework for the study of human ecosystems in urban areas!Pickett, S.T.A., W.R. Burch, Jr., S.E. Dalton, T.W. Foresman, J.M. Grove and R.A. Rowntree!1997!Urban Ecosystems. 1!Articles in Journals!Miscellaneous Publications!!PDF!Pickett, S.T.A., W.R. Burch, Jr., S.E. Dalton, T.W. Foresman, J.M. Grove and R.A. Rowntree. 1997. A conceptual framework for the study of human ecosystems in urban areas. Urban Ecosystems. 1: 185-199!!!policy !
10!7/10/2002 5:25:00 PM!Research in urban forestry!McPherson, E.G!1996!Forestry Research West. May 1996!Miscellaneous!Miscellaneous Publications!cufr_10_EM96_61.PDF!PDF!McPherson, E.G. 1996. Research in urban forestry. Forestry Research West. May 1996: 5-6!!!
11!7/10/2002 5:26:00 PM!The critical role of urban forest research!McPherson, E.G. and N.S. Luttinger!1996!Western Arborist. 22(4)!Miscellaneous!Miscellaneous Publications!cufr_11_EM96_20.PDF!PDF!McPherson, E.G. and N.S. Luttinger. 1996. The critical role of urban forest research. Western Arborist. 22(4): 53!!!
12!7/10/2002 5:27:00 PM!Toward ecosystem management: shifts in the core and the context of urban forest ecology!Rowntree, R.A!1994!In: Bradley, G.A. (ed). Urban forest landscapes: integrating multidisciplinary perspectives. Seattle: University of Washington Press!Articles in Conference Proceedings!Miscellaneous Publications!cufr_12_RR94_42.PDF!PDF!Rowntree, R.A. 1994. Toward ecosystem management: shifts in the core and the context of urban forest ecology. In: Bradley, G.A. (ed). Urban forest landscapes: integrating multidisciplinary perspectives. Seattle: University of Washington Press: 43-59!!The core of urban forest ecology is the body of scientific knowledge found in the literature. The formation of this core began in the 19505 and 1960s and took shape in the 1970s and 1980s with formal studies of structure and function. During the following ten years, the idea of the urban forest ecosystem was introduced, and is now the basis for further development of the scientific core. The context for this core is provided by statements of public policy and perceptions of land management needs. An important shift is occurring in context as land management organizations, ranging from urban-based alliances to state and federal agencies, embrace the ecosystem concept as an approach to understanding and governing complex mixtures of biophysical and human phenomena using a hierarchy of time and space scales. This rapid shift in context places a burden on the scientific core to articulate and test models of urban forest ecosystems. To accomplish this, an approach to research is needed that will help us understand how urban, periurban, and exurban lands interact functionally with other components of the larger landscape. Part of tlus approach requires scientists and managers to develop a common vocabulary and set of realistic expectations to confront problems of systems complexity and uncertainty!(Millbrook, New York) has helped scientists free themselves of the constraints of viewing the urban forest in jurisdictional or Census Bureau terms by suggesting that we use an "urban-to-rural gradient" of land use intensity to explain the continuum of vegetation change from city to country. Bradley has recently updated a model for understanding the sequence of. land uses along this gradient in a way that illuminates the relationship between the hierarchy of urban-influenced uses and vegetation structures that will occur .along the gradient (Bradley 1984; Bradley and Bare 1993). size and :ture and I surfaces :ne many egetation .~st ecosy-or insects lutrients, :rs. When :tion. The anctional :s and ice manage-atial and ,~d "cata-. with the :osystem. activities ~fa single incorpo-:cological ~mups of :t, census limits), influence s scheme i stands, their current and future status is governed entirely by invisible but powerful i~ili: human processes of land speculation, regulation, taxation, and development. Therefore, their existence is wholly determined by sodoeconomic processes based in the general local urban culture. : ~i-and~. this line of " " s tructure :~..~~-~:i: Following reasoning raises the question Aren t all forests whose ~~iand/or function are predominantly governed by urban-based processes--visible or :5~~:.iinvisible---to be considered urban forests?" Forests whose current and future structure ::~~~Land function are determmed ormopally by urban forces are certainly different from ~"~'forests~ - evolving under nonurban conditions. Further development of th~s hne of reason- ~,.- ,.:~..:. ~%~.. .~ .il :ts spatial . ~onu rban ag of the ,undaries .rbanized jurisdic-:est if we attribute ;ence of a • nutrient yes. SAs may se woods and other ever, one : in these Needed: A Systems Approach Embracing Multiple Scales of Space and Time There is a need for a systems-orientedapproach to guide the core and context of Urban forest ecology into the future. This need .is nurtured by modern changes in the urbanization process and resulting settlement patterns. It is nurtured also by changes in the kinds of questions being asked of scientists and managers. The ease of telecommunicat-ing with modems and faxes encourages more dispersed settlement in high-amenity Toward Ecosystem Management / 47 i.:' .... 2~'T - Eco: exurban wildlands. A portion of the western slope of the Sierra Nevada lies just to the east of Sacramento, California. This area is being populated by people with urban values, urban-generated equity, and urban histories. They have sodoeconomic links with the Sacramento urban area. There are biophysical links as well. The structure of the Sacramento urban forest determines how much automobile-emitted air pollution will migrate on the easterly flow of air to the forests surrounding these homes on the west slope of the Sierra. This air pollution can make ,a critical difference to Sierra forest health. Conversely, the health of the Sierra forests directly affects the people in the Sacramento urban forest. A recent forest fire in the Sierra forests disrupted the water supply and damaged electric-generating capabilities. All of this has an impact on what is done in the Sacramento urban forest. Reduced hydroelectric-generating capacity in the Sierra increases the need for planting energy-saving trees in Sacramento. Another example points up the need to have a systems approach that can link biophysical and socioeconomic relationships across long distances in a meaningful way. McPherson (1991) calculated that 17 percent of the water requirements of a yard tree planted to reduce a householder's air-conditioning energy use was saved by reducing the power plant's cooling water use. If we can account for changes in the flux of energy, pollution, and water across ecosystem boundaries, as in these examples, we will have a truer accounting of the spatial distribution of benefits andcosts resulting from changes in urban forest structures and functions. Because of the way urban forests are linked by a large number of biophysical and human processes to periurban and exurban forests, we need a concept that can take urban forestry forward in both science and management. The ecosystem concept allows the urban forester to see structural and functional characteristics inside the urban forest in relation to characteristics in adjacent vegetation systems. This helps, for example, in understanding the ecological consequences of a city's expansion into undeveloped wildlands, or of urban exotics escaping into native forest stands. We now look at how the ecosystem concept is beginning to dominate the policy-management context for urban forest ecology, today, and what attributes of the concept may govern the future evolution of both core and context of urban forest ecology. RENAISSANCE FOR THE ECOSYSTEM CONCEPT The year 1995 will mark the sixtieth anniversary of the publication of A.G. Tansley's classic paper advancing the notion that "it is the [eco]systems so formed which.., are the basic units of nature on the face of the earth" (Tansley 1935:299). (Readers interested in the development of the ecosystem concept are referred primarily to Go.ley 1993, with examples of important papers available in Real and Brown 1991.) It took more than thirty years before a full articulation of the ecosystem concept in natural resource management was published by leading ecologists and resource scientists (Van Dyne. 1969). Another quarter century had to pass before federal and state land management agencies adopted ecosystem management as policy. This was as bold and challenging a step as the introduction of Pinchot's "multiple use" Concept of the early 1900s. (For a concise review of the early history of forest ecosystem policy, see Caldwell 1970.) The new philosophy requires that the public and private sectors join to plan and manage ecosystems that cross jurisdictional boundaries and comprise multiple ownerships, thus it is particularly important as context for urban forestry. The policy emphasizes that the ecological k t: r f I /- 1 1 t 48 / Rowntree ysical and t can take ept allows ban forest ;ample, in teveloped ak at how ~ntext for :he future m ill l • . i i lti s just to the il|i "ban values, i ...... ks with the ~'; " :~ .... f the Sacra- ;ii ~ill migrate ii ~I: est slope of :~ ~i -est health. ~.::~ ~:::~(~- private property. Nevertheless, federal and state agencies are adopting the'policy,; and ~' .: ~acramento ..~'i Prrio~::eiPoT~o~a N~:r~el~ksi ft?e~c :n~ ~f A agencC~: ;oee: tde°r sP ?g t lt~epolE ciCl~ 2d ~l mpply and : i]~ done in the -v ~:~ :[~ Sierra in- ~t~ n link bio- ' i]~. ngful way. • .1~ yard tree ~i~ 7 reducing 'ii~ of energy, : ~: Ecosystem Management as Context for Urban Forest Science and Practice ~,~.~.~ ~-.~: ~ ~:- will have a ~,.~.~:~ In February 1994, the Chief of the U.S. Forest Service described the main orientation of ~i~ -n changes ~"~::.: ecosystem management as a land policy (USDA Forest Service 1994a): "Ecosystem ~"~i~ management is a holistic approach to natural resource management, moving beyond a : ;'~ i~.~: compartmentalized approach focusing on individual parts of the forest. It's an approach i:~- .. ~.. • ~ -~ that steps back from the forest stand and focuses on the forest landscape and its position .~. • :~:; " in the larger environment in order to integrate the human, biological, and physical Tansley's :h... are nterested 993, with mn thirty .agemen t Another adopted p as the :e review ilosophy hat cross ficularly zological ii dimensions of natural resource management. The purpose is to achieve sustainability of ~, all resources." Applied to urban forest ecology, this would suggest that we stop viewing urban, periurban, and exurban forests as separate compartments and focus on what connects these systems and how actions in one system affect the operation of the systems linked to it. " In most statements about, ecosystem management, Forest Service policy makers have stressed that it is a science-based approach to land management. Thus it is pertinent to ?? our discussion to read how the research branch of this agency has resPonded to the new policy. This research policy statement sharpens the focus of the evolution and develop- ~ ment of urban forest ecology's core and context. The Forest Service Research (FSR) : ~. Strategic Plan for the 1990s (USDA Forest Service 1992) defines three high priority i.-~:.i . research problems that are closely related to the work urban forest scientists do. The ~ headings are taken from the FSR Strategic Plan. I have added comments relating the Plan to urban forest ecology's core and context. :~ :: 1. Understandh~g Ecosysttnns. The FSR plan seeks to understand the basic structure and function of ecosystems. Urban forest ecc)logy examines the l~uman-induced attributes of ~i~i~ ecosystems, specificaUy the results of human land use changes, especially those occur- ~i.:.q ring when land is developed and used for residential, commercial, and industrial ~:'~ 2. Understanding People and Nal~wal Resource Relationships. If we are to grasp the : ecological changes resulting from shifts in land use, and inform land managers. how to i.i[ antidpate and mitigate them, our research should understand those forces motivating spatial and temporal migrations of land uses. This type of demographic, cultural, and :~] sociological information is required if we are to predict where future uses will occur and ~I...~.~;~ '?i Toward Ecosystem Management/49 2.' i, ~, .i• 5 what they will do to the land. In order to assign values(benefits or costs) to alternative ecosystem and/or landscape vegetation structures, we will have to understand what drives those values and how they are best expressed; quantitatively and qualitatively, for different groups of people. 3. Understanding and Expanding Resource Optiopts. The ecosystem management policy implies very strongly that resource options should be preserved for future generations. To do that requires scientists and managers to employ an ecological accounting system that describes who will benefit and who will pay, when and where, for a given resource decision. Ecosystem management is an accounting system that links resource systems in space and in time. How Does Urban Forest Science Respond? For the scientific core and policy context to be efficiently integrated, they must inform one another. Articulation of the general ecosystem management policy followed by the specific ecosystem management research policy is context informing core. How can science respond in order to inform land management? First, it has to identify the central question that will drive the research and advice to management. That central question can be stated as "How do, and how should, vegetation-soil complexes (and associated biophysical attributes of the ecosystem) change as people settle and urbanize the land?" Or, "How do various land uses, manifested in various spatial-temporal patterns, change forest vegetation and soils at different scales of inquiry?" And "How do these patterns translate into benefits and costs?" Part of the problem is we do not fully understand how to develop information about these altered ecosystems, or parts of them, that can be utilized up and down the interscalar ladder. For example, we can examine how effective a tree's shade is in reducing the need for air-conditioning in a house. Up the spatial scale, we can model a neighborhood or town tree-planting program to increase the magnitude of these savings. Further up the spatial scale, we can design a tree-planting plan for an electric utility's service area that comprises hundreds of such towns. But, this proposed increase in tree density will have unknown effects on micro, meso, and macro climates, as it will on regional water, carbon, and hydrocarbon budgets and on regional air quality. There will be some good effects, some bad effects. So, just as we inquired up the ladder of spatial scales we must inquire up the ladder of temporal scales to see who will bear the costs and who will reap the benefits over time. Perhaps, in this example, the current genera tion of householders will bear the cost of planting, a second generation will reap the benefits of lower energy bills, and their children's generation will bear the cost of removing a large population of aging trees. Research must begin by designing studies along three dimensions: (1) from small to large spatial scales, (2) from small to large temporal scales, and (3) from low to high levels of ecosystem disturbance from land uses. The third can be described by experimental sites or domains along a gradiezat from low to high modification of presettlement ecosystem structure. This can be called the "urban-to-rural land use gradient," though it does not always occur in space as a smooth continuum from city to country. The experimental domains are defined by their land use attributes, such as dense commer- cial, sparse residential, or transpot'tation corridor. It is at this point that the types of land use have to be limited to focus the research. For example, urban forest ecology should not include wildland recreational use of a nonresidential character (e.g., hiking, camp- 50 / Rowntree , , : ~ m. I II I I I I I to alternative ~rstand what tualitatively, ~ment policy generations. ~ting system,en resource :e sys terns in nust inform )wed by the .~. How can , the central etation-soil • . as people in various ".ales of in"Jart of the ese altered lar ladder. e need for )d or town the spa tial that corn-will have .~r, carbon, xt effects, st inquire • reap the Iders wiil .~rgy bills, 1 of aging • small to gh levels :rimental :ttlemen t • though .try. The :ommer-s of land should ~, camp- ing). Yet the study of how a second-home residential, commercial, and recreational community set in a mountain forest ecosystem is changing the functional role Of vegetation and soils takes advantage of the core skills of urban forest ecologists. If research is conducted at different spatial and temporal scales, it will illuminate the linkages between knowledge at one scale and knowledge at another. This will also reveal the links between the various experimental domains along the gradient of ecosystem modification. For example, learning that increasing the density of tree cover in an urban center loads ozone precursors (volatile hydrocarbons) on downwind forests (near the rural or unmodified end of the gradient) helps us understand the elusive relations that impart a benefit to one domain (in thi,~ case the urban center) and a cost to another. This approach can result in a nested set of studies from smaller to larger spatial and temporal scales. "Nested" means that the studies are designed, often concurrently, so that results generated at one scale Can be evaluated for use at smaller and larger scales• This interscalar approach is also helpful in building decision support models that will address the scale of, for example, the homeowner who wants to steward his or her trees through a season of drought (a small spatial-temporal scale) to an interagency council wanting to know what the cumulative effects .of private land development in eleven counties will be twenty-five years from now. In evaluating how interscalar information is used, scientists will pay particular aI:tention to two inherent problems: (1) the expam sion of error as small-scale information is "blown up" to larger scales; (2) different variables becoming important at different scales, making it difficult to assume that processes operating at one scale operate similarly at another. What follows is an example of how the questions discussed above can be restated so as to organize studies into two groups. In practice, however, a single study can address both of the following questions: 1. How has presettlement forest struct~lre and fimction changed as a result of different settlement patterns? This work can be conducted at three spatial scales of inquiry~the community, the county, and the mulficounty region. There are various tempora. scales, but the intent is to speak to the problem of long-term, cumulative effects of settlement, tree removal, soil disturbance, and revegetation, including tree planting. Presetflement, and preurban, forest structure is a ba,~eline condition against which changes can be measured and value judgments made• The scales are described below in terms of political units, but the ecosystem approach precludes drawing discrete boundaries around political or jurisdictional areas. In the measurement of both structure and function, the researcher can include adjacent and surrounding areas by looking one level up the scale. C~nmunity Scale. Presettlement forest structure can be documented from historical sources for communities in different forest types (McBride and Jacobs 1975, 1986). Contemporary forest structure and function are specified and compared to presettle-ment structure to learn how community land uses have changed the ecosystem• For example, research in the upper montane Sierra forest type at the community of Bear Valley, California, uses an undeveloped forest nearby as the presettlement "control" forest. The road network and water supply reservoir in Bear Valley have modified the natural distribution of water for meadow and tree growth. A prohibition against tree removal works together with these changes in water distribu Lion to change the trajectory of forest succession from that occurring ,on the control plot (McBride and Rowntree, in preparation)• This study is developing a benefit-cost array that will support a: forest i Toward Ecosystem Management / 51 i t. I. I: I: i I ,i ., i f , . .:,Z .z: .. management plan for Bear Valley that utilizes knowledge about these changes. (The community wishes to arrest succession and manage for early- to middle-seral plant associations.) It is being determined how representative Bear Valley is of all upper montane Sierra communities and to what degree these results can be extrapolated throughou t that forest type. In other regions of the coun try, community scale studies can; for example, examine how exotic tree species (such as Norway maple) compete with, and replace, natives (such as sugar maple), and how imported natives might change the genetic architecture of a local nativepopulation of trees. County Scale. County general plans specify where residential and commercial land uses can occur and at what densities. An example of research at this scale is to take a county plan and determine what changes will occur to forest and ecosystem structure and function as the general plan is implemented. This determination considers both tree removals and tree plantings that, among otlier things, bear on natural regeneration, or lack of it, and the mixing of native and exotic species and genetic material. Future projections are augmented by an analysis documenting historically the cumulative effects of land use change to the present. Work at this scale feeds immediately into regional scale research (Zipperer 1993). Once these structural scenarios are complete, studies under question 2, below, can examine changes to function, such as modified countywide water, carbon, and pollutant fluxes. Regional Scale. Here, information from community and county scales is aggregated upward in spatial scale to a region of abou t three to eleven counties attempting to discern large-scale patterns in land use induced changes. Often, the region under study contains both developed and undeveloped land, and there is a range of land use/vegetation mixtures. At the regional spatial scale, results are often expressed at large temporal scales. For example, a seven-county study of future impacts of residential and commercial land use change employs county general plans as the data base for constructing a twenty-five year "build-out scenario" that is superimposed on the existing vegetation map for the seven-county area. This describes what vegetation changes would occur if building proceeds according to the counties' general plans (Rowntree et al. 1993). The results form the basis for calculating loss of wildlife habitat, changes in visual and recreational quality, and (see question 2 below) changes in regional water, energy, and pollutant patterns. 2. How have fluxes or flows of energy, water, and pollutants changed with land use induced changes in forest structure and fimction? These studies also should be conducted at several spatial scales and seek to understand modified fluxes into, through, and out of the ecosystem oriandscape when land use modifies vegetation and soil structure. Site Scale. Research in urban forest ecology has, for a number of years, measured changes in energy flux resulting from changes in vegetation, particularly as these relate to human benefits and costs, such as studies measuring energy savings to a homeowner from the reconfiguration of trees and landscape plants around the residence to form windbreaks and shade trees (Heisler .986, 1990). Associated changes in water utilization can be calculated for any changes in vegetation configuration that may save energy, and the two are combined to estimate a net savings or cost. Basic research at the site scale seeks to understand the flux of incoming solar radiation as it bears on winter solar heating potential (e.g., amounts "of winter sun transmission through the crowns of different species), human thermal comfort or stress, and human exposure to the ultraviolet (UV) portion of the light spectrum (Yang et al., in press). 52 / Rowntree L~ 'I:G, - ges. (The ~.ral plant all upper "apolated ~dies can, with, and ange the "cial land to take a structure both tree :ation, or ". Future "nulative rely into omplete, nodified ~regated )discern contains getation ~mporal :ommer-ucting a getation occur if 93). The ual and "gy, and : and use ~ducted and out ture. .~asured e relate ~owller :o form .ization o-~/, and te scale ;r solar wns of .~ ultra- Other flux studies at the site scale link: the interaction of energy and water, such as ambient air cooling potential of trees and ground cover in various-configurations. Together with the shading potential of l~rees, evapotranspiration (ET) cooling has the potential for reducing air-conditioning energy use. However, to engage in ET a treeimust have access to soil water, and in urban areas soils are often dry due to rainfall runoff from impervious surfaces or too compacted to hold and deliver sufficient water for effective ET cooling. Thus our research must understand the interaction of these factors (Simpson 1993). In addition, there is potentially a wide range Of "pumping rates" among the species used for residential and commercial planting. Rates at which different natives and cultivars use water, intercept and transmit solar radiation, produce volatile hydrocarbons, absorb noxious gases, and collect airborne particulates should be examined at the site scale to establish basic flux relations, then extrapolated to larger spatial scales. Parking lots are important site-scale research locales. Without trees they become urban heat islands, produce high amounts of polluted runoff, and are places where people bear high heat and UV loads. Tre~.~s modify the energy and water fluxes so that there is less heat and UV stress on people, less heat is advected (horizontally) to adjacent sites,• and less energy and gas (and less air pollution)are used to cool automobile interiors. Research at the site scale can refine these facts, establish relationships, quantify benefits and costs, and form the basis for aggregation to larger spatial scales. Community Scale. Because towns and cities are political jurisdictions, this scale is useful in providing certain types of planning and management information dealing with energy, water, and pollutant flux. Other kinds of information are better passed to managers at the county or regional scale~ Some scientific questions are more effectively addressed by adding a scale between site and community, such as "neighborhood." For example, Simpson (1993) seeks to answer the question "What is the minimum area of trees, at high urban densities, required to•achieve measurable ET cooling?" This requires testing at several scales ranging from site tocommunity. Similarly, Nowak (1994a, b) employs measurements of urban forest leaf area at different scales to estimate the quantity of pollutants removed from the atmosphere. ' Scientists can develop a typology of' experimental sites along the urban-to-rural gradient, such as high density-urban commercial areas, parking lots, quarter acre single-family residential communities, and freeway interchanges. For each type, the range of fluxes for water, energy, and pollutants can be established from empirical measurements and simulation studies that rely on inherent site attributes as well as on the way the site is linked to adjacent sites. County and Regional Scales. Models of water, energy, and pollutant flux can be constructed at the county and regional scales based on relations established at the site and community scales. At file regional scale, we can begin to see interactions betweenlarge urbanizing areas and adjacent forested areas. For example, three of the major urbanizing regions in the West--the Colorado Front, the Salt Lake Valley, and the Sacramento-San Joaquin Valley--are adjacent to major :Forested mountain ranges, and tile urban air pollution affects vegetation, soils, and runoff quality in the mountains. Because' these cities rely on mountain runoff for water, air pollutants can theoretically be returned to the cities in the water. This is an example of how accounting for fluxes between two ecosystems can illuminate the role of the urban forest. Research can now begin to model the fraction of gaseous and particulate air pollution removed from the airstream by various densities and Configurations of urban vegetation in both present and 'future Toward Ecosystem Management / 53 L~ Ur urbanized areas.This will estimate reductions in future air pollution loads on adjacent mountain forest lands. The model can also estimate the production of ozone precursors (volatile hydrocarbons) by the urban vegetation, water use and the effects of runoff, energy' use, and carbon sequestering and storage. DIFFICULTIES WITH THE ECOSYSTEM CONCEPT Whether it is used in core scientific studies or in the policy and management context, the ecosystem concept is not without its problems. For natural systems, some .of these difficulties are minimized. For modified systems where humans are rearranging structure and function, some of these difficulties are exacerbated. The following discussion includes, but is not limited to, problems that confront urban forest ecologists. Where Do Humans Fit In? There are few ecosystems today that haven't been modified, directly or indirectly, by humans. However, a question that comes up early in any discussion about applying the ecosystem concept to human-modified landscapes is "How does one accommodate the activity of humans in a model of structure, function, and flux?" A corollary is "Are humans internal or external to the ecosystem?" (USDA Forest Service 1994b). They can be viewed usefully as both internal and external components. That is, humans are tool-using "megafauna" operating within an ecosystem, albeit with more consequence than other fauna. They rearrange the flux of energy, water, and matter. (In smaller amounts, so does a hummingbird.) In the Sierra Nevada Ecosystem Project (SNEP), analysis proceeds on the assumption that ecosystems are being modified by humans internal to Sierran ecosystems, but also as forces producing fluxes into those systems from outside (SNEP 1994). The point is that ecosystem theory and ecosystem science easily accommodate human activity. In fact, the usefulness of the ecosystem concept to human society may be largely in the area of understanding and guiding interactions between humans and nature. Ecosystem theory incorporates feedback loops, and these can be used to clarify human-ecosystem interaction. For example, humans perceive a given ecosystem state. They evaluate it in relation to their needs andusually make changes. They watch how these changes affect system properties and processes and evaluate the new system state. Further changes are made, and so On. The feedback of human evaluation and modifications into the sequence of ecosystem states either amplifies or dampens the degree to which an ecosystem's trajectory will vary from what would have occurred naturally. Complexity Reality is complex, and the ecosystem concept is a mental construct that attempts to model the real world. When it does fairly well at that, it approaches a complexity that may frustrate its use in science and/or management. The ecosystem concept requires a high level of scientific participation if it is to reach its potential. Can the core of urban forest ecology participate at the reqIaired level? As a science, urban forest ecology is just beginning to deal with complex systems. ? For example, scientists and practitioners have long believed that adding trees will make a city cooler. Tree-planting programs and demonstration projects have been based on this idea. Evapotranspiration (ET) cooling is one of the oldest hypotheses in urban 54/Rowntree adjacent ?cursors f runoff, -text, the of these ~g struc-scussion ~tly, by ying the date the is "Are "hey can lans are equence smaller (SNEP), humans systems ." human e largely • nature. human-te. They )w these m state. ~odifica-egree to wally. :mpts to xity that :quires a Jf urban is just ees will .'n based n urban climatology, yet the scientific information is inadequate to indicate how many degrees reduction in average air temperature will occur with an addition of a number of trees in any given pattern (Simpson 1993). The physics of evapotranspiration and heat transfer suggest that the relationship is based on sound theory. If so, why don't we have a more precise understanding of the relationship? First, the relationship, like so many aspects of urban forest ecology, is more complex than it seems. There is great variation in the rate that different species transpire water. Many urban trees have too little water and too much radiation, and consequently close up their stomata and don't transpire for much of the day. An excessive density of trees restricts airflow, and heat and moisture build up in and below the canopy. Years ago, it was sufficient to assume there was roughly a linear relationship: more trees equals a cooler city. This assumption adequately supported tree-planting programs. Today, however, cities and electric utilities demand a more precise relationship. How many trees in what configuration will bring do.~vn temperatures by how much over how large an area? The more precise relationship is.~'equired for benefit-cost analyses, yet it will be years before scientists can produce these numbers for planners and managers. A similar problem may develop in the context of ecosystem management. At first, the idea is attractive, but we don't appreciate the information and knowledge requirements of implementing it. As time passes, urban forest management becomes committed to it, but scientists cannot participai:e at the level required to make ecosystem analysis and management work. At the outset of this chapter, it was sta ted that we have to understand how the core and context of urban forest ecology inform and support one another. For ecosystem management to work--given its inherent complexity~there has to be (1) improved communication between scientists and managers (i.e., core and context need to efficiently inform one another), and (2) a realistic ratio between program and science funding. Program funds nurture the activities of urban forestry which in turn create the demand level for scientific information. Over the last fifteen years, the ratio between Forest Service program funds (administered to the states by the State and Private Forestry branch of the agency) and funds dedicated to urban forest research has been in a range between 10:1 and 20:1 (program to research). As urban forest ecology shifts to a higher plane of scientific expectation in the context of ecosystem management, the ratio will have to change in order to reduce the disparity between demand for knowledge and the scientific core's ability to provide it.. Uncertainty ; Uncertainty in ecosystem management might be described as the disparity between what we know and what we believe we should know about how these systems work. Because the ecosystem concept is a more complete representation of reality than previous mental constructs, one feels clo!
13!7/10/2002 5:28:00 PM!Urban forestry: forestry's final frontier?!McPherson, E.G!2001!Presentation for the Starker Lecture Series, College of Forestry, Oregon State University, Corvallis, OR. November 15, 2001!PowerPoint Presentations!Miscellaneous Publications!cufr_13_EM01_58.PDF!PDF!McPherson, E.G. 2001. Urban forestry: forestry's final frontier?. Presentation for the Starker Lecture Series, College of Forestry, Oregon State University, Corvallis, OR. November 15, 2001!!!by American Forests are quantifying the loss of tree canopy cover as cities expand. In response, some cities have adopted urban growth boundaries and smart-growth initiatives. Integrating green infrastructure into the land-planning process is a smart-growth principle with implications for the future of forestry and urban forestry (Benedict and McMahon 2002). As the discipline of urban forestry matures, it is approaching convergence with its well-established relative. The concepts of forest structure, function, and value that underpin forest management are finding parallels in urban forestry. Structure Most ecological measures used to describe forest structure can be fruitfully applied to urban forests. Forest structure--the species composition, age diversity, and spatial arrangement of trees and associated vegetation in the landscape--is determined largely by such natural factors as climate, soil types, seed sources, and dispersal processes. Just as influential in urban forests, however, are development patterns that create space for trees, and hum~m management that determines what is planted and removed, as well as how vegetation is manipulated. Urban environments are heterogeneous, a complex mix of land cover types and uses. Like some forests, street tree populations are intensively managed, and at the other extreme, forest stands on urban vacant lots develop in ways similar to rural forest stands (Rowntree 1984). Growing conditions for trees are highly variable. Where trees are well adapted and sites are favorable, growth rates of city trees can be twice those of forest trees because of watering, fertilizing, and reduced competition. Species richness--the number of species in a population--is usually greater in urban forests than in rural forests. In southern California communities, open-grown street tree populations frequently contain more than 200 species. Richness decreases in colder climates, where minimum temperatures reduce the number' of broadleaf evergreen species and preclude palms (McPherson and Rown-tree 1989). However, species composition is similar in both forests and cities when the distribution of individuals ' among species is considered. In both cases, a few well-adapted species tend to dominate. Ecologists have found that forest structures vary along urban-to-rural gradients that extend from city centers, through suburban development, and into the rural hinterlands (McDonnell et al. 1993). Significant variations in climate, soil, flora, and fauna along the gradient reflect the influences of pre-settlement vegetation, people, development patterns, and natural factors April/May 2003 • Journal of Forestry 21 (McBride and Jacobs 1986). Our urban ecosystem studies in Chicago and Sacramento revealed that tree density, basal area, and canopy cover increased along the urban-rural gradient in Chicago but decreased in Sacramento, where surrounding rural lands were largely grassland communities in-. stead of forests (Nowak 1994; McPher-son 1998). Convergence in Structure Tree biometrics. Our preliminary research results suggest that the architecture of open-grown trees differs fundamentally from that of forest trees (McPherson and Simpson 1999). Open-grown trees appear to have substantially more above-ground biomass in their JToliage and branches, whereas forest trees have more biomass in their boles. Al?plying forest-derived biomass equations to calculate air pollutant uptake by urban forests could lead to inaccurate findings. Understanding tree growth and the effects of silvicultural treatments on individual trees in sparse stands is one point of biometric convergence. For example, new biometric information on individual trees "will help the next generation of physics-based fire models better simulate effects of tirol treatments on fire spread at the wildland-urban interface. Characterizing the wildland-urban interface. Very little is known about the structure of this frontier between forest and city. We need, for example, information on relationships among population density, building density, and tree density to better assess the cost-ef-fectiveness of fuel management strategies (DeJong and McPherson, submitted). Also important is the use of remote sensing to detect critical and threatened habitats. Field studies would help us understand how the structure of these habitats is affected by such urban processes as development, introduction of exotic species, and management practices. Canopy change detection. Foresters use the new generation of satellites to obtain hyperspectral, high-resolution data, but this technology has not been applied in cities. We need specific studies to determine the feasibility of using different types of imagery to identify urban tree species, vegetation height, and leaf area. Invasive plants and restoration. Foresters and ecologists study disturbance in forests and natural communities, but we know very little about disturbance and restoration in urban environments. Cultivated landscapes are the dispersion points for many exotic invasive plant species, but methods for assessing and predicting their invasive-ness are lacking. Similarly, there are few guidelines for urban tree selection to prevent the introduction of invasive species to surrounding ecosystems. Ecologists are just beginning to develop a taxonomy of urban disturbances by disturbance agent and community type. Understanding the impacts of disturbances on vegetation structure is the first step toward developing restoration strategies. There are no better laboratories for studying disturbance ecology: than our cities. Function and Value Function, the dynamic operation of the forest, includes biogeochemical cycles, gas exchange, primary productivity, competition, succession, and regeneration. In forests, these functions are largely natural processes; intervention is usually limited to silvicultural practices. In Urban environments, forest functions are frequently related to the human environment. Trees are usually selected, planted, trimmed, and nurtured by people, often with specific intentions, as when a tree is planted in a front yard to shade the driveway ~ind frame the residence. The functional benefits provided by this {ree depend on structural attributes, such as species and location, as well as management activities that influence its growth, crown dimensions, and health. The value of these benefits is highly personal and may be quantifiable (e.g., cooling savings) or intangible (e.g., increased satisfaction). Urban forest functions are thus often oriented toward human outcomes, such as shade, beauty, and privacy. Perhaps the most fundamental difference between forestry and urban forestry is the way trees are valued. Most people believe that city trees are more valuable alive than dead, whereas trees in forests obtain their greatest market value after they are cut (see sidebar). Trees in cities are imbued with meaning; some are landmarks, others are memorials. People develop emotional attachments to trees that give them special status and value. Removing hazardous trees can be difficult when it means severing the connection between residents and the trees they love. For many, feelings of attachment to trees in cities influences feelings for preservation of trees in forests. Convergence in Function and Value Waste-wood utilization. Model waste-wood utilization programs exist in some cities. Lompoc, California, for example, uses a portable mill to make lumber for picnic tables, benches, and tables from Urban sawlogs. Nevertheless, most urban waste wood is chipped for mulch or taken to landfills. Foresters with expertise in wood science, forest products, and economics could assist urban foresters in developing new products from this resource, identifying new markets, and building a substantial consumer base. Urban wildlife. Wildlife connects people with nature. Because people enjoy seeing wildlife in cities, urban forest landscapes need to be designed and managed to nurture desirable urban wildlife and prevent certain species from becoming a nuisance. In the Pacific Northwest, the streams that salmon species inhabit link urban and rural environments. Foresters who manage forestlands with salmon in mind can help urban foresters develop management plans for wooded riparian areas near cities. And they can assist in developing realistic guidelines for landscape design and management that will restore fish to an areas streams. Tree improvement. Foresters who specialize in tree improvement could work with local growers and other members of the green industry to develop improved trees for urban environments. Traditionally, nurseries have selected new introductions for their ornamental or aesthetic attributes, such as flower color, fall leaf color, and crown shape or size. There are other a> tributes, however, that might reduce the costs associated with maintaining 22 Journal of Forestry • April/May 2003 '$1,10"1.30 trees in cities. For example, deep-root-ing patterns could reduce conflicts with sidewalks. Increased tolerance to drought-related stressors could improve survival rates where climates are becoming hotter and drier. Forest Management Forestry has a rich tradition of theory and practice related to forest ecosystem management. Managers view a forest as a collection of stands to be treated as an integrated unit. In the forest, stands are relatively easy to identify because of their distinctive structure and species composition. They are more difficult to discern in cities because the boundaries between plant communities are vague, seldom following environmental gradients. Urban forest stands may coincide with neighborhood development--trees in the same neighborhood are usually planted at approximately the same time and tend to reflect the horticultural preferences of that era (Whitney and Adams 1980). Nevertheless, much like foresters, urban foresters manipulate the composition of species, stand density, and structure to achieve management objectives. They strive to obtain optimal stocking levels for each stand, recognizing that conditions can change from site to Site within an urban forest stand. One forest management concept that has not been very useful for urban foresters is economic rotation. The urban forestry analog is "useful life-span," the" idea that after a species reaches a certain age, the annual cost of its maintenance will exceed the value of its benefits. Urban forest plans have recommended planting tree species with different useful lifespans to promote age diversity. However, this notion has failed in practice because the public seldom allows managers to remove healthy trees solely because they have reached the end of a predetermined useful lifespan. Managing costs is particularly important in urban forests because of the many potential conflicts between trees and the surrounding infrastructure. In California, municipal programs spend, on average, $19 per tree each year to plant, trim, protect, and remove public What Is the Value of a Tree? To answer this question, the net present values (NPV) of a forest tree (Dou-glas-fir, Pseudotsuga menziesil)and a street tree (red oak, Quercus rubra) in Oregon were calculated for 40 years after planting using a 4.5% discount rate (table 1). Costs for planting and managing the street tree are about 60 times greater than for the forest tree (present value, PV, of $463 for red oak and $7 for Douglas-fir). However, the present value of benefits for the city tree Table 1.40-year stream of benefits and costs discounted (4.5%) to their present values (PV) for a typical Douglas-fir in managed forestland and a red oak streettree in Oregon. Dollars Present value Dollars Present value costs per tree benefits per tree Forest tree (Dougias-fir) Site preparation $ 0.39 Timber harvest $ 10.39 Planting 0.93 Brush control 0.34 Preeommercial thinning 0.23 Timber harvest 5.08 Annual administration 0.49. Total $ 7.46 $ t 0.39 Net present value $ 2.93 City street tree (red oak) Planting 122.00 Energy savings 93.09 Pruning 187.03 CO2 reduction 49.15 Removal and disposal 37.50 Air pollutant uptake 36.20 Infrastructure and cleanup 58.58 Stormwater runoff 187.98 Administration and other 58.23 Aesthetics and other 734.88 Total $ 463.33 Net present value $ 637.98 is 110 times greater than the forest tree (PV of $1,101 for red oak and $10 for Douglas.fir). Forty years after planting, the NPV of a Douglas4ir is $3, substantiall,) less than the red oak's estimated $638. This analysis suggests that the value of a city tree is considerably greater than that of a similar-aged forest tree. However, it does not account for other benefitS produced bythe forest tree prior to harvest, such as wildlife habitat and watershed protection. The value of benefits for the city tree are implied, since trees are not paid directly for the ecological and social ser: vices they provide. Prices are based on regional elec{ricity and natural gas prices and control costs that reflect society's willingness to pay for air quality and stormwater runoff improvements. NOTE: The forestland scenario was modeled by FPS; a forest planning tool de, signed by Jim Arney (Oregon Department of Forestry): Pare Overhulser, resource analyst with the Oregon Department of Forestry, provided assistance. The city tree scenario relied on data from the Western Washington and Oregon Community Tree Guide: Benefits, Costs, and Strategic Planting (McPherson et al. 2002). Findings were based on growth curves developed from a sample of 75 red oak street trees in Longview, Washington, computer modeling of benefits;and a regional survey of municipal tree care costs. April/May 2003 • Journal of Forestry 23 trees (Thompson and Ahem 2000). However, annual benefits from a large tree can exceed $1 O0 iMcPherson,et al. 2002). Like foresters, urban forest managers face tradeoffs between short-term eoanomic interests and long-term ecological issues. Short-term interests frequently involve election or budget cycles, but net benefits from trees increase as they live 30 to 50 years or more. The concept of sustained yield of benefits from the urban forest has theoretical application but is difficult to measure (Clark et al. 1997)~. Yield of benefits:, measured as board feet of timber harvested, Watershed values, or wildlife habitat, has been more successfully quantified in forests than in cities. Converg,ence in Management Small-stand management. Many communities have been sculpted from a forest matrix and have, as a result,. scores of small, relict forest stands. Frequently, people and the development process have had heavy impacts on these stands. Foresters need to develop • principles and practices of silviculture for application to small stands. The often-linear shape of these small stands and their roles as connectors, recreational assets, and refugia for native plants arid animals will influence management prescriptions. Decision support for planning. Foresters have developed sophisticated decision support tools, such as GIS mapping, stand growth models; visual assessment simulations, and economic analysis programs. Mthough some' urban foresters use tree inventory, and management systems, these programs lack the decision support technology and visualization capabilities needed to project the future impacts of alterna-• tive management strategies. Forest health monitoring. Urban trees are susceptible to threats from pests and diseases and are subject to a variety of abiotic disorders. Although the USDA FOrest Service and partnering states spend millions of dollars annually to monitor forest health, they spend very little monitoring urban forests. Protection efforts are mounted in reaction to local crises, and remedies are often too late to curb the damage. Many of the concepts developed to monitor forest health apply to trees in cities, but in cities people may be more critical to tree health than the physical environment, in ways both positive and negative. Foresters and urban foresters can develop more holistic approaches for health monitoring. Hazard tree reporting is relevant to foresters in high-use recreational areas as well as in cities. California has a tree failure report program, in which data from tree failures are recorded in a central database (Costello and Berry 1991). Species profiles are develgped that describe how, where, when, and why each species is likely to fail. This volunteer-based program deserves greater support from both the foresfry and the urban forestry communities. Watershed restoration. Watersheds linkthe city with the surrounding forests and provi& a definable organizing structure for studying a region's ecosystem. Foresters and urban foresters could work side by side to determine• how the quality of water, air, soil, vegetation, and wildlife habitat changes from the headwaters of rivers to their confluence with downstream, water-bodies. To address this issue, we need to understand theindividual and cu* mulative effects of urbanization and land management practices on land, air, and water xesources along the urban-rural gradient. A second issue is determining the best management. practices fol~ sustaining healthy watersheds in urban, suburban, and rural lands. Conclusions : As Americans become increasingly urban, urban forests become increasingly important. These forests provide local, regional, and even global benefits. Stewardship of urban forests connects people to nature and to each other. If a new land ethic is going to emerge during the 21st century, it will spring from our cities. The wildland-urban interface is the geographic center of convergence for forestry and urban forestry, but in subtle ways the disciplines are finding common interests along the entire urban-rural gradient. Because forest management will continue to be influenced by the changing attitudes, perceptions, and lifestyles of urban residents, convergence offers mutual bene- fits to forestry and urban forestry. Forestry can benefit from • Working with an urban public that,is more accepting of management. • Connecting urban residents with nearby nature as a pathway for rein-vestment in forest management. • Sharing expertise that urban foresters have acquired by working with diverse stakeholders in the public arena. • Creating more livable cities,• reducing sprawl, and conserving forest-land and the natural resource base it supports. Urban forestry can benefit from • Including more forest management theory in urb~m forestry. • Extending the impressive range of scientific expertise and technological sophistication developed in forestry. • Increasing support by the forest products industry and the academic community. During the past century we have learned how to manage forests for spotted owls and songbirds. We can design zoos that approximate natural habitats for giraffes and chimpanzees. Yet we have not succeeded in protecting green space near cities or creating environments that make people happy. The next frontier is where forestry and urban forestryjoin together to construct healthier habitats for humans. Literature Cited BENEDICT, M.A., and E.T. Mc.MAHON. 2002. Green infrastructure: Smart conservation for the 21 st century. Renewable Resources JournallO (3): 12-17. BRADLEY, G. 1995. Integrating multidisciplinary perspectives. In Urban forest landscapes: Integrating mul-tidisciplinaryperspeetives, ed. G. Bradley, 3-11. Seattle; University of Washington Press. CLARK, J.R., N.P. MATHENV, G. CROSS, and V. WAKE. 1997. A model of urban forest sustainability. Journal of Arboricuhure 23(1):17-30. COSTELLO, L.R., and A.M. BERRY. 1991. The California tree failure report program: An overview. Journal of Arbor;culture 17(9):250-55. DEJONG, L., and E.G. MCPHERSON. Submitted. Application of urban forestry to fire management at the wildland-urban interface. Journal of Arbor;culture. DWYER, J.E, D.J. NOWAK, M.H. NOBLE, and S.M. SISINNI, eds. 2000. Conneeting people with ecosystems in the 21st century: An assessment of the nation's urban forests. General Technical Report PNW-GTR-490. Portland, OR: USDA Forest Service, Pacific Northwest Research Station. journal of Forestry • April/May 2003 , . / HOPKINS, G., ed. 1978. Proceedings of the National Urban Forestry Conference. Volumes 1 and 2. Syracuse, NY: SUNY College of Enviror;mental Science and Forestry. McBPdDE, J., and D. JACOBS. 1986. Presett.ement forest structure as a factor in urban forest development. Urban Ecology 9:245-66. MCDONNELL, M.J., S.T.A. PICKETT, and R.V. POUYAT. 1993. The application of the ecological gradient paradigm to the study of urban effects. In Humans as components of ecosystems: Subtle human effects and the ecology of populated areas, eds. M.J. McDonnell and S.T.A. Pickett, 175-89. New York: Springer-Verlag. MCPHERSON, E.G. 1998. Structfire and sustainability of Sacramento's urban forest. Journal of Arboricuhure 24(4):I 74-90. -. 2000. Expenditures associated with conflicts between street tree root growth and hardscape in California, United States. Journal of Arboriculture 26(6): 289-97. MCPHERSON, E.G., and R.A. ROWNT~E. 1989. Using structural measures to compare twenty-two US street tree populations. Landscape Journal 8(1):13-23. MCPHERSON, E.G., and J.R. SIMPSON. 1999. Carbon dioxide reductions through urban foresW: Guidelines for professional an4 volunteer tree planters. General Technical Report PSW-171. Albany, CA: USDA Forest Service, Pacific Southwest Research Station. MCPHERSON, E.G., S.E. MACO, J.R. SIMPSON, P.J. PEPER, Q. XIAO, A.M. VANDERZANDEN, and N. BELL. 2002. Western Washington and Oregon community tree guide: Benejhs, costs, and strategic planting. Sil-verton, OR: International Society of Arboriculture, Pacific Northwest Chapter. NOWAK, D.J. 1994. Urban forest structure: The state of Chicago's urban forest. In Chicago's urban forest ecosystem: Results of the Chicago urban forest climate project; eds. E.G. McPherson, D.J. Nowak, and R.A. Rown-tree, 3-18. General Technical Report NE-186. Rad-nor, PA: USDA Forest Service, Northeastern Forest Experiment Station. ROWNTREE, R.A. I984. Forest canopy cover and land use in four eastern United States cities. Urban Ecology 8:55-67. TEMPLETON, S.R., and G. GOLDMAN. 1996. Urban forestry adds $3.8 billion in sales to California economy. California Agriculture 50( 1 ):6-10. THOMPSON, R.P., and J.J. AHERN. 2000. The state of "urban and communi{y forestry in California. Technical Report Number 9. San Lu.s Obispo, CA: Urban Forest Ecosystem Institute. WHITNEY, J., and S. ADAMS. 1980. Man as a maker of new plant communities. Journal of Applied Ecology 17:43148. E. Gregory McPherson (egmcpherson@ ucdavis.edu) is director, Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, University of California, Davis, CA 95616-858Z Sales 800-647-5368 Catalog Request: 800-360-7788 ©20~ Fores'm/Suppliers, Inc. All rights reserved. When your job is the outdoors, your work is only as good as the tools you use. That'.s why Forestry Suppliers, Inc., features more than 9,000 top-quality products geared especially to outdoor professionals from agriculture to zoology--and just about all points in-between. Every product we sell comes with the best technical support and customer service in the business, and each is backed by a 100% Satisfaction Guarantee. Check us out for yourself. Give us a call or log on to wtvw.forestry-suppliers.com to get your own free copy of our latest 650 + page catalog today. April/May 2003 • Journal of Forestry 25 :lhe prod uctivity and extensiveneis of southern forests in general, and pine plantations inpar-• ticular, has placed the South at the forefront of production forestry in the United States. That industrial Ioblolly pine plantations are very produdive is a result of researchers and managers developing and applying increasingly intensive silvicultural practices. Our estimates of the percentage of productivity gains attributable to improvements made in individual management practices are based on our collective experience, anecdotal information, and discussions with knowledgeable colleagues. Such informed judgments arebased on potential productivity revealed by designed experiments coupled with estimates of how well technology has been im-plernented. Keywords: economics; plantations; silviculture; timber markets Productivity of SOuthern Pine Plantations 7here Are We and How Did Get Here? I John A. Stanturf, Robert C. Kellison, F.S. Broerman, and Stephen B. Jones A distinctive feature of forestry in t .~ the South is the extensive area . l.of intensively managed loblolly pine (Pinus taeda L.) plantations along the Atlantic and Gulf coasts. Plantations of all types occupy 17 percent of southern timberland (Guldin and Wigley 1998; Conner and Hartsell 2002) and most are privately owned by forest industry or other corporations (Guldin and Wigley 1998). Nonindustrial private forestland (NIPF) owners hold only 10 percent of their land in plantations, although that amounts to 13.8 million acres (Guldin and Wigley 1998; Conner and Hartsell 2002). The scope of plantation management in the South was summarized by Guldin and Wigley: • One of six acres of timberland is a plantation. • Of every 1.00 acres of plantations in the South, 94 are privately owned (54 acres by industry, 40 acres by NIPF owners). • Of the six acres out of 100 acres that are publicly owned, four are in national forests and two are owned by Above: Female cones (left) and male flowers (right) of Ioblolly pine (Pinus toedo t.). 26 Journal of Forestry • April/May 2003!
14!7/10/2002 5:30:00 PM!Urban forestry issues in North America and their global linkages!McPherson, E.G!2000!Presentation for the 20th Session of the North American Forestry Commission Food and Agriculture Organization of the United Nations, St. Andrews, New Brunswick, Canada. June 12-16, 2000!Miscellaneous!Miscellaneous Publications!cufr_14_EM00_66.PDF!PDF!McPherson, E.G. 2000. Urban forestry issues in North America and their global linkages. Presentation for the 20th Session of the North American Forestry Commission Food and Agriculture Organization of the United Nations, St. Andrews, New Brunswick, Canada. June 12-16, 2000!!!by American Forests and others indicate that as temperate climate cities sprawl outward there is loss of tree canopy cover. Land around Puget Sound, Washington was once heavily forested and now has less than 20% tree cover (Glickman, 1999). This de-greening has resulted in loss of critical natural areas and the ecological services they provide. • Planning and Management: Constraints to planning and managing healthy urban forests have been described (Meza, 1992; Tschanz and Sacamano, 1994; Kenney, 1996; Konijnendijk, 1999; Nilsson et al., 2000) and include: • Inadequate funding for municipal tree care programs. This includes resources needed to respond to natural catastrophes (e.g., ice storms, hurricanes) and to conduct urban forest inventories, develop management plans, enforce ordinances, and monitor tree health. • Inadequate space for trees within the urban infrastructure. • Overuse of park and natural spaces. • Harsh growing conditions that make tree survival an achievement. • Lack of information on the tolerances of urban tree cultivars to environmental constraints such as de-icing salts and ozone. • Poor tree selection that creates maintenance problems. • Poor nursery stock and failure to provide adequate care after planting. • Many municipal urban forests are dominated by relatively few species and genetic diversity is limited. • Poor tree care practices by citizens and untrained arborists. • Too few communities have working tree inventories and very few have urban forest management plans. • Limited adoption and enforcement of ordinances that regulate street tree removal and types of species planted, protect trees during construction, preserve heritage trees, and require planting with new development. • Jurisdictional complexity that frequently results in agencies working at cross-purposes or duplicating each other. Development of regionwide policies and standards for best management practices is lacking. • Limited outreach to professionals and residents. • Limited grass-roots participation in tree planting and stewardship. • Lack of public awareness about the benefits of healthy urban forests. New Opportunities and Global Linkages Urbanization is occurring on a global scale, making urban forestry an increasingly relevant aspect of the forestry profession. Urban forests provide benefits that go well beyond their beauty (McPherson et al. 1999). They represent an increasingly precious form of "natural capital" and the ecological services they provide are vital to sustaining • quality of life in our growing communities. Many of these services address issues that are regional and global in scope, such as air quality/climate change, water resource management, and impacts of urban sprawl on natural resources. At the same time, the essence of urban forestry is the people-to-land and people-to-people connections that can transform the way we live. Those connections are made at the grassroots level and they have profound implications for how people care for the land that nourishes their bodies and spirits. There are an imposing number of constraints that need to be overcome before the potential benefits of urban forestry can be realized. Perhaps most acute is the failure of society to fully value the services that judiciously planned and managed urban forests provide. Increasingly we are seeing that livable communities are economically powerful communities; places where a high quality of life attracts the best-educated and trained workers and entrepreneurs, where good schools and strong families fuel creativity and a sense of community. Urban forests are vital components of communities that are striving to be more than plots of bulldozed land, networks of roads, and collections of buildings. Initiatives are needed to demonstrate the potential for urban forestry to enhance quality of life in North American cities. Sustainable Urban Ecosystems For the last 50 years the establishment and care of urban forests has relied on the use of increasingly sophisticated machines, chemical formulations, and technologies with the goal of maximizing plant growth and appearance. Recently, increased environmental awareness has brought attention to some adverse impacts associated with this approach, such as detection of pesticide residues in ground water, sound and air pollution from small engines, and excessive green waste and water use. As the green infrastructure expands we face the challenge of designing and managing landscapes as functioning ecosystems rather than "pictures." The concept of sustainable urban ecosystems recognizes the interconnection of natural resources, human resources, site design, building design, energy management, water supply, waste prevention, and facility maintenance and operation. Sustainable urban ecosystems are landscapes designed and managed to minimize impact on the environment and maximize the value received for the dollars expended in the long term. In principle, they are economically beneficial because the full life cycle of processes and products is evaluated and optimized. Regional Urban Forest Plans Leadership and vision that soars above jurisdictional boundaries is needed to realize the many environmental, social, and economic benefits urban forests can provide. Implementation of regional urban forest plans can foster multi functional regional greenspace systems with connecting corridors and easy access. More efficient delivery of tree care services can result from greater collaboration among agencies. Multiple sets of policies, ordinances, standards, and specifications can be merged. Developing a shared awareness of the benefits healthy trees can produce among the business, utility, and public works communities can generate support for coordinated regional Conclusion urban forest inventory, maintenance, and health monitoring programs. Watershed Restoration Project in North America One wayto implement concepts outlined above is through parallel and collaborative watershed restoration projects. Three "sister" watersheds could be studied, one each in Canada, Mexico, and the U.S. Watersheds or catchments provide a definable organizing structure for study of a region's ecosystem. A central question that this work could address is "How does the quality of water, air, soil, vegetation, and wildlife habitat change/ts one travels from the headwaters of rivers to their confluence with downstream water bodies?" Answering this question requires understanding the individual and cumulative effects of urbanization and land management practices on land, air, and water resources (e.g., watershed health) along the urban-rural gradient. A second question is "What are the Best Management Practices (BMPs) for sustaining healthy watersheds in urban, suburban, and rural lands?" The last question is "How can international and national resources be best applied to facilitate local efforts to create landscapes for sustainable living?" To address these questions a number of steps can be undertaken: 1. Select 3 to 5 catchments along an urban-rural gradient for the demonstration in each region. 2. Assist local collaborators to identify environmental indicators to assess the condition of water, air, forest, and wildlife resources. 3. Develop volunteer-based inventory and monitoring protocols, as well as necessary training materials. 4. Conduct training programs, collect data, and assess baseline conditions for each catchment. Center some plots on school sites and implement educational programs. 5. Using GIS technologies already developed by American Forests and T.R.E.E.S., create maps that display ecosystem structure and environmental conditions for each catchment. 6. Develop an Internet web site to display this information so that residents of each catchment can better understand changing conditions along the urban-rural gradient and differences ~tmong "sister" watersheds in each country. 7. Model and display impacts of current ecosystem structure on fluxes of energy, water and materials. Assess extent to which vegetation and other natural resources regulate/mitigate byproducts of human consumption and quantify the value of ecological services provided by the urban forest. 8. Identify Best Management Practices to improve environmental quality and develop computer-based tools (science education) that students and residents can use to assess impacts and cost-effectiveness of BMPs. 9. Work with local citizenry to implement BMPs and develop "Demonstration Forests" within each catchment to highlight ecosystem management practices. Promote information exchange among sister watersheds. 10. Develop media relations and fund-raising programs to promote reinvestment in management of urban and rural catchments. 11. Evaluate program successes and failures and assess the transferability of this approach to other urban areas in developed and developing countries. A demonstration project to develop, implement, and initially evaluate a community-based watershed restoration process in three highly urbanized regions will foster new partnerships among NAFC entities, within national forestry organizations (e.g., in the U.S. that is the National Forest System, State & Private Forestry, Research), as well as with a variety of urban constituencies. It will advance urban ecosystem science, develop shared goals for creating more sustainable urban ecosystems, prompt development of regional urban forest plans, and leverage new resources for management of our urban and rural forest lands. International organizations such as the North American Forestry Commission can be instrumental in providing support for initiatives that will demonstrate the role and potential of urban forestry. First and foremost is the need for coordinated efforts between countries, research and academic entities, public and private sectors, volunteer groups and individual citizens (Carter, Undated). Implementation of initiatives will improve the knowledge base, strengthen institutional capabilities, encourage local participation, and promote more integrated urban forest planning and management. Acknowledgments References 6 I received very helpful comments on earlier versions of this paper from Drs. Ole Hendrickson (Scientific Advisor -Biodiversity, Canadian Forest Service), Rowan Rowntree (Senior Scientist Emeritus, U.S. Forest Service), Thomas Randrup (Senior Consultant, Danish Forest and Landscape Research Institute), Ed Dickerhoof (Urban Forest Research Liaison, US Forest Service), and Ing. Ruben Lazos Valencia (Executive Director of Special Projects, Natural Resources Commission, Mexico City). Simon Wilkins (Integrated Pest Management, City of Calgary) provided timely informationon urban forestry issues in Canada. Akbari, H., Davis, S., Dorsano, S., Huang, J. and Winnett, S. (Editors), 1992. Cooling Our Communities: A Guidebook On Tree Planting and Light-Colored Surfacing. U.S. Environmental Protection Agency, Washington, DC. Carter, E.J. Undated. The Potential of Urban Forestry in Developing Countries: A Concept Paper. Food and Agriculture Organization of the United Nations, Rome, Italy. Chacalo, A., Aldama, A. and Grabinsky, J. 1994. Street tree inventory in Mexico City. J. Arbor., 20: 222-226. Dwyer, J.F., McPherson, E.G., Schroeder, H.W. and Rowntree, R.A. 1992. Assessing the benefits and costs of the urban forest. J. Arbor., 18: 227-234. Dwyer, J.F., Nowak, D.J., Noble, M.H. and Sisinni, S.M. In Press. Assessing Our Nation's Urban Forests: Connecting People With Ecosystems in the 21 st Century. USDA Forest Service, North Central Research Station, Evanston, IL. Glickman, D. 1999. Keynote Address. In: C. Kollin (Editor), Building Cities of Green: 1999 National Urban Forest Conference. American Forests, Washington, DC. pp. 4-7. Kenney, A. 1996. The State of Canada's Municipal Forests. Urban Forests Centre, University of Toronto, Toronto, Canada. Konijendijk, C.C. 1999. Urban Forestry: Comparative Analysis of Policies and Concepts in Europe. Contemporary Urban Forest Policy-Making in Selected Cities and Countries of Europe, EFI Working Paper 20. European Forestry Institute, Juensuu, Finland. Kuchelmeister, G. 1998. Urban Forestry in the Asia-Pacific Region--Status and Prospects, Asia-Pacific Forestry Sector Outlook Study, Working Paper No: APFSOS/SP/44. Forestry Policy and Planing Division, Rome, Italy. McPherson, E.G. and Simpson, J.R. 1999. Carbon Dioxide Reductions Through Urban Forestry: Guidelines for Professional and Volunteer Tree Planters (General Technical Report No. PSW-171). USDA Forest Service, Pacific Southwest Research Station, Albany, CA. McPherson, E.G., Simpson, J.R., Peper, P.J. and Xiao, Q. 1999. Benefit-cost analysis of Modesto's municipal urban forest. J. Arbor., 25: 235-248. Meza, H.M.B. 1992. Current situation of the urban forest in Mexico City. J. Arbor., 18: 33-36. Nilsson, K., Randrup, T.B., and Wandall, B.I.M. 2000. Trees in the Urban Environment. In: J. Evans (Editor), The Forest Handbook. Blackwell Science, Oxford. Nowak, D.J. 1994. Air pollution removal by Chicago's urban forest. In: E.G. McPherson, D.J. Nowak and R.A. Rowntree (Editors), Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project (General Technical Report No. NE-186). Northeastern Forest Experiment Station, Radnor. pp. 63-82. Nowak, D.J. In Press. The interactions between urban forests and global climate change. In: K. Abdollahi and Z.H. Ning (Editors), The Urban Forest and Global Climate Change. Franklin Press, Baton Rouge, LA. Plumb, T.R., Wolf, M.M. and Shelly, J. 1999. California Urban Woody Green Waste Utilization. Urban Forest Ecosystems Institute, California Polytechnic State University, San Luis Obispo, California. Roberts, L. (Editor) 1996. World Resources 1996-97: The Urban Environment. Oxford University Press, New York, NY. Rowntree, R.A. 1995. Shifts in the Core and the Context of Urban Forest Ecology. In: G. Bradley (Editor), Urban Forest Landscapes: Integrating Multidisciplinary Perspectives. University of Washington Press, Seattle, WA. pp. 43-59. Scott, K.I., McPherson, E.G. and Simpson, J.R. 1998. Air pollutant uptake by Sacramento's urban forest. J. Arbor., 24: 224-234. Simpson, J.R. 1998. Urban forest impacts on regional space conditioning energy use: Sacramento County case study. J. Arbor., 24: 201-214. Taha, H. 1996. Modeling impacts of increased urban vegetation on ozone air quality in the South Coast Air Basin. Atmos. Envir., 30: 3423-3430. Templeton, S.R. and Goldman, G. 1996. Urban forestry adds $3.8 billion in sales to California economy. California Agriculture, 50(1): 6-10. Tschantz, B.A. and Sacamano, P.L. 1994. Municipal Tree Management in the United States. International Society of Arboriculture, Savoy, IL. Xiao, Q., McPherson, E.G., Simpson, J.R. and Ustin, S.L. 1998. Rainfall interception by Sacramento's urban forest. J. Arbor., 24: 235-244. Planning Management of Green Areas in Mexico City Ing. Ruben Lazos Valencia Executive Director of Special Projects Natural Resources Commission and Rural Development Ministry of Environment Mexico City The public green areas in Mexico City are an important civic resource and heavily impacted by users. In the past little thought was given to the type of species planted, funding for long-term maintenance, irrigation design, and visual quality of the landscape. As a result, management was costly. To rectify this situation a plan was created to improve the condition of these green areas and increase their financial self-sufficiency. Three aspects of the plan are Planning, New Technologies, and Maintenance. Prior to the current administration Mexico City had 4 mz of greenspace per inhabitant. Recently, creation of new parks has increased greenspace to 7 m2 per capita, but this amount still falls short of the recommended 9 m2 to 12 m2. The government has two programs to improve the situation: the rehabilitation of existing greenspace that has fallen into disrepair and the creation of new parks. New Technologies Several new concepts are being applied to the design and management of green areas in Mexico City. To avoid overcrowding all new trees are planted a minimum of 8 m apart. Soils that have been altered by addition of earthquake rubble are improved with compost. Plantings are mulched with chipped material from pruned plants and slow release fertilizers are added at the time of planting. Subsidence of land in the old lake bottom of the Valley of Mexico has been compounded by increased impervious surfaces that reduce infiltration of rainwater. Pervious paving materials are now being used that have the same structural characteristics as regular asphalt and concrete, but allow runoff to infiltrate. Another important innovation is "Naturization," the establishment of green areas where there is no space to plant trees because development is so dense. Rooftop gardens are the primary means of achieving Naturization. Drought tolerant species such as succulents native to the region are planted after the roof has been structural reenforced, waterproofed, and a drainage layer constructed into which the planter boxes are'placed. These rooftop gardens keep the city cooler in the summer and trap air pollutants. Maintenance One of the greatest challenges in Mexico City is funding the maintenance of green areas. Although contractors maintain new plantings for one year, funds for subsequent care are often lacking. To create a more sustainable source of funding trust funds are now being established to support park maintenance. A portion of the funds generated from park concessions and advertising are used for maintenance and improvements. Local businesses make tax deductible contributions to the trusts and local councils determine how the funds are spent. Also, private businesses are directly participating in financing and maintenance by "Adopting a Green Area" that borders their land. Using the Best to Make it Better: Applying the Best Practices of Urban and Community Forestry to Make Cities Livable and Sustainable Andy Lipkis, President The T.R.E.E.S. Project TreePeople Los Angeles, California Urban and community forestry holds the key to saving our cities in ways that we could not have envisioned twenty-five years ago when TreePeople first got started. What began as simple tree planting has now grown into a project that extends to urban infrastructure management. I created T.R.E.E.S. (Trans-Agency Resources for Environmental and Economic Sustainability) to achieve an integrated approach to managing the urban ecosystem as an urban/forest watershed through multi-agency partnerships and an educated, empowered citizenry. This unified, systemic approach represents a new paradigm. It also requires profound new levels of education about how to live in a wholesome relationship with nature. It casts individuals and families in the role of stewards-or "urban ecosystem managers., And it allows agencies to serve as educators, facilitators, and monitors rather than as enforcers. The T.R.E.ES. project has four main elements and goals: 1) Re-design urban sites to function as mini urban-forest watersheds; 2) demonstrate that the designs actually work; 3) create a cost-benefit analysis and computer model that quantifies the environmental and social gains-or losses that would come from employing these designs on a large scale basis--i.e.: managing urban infrastructure from an integrated watershed approach; and 4) bring the key agencies and stakeholders together to devise an implementation plan for financing and carrying out a large-scale retrofit of the watershed. Fulfilling the vision of a sustainable city will not take any new money but only a different way of spending what is already being planned. Funds are being spent every day on both new projects and redevelopment projects that could instead be made available for watershed improvement. For instance, the Los Angeles area anticipates an investment of up to $20 billion over the next 10 years in water supply, flood control and stormwater pollution facilities. The maj or differences between the kind of fixes spelled out in T.R.E.E.S. and the huge engineered fixes of the past are that this urban forest watershed approach requires more time for implementation and a high degree of public awareness and participation. However, we are seeing that the multiple benefits of safety, pollution prevention, economic development, and beauty resulting from this approach far outweigh the benefits of single purpose projects. The truly good news is that stakeholder agencies are investing in these approaches. For detailed descriptions of every phase of the T.R.E.E.S. project, please visit our web site at www.treepeople.org/trees. F:\PUBShaafcms4.wlxt!
17!7/18/2002 2:36:00 PM!Effects of urban trees on regional energy use and avoided carbon!Simpson, J.R. and E.G. McPherson!2000!In: Preprints, 3rd urban environment symposium; 2000 August 14-18; Davis, CA. Washington, DC: American Meteorological Society!Articles in Conference Proceedings!Guidelines for Energy Conservation and Carbon!cufr_17_JS00_46.PDF!PDF!Simpson, J.R. and E.G. McPherson. 2000. Effects of urban trees on regional energy use and avoided carbon. In: Preprints, 3rd urban environment symposium; 2000 August 14-18; Davis, CA. Washington, DC: American Meteorological Society: 143-144!!!
18!7/18/2002 2:41:00 PM!Sacramento's urban forest ecosystem!McPherson, E.G!1997!Urban Green Tech. 24!Articles in Conference Proceedings!Sacramento Urban Forest Ecosystem Study!!PDF!McPherson, E.G. 1997. Sacramento's urban forest ecosystem. Urban Green Tech. 24: 23-28!!!costs !
19!7/18/2002 2:44:00 PM!Urban forest ecology: conceptual points of departure!Rowntree, R.A!1998!Journal of Arboriculture. 24(2)!Articles in Journals!Sacramento Urban Forest Ecosystem Study!cufr_19_RR98_84.PDF!PDF!Rowntree, R.A. 1998. Urban forest ecology: conceptual points of departure. Journal of Arboriculture. 24(2): 61-71!Concepts, ecological history!The ecological view in urban forestry evolved from diverse roots beginning over 100 years ago and is currently expressed in formal programs of research and practice. Among the most useful concepts in urban forest ecology are structure, function, diversity, dominance, mosaic-gradients, and ecosystems. These concepts assist in understanding changes in ecological states that produce changes in the distribution of benefits and costs. The ecological history of urban forestry provides these concepts as points of departure for two special issues of the Journal of Arboriculture devoted to the Sacramento urban forest ecosystem!. Toronto, Ont. 417 pp. Bassuk, N., and T. Whitlow. 1988. Ecophysiology of urban trees and their management: The North American experience. Hortscience 23:542-546. Barbour, M.G., J.H. Burke, and W.D. Pitts. 1980. Terrestrial Plant Ecology. Benjamin/Cummings, Menlo Park, CA. 602 pp. Botkin, D.B. 1990. Discordant Harmonies: A New Ecology for the 21 st Century. Oxford Univ. Press, New York, NY. 241 pp. Bradley, G. (Ed.). 1984. The Urban Forest Interface: Land Use and Forest Resources in a Changing Environment. Univ. of Washington Press, Seattle, WA. 222 pp. Clark, J.R., N.P. Matheny, G. Cross, and V. Wake. 1997. A model of urban forest sustainability. J. Arboric. 23:17-30. Costanza, R., B.G. Norton, and B.D. Haskell (Eds.). 1992. Ecosystem Health: New Goals for Environmental Management. Island Press, Washington, DC. 269 p. Derrenbacher, W.E. 1969. Plants and Landscape: An Analysis of Ornamental Plantings in Four Berkeley Neighborhoods. M.A. thesis, University of California, Berkeley, CA. Detwyler, T.R. 1972. Vegetation of the city, pp 229-259. In Detwyler, T.R., and M.G. Marcus (Eds.). Urbanization and Environment. Duxbury Press, Belmont, CA. Dwyer, J.F., H.W. Schroeder, and P.H. Gobster. 1994. The deep significance of urban trees and forests, pp 137-150. In Platt, R.H., Rowntree, R.A., and P.C. Muick (Eds.). The Ecological City: Preserving and Restoring Urban Biodiversity. Univ. of Massachusetts Press, Amherst, MA. Journal of Arboriculture 24(2): March 1998 69 East Bay Hills Vegetation Management Consortium. 1995. Fire Hazard Mitigation Program and Fuel Management Plan for the East Bay Hills. Report prepared by Amphion Environmental, Inc., Oakland, CA. Forest Ecosystem Management Assessment Team. 1993. Forest Ecosystem Management: An Ecological, Economic, and Social Assessment. Report prepared for USDA Forest Service and other federal agencies. Gilbert, O.L. 1989. The Ecology of Urban Habitats. Chapman and Hall, London. 369 pp. Greig-Smith, D. 1983. Quantitative Plant Ecology. Univ. of California Press, Berkeley, CA. 234 pp. Grey, G.S., and F.J. Deneke. 1978. Urban Forestry. Wiley, New York, NY. 279 pp. Heisler, G.M. 1986. Effects of individual trees on the solar radiation cfimate of small buildings. Urban Ecol. 9:337-359. Heisler, G.M. 1990. Mean wind speed below building height in residential neighborhoods with different tree densities. ASHRAE Transac. 96(1):1389-1396. Herrington, L. P. 1980. Preface, p. x-iv. In Hopkins, G. (Ed.). Proceedings, National Urban Forestry Conf, Washington, DC. Nov. 13-16, 1978. SUNY Coll. Envir. Sci. and For., Syracuse, NY. Hopkins, G. (Ed.). 1980. Proceedings, National Urban Forestry Conference, Washington DC., Nov. 13-16, 1978. SUNY Coll. Envir. Sci. and For., Syracuse, NY. International Society of Arboriculture. 1991. Findings from Research Summit on Urban Ecology. International Society of Arboriculture, Savoy, IL. Leblanc, F., and D.N. Rao. 1973. Evaluation of the pollution and drought hypothesis in relation to lichens and bryophytes in urban environment. Bryologist. 76:1-19. Li, H.L. 1969. Urban botany: Need for a new science. Bioscience. 19:882-883. Lipkis, A. 1997. Personal communication. The Tree People, Los Angeles, CA. Lowenthal, D. 1965. Introduction, pp x-xxix In Marsh, G.P. (1864) Man and Nature: Or, Physical Geography as Modified by Human Action. Harvard Univ. Press (Belknap), Cambridge, MA (1965). Marsh, G.P. 1864. Man and Nature: Or, Physical Geography as Modified by Human Action. Harvard Univ. Press (Belknap), Cambridge, MA (1965). McBride, J., and D. Jacobs. 1975. Urban forest development: A case study, Menlo Park, California. Urban Ecol. 2:1-14. McBride, J., and D. Jacobs. 1979. Urban forest structure: A key to urban forest planning. Calif. Agric. 33(5):24. McPherson, E.G. 1993. Monitoring urban forest health. J. Environ. Monitor. Assess. 26:165-174. McPherson, E.G. 1994a. Energy-saving potential of trees in Chicago, pp 95-114. In McPherson, E.G., Nowak, D.J., and R.A. Rowntree (Eds.). 1994. Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. USDA For. Serv. Northeast For. Exp. Sta. Gen. Tech. Rpt. NE-GTR-186. McPherson, E.G. 1994b. Benefits and costs of tree planting and care in Chicago, pp 115-134. In McPherson, E.G., Nowak, D.J., and R.A. Rowntree (Eds.). 1994. Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. USDA For. Serv. Northeast For. Exp. Sta. Gen. Tech. Rpt. N'E-GTR-186. McPherson, E.G. In press. Structure and sustainability of Sacramento's urban forest. J. Arboric. McPherson, E.G., D.J. Nowak, and R.A. Rowntree (Eds.). 1994. Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. USDA For. Serv. Northeast For. Exp. Sta. Gen. Tech. Rpt. NE-GTR-186. McPherson, E.G., and R.A. Rowntree. 1989. Using structural measures to compare twenty-two U.S. street tree populations. Landscape J. 8:13-23. Miller, R.W. 1988. Urban Forestry: Planning and Managing Urban Greenspaces. Prentice-Hall: Englewood Cliffs, NJ. 404 pp. Moll, G. 1995. Urban ecosystem analysis. In Kollin, C. (Ed). 1995. Proceedings of the 7th National Urban Forest Conference, New York, NY, Sept. 12-16, 1995. American Forests: Washington DC. Morel, H., and J. Gottmann. 1961. The woodlands, their uses and wildlife, pp 341-383. In Gottmann, J. (Ed.). Megalopolis: The Urbanized Northeastern Seaboard of the United States. Twentieth Century Fund, New York, NY. Mumford, L. 1956. The natural history of urbanization, pp 382-400. In Thomas, W.L. (Ed.). Man's Role in Changing the Face of the Earth. Univ. of Chicago Press: Chicago, IL. Nowak, D.J. 1992. Urban Forest Structure and Development: An Analysis of Oakland, CA. Ph.D. dissertation, Dept. of Forestry and Resource Mgt., Univ. of California, Berkeley, CA. Nowak, D.J. 1994a. Urban forest structure: The state of Chicago's urban forest, pp 3-18. In McPherson, E.G., Nowak, D.J., and R.A. Rowntree (Eds.). 70 Rowntree: Concepts in Urban Forest Ecology 1994. Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. USDA For. Serv. Northeast For. Exp. Sta. Gen. Tech. Rpt. NE-GTR-186. Nowak, D.J. 1994b. Atmospheric carbon dioxide reduction by Chicago's urban forest, pp 83-94. In McPherson, E.G., Nowak, D.J., and R.A. Rowntree (Eds.). 1994. Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. USDA For. Serv. Northeast For. Exp. Sta. Gen. Tech. Rpt. NE-GTR-186. NE-GTR-186. Nowak, D.J. 1994c. Air pollution removal by Chicago's urban forest, pp 63-82. In McPherson, E.G., Nowak, D.J., and R.A. Rowntree (Eds.). 1994. Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. USDA For. Serv. Northeast For. Exp. Sta. Gen. Tech. Rpt. NE-GTR-186. Nowak, D.J. 1996. Estimating leaf area and leaf biomass of open-grown deciduous urban trees. For. Sci. 42(4):504-507. Nowak, D.J. 1998. Personal communication. Syracuse, NY. Nowak, D.J., R.A. Rowntree, E. G. McPherson, S.M. Sisinni, E.R. Kerkmann, and J.C. Stevens. 1996. Measuring and analyzing urban tree cover. Landscape and Urban Planning 36:49-57. Numata, M. 1975. The impact of urbanization on vegetation in Japan, pp 1-11. In Numata, M. (Ed.). Studies in Urban Ecosystems. Chiba Univ., Chiba, Japan. Platt, R.H., R.A. Rowntree, and P.C. Muick (Eds.). 1994. The Ecological City: Preserving and Restoring Urban Biodiversity. Univ. of Massachusetts Press. Amherst, MA. 291 pp. Pouyat, R.V., M.J. McDonnell, and S.T.A. Pickett. 1995. The effect of urban environments on soil characteristics in oak stands along an urban-rural land use gradient. J. Envir. Qual. 24:516-526 Richards, N.A. 1993. Reasonable guidelines for street tree diversity. J. Arboric. 19(6):344-349. Richards, N.A., and J.C. Stevens. 1979. Streetside space and street trees in Syracuse, New York. Ocas. Publ., Coll. of Environmental Science and Forestry, State Univ. of New York: Syracuse. 73 pp. Rodbell, P.D. (Ed.). 1990. Making Our Cities Safe for Trees: Proceedings of the 4th Urban Forestry Conference, Oct. 15-19, 1989, St. Louis, MO. American Forestry Assoc., Washington DC. Rowntree, L.B. 1994. Afforestation, fire, and vegetation management in the East Bay Hills of the San Francisco Bay Area. Yearbook of the Association of Pacific Coast Geographers. 56:7-30. Rowntree, R.A. (Ed.). 1984a. Ecology of the urban forest--I. Urban Ecol. (special issue). 8(1/2):1-178. Rowntree, R.A. 1984b. Forest canopy cover and land use in four eastern United States cities. Urban Ecol. 8(1/2):55-67. Rowntree, R.A. (Ed.). 1986. Ecology of the urban forest--ft. Urban Ecol. (special issue). 9(3/4):227-440. Rowntree, R.A. (Ed.). 1988. Urban forest ecology--II1. Landscape and Urban Planning (special issue) 15(1-2):1-194. Rowntree, R.A., G. Greenwood, and R. Marose. 1993. Land use development and forest ecosystems: linking research and management in the Central Sierra, pp 389-398. In Ewert, A.W., D.J. Chavez, and A. W. Magill (Eds.). Culture, Conflict, and Communication in the Wildland-Urban Interface. Westview Press, San Francisco, CA. Rowntree, R.A. 1994. Towards ecosystem management: Shifts in the core and context of urban forest ecology, pp 43-59. In Bradley, G.A. (Ed.). Urban Forest Landscapes: Integrating Multidisciplinary Perspectives. Univ. of Washington Press: Seattle, WA. Sampson, R.N., and R.A. Rowntree. 1992. The living city, pp 16-21. In Rodbell, P.D. (Ed.). Alliance for Community Trees: Proceedings of the Fifth National Urban Forestry Conference, Nov. 15-19, 1991. Los Angeles, CA. American Forestry Assoc. Washington DC. Schmid, J.A. 1975. Urban vegetation--A review and Chicago case study. Res. Pap. 161. Dept. of Geography, Univ. of Chicago. Chicago, IL. Seaward, M.R.D. 1979. Lower plants and the urban landscape. Urban Ecol. 4:217-225. Segal, S. 1969. Ecological Notes on Wall Vegetation. Junk, The Hague, Netherlands. 325 pp. Stearns, F.W. 1971. Urban botany: An essay on survival Univ. Wis. Field Stn. Bull. 4(1):1-6. Sukopp, H., H. Blume, and W. Kunick. 1979. The soil, flora and vegetation of Berlin's waste lands, pp 115-134. In Laurie, I.C. (Ed.). Nature in Cities. Wiley, New York, NY. Taoda, H. 1977. Bryophytes in the urban system, pp 99-117. In Numata, M. (Ed.). Interdisciplinary Studies of Urban Ecosystems in the Metropolis of Tokyo. Chiba Univ., Chiba, Japan. Thomas, W.L. 1956a. Introductory, pp xxi-xxxviii. In Thomas, W.L. (Ed.). Man's Role in Changing the Face of the Earth. Univ. of Chicago Press, Chicago, IL. Thomas, W.L. (Ed.). 1956b. Man's Role in Changing the Face of the Earth. Univ. of Chicago Press, Chicago, IL. 1193 pp!
20!7/18/2002 2:46:00 PM!From nature to nurture: the history of Sacramento's urban forest!McPherson, E.G. and N. Luttinger!1998!Journal of Arboriculture. 24(2)!Articles in Journals!Sacramento Urban Forest Ecosystem Study!cufr_20_EM98_19.PDF!PDF!McPherson, E.G. and N. Luttinger. 1998. From nature to nurture: the history of Sacramento's urban forest. Journal of Arboriculture. 24(2): 72-88!Urban forest, forest history, forest management, historical development!Over the course of 150 years, a combination of cultural and natural processes drove Sacramento's transition from City of the Plains to the City of Trees. This paper describes how the many authors of Sacramento's treescape have affected the health, management, and public perception of the city's trees. Local government directed early street and park tree plantings and banned problem tree species by ordinance. During the first half of the 20th century, participation in street tree planting and preservation by groups such as the Chamber of Commerce, Boy Scouts, Science Teachers Association, and "tree enthusiasts" raised public awareness and civic pride. The large trees shading city streets became a community icon, frequently described as the "crowning jewel of Sacramento." More recently, concern about street tree health associated with declining funds for municipal tree care has spawned new partnerships that involve trained volunteers in Dutch elm disease control, residents in energy-conserving yard tree planting, and a public task force in developing policy recommendations to perpetuate Sacramento's legacy as the City of Trees!
21!7/18/2002 2:49:00 PM!Residential tree planting and care: a study of attitudes and behavior in Sacramento, California!Summit, J. and E.G. McPherson!1998!Journal of Arboriculture. 24(2)!Articles in Journals!Sacramento Urban Forest Ecosystem Study!cufr_21_JS98_53.PDF!PDF!Summit, J. and E.G. McPherson. 1998. Residential tree planting and care: a study of attitudes and behavior in Sacramento, California. Journal of Arboriculture. 24(2): 89-97!Urban forestry; tree maintenance; public policy!Site surveys were conducted on residential properties in Sacramento, California, and residents were given questionnaires about whether they had added trees to their properties, their motivations for planting trees, and the extent and frequency of their maintenance of the trees on their properties. These surveys indicate that most residents (68% of the sample) plant trees on their properties; that residential areas are relatively densely planted (with room for about 9% more trees than are already in place); that issues of comfort (shade) and appearance play more of a role in the decision to plant trees than do concerns about energy savings, environmental benefit, or privacy; that tree planting tends to be greatest early in a resident's tenure in a home; and that convenience is a strong predictor of the types of tree maintenance provided by residents relative to that provided by contractors!
23!7/18/2002 2:53:00 PM!Structure and sustainability of Sacramento's urban forest!McPherson, E.G!1998!Journal of Arboriculture. 24(4)!Articles in Journals!Sacramento Urban Forest Ecosystem Study!cufr_23_EM98_15.PDF!PDF!McPherson, E.G. 1998. Structure and sustainability of Sacramento's urban forest. Journal of Arboriculture. 24(4): 174-190!Urban forest development; urban ecology; urban ecosystem!The urban forest of Sacramento County, California, contains approximately 6 million trees. Tree density and basal area decrease along an urban-rural gradient from city (73 trees/ha, 13.4 m2/ha), to suburban (64 trees/ha, 4.5 m2/ha), to rural (10 trees/ha, 0.9 m2/ha) sectors. Within the city and suburban sectors, where 90% of all residents live, approximately 75% of total tree numbers, basal area, and leaf area occurs on residential land. Sacramento's urban forest is relatively sustainable. Seventy percent of the trees are in excellent or good condition, the population is well distributed by age and species, and the most abundant species are reasonably well suited to local conditions. Factors likely to trigger change in Sacramento's urban forest during the next 50 years are described (e.g., water conservation, development patterns, landscape maintenance issues) and species with potential to thrive in these conditions are listed for future planting and evaluation. A comparison of canopy cover, density, and basal area of trees in the city sectors of Sacramento and Chicago, Illinois, reveal surprising similarities. However, in Sacramento these values decrease along the urban-rural gradient, while in Chicago they increase. As human influences wane along the gradient, such factors as climate, soils, competition, and natural regeneration become more important forces in causing urban forest structure to approach presettlement conditions!costs !
25!7/18/2002 2:56:00 PM!Urban forest impacts on regional cooling and heating energy use: Sacramento County case study!Simpson, J.R!1998!Journal of Arboriculture. 24(4)!Articles in Journals!Energy Effects of Urban Forests in Sacramento!cufr_25_JS98_45.PDF!PDF!Simpson, J.R. 1998. Urban forest impacts on regional cooling and heating energy use: Sacramento County case study. Journal of Arboriculture. 24(4): 201-214!!Urban forests impact energy use for cooling and heating as a result of their moderating influence on climate. To evaluate the regional magnitude of these impacts, a large-scale analysis framework was developed and applied to Sacramento County, California, as a case study. Heating, cooling, and peak electrical energy use changes resulting from modification of solar radiation, air temperature, and wind speed by the existing urban forest were estimated for representative residential and commercial buildings. This is combined with building age and size, canopy and tree cover, and tree density (trees/ha) for 71 county subdivisions. Annual cooling savings are approximately 157 GWh (US$18.5 million) per year-12% of total air conditioning in the county. Net effects on heating are small, with 145 T J (US$1.3 million) saved annually. Peak energy-use reductions result in avoided costs of US$6 million. The resulting large-scale analysis incorporates a manageable level of detail not previously available. Sensitivity of results to selected input data is demonstrated!costs !
26!7/18/2002 2:57:00 PM!Atmospheric carbon dioxide reduction by Sacramento's urban forest!McPherson, E.G!1998!Journal of Arboriculture. 24(4)!Articles in Journals!Sacramento Urban Forest Ecosystem Study!cufr_26_EM98_9.PDF!PDF!McPherson, E.G. 1998. Atmospheric carbon dioxide reduction by Sacramento's urban forest. Journal of Arboriculture. 24(4): 215-223!Climate change; urban ecosystem, sequestration!Sacramento County's 6 million trees store 8 million tons of CO2 (31 t/ha), and annually sequester 238,000 t (0.92 V ha). Air-conditioning (157 GWh) and space-heating (145 T J) savings from the urban forest further reduce emissions by 75,600 t of CO2 annually (0.29 V ha). These avoided emissions are only 32% of the amount sequestered, due to a clean, hydroelectric energy supply. Annual CO2 release associated with tree maintenance is estimated at 9,400 t (0.04 t/ha), or 3% of the amount sequestered and avoided. In net, the urban forest removes approximately 304,000 t (1.2 t/ha) each year, with an implied value of US$3.3 million ($0.55/tree). Carbon dioxide reduction by Sacramento's urban forest offsets the total amount of CO2 emitted as a byproduct of human consumption by 1.8%. Most benefits accrue on residential lands in the city and suburban sectors, where rates of storage and sequestration are about one-half those reported for U.S. forests. Guidelines for managing urban forests to reduce atmospheric CO2 are presented!, 41-64. Husch, B., C.I. Miller, and T.W. Beers. 1982. Forest Mensuration. John Wiley and Sons, New York, NY. Jo, H.K., and E.G. McPherson. 1995. Carbon storage and flux in urban residential greenspace. J. Environ. Manag. 45:109-133. Ker, M.F. 1980. Tree Biomass Equations For Ten Major Species in Cumberland County, Nova Scotia. Canadian For. Sew., Maritimes For. Res. Centre. Inf. Rep. M-X-108, 26. Lieth, H. 1963. The role of vegetation in the carbon dioxide content of the atmosphere. J. Geophys. Res. 68:3887-3898. McPherson, E.G. 1994. Using urban forests for energy efficiency and carbon storage. J. For. 92:36-41. McPherson, E.G. 1998. Structure and sustainability of Sacramento's urban forest. J. Arboric. 24(4):174-190. Means, J.E., H.A. Hansen, G.J. Koerper, P.B. Alaback, and M.W. KIopsch. 1994. Software for Computing Plant Biomass--BIOPAK Users Guide. USDA For. Serv. Pac. Northwest Res. Sta. Monteith, D.B. 1979. Whole-Tree Weight Tables For New York. AFRI Res. Rep. 40:67. Moy, K. 1995. SMUD to sign contract to cut global warming. Sacramento Bee. Jan. 17. Norse, E. 1990. Ancient Forests of the Northwest. The Wilderness Society and Island Press, Washington, DC. Nowak, D. 1993. Atmospheric carbon reduction by urban trees. J. Environ. Manag. 37:207- 217. Nowak, D.J. 1994. Atmospheric carbon dioxide reduction by Chicago's urban forest, pp 83-94. In McPherson, E.G., D.J. Nowak, and R.A. Rowntree (Eds.). Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. USDA For. Serv. Northeast. For. Exp. Sta., Radnor, PA. Phillips, D.R. 1981. Predicted Total-Tree Biomass of Understory Hardwoods. USDA For. Serv., Asheville, NC. Pillsbury, N.H., and M.L. Kirkley. 1984. Equations for Total, Wood, and Saw-Log Volume for Thirteen California Hardwoods. USDA For. Serv., Portland, OR. Pillsbury, N., and R. Thompson. 1995. Tree Volume Equations For Fifteen Urban Species in California. Urban Forest Ecosystems Institute. Calif. Polytech. St. Univer., San Luis Obispo, CA. Rowntree, R.A., and D.J. Nowak. 1994. Quantifying the role of urban forests in removing atmospheric carbon dioxide. J. Arboric. 17:269-275. Sacramento Area Council of Governments. 1995. Population estimates for the Sacramento-Yolo CMSA. In 1995 Data Summary. Sacramento, CA. Sherrill, S., C. Sherrill, and M. Romanos. 1997. The nuts and bolts of turning waste trees into good wood. Pop. Woodworking. 17:30-33. Simpson, J.R. 1998. Urban forest impacts on regional cooling and heating energy use: Sacramento County case study. J. Arboric. 24(4):201-214. Simpson, J.R., and E.G. McPherson. 1995. Impact Evaluation of the Sacramento Municipal Utility District's Shade Tree Program. USDA For, Serv. West, Ctr. for Urban For. Res. and Educ., Davis, CA. Simpson, J.R., and E.G. McPherson. 1998a. Simulation of tree shade impacts on residential energy use for space conditioning in Sacramento. Atmos. Environ.: Urban Atmos. 32:69-74. Journal of Arboriculture 24(4): July 1998 223 Simpson, J.R., and E.G. McPherson. 1998b. A tool for evaluating carbon reduction by urban forestry programs, pp 58-61. In Kollin, S. (Ed.). Proceedings of the Eighth National Urban Forest Conference. American Forests, Washington DC. Small, B.M. 1997. Tree Growth under Sacramento Shade. Sacramento Tree Foundation, Sacramento, CA. Standish, J.T., G.H. Manning, and J.P. Demaerschalk. 1985. Development of Biomass Equations for British Columbia Tree Species. Inf. rep. BC-X-264. Can. For. Serv. Pac. For. Ctr., Vancouver, BC. Stanek, W., and D. State. 1978. Equations Predicting Primary Productivity (Biomass) of Trees, Shrubs and Lesser Vegetation Based on Current Literature. Can. For. Sew., Victoria, BC. Summit, J., and E.G. McPherson. 1998. Residential tree planting and care: A study of attitudes and behaviors in Sacramento, Califomia. J. Arboric. 24(3):89-97. Swift, J., and L. Liebe. 1995. Portland Today: Urban Environment Update. City of Portland, Portland, OR. Tritton, L.M., and J.W. Hornbeck. 1982. Biomass Equations for Major Tree Species of the Northeast. USDA For. Sew., Broomall, PA. Wenger, K.F. 1984. Forestry Handbook. John Wiley and Sons, New York, NY. Whittaker, R.H., and G.E. Likens. 1973. Carbon in thebiota, pp 281-302. In Woodell, G.M., and E.V. Pecans (Eds.). Proceedings of the 24th Brookhaven Symposium in Biology, May 16-18, 1972. Upton, NY. US Atomic Energy Commission. Technical Info. Services. Office of Information Services. Young, H.E., J.H. Ribe, and K. Wainwright. 1980. Weight Tables For Tree and Shrub Species in Maine. Life Sci. and Agdc. Exp. Stn. Misc. Rep. 230:84. Pacific Southwest Research Station USDA Forest Service c/o Department of Environmental Horticulture University of California Davis, CA 95616 Resumen. Los 6 millones de &rboles del Condado de Sacramento (California) almacenan 8 millones de toneladas de bi6xido de carbono (31 t/ha), y retiran anualmente 238,000 toneladas (0.92 t/ha). Los ahorros de aire acondicionado (157 GWh) y espacio de calentamiento (145 T J) del bosque urbano reducen adem&s la emisi6n de 75,600 toneladas de bi6xido de carb6n anualmente (0.29 t/ha). Estas emisiones evitadas son solamente 32% de la cantidad retirada, debido a un suministro limpio de energfa hidroel~ctrica. La liberaci6n anual de bi6xido de carbono, asociada con el mantenimiento del arbol, es estimada en 9,400 toneladas (0.04 t/ha), o 3% de la cantidad retirada y evitada. En terminos netos, el bosque urbano remueve aproximadamente 304,000 toneladas (1.2 t/ha) carla afio, con un valor implicado de US$3.3 millones ($0.55 por ~rbol). La reducci6n del bi6xido de carbono por el bosque urbano de Sacramento compensa la cantidad total de bi6xido de carbono, emitido como un producto secundario del consumo humano, en 1.8%. Los mayores beneficios se acumulan en Areas residenciales en la ciudad y sectores suburbanos, donde las tasa de almacenaje y retiro son cerca de la mitad de los reportados para los bosques de los Estados Unidos. Se presentan normas para el manejo de los bosques urbanos con el fin de reducir el bi6xido de carbono atmosf~rico.  10 n/a General softwoods 2.5-55 5-30 Maple 2.5-66 n/a Birch 2.5-51 n/a Pecan 5-51 n/a Hackberry n/a n/a Camphor 13-69 5-17 Dogwood < 12.7 n/a Eucalyptus n/a n/a Ash 5-51 n/a Juniper n/a n/a Walnut n/a n/a Sweetgum 14-54 7-20 Spruce 2.5-66 n/a Pine n/a n/a London plane n/a n/a Poplar 5-84 n/a Aspen 6-35 5-26 Cottonwood 6-32 7-25 Cherry 5-51 n/a Blue oak 10-70 n/a Holly oak 13-52 n/a California black oak 10-110 n/a Valley oak 10-100 n/a Interior live oak 10-70 n/a Giant redwood 97-614 n/a Elm 17-56 n/a Frangi and Lugo 1985 Harris et al. 1973 Monteith 1979 Young et al. 1980 Young et al. 1980 Brenneman et al. 1978 Hahn 1964 Pillsbury and Thompson 1995 Phillips 1981 Pillsbury and Thompson 1995 Brenneman et al. 1978 Hahn 1984 Hahn 1984 Pillsbury and Thompson 1995 Young et a1.1980 Pillsbury and Thompson 1995 Hahn 1984 Ker 1980 Standish et al. 1985 Standish et al. 1985 Brenneman et al. 1978 Pillsbury and Kirkley 1984 Pillsbury and Thompson 1995 Pillsbury and Kirkley 1984 Pillsbury and Kirkley 1984 Pillsbury and Kirkley 1984 Means et a1.1994 Pillsbury and Thompson 1995 was calculated as the difference between CO2 stored in successive years. Annual tree height and diameter growth were calculated for trees in different size classes based on limited measurements of Sacramento street and yard trees with known planting dates (Table 2) (Simpson and McPherson 1995; Small 1997). To account for the fact that dead trees (condition = 0%) should not grow at all and healthy trees (condition = 90%) should grow more than trees in poor condition (condition = 20%), the appropriate annual height and diameter increments selected for each tree in the current year were multiplied by each tree's surveyed condition. These adjusted height and diameter growth increments were added to the current tree height and diameter to estimate dimensions for the next year. It is assumed that there are no changes in tree condition or numbers (no mortality or tree planting) during the hypothetical growing season. Standard errors (se) are reported for estimates of CO2 storage and sequestration (see Appendices A and B in McPherson 1998 [page 189 of this issue] for furTable 2. Annual tree growth increments for different tree size classes used to model carbon dioxide sequestration (units in parentheses are feet and inches), Height Dbh Height growth Dbh growth class (rn) (m/yr) class (cm) (crn/yr) 2-7.9 (6.6-25.9) 0.5 (1.6) 1-24.9 (0.4-9.8) 1.8 (0.7) 6-12.4 (26-40.7) 0.4 (1.3) 25-44.9 (9.9-17.7) 1.5 (0.6) 12.5-14.9 (40.8-48.9) 0.3 (1.0) 45-59.9 (17.8-23.6) 1.0 (0.4) 15-18.4 (49-60.4) 0.2 (0.7) 60+ (23.7+) 0.3 (0.1) 18,5+ (60.5+) 0.1 (0.3) pesticides. Fuel use was converted to CO2 and the average release rate per tree was calculated as kg per cm dbh. Implied costs and per capita emissions. The value to society of reducing atmospheric CO2 (e.g., sea level rise, flooding, habitat loss) is reflected in the implied cost values assigned by state energy commissions. Electric utilities are required to use these values when evaluating the environmental costs associated with different power sources. This study assumes a value of US$11 per t CO2 (California Energy Commission 1992). Because CO2 is an unregulated pollutant, only a few communities have inventoried emissions. Portland, Oregon (Swift and Liebe 1995), and Austin, Texas (City of Austin 1997), estimated annual per capita CO2 emissions at 23 and 15 t per capita, respectively. Because emission data are lacking for Sacramento and the climate and development pattern of Sacramento more closely resemble Austin than Portland, Sacramento emissions are assumed to be 15 t per capita. This value is used to determine the percentage of annual emissions offset by Sacramento's urban forest. 218 McPherson: CO2 Reduction by Urban Forests are assumed to be professionally visited on a 5-year cycle and appropriate release rates are applied to trees in each dbh class. To estimate CO2 release per tree serviced, information was obtained from the Sacramento Tree Services Division on the amount of gasoline, diesel, and oil consumed annually and the number of trees pruned, removed, inspected, and treated with Table 3. Carbon dioxide fluxes for sectors and the entire study area (net value assumes implied price of US$11/t), Sector City se Suburban se Rural se Total se No. trees (1,000s) 1,733 350 2,371 254 1,939 471 6,043 Stored (k ton) 4,060 1,953 1,517 253 2,487 1,062 8,064 Stored (k ton/ha) 172 83 41 7 13 5 31 Sequestered (k ton) 74 16 96 12 68 18 238 Sequestered (k ton/ha) 3.1 0.7 2,6 0.3 0.3 0.1 0.9 Avoided (k ton) 33 35 8 76 Avoided (k ton/ha) 1.4 0.9 0.0 0.3 Released (k ton) 4.0 3.7 1.7 9.4 Released (k ton/ha) 0.2 0.1 0.0 0.0 Net removed (k ton) 103 127 74 304 Net removed (k ton/ha) 4.5 3.5 0.4 1.2 Net value ($) 1,132 1,397 817 3,346 Net value (S/ha) 48 38 4 13 639 2,238 9 27 0.1 and some urban forests (e.g., Oakland, California) have relatively large numbers of small-sized trees, while the city of Sacramento has a higher percentage of large-diameter trees (10% with dbh of > 77 cm [30 in.]). For example, the average amount of CO2 stored per tree in the city of Sacramento is 2,343 kg (5,165 Ib), compared to 336 kg (741 Ib) in Oakland and 759 kg (1,674 Ib) in the city of Chicago. A second factor influencing CO2 storage is tree density. Tree density in the rural sector of Sacramento is 10 trees per ha (McPherson 1998) and CO2 storage is only 13 t per ha (Table 3). Although on average trees are larger in the rural sector than in the suburban sector, the lower tree density yields a lower storage rate. Natural forests (100s to 1,000s trees/ha) and urban forests with large wildland tree cover, such as Oakland (120/ha), tend to have higher tree densities than urban forests. In general, data from Sacramento, Chicago, and other cities indicate that urban forests have fewer, but on average, larger-sized trees per ha compared to natural forests. Although there is great variation in the amount of CO2 stored by different natural forest types, overall, urban forests typically store about one-half as much CO2 as natural forests. Carbon dioxide storage by Sacramento's urban forest varies geographically, reflecting spatial differences in tree size and density (Figure 1). On a per-hectare basis, relatively low rates of storage occur in the rural sector, as well as in the Sacramento core commercial area (see the inset in Figure 1). Older, residential areas surrounding the old city center (Figure 1 inset) have the highest storage rates (100 to 167 t/ha). Storage rates range from 20 to 100 t per ha in the more recently developed suburban areas extending south and northeast from the city center. One corridor runs south following the Sacramento River and Interstate 5. A second corridor extends northeast through progressively more recent suburban development to the Folsom area (Figure 1). Results And Discussion Carbon storage and sequestration. Approximately 8 million t (se = 2.2 million t) of CO2 (31 t/ha) have accumulated and are presently stored in Sacramento County's 6 million trees (Table 3). The city sector's 1.7 million trees store 50% of the total amount stored, or 172 t per ha. Storage per unit land area in the suburban sector is 41 t per ha. In comparison, trees in the cities of Chicago and Oakland store 52 and 40 t per ha on average, respectively (Nowak 1993, 1994). Forest systems in the United States store 202 t per ha (Birdsey 1992); urban forests in the United States are reported to store about 100 t per ha (Rowntree and Nowak 1991). Differences in the diameter distribution of tree populations influences CO2 storage. Most natural forests Journal of Arboriculture 24(4): July 1998 219 5 0 5 10 Sacramento County's 6 million trees are estimated to sequester about 238,000 t (0.92 t/ha) of COs over the course of a year (Table 3). While CO2 is principally stored in the city sector, where the "big" trees are most plentiful, sequestration is greatest in the suburban sector (40% of total), where the largest number of trees are found (2.4 million). Carbon dioxide sequestration rates are similar for the city (3.1 t/ha) and suburban (2.6 t/ha) sectors, but substantially less for the rural sector (0.4 t/ha) due to lower tree density. This pattern is evident in Chicago as well. However, unlike Sacramento, tree density and sequestration in Chicago increase along the urban-to-rural gradient, rising from 2.4 t per ha in the city (69 trees/ha) to 3.8 t per ha in the rural sector (171 trees/ha) (Nowak 1994). Trees in natural forests sequester about twice as much CO2 as urban forests per unit land area, between 4 and 8 t per ha on average (Birdsey 1992). However, Metric tons/Ha SubRADs [] 0.0- 19.9 Roads [] 20.0- 59.9 [] 60.0- 99.9 [] 100.0 - 139.9 15 Mills ' B 140.0 - 167.0 because urban trees tend to grow faster than rural trees, they sequester more CO2 on a per tree basis (Jo and McPherson 1995). Average annual sequestration rates ranged from 35 to 43 and 22 to 36 kg per tree for the three sectors in Sacramento and Chicago, respectively. Avoided power plant emissions. Building shade, summer cooling, and wind-speed reductions attributed to the region's urban forest reduce electricity consumed annually for air conditioning by 11% (157 GWh) and natural gas heating use by 0.7% (145 T J) (Simpson 1998). By conserving this amount of energy over the course of a year, approximately 75,600 t (0.29 t/ha) of CO2 emissions are avoided (Table 3). Air-conditioning savings provide 83% (63,000 t) of the total CO2 emission reductions from trees in Sacramento County. Trees in the rural sector produce only 11% of the county-wide total because relatively few trees are near buildings. The remaining CO2 emission reductions are nearly evenly distributed between the city and suburban sectors. Trees in these largely urbanized sectors are responsible for average annual emission reductions of 1.4 and 0.93 t per ha, respectively (Table 3). On an average annual per tree basis, avoided CO2 emissions are 19, 15, and 4 kg for the city, suburban, and rural sectors. Avoided emissions are about one-third of the amount of CO2 sequestered in trees. This finding differs from other studies that projected much higher CO2 avoided:sequestered ratios of 15:1 and 4:1 for national urban tree planting programs (Akbari et al. 1989; Nowak 1993). However, a very low ratio of 1:28 was reported for Chicago (Nowak 1994). The relatively low Figure 1. Carbon dioxide stored in tree biomass per unit land area is greatest in older areas surrounding the city center (inset) and diminishes in areas of recent suburban growth to the northeast and south. (20,000) 100,000 50,000- 40,000- (10,000) 220 McPherson: CO2 Reduction by Urban Forests ratios for Sacramento and Chicago are due in part to local supplies of clean, hydroelectric and nuclear-generated electricity. Applying the average national power plant emission factor (1,300 kg/MWh, Akbari et el. 1989) in Sacramento results in a nearly 1:1 ratio, as avoided emissions would increase to 222,000 t. Also, the low ratios for urban forests in Sacramento and Chicago reflect the difference between energy savings from the frequently haphazard locations of existing trees and larger savings projected for programs designed to strategically locate trees for energy conservation purposes. Carbon dioxide release. In 1996, the Sacramento Tree Services Division's vehicle fleet and fossil-fuel powered equipment released 1,720 kg of CO2 while visiting approximately 55,750 street and park trees (Fitch, personal communication 6/10/97). Assuming an average dbh of 61 cm (24 in.), the CO2 emission rate is 0.51 kg per cm dbh. Given the location and diameter distribution of the county's 6 million existing trees, approximately 9,422 t of CO2 are released annually in their maintenance (Table 3). This amount is 3% of total CO2 sequestered and avoided annually by Sacramento's urban forest. Eighty percent of total annual CO2 released by tree maintenance occurs in the city and suburban sectors, with the remaining 20% in the rural sector. In the city and suburban sectors the release rates are 0.17 and 0.10 t per ha and 2.3 and 1.6 kg per tree, respectively. Values are much lower for rural sector trees because 24% of these trees are located in vacant/wild lands where no maintenance is assumed. Net carbon dioxide conservation. Net atmospheric CO2 reduction by Sacramento's urban forest is approximately 304,000 t (1.2 t/ha) of atmospheric CO2 over the course of a year (Table 3). The implied value of this annual benefit is about US$3.3 million dollars, or $0.55 per tree on average. Net benefits are greatest in the suburban sector ($1.4 million), where the largest number of trees are located. However, on a land area basis, the implied value of benefits are greatest in the city sector ($48/ha, $0.65/tree). The distribution of CO2 removal and release varies widely by land use, as well as by sector (Figure 2). Countywide, 61% of net CO2 removal occurs in residential land uses, 20% in vacant/wild lands, and 13% in institutional lands. However, in the more urbanized city and suburban sectors, 75% of all removal takes place in residential land uses. This result coincides with the finding that within these 2 sectors, where 90% of all residents live, about 75% of total tree numbers, basal area, and leaf area occur on residential land (McPherson 1998). Relatively more CO2 is removed in multifamily residential and institutional lands within the City Sector 80,000 60,000 40,000 ~" 20,000 O ° [] 0 ~ Res-Lo Res-Hi Com/Ind Instit Trans Ag VacNVild • Sequestered [] Avoided • Released Suburban Sector 80,000 60,000 4o,ooo 20,000 0 (20,000)- Res-Lo Res-Hi Com/Ind Instit Trans Ag Vac/Wild Rural Sector Res-Lo Res-Hi Com/Ind Instit Trans Ag VacNVild Figure 2. Annual CO2 removal and release occurs primarily in low-density residential areas (1 to 3 units per structure) within the city and suburban sectors, and in vacant/wild lands in the rural sector, city sector than in the suburban sector. However, trees in vacant/wild lands within the suburban sector remove substantially more CO2 than do the relatively small number of vacant/wild trees in the city (Figure 2), Trees in vacant/wild land uses account for 60% of all CO2 removal in the rural sector. Carbon dioxide emitted as a byproduct of Sacramento County residents' consumption (e.g., transportation, electricity and natural gas use, other Journal of Arboriculture 24(4): July 1998 221 gas-powered machines) is estimated to be 17 million t (17 Mt) per year. The net impact of Sacramento's urban forest on CO2 removal is to offset these emissions by approximately 1.8%. The 8 Mt of CO2 stored in Sacramento's trees, which has taken many years to accumulate, is equivalent to nearly 50% of the region's total annual emissions. This storage rate is relatively greater than reported for Chicago, where stored CO2 in tree biomass equaled the amount released from the residential sector during a 5-month period (including transportation use) (Nowak 1994). This difference reflects regional variations in lifestyle, commuting patterns, climate, and building energy use; as well as different urban forest composition and structure. Managing urban forests for 002 reductions. Ultimately, all the CO2 presently stored in Sacramento's trees will be lost upon their death and removal. By maintaining the health of mature trees, the rate at which CO2 is lost via tree removal and decomposition can be forestalled. By planting new trees, increasing amounts of CO2 can be stored until an equilibrium is reached, with sequestration by replacement plantings offsetting decomposition from dead trees. The Sacramento Municipal Utility District (SMUD) and Sacramento Tree Foundation (STF) have pledged to plant 500,000 shade trees to achieve 200,000 t of CO2 reductions per year by the year 2000 (155,000 t from sequestration and 50,000 t from energy savings) (Moy 1995). Net CO2 stored as a result of planting 188,000 trees from 1991 to 1995 is estimated to be 350,000 t in the year 2030, with 60% of net benefits from sequestration (Simpson and McPherson 1998b). This reduction is equivalent to 4% of the 8 Mt of CO2 currently stored in the region's urban forest. Because trees provide the potential for longer-term storage compared to nonwoody vegetation, net CO2 storage can be increased more effectively through judicious tree management than by altering other landscape components (i.e., soils, grasses, herbaceous plants). Additionally, tree maintenance appears to have a relatively minor impact on net CO2 reductions. Selecting trees that are well suited to local growing conditions, proper planting and establishment, and regular maintenance to promote vigorous growth and reduce mortality are likely to have more profound impacts on long-term CO2 reductions than attempts to reduce CO2 release associated with tree care. These findings suggest that trees in residential lands are the principal site of CO2 storage and sequestration. Although residential landscapes are seldom designed and managed to maximize their ability to serve as CO2 sinks, several design and management guidelines can be applied to increase CO2 reductions: • Maximize use of woody plants, especially trees, because they store more CO2 than do herbaceous plants and grass (Jo and McPherson 1995). • Increase tree-stocking levels where feasible and immediately replace dead trees to compensate for CO2 lost through tree and stump removal. • Create a diverse assemblage of habitats, with trees of different ages and species, to promote a continuous canopy cover over time. • Select species that are adapted to local climate, soils, and other growing conditions. Adapted plants should thrive in the long run and consume relatively little CO2 through maintenance. • Group species with similar landscape maintenance requirements together and consider how irrigation, pruning, fertilization, weed, pest, and disease control can be minimized. • Reduce CO2 associated with landscape management by using push mowers (not gas or electric), handsaws (not chainsaws), pruners (not gas or electric shears), rakes (not leaf blowers), and employ landscape professionals who don't have to travel far to your site. • Consider the project's lifespan when making species selection. Fast-growing species will sequester more CO2 initially than slow-growing species, but may not live as long. • Provide a generous below-ground environment for the trees in order to maximize initial CO2 sequestration and longevity. • When trees die or are removed, salvage as much wood as possible for use as furniture and other long-lasting products to forestall decomposition (Sherrill et al. 1997). • Plant trees, shrubs, and vines in strategic locations to maximize summer shade and reduce winter shade, thereby reducing atmospheric CO2 emissions associated with power production. Although not a panacea for reducing the risks of global climate change, Sacramento's urban forest plays an important role through offsetting regional CO2 emissions by nearly 2% annually. SMUD and STF's shade tree program demonstrates the potential for urban forestry to be one of many measures employed by electric utilities to offset their CO2 emissions. The tree program is projected to achieve 3% of SMUD's total emission reduction target. In this new era of utility deregulation and environmental protection, an increasing number of electric utilities are likely to follow SMUD's example. Electric utilities, local communities, 222 McPherson: CO2 Reduction by Urban Forests and residential customers stand to benefit from cost-effective shade tree programs that attract new customers, improve quality of life, conserve energy, and offset CO2 emissions. Acknowledgments. This study would not have been possible without field data collected by the following individuals: Vance Howard, Richard Bagaoisan, Melissa Kaufman, Tin-Wah Wong, Nina Luttinger, Uma Ramakrishnan, Katherine McGuinn, Linda Roberson, and Ali Griffith. Ellen Zygory and Warren Roberts (both at the UC-Davis Arboretum) provided invaluable assistance with plant identification. Sylvia Mori (U.S. Forest Service) provided helpful statistical consultation. Klaus Scott, Andrew Hertz (U.S. Forest Service), and Qingfu Xaio (UC-Davis) managed the database and produced maps. Drs. Alison Berry, Jim Harding, and Dave Burger (UC-Davis Department of Environmental Horticulture) provided additional assistance throughout the course of the study. Acquisition of aerial photography, demographic, and geographic information was made possible by Craig Crouch and Rick Stassi (County of Sacramento), Dennis Ybarra (City of Sacramento), and Robert Faseler and Ken Gebert (Sacramento Area Council of Governments). I received valuable comments on earlier versions of this manuscript from Dr. Jim Simpson (U.S. "Forest Service) and Peggy Sand (Minnesota DNR). Literature Cited Akbari, H., J. Huang, P. Martien, L. Rainer, A. Rosenfeld, and H. Taha. 1989. Saving energy and reducing atmospheric pollution by controling summer islands, pp 31-44. In Garbesi, K., H. Akbari, and P. Martien (Eds.). Controlling Summer Heat Islands. Lawrence Berkeley Laboratory, Berkeley, CA. Birdsey, R. 1992. Carbon Storage and Accumulation in United States Forest Ecosystems. USDA For. Serv. Northeast. For. Exp. Sta., Radnor, PA. Brenneman, B.B., D.J. Fredrick, W.E. Gardner, L.H. Schoenhofen, and P.L. Marsh. 1978. Biomass of species and stands of West Virginia hardwoods. Proceedings Central Hardwood Forest Conference II. pp 59-178. California Energy Commission. 1992.1992 Electricity Report: Appendix F. California Energy Commission, Sacramento, CA. City of Austin. 1997. City of Austin Carbon Dioxide Reduction Strategy. City of Austin, Austin. TX. Dorney, J.R., G.R. Guntenspergen, J.R. Keough, and F. Stearns. 1984. Composition and structure of an urban woodyplant community. Urb. Ecol. 8:69-90. Frangi, J.L., and A.E. Lugo. 1985. Ecosystem dynamics of a subtropical floodplain forest. Ecol. Monogr. 55:351-369. Hahn, J.T. 1984. Tree Volume and Biomass Equations for the Lake States. USDA For. Serv., St. Paul, MN. Harris, W.F., R.A. Goldstein, and G.S. Henderson. 1973. Analysis of forest biomass pools, annual primary production and turnover of biomass for a mixed deciduous forest watershed. IUFRO Biomass Studies, 41-64. Husch, B., C.I. Miller, and T.W. Beers. 1982. Forest Mensuration. John Wiley and Sons, New York, NY. Jo, H.K., and E.G. McPherson. 1995. Carbon storage and flux in urban residential greenspace. J. Environ. Manag. 45:109-133. Ker, M.F. 1980. Tree Biomass Equations For Ten Major Species in Cumberland County, Nova Scotia. Canadian For. Sew., Maritimes For. Res. Centre. Inf. Rep. M-X-108, 26. Lieth, H. 1963. The role of vegetation in the carbon dioxide content of the atmosphere. J. Geophys. Res. 68:3887-3898. McPherson, E.G. 1994. Using urban forests for energy efficiency and carbon storage. J. For. 92:36-41. McPherson, E.G. 1998. Structure and sustainability of Sacramento's urban forest. J. Arboric. 24(4):174-190. Means, J.E., H.A. Hansen, G.J. Koerper, P.B. Alaback, and M.W. KIopsch. 1994. Software for Computing Plant Biomass--BIOPAK Users Guide. USDA For. Serv. Pac. Northwest Res. Sta. Monteith, D.B. 1979. Whole-Tree Weight Tables For New York. AFRI Res. Rep. 40:67. Moy, K. 1995. SMUD to sign contract to cut global warming. Sacramento Bee. Jan. 17. Norse, E. 1990. Ancient Forests of the Northwest. The Wilderness Society and Island Press, Washington, DC. Nowak, D. 1993. Atmospheric carbon reduction by urban trees. J. Environ. Manag. 37:207- 217. Nowak, D.J. 1994. Atmospheric carbon dioxide reduction by Chicago's urban forest, pp 83-94. In McPherson, E.G., D.J. Nowak, and R.A. Rowntree (Eds.). Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. USDA For. Serv. Northeast. For. Exp. Sta., Radnor, PA. Phillips, D.R. 1981. Predicted Total-Tree Biomass of Understory Hardwoods. USDA For. Serv., Asheville, NC. Pillsbury, N.H., and M.L. Kirkley. 1984. Equations for Total, Wood, and Saw-Log Volume for Thirteen California Hardwoods. USDA For. Serv., Portland, OR. Pillsbury, N., and R. Thompson. 1995. Tree Volume Equations For Fifteen Urban Species in California. Urban Forest Ecosystems Institute. Calif. Polytech. St. Univer., San Luis Obispo, CA. Rowntree, R.A., and D.J. Nowak. 1994. Quantifying the role of urban forests in removing atmospheric carbon dioxide. J. Arboric. 17:269-275. Sacramento Area Council of Governments. 1995. Population estimates for the Sacramento-Yolo CMSA. In 1995 Data Summary. Sacramento, CA. Sherrill, S., C. Sherrill, and M. Romanos. 1997. The nuts and bolts of turning waste trees into good wood. Pop. Woodworking. 17:30-33. Simpson, J.R. 1998. Urban forest impacts on regional cooling and heating energy use: Sacramento County case study. J. Arboric. 24(4):201-214. Simpson, J.R., and E.G. McPherson. 1995. Impact Evaluation of the Sacramento Municipal Utility District's Shade Tree Program. USDA For, Serv. West, Ctr. for Urban For. Res. and Educ., Davis, CA. Simpson, J.R., and E.G. McPherson. 1998a. Simulation of tree shade impacts on residential energy use for space conditioning in Sacramento. Atmos. Environ.: Urban Atmos. 32:69-74. Journal of Arboriculture 24(4): July 1998 223 Simpson, J.R., and E.G. McPherson. 1998b. A tool for evaluating carbon reduction by urban forestry programs, pp 58-61. In Kollin, S. (Ed.). Proceedings of the Eighth National Urban Forest Conference. American Forests, Washington DC. Small, B.M. 1997. Tree Growth under Sacramento Shade. Sacramento Tree Foundation, Sacramento, CA. Standish, J.T., G.H. Manning, and J.P. Demaerschalk. 1985. Development of Biomass Equations for British Columbia Tree Species. Inf. rep. BC-X-264. Can. For. Serv. Pac. For. Ctr., Vancouver, BC. Stanek, W., and D. State. 1978. Equations Predicting Primary Productivity (Biomass) of Trees, Shrubs and Lesser Vegetation Based on Current Literature. Can. For. Sew., Victoria, BC. Summit, J., and E.G. McPherson. 1998. Residential tree planting and care: A study of attitudes and behaviors in Sacramento, Califomia. J. Arboric. 24(3):89-97. Swift, J., and L. Liebe. 1995. Portland Today: Urban Environment Update. City of Portland, Portland, OR. Tritton, L.M., and J.W. Hornbeck. 1982. Biomass Equations for Major Tree Species of the Northeast. USDA For. Sew., Broomall, PA. Wenger, K.F. 1984. Forestry Handbook. John Wiley and Sons, New York, NY. Whittaker, R.H., and G.E. Likens. 1973. Carbon in thebiota, pp 281-302. In Woodell, G.M., and E.V. Pecans (Eds.). Proceedings of the 24th Brookhaven Symposium in Biology, May 16-18, 1972. Upton, NY. US Atomic Energy Commission. Technical Info. Services. Office of Information Services. Young, H.E., J.H. Ribe, and K. Wainwright. 1980. Weight Tables For Tree and Shrub Species in Maine. Life Sci. and Agdc. Exp. Stn. Misc. Rep. 230:84. Pacific Southwest Research Station USDA Forest Service c/o Department of Environmental Horticulture University of California Davis, CA 95616 Resumen. Los 6 millones de &rboles del Condado de Sacramento (California) almacenan 8 millones de toneladas de bi6xido de carbono (31 t/ha), y retiran anualmente 238,000 toneladas (0.92 t/ha). Los ahorros de aire acondicionado (157 GWh) y espacio de calentamiento (145 T J) del bosque urbano reducen adem&s la emisi6n de 75,600 toneladas de bi6xido de carb6n anualmente (0.29 t/ha). Estas emisiones evitadas son solamente 32% de la cantidad retirada, debido a un suministro limpio de energfa hidroel~ctrica. La liberaci6n anual de bi6xido de carbono, asociada con el mantenimiento del arbol, es estimada en 9,400 toneladas (0.04 t/ha), o 3% de la cantidad retirada y evitada. En terminos netos, el bosque urbano remueve aproximadamente 304,000 toneladas (1.2 t/ha) carla afio, con un valor implicado de US$3.3 millones ($0.55 por ~rbol). La reducci6n del bi6xido de carbono por el bosque urbano de Sacramento compensa la cantidad total de bi6xido de carbono, emitido como un producto secundario del consumo humano, en 1.8%. Los mayores beneficios se acumulan en Areas residenciales en la ciudad y sectores suburbanos, donde las tasa de almacenaje y retiro son cerca de la mitad de los reportados para los bosques de los Estados Unidos. Se presentan normas para el manejo de los bosques urbanos con el fin de reducir el bi6xido de carbono atmosf~rico. ">!
27!7/18/2002 2:59:00 PM!Air pollutant uptake by Sacramento's urban forest!Scott, K.I., E.G. McPherson and J.R. Simpson!1998!Journal of Arboriculture. 24(4)!Articles in Journals!Sacramento Urban Forest Ecosystem Study!cufr_27_KS98_43.PDF!PDF!Scott, K.I., E.G. McPherson and J.R. Simpson. 1998. Air pollutant uptake by Sacramento's urban forest. Journal of Arboriculture. 24(4): 224-234!!A dry deposition model was employed to estimate air pollutant uptake by Sacramento's urban forest. Assuming 1990 air pollutant concentrations, model simulations estimated that approximately 1,457 metric tons of air pollutant are absorbed annually, at an implied value of US$28.7 million. The growing season daily uptake for ozone was approximately 2.4 metric tons per day, while particulate matter < 1 0 ÂƒÝ diameter, PM10) uptake was slightly greater, at 2.7 metric tons per day. Daily uptake of NO2 and particulate matter represented 1% to 2% of anthropogenic emissions for the county. Estimated growing-season annual air pollutant uptake rates averaged 10.9 kg/(ha land area per yr) for the entire study area, 13.9 kg/(ha land area per yr) for urban areas and 4.2 kg/(ha land area per yr) for rural areas. Pollutant uptake rates decreased with decreasing tree canopy cover, along an urban-to-rural gradient!
28!7/18/2002 3:01:00 PM!Rainfall interception by Sacramento's urban forest!Xiao, Q., E.G. McPherson, J.R. Simpson and S.L. Ustin!1998!Journal of Arboriculture. 24(4)!Articles in Journals!Sacramento Urban Forest Ecosystem Study!cufr_28_XQ98_55.PDF!PDF!Xiao, Q., E.G. McPherson, J.R. Simpson and S.L. Ustin. 1998. Rainfall interception by Sacramento's urban forest. Journal of Arboriculture. 24(4): 235-244!Urban forest; rainfall interception; numerical modeling; Kriging; geographic information system; remote sensing; urban runoff!A one-dimensional mass and energy balance model was developed to simulate rainfall interception in Sacramento County, California. The model describes tree interception processes: gross precipitation, leaf drip, stem flow, and evaporation. Kriging was used to extend existing meteorological point data over the region. Regional land use/land cover and tree canopy cover were parameterized with data obtained by remote sensing and ground sampling. Annual interception was 1.1% for the entire county and 11.1% of precipitation falling on the urban forest canopy. Summer interception at the urban forest canopy level was 36% for an urban forest stand dominated by large, broadleaf evergreens and conifers (leaf area index = 6.1) and 18% for a stand dominated by medium-sized conifers and broadleaf deciduous trees (leaf area index = 3.7). For 5 precipitation events with return frequencies ranging from 2 to 200 years, interception was greatest for small storms and least for large storms. Because small storms are responsible for most pollutant washout, urban forests are likely to produce greater benefits through water quality protection than through flood control!costs !
29!7/18/2002 3:03:00 PM!BACT analysis: are there cost effective air quality benefits from trees?!McPherson, E.G., J.R. Simpson and K.I. Scott!1996!In: Proceedings of the 9th joint conference on the applications of air pollution meteorology with the Air and Waste Management Association. Boston: American Meteorological Society!Articles in Conference Proceedings!Effects of Residential Trees on Air Quality i!cufr_29_EM96_27.PDF!PDF!McPherson, E.G., J.R. Simpson and K.I. Scott. 1996. BACT analysis: are there cost effective air quality benefits from trees?. In: Proceedings of the 9th joint conference on the applications of air pollution meteorology with the Air and Waste Management Association. Boston: American Meteorological Society: 355-359!!Trees absorb gaseous pollutants through leaf stomata and can bind or dissolve water soluble pollutants onto moist leaf surfaces. Tree canopies also intercept particulates and reduce local air temperatures. Urban trees may reduce ambient air ozone concentrations, either by direct absorption of ozone or other pollutants such as NO2, or by reducing air temperatures, which reduces hydrocarbon emission and ozone formation rates (Cardelino and Chameides 1990). On the other hand, biogenic hydrocarbon emissions from trees may playa role in ozone formation. The role of trees in air quality has become coupled with concern over the costs and benefits of large-scale urban tree planting programs (Corchnoy et al. 1992). For example, Sacramento Shade, a partnership between the Sacramento Municipal Utility District (SMUD) and the non-profit Sacramento Tree Foundation, is assisting residents plant about 50,000 trees annually near homes to reduce air conditioning demand. It is one of SMUD's most cost-effective energy efficiency programs. An additional benefit of shade tree programs is lowered CO2 emissions from power plants and increased storage of atmospheric CO2 in tree biomass. However, their 10 year goal of planting 500,000 new trees has air quality managers concerned about the impact of hydrocarbon emissions on ozone levels in the country's fifth smoggiest region. Air quality management districts provide pollution abatement credits to businesses and institutions by permitting the use of controls or processes, provided they are technically feasible and cost effective, based upon guidelines in Best Available Control Technology (BACT) manuals. Typically BACT analysis is applied to stationary sources, but we apply it here to determine if a large-scale urban tree planting like Sacramento Shade can be a cost effective means to improve air quality!
30!7/18/2002 3:05:00 PM!Simulation of tree shade impacts on residential energy use for space conditioning in Sacramento!Simpson, J.R. and E.G. McPherson!1998!Atmospheric Environment: Urban Atmospheres. 32(1)!Articles in Journals!Effects of Residential Trees on Air Quality i!cufr_30_JS98_50.PDF!PDF!Simpson, J.R. and E.G. McPherson. 1998. Simulation of tree shade impacts on residential energy use for space conditioning in Sacramento. Atmospheric Environment: Urban Atmospheres. 32(1): 69-74!Air conditioning, tree planting, tree shade, urban forest!Tree shade reduces summer air conditioning demand and increases winter heating load by intercepting solar energy that would otherwise heat the shaded structure. We evaluate the magnitude of these effects here for 254 residential properties participating in a utility sponsored tree planting program in Sacramento, California, Tree and building characteristics and typical weather data are used to model hourly shading and energy used for space conditioning for each building for a period of one year. There were an average of 3.1 program trees per property which reduced annual and peak (8 h average from 1 to 9 p.m. Pacific Daylight Time) cooling energy use 153 kWh (7,1 %) and 0.08 kW (2,3%) per tree, respectively. Annual heating load increased 0.85 GJ (0.80 MBtu, 1.9%) per tree. Changes in cooling load were smaller, but percentage changes larger, for newer buildings. Averaged over all homes, annual cooling savings of $15.25 per tree were reduced by a heating penalty of $5.25 per tree, for net savings of $10.00 per tree from shade. We estimate an annual cooling penalty of $2.80 per tree and heating savings of $6.80 per tree from reduced wind speed, for a net savings of $4.00 per tree, and total annual savings of $14.00 per tree ($43.00 per property). Results are found to be consistent with previous simulations and the limited measurements available!
30!7/18/2002 3:05:00 PM!Simulation of tree shade impacts on residential energy use for space conditioning in Sacramento!Simpson, J.R. and E.G. McPherson!1998!Atmospheric Environment: Urban Atmospheres. 32(1)!Articles in Journals!Energy Effects of Urban Forests in Sacramento!cufr_30_JS98_50.PDF!PDF!Simpson, J.R. and E.G. McPherson. 1998. Simulation of tree shade impacts on residential energy use for space conditioning in Sacramento. Atmospheric Environment: Urban Atmospheres. 32(1): 69-74!Air conditioning, tree planting, tree shade, urban forest!Tree shade reduces summer air conditioning demand and increases winter heating load by intercepting solar energy that would otherwise heat the shaded structure. We evaluate the magnitude of these effects here for 254 residential properties participating in a utility sponsored tree planting program in Sacramento, California, Tree and building characteristics and typical weather data are used to model hourly shading and energy used for space conditioning for each building for a period of one year. There were an average of 3.1 program trees per property which reduced annual and peak (8 h average from 1 to 9 p.m. Pacific Daylight Time) cooling energy use 153 kWh (7,1 %) and 0.08 kW (2,3%) per tree, respectively. Annual heating load increased 0.85 GJ (0.80 MBtu, 1.9%) per tree. Changes in cooling load were smaller, but percentage changes larger, for newer buildings. Averaged over all homes, annual cooling savings of $15.25 per tree were reduced by a heating penalty of $5.25 per tree, for net savings of $10.00 per tree from shade. We estimate an annual cooling penalty of $2.80 per tree and heating savings of $6.80 per tree from reduced wind speed, for a net savings of $4.00 per tree, and total annual savings of $14.00 per tree ($43.00 per property). Results are found to be consistent with previous simulations and the limited measurements available!
31!7/18/2002 3:08:00 PM!Estimating cost effectiveness of residential yard trees for improving air quality in Sacramento, California, using existing models!McPherson, E.G., J.R. Simpson and K.I. Scott!1998!Atmospheric Environment: Urban Atmospheres. 32(1)!Articles in Journals!Effects of Residential Trees on Air Quality i!cufr_31_EM98_28.PDF!PDF!McPherson, E.G., J.R. Simpson and K.I. Scott. 1998. Estimating cost effectiveness of residential yard trees for improving air quality in Sacramento, California, using existing models. Atmospheric Environment: Urban Atmospheres. 32(1): 75-84!!!air !
32!7/18/2002 3:09:00 PM!Technical potential for shade tree planting in Sacramento County!McPherson, E.G. and J.R. Simpson!1995!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!Published Reports!Technical Potential for Tree Planting in Sacramento!cufr_32_EM95_70.PDF!PDF!McPherson, E.G. and J.R. Simpson. 1995. Technical potential for shade tree planting in Sacramento County. Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research. 79!!!
32!7/18/2002 3:09:00 PM!Technical potential for shade tree planting in Sacramento County!McPherson, E.G. and J.R. Simpson!1995!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!Published Reports!Energy Effects of Urban Forests in Sacramento!cufr_32_EM95_70.PDF!PDF!McPherson, E.G. and J.R. Simpson. 1995. Technical potential for shade tree planting in Sacramento County. Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research. 79!!!
401!10/10/2003 3:32:00 PM!Community Forest Planning: Lessons Learned!McPherson, E.G!2003!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!PowerPoint Presentations!Technical Potential for Tree Planting in Sacramento!cufr_401.pdf!PDF!McPherson, E.G. 2003. Community Forest Planning: Lessons Learned!!!
33!7/18/2002 3:10:00 PM!Impact evaluation of the Sacramento Municipal Utility District's shade tree program!Simpson, J.R. and E.G. McPherson!1995!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!Published Reports!Technical Potential for Tree Planting in Sacramento!!PDF!Simpson, J.R. and E.G. McPherson. 1995. Impact evaluation of the Sacramento Municipal Utility District's shade tree program. Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research. 35!!!
33!7/18/2002 3:10:00 PM!Impact evaluation of the Sacramento Municipal Utility District's shade tree program!Simpson, J.R. and E.G. McPherson!1995!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!Published Reports!Energy Effects of Urban Forests in Sacramento!!PDF!Simpson, J.R. and E.G. McPherson. 1995. Impact evaluation of the Sacramento Municipal Utility District's shade tree program. Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research. 35!!!
34!7/18/2002 3:12:00 PM!Estimating urban forest impacts on climate-mediated residential energy use!Simpson, J.R. and E.G. McPherson!1996!In: Proceedings of the 12th conference on biometeorology and aerobiology. Boston: American Meteorological Society!Articles in Conference Proceedings!Technical Potential for Tree Planting in Sacr!cufr_34_JS96_48.PDF!PDF!Simpson, J.R. and E.G. McPherson. 1996. Estimating urban forest impacts on climate-mediated residential energy use. In: Proceedings of the 12th conference on biometeorology and aerobiology. Boston: American Meteorological Society: 462-465!!Interactions between urban trees and the environment are numerous. Trees can reduce runoff by intercepting precipitation, absorb pollutants and emit hydrocarbons, and modify solar radiation, air temperature, wind speed and relative humidity. Of particular interest in recent years has been the reduction in energy use for building space conditioning possible through microscale/local scale climate modification that results from urban trees and landscaping. Computer simulations using prototypical building and tree configurations for cities across the U.S. indicate that shade from a single well-placed, mature tree (about 25-ft crown diameter) reduces annual air conditioning use 2 to 8 percent (40-300 kWh) and peak cooling demand 2 to 10 percent (0.15-0.5 kW) (Huang et al. 1987, Huang et al. 1990, Heisler 1991, Akbari and Taha 1992, McPherson and Sacamano 1992, Sand and Huelman 1993, McPherson 1994, Simpson et al. 1994). Sacramento Shade, a collaborative tree planting program between the Sacramento Municipal Utility District (SMUD) and the Sacramento Tree Foundation, has as its goal the planting of 500.000 shade trees by the year 2000. Over 170,000 of these trees have been planted to date in residential landscapes in order to increase shade on residential buildings and reduce air conditioning demand. In this paper, shade impacts for a large sample of participants in this program are evaluated. In addition, effects of air temperature and wind reduction from increased tree canopy are estimated to place shade effects in context!
35!7/18/2002 3:14:00 PM!Potential of tree shade for reducing residential energy use in California!Simpson, J.R. and E.G. McPherson!1996!Journal of Arboriculture. 22(1)!Articles in Journals!Energy Effects of Urban Forests in California!cufr_35_JS96_49.PDF!PDF!Simpson, J.R. and E.G. McPherson. 1996. Potential of tree shade for reducing residential energy use in California. Journal of Arboriculture. 22(1): 10-18!!Electric utilities in California currently sponsor planting of approximately 75,000 yard trees annually as an energy conservation measure. In this study we evaluated the potential effects of tree shade on residential air conditioning and heating energy use for a range of tree orientations, building insulation levels and climate zones in California using computer simulation. Trees shading a home's west exposure produced the largest savings, both annual (kWh) and peak (kW), for all climate zones and insulation levels considered. Next largest savings were for southwest (annual and peak) and east (annual only) locations. Three trees (two on the west, one on the east side) reduced annual energy use for cooling 10 to 50 percent (200 to 600 kWh, $30 to $110) and peak electrical use up to 23 percent (0.7 kW). Except in climates with little air-conditioning demand, cooling load reductions were always greater than increased heating loads associated with shade from south side trees in winter. Air-conditioning savings, both peak and annual, were larger in warmer climates and uninsulated buildings; percentage savings were larger in cooler climates and for more energy efficient buildings. Recommendations are made regarding locating yard trees to maximize energy savings!
36!7/18/2002 3:16:00 PM!Benefits and costs of Modesto's municipal urban forest!McPherson, E.G., J.R. Simpson, P.J. Peper and Q. Xiao!1999!Journal of Arboriculture. 25(5)!Articles in Journals!Quantifying Benefits and Costs of Modesto's U!cufr_32_em01_71.pdf!PDF!McPherson, E.G., J.R. Simpson, P.J. Peper and Q. Xiao. 1999. Benefits and costs of Modesto's municipal urban forest. Journal of Arboriculture. 25(5): 235-248!!this study answers the question: do the accrued benefits from modesto's urban forest justify an annual municipal budget that exceeds $2 million? results indicate that the benefits residents obtain from modesto's 91,179 public trees exceeded management costs by a factor of nearly 2. in fiscal year 1997-1998, modesto spent $2.6 million for urban forestry ($14.36/resident, $28.77/tree), and 74% of this amount was for mature tree care. total annual benefits from modesto's urban forest were $4.95 million ($27.12/ resident, $54.33/tree). net benefits for fy 1997-1998 were $2,329,900 ($12.76/resident, $25.55/tree). annual air-pollutant uptake was 154 metric tonnes (3. 7 lb/tree), with an implied value of $1.48 million ($16/tree). aesthetics and other benefits had an estimated value of $1.5 million ($17/tree). building shade and cooler summer temperatures attributed to street and park trees saved 110,133 mbtu, valued at $870,000 (122 kwh/tree, $10/tree). smaller benefits resulted from reductions in stormwater runoff (292,000 m1 or 845 gal/tree, $616,000 or $7/tree) and atmospheric carbon dioxide (13,900 t or 336 lb/tree, $460,000 or $5/tree). due to the population's relatively even-aged structure and heavy reliance on mature modesto ash for benefits, management strategies are needed that may reduce net benefits but increase diversity and stability!
38!7/18/2002 3:24:00 PM!Tree guidelines for San Joaquin Valley communities!McPherson, E.G., J.R. Simpson, P.J. Peper and Q. Xiao!1999!Sacramento, CA: Local Government Commission!Tree Guides!Quantifying Benefits and Costs of Modesto's U!2/cufr_38.pdf!PDF!McPherson, E.G., J.R. Simpson, P.J. Peper and Q. Xiao. 1999. Tree guidelines for San Joaquin Valley communities. Sacramento, CA: Local Government Commission. 63!!!costs !
40!7/18/2002 3:27:00 PM!A tool for evaluating atmospheric carbon reduction by urban forestry programs!Simpson, J. and E.G. McPherson!1998!In: Kollin, C. (ed). Cities by nature's design: Proceedings of the 8th national urban forest conference; 1999; Atlanta. Washington, D.C.: American Forests!Articles in Conference Proceedings!Guidelines for Energy Conservation and Carbon!cufr_40_JS98_78.pdf!PDF!Simpson, J. and E.G. McPherson. 1998. A tool for evaluating atmospheric carbon reduction by urban forestry programs. In: Kollin, C. (ed). Cities by nature's design: Proceedings of the 8th national urban forest conference; 1999; Atlanta. Washington, D.C.: American Forests: 58-61!!urban forestry can be a cost effective option to achieve substantial greenhouse gas reduction in addition to other social, economic, and ecological benefits. the paper describes an analysis tool that utilities and other organizations can use to evaluate and report carbon emissions avoided and sequestered by urban forestry programs. the result combines regional default data from look-up tables with user-supplied data to compute net co2 reduction from these programs. uses include 1) projecting future co2 reductions from proposed programs, 2) reporting co2 reductions from existing programs, and 3) design of cost effective urban forestry programs. development and application of this tool is demonstrated here using the sacramento shade program as an example. sacramento shade is a partnership between the sacramento municipal utility district (smud) and the sacramento tree foundation (stf). the program's goal is to plant 500,000 shade trees by the year 2000, and thus far over 250,000 trees have been planted. the program has produced a considerable database of information regarding structure and function of sacramento's urban forest (e.g. hildebrandt, 1996; joanna julien, personal communication)!
41!7/18/2002 3:30:00 PM!Guidelines for tree planting to reduce atmospheric carbon dioxide in Chula Vista, CA!McPherson, E.G. and J.R. Simpson!1998!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!Published Reports!Guidelines for Energy Conservation and Carbon!cufr_41_EM98_69.PDF!PDF!McPherson, E.G. and J.R. Simpson. 1998. Guidelines for tree planting to reduce atmospheric carbon dioxide in Chula Vista, CA. Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research. 13!!!air !
42!7/18/2002 3:32:00 PM!Guidelines for evaluating atmospheric carbon dioxide reductions by urban forestry programs!Simpson, J. and E.G. McPherson!1999!In: Kinsman, J., C. Mathai, M. Baer, E. Holt and M. Trexler, (eds). Global climate change: science, policy, and mitigation/adaptation strategies. VIP-89. Vol II. Sewickley, PA: Air and Waste Management Association!Articles in Conference Proceedings!Guidelines for Energy Conservation and Carbon!cufr_42_JS99_44.PDF!PDF!Simpson, J. and E.G. McPherson. 1999. Guidelines for evaluating atmospheric carbon dioxide reductions by urban forestry programs. In: Kinsman, J., C. Mathai, M. Baer, E. Holt and M. Trexler, (eds). Global climate change: science, policy, and mitigation/adaptation strategies. VIP-89. Vol II. Sewickley, PA: Air and Waste Management Association: 789-790!!!
43!7/18/2002 3:34:00 PM!Carbon dioxide reductions through urban forestry: guidelines for professional and volunteer tree planters!McPherson, E.G. and J.R. Simpson!2000!PSW GTR-171. Albany, CA: USDA Forest Service, Pacific Southwest Research Station!General Technical Reports!Guidelines for Energy Conservation and Carbon!cufr_43.pdf!PDF!McPherson, E.G. and J.R. Simpson. 2000. Carbon dioxide reductions through urban forestry: guidelines for professional and volunteer tree planters. PSW GTR-171. Albany, CA: USDA Forest Service, Pacific Southwest Research Station!urban forestry , carbon dioxide, sequestration, avoided energy!Carbon dioxide reduction through urban forestry-Guidelines for professional and volunteer tree planters has been developed by the Pacific Southwest Research Station's Western Center for Urban Forest Research and Education as a tool for utilities, urban foresters and arborists, municipalities, consultants, non-profit organizations and others to determine the effects of urban forests on atmospheric carbon dioxide (CO2) reduction. The calculation of CO2 reduction that can be made with the use of these Guidelines enables decision makers to incorporate urban forestry into their efforts to protect our global climate. With these Guidelines, they can: report current and future CO2 reductions through a standardized accounting process; evaluate the cost-effectiveness of urban forestry programs with CO2 reduction measures; compare benefits and costs of alternative urban forestry program designs; and produce educational materials that assess potential CO2 reduction benefits and provide information on tree selection, placement, planting, and stewardship!
44!7/18/2002 3:36:00 PM!Energy and air quality improvements through urban tree planting!Simpson, J.R. and E.G. McPherson!2000!In: Kollin, C., (ed). Building cities of green: proceedings of the 1999 national urban forest conference; Seattle. Washington, D.C.: American Forests!Articles in Conference Proceedings!Guidelines for Energy Conservation and Carbon!cufr_44_JS00_47.PDF!PDF!Simpson, J.R. and E.G. McPherson. 2000. Energy and air quality improvements through urban tree planting. In: Kollin, C., (ed). Building cities of green: proceedings of the 1999 national urban forest conference; Seattle. Washington, D.C.: American Forests: 110-112!!Numerous benefits are associated with urban trees. Two important and interrelated benefits are reduced space conditioning (cooling and heating) energy use, and improved air quality. Urban trees have a moderating effect on extremes of climate by reducing solar irradiance, air temperature and wind speed. Reduced energy use results in fewer emissions of carbon dioxide (CO2) hydrocarbons and other pollutants. Besides these "avoided" emissions, trees provide the additional benefit of removing CO2 from the atmosphere and storing it as biomass (wood is about 50% carbon). Credits for ozone related pollutants are currently actively traded in many regions, and trading in greenhouse gas (GHG) emission allowances and/or emission reduction/ sequestration credits are sure to follow. These benefits from urban trees could be used to fund urban forestry programs that produce them. In the case of air quality, this would allow emitters with expensive reduction options (e.g. industry) to offset their emissions by financing lower cost reductions possible from urban tree programs. The purpose of this paper is to present preliminary results of ongoing research to evaluate the net cost of reducing emissions with urban forestry!
46!7/18/2002 3:39:00 PM!Tree planting to optimize energy and CO2 benefits!Simpson, J.R. and E.G. McPherson!2001!In: Kollin, C. (ed). Investing in natural capital: proceedings of the 2001 national urban forest conference; 2001 September 5-8; Washington, D.C. Washington, D.C.: American Forests!Articles in Conference Proceedings!Guidelines for Energy Conservation and Carbon!cufr_46_JS01_52.PDF!PDF!Simpson, J.R. and E.G. McPherson. 2001. Tree planting to optimize energy and CO2 benefits. In: Kollin, C. (ed). Investing in natural capital: proceedings of the 2001 national urban forest conference; 2001 September 5-8; Washington, D.C. Washington, D.C.: American Forests: 81-84!!Forests take up carbon dioxide directly from the atmosphere and store it as biomass. Urban forests have the additional benefit of reducing heating and cooling energy use, hence emissions from fossil fuels, referred to as avoided CO2. Little specific, quantitative information is available regarding what effects regional differences in climate, tree growth, construction practices and heating/cooling fuel mix might have on energy savings and avoided carbon. In this presentation we quantify the effects of those differences on space-conditioning energy use and avoided C02 for 11 representative regions of the United States. Practical applications of the results for locating urban trees with the goal of maximizing energy savings and avoided carbon in different regions are discussed!
47!7/18/2002 3:41:00 PM!Benefits and costs of Santa Monica's urban forest!McPherson, E.G., J.R. Simpson, P.J. Peper and Q. Xiao!2001!Davis, CA: USDA Forest Service, Pacific Southwest research station, center for urban forest research!Published Reports!Quantifying Benefits and Costs of Santa Monic!cufr_32_em01_71.pdf!PDF!McPherson, E.G., J.R. Simpson, P.J. Peper and Q. Xiao. 2001. Benefits and costs of Santa Monica's urban forest. Davis, CA: USDA Forest Service, Pacific Southwest research station, center for urban forest research. 44!!!
48!7/18/2002 3:43:00 PM!Tree guidelines for coastal Southern California communities!McPherson, E.G., J.R. Simpson, P.J. Peper, K.I. Scott and Q. Xiao!2000!Sacramento, CA: Local Government Commission!Tree Guides!Quantifying Benefits and Costs of Santa Monic!2/cufr_48.pdf!PDF!McPherson, E.G., J.R. Simpson, P.J. Peper, K.I. Scott and Q. Xiao. 2000. Tree guidelines for coastal Southern California communities. Sacramento, CA: Local Government Commission. 98!!!costs !
49!7/18/2002 3:45:00 PM!Street tree growth rates and benefit-cost quantification!McPherson, E.G!2000!In: Kollin, C., (ed). Building cities of green: proceedings of the 1999 national urban forest conference; Seattle, Washington. Washington, D.C.: American Forests!Articles in Conference Proceedings!Quantifying Benefits and Costs of Modesto's U!cufr_49_EM00_64.PDF!PDF!McPherson, E.G. 2000. Street tree growth rates and benefit-cost quantification. In: Kollin, C., (ed). Building cities of green: proceedings of the 1999 national urban forest conference; Seattle, Washington. Washington, D.C.: American Forests: 139-142!!This study answers the question: Do the accrued benefits from Modesto's urban forest justify an annual budget that exceeds $2 million? Results indicate that the net benefits from Modesto's 91,719 public trees exceed management costs by a factor of nearly 2 and totaled $2, 329, 900 ($12.76/resident, $25.55/tree). Due to the tree population's relatively even-aged structure and heavy reliance on mature Modesto ash for benefits, management strategies are needed that may reduce net benefits but increase diversity and stability!
50!7/18/2002 3:47:00 PM!A practical approach to assessing structure, function, and value of street tree populations in small communities!Maco, S.E!2002!Davis, CA: University of California. M.S. Thesis!Dissertations/Thesis!A Practical Approach to Benefit Cost Analysis!cufr_50.pdf!PDF!Maco, S.E. 2002. A practical approach to assessing structure, function, and value of street tree populations in small communities. Davis, CA: University of California. M.S. Thesis. 218!!This study demonstrated an approach to quantify the structure, benefits, and costs of street tree populations in resource-limited communities without tree inventories. Using the city of Davis, CA as a model, existing data on the benefits and costs of municipal trees were applied to the results of a sample inventory of the city's public and private street trees. Results indicate that Davis maintains nearly 24,000 public street trees that provide $1.2 million in net annual environmental and property value benefits, with a benefit-cost ratio of 3.8. The city can improve long-term stability of this resource by managing diversity, canopy cover, and maintenance on a city zone basis!
51!7/18/2002 3:48:00 PM!Benefits and costs of LADWP's!McPherson, E.G. and J.R. Simpson!2001!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!Published Reports!LADWP's "Trees for a Green LA" Shade Tree Program Evaluation!cufr_51_EM01_18.pdf!PDF!McPherson, E.G. and J.R. Simpson. 2001. Benefits and costs of LADWP's. Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research. 10!!!
52!7/18/2002 3:50:00 PM!Tree guidelines for Inland Empire communities!McPherson, E.G., J.R. Simpson, P.J. Peper, Q. Xiao, D.R. Pittenger and D.R. Hodel!2001!Sacramento, CA: Local Government Commission!Tree Guides!Quantifying Benefits and Costs of Claremont's!2/cufr_52.pdf!PDF!McPherson, E.G., J.R. Simpson, P.J. Peper, Q. Xiao, D.R. Pittenger and D.R. Hodel. 2001. Tree guidelines for Inland Empire communities. Sacramento, CA: Local Government Commission. 116!!!costs !
54!7/18/2002 3:54:00 PM!New advances in quantifying the environmental benefits of trees!McPherson, E.G!2001!In: Kollin, C. (ed). Investing in natural capital: proceedings of the 2001 national urban forest conference; 2001 September 5-8; Washington, D.C. Washington, D.C.: American Forests!Articles in Conference Proceedings!Miscellaneous Benefit-Cost Literature!cufr_54_EM01_14.PDF!PDF!McPherson, E.G. 2001. New advances in quantifying the environmental benefits of trees. In: Kollin, C. (ed). Investing in natural capital: proceedings of the 2001 national urban forest conference; 2001 September 5-8; Washington, D.C. Washington, D.C.: American Forests: 20-22!!The urban forest provides environmental services that are often unpriced and underappreciated. This paper summarizes the latest research and technology tools developed to help managers optimize these benefits!at the Center for Urban Forest Research are: • Providing objective, refiable, and accurate science-based information on urban forest benefits and costs for policy-making end management. • Measuring and modeling of urban forest effects on fluxes of energy, water, end materials in urban ecosystems. • Developing new analytical techniques and knowledge concerning growth, dimensions, biomass, and leaf area of urban trees. • Producing an integrated suite of technology transfer products that link state of the art science with the needs of targeted sets of users. References: Costello, L. R., E. G. McPherson, D. W. Burger, end L. L. Dodge, Editors. 2000. Strategies to Reduce Infrastructure Damage by Tree Roots. Cohasset, CA: Western Chapter, International SocieW of Arboriculture. McPherson. E. G. 2000. Expenditures associated with conflicts between street tree root gr0~Nth and hardscape in California, United States. Journal of Arboriculture 26, No.6: 289-297. McPherson, E. G. and J. R. Simpson. 1999. Carbon Dioxide Reductions Through Urban Forestry: Guidelines for Professional end Volunteer Tree Planters. (General Technical Report PSW-171), Albany, CA: USDA Forest Service° Pacific Southwest Research Station. McPherson, E. G., J. R. Simpson, P. J. Peper, and (1. Xiao, 1999. Benefit-cost analysis of Modesto's municipal urban forest. Journal of Arboriculture 25. No. 5: 235-248. McPherson, E. G., J. R. Simpson, P, J. Paper, and (1, Xiao. 1999. Tree Guidelines for Sen Joaquin Valley Communities. Sacramento, CA: Local Government Commission. McPherson, E. G., J. R, Simpson, R J, Paper. K. I. Scott, and Ct. Xiao. 2000. Tree Guidelines for Coastal Southern California Communities, Sacramento, CA: Local Government Commission. McPherson, E. G., J. R. Simpson, P, J. Paper, Q. Xiao, D. R. Pittenger. and D. R. Hodel. 2001. Tree Guidelines for Inland Empire Communities, Sacramento, CA; Local Government Commission. Paper. P, J., E. G. McPherson, and S, M. Mori. 2001. Predictive equations for dimensions and leaf area of coastal Southern California street trees. Journal of Arboriculture 27, No.4: 169-180. Xiao, C1., E. G, McPharson, J, R. Simpson, and S. L. Ustin. 1998. Rainfall interception by Sacramento's urban forest. Journal of Arboriculture 24, No.4: 235-244. Xiao, Q., E. G. McPherson, S. L. Ustin, M. E. Grismer, and J. R. Simpson. 2000s. Winter rainfall interception by two mature open grown trees in Davis, California. Hydrological Processes 14: 763-784. Xiao. Q,, E. G. McPherson, S, L. Ustin. and M, E. Grismer. 200Ob. A new approach to modeling tree rainfall interception. Journal of Geographical Research Atmospheres 105: 2g,173-2g,188. ® ,i ,y 2 AIR QUALITY, ENERGY. AND THE URBAN HEAT ISLAND MODERATOR: PATRICE CARROLL, US ENVIRONMENTAL PROTECTION AGENCY. PHILADELPHIA, PA URBAN FOREST STRUCTURE, BENEFITS AND VALUE, DAVID J. NOWAK AND JOHN F. DWYER 24 CREATING AN ENERGY-EFFICIENT URBAN FOREST, MISHA SARKOVICH .27!
55!7/18/2002 3:56:00 PM!Quantifying urban forest structure, function, and value: the Chicago urban forest climate project!McPherson, E.G., D. Nowak, G. Heisler, S. Grimmond, C. Souch, R. Grant, and R.A. Rowntree!1997!Urban Ecosystems. 1!Articles in Journals!Miscellaneous Benefit-Cost Literature!cufr_55_EM97_26.PDF!PDF!McPherson, E.G., D. Nowak, G. Heisler, S. Grimmond, C. Souch, R. Grant, and R.A. Rowntree. 1997. Quantifying urban forest structure, function, and value: the Chicago urban forest climate project. Urban Ecosystems. 1: 49-61!urban forests; urban ecology; urban climate; hydroclimate; air pollution; energy conservation; carbon removal; benefit-cost analysis!This paper is a review of research in Chicago that linked analyses of vegetation structure with forest functions and values. During 1991, the region's trees removed an estimated 5575 metric tons of air pollutants, providing air cleansing worth $9.2 million. Each year they sequester an estimated 315800 metric tons of carbon. Increasing tree cover 10% or planting about three trees per building lot saves annual heating and cooling costs by an estimated $50 to $90 per dwelling unit because of increased shade, lower summertime air temperatures, and reduced neighborhood wind speeds once the trees mature. The net present value of the services trees provide is estimated as $402 per planted tree. The present value of long-term benefits is more than twice the present value of costs!
56!7/18/2002 4:00:00 PM!Urban forest landscapes: how greenery saves greenbacks!McPherson, E.G!1996!In: Wagner, C., (ed). 1996. Annual meeting proceedings. Washington, D.C.: American Society of Landscape Architects!Articles in Conference Proceedings!Miscellaneous Benefit-Cost Literature!cufr_56_EM96_16.PDF!PDF!McPherson, E.G. 1996. Urban forest landscapes: how greenery saves greenbacks. In: Wagner, C., (ed). 1996. Annual meeting proceedings. Washington, D.C.: American Society of Landscape Architects: 27-29!!!
57!7/18/2002 4:02:00 PM!Results of the Chicago urban forest climate project!McPherson, E.G., D. Nowak, G. Heisler, S. Grimmond, C. Souch, R. Grant and R. Rowntree!1995!In: Kollin, C. (ed). Proceedings of the 7th national urban forest conference; 1995 September 12-16; New York. Washington, D.C.: American Forests!Articles in Conference Proceedings!Miscellaneous Benefit-Cost Literature!cufr_57_EM95_25.PDF!PDF!McPherson, E.G., D. Nowak, G. Heisler, S. Grimmond, C. Souch, R. Grant and R. Rowntree. 1995. Results of the Chicago urban forest climate project. In: Kollin, C. (ed). Proceedings of the 7th national urban forest conference; 1995 September 12-16; New York. Washington, D.C.: American Forests: 85-88!!The 3-year Chicago Urban Forest Climate Project examined bow trees affect components of the regional urban ecosystem. During 1991, the region's trees removed an estimated 6,145 tons of air pollutants, providing air cleansing worth $9.2 million. Planting about three trees per building lot is estimated to save annual beating and cooling costs by $50 to $90 per dwelling unit. The net present value of services trees provide is estimated as $38 million, or $402 per planted tree. The present value of long-term benefits are more than twice the present value of costs!
58!7/18/2002 4:04:00 PM!Net benefits of healthy and productive urban forests!McPherson, E.G!1995!In: Bradley, G.A., (ed). Urban forest landscapes: integrating multidisciplinary perspectives. Seattle: University of Washington Press!Articles in Conference Proceedings!Miscellaneous Benefit-Cost Literature!cufr_58_EM95_13.PDF!PDF!McPherson, E.G. 1995. Net benefits of healthy and productive urban forests. In: Bradley, G.A., (ed). Urban forest landscapes: integrating multidisciplinary perspectives. Seattle: University of Washington Press: 180-194!!In California, urban forestry programs are facing new challenges due to dwindling municipal budgets, fewer trees, planting of smaller trees, and declining government support. However, changes in environmental policy, such as the use of market incentives to promote environmentally sound behavior, are providing new opportunities for urban forestry to broaden its base of support. Quantifying the benefits and costs associated with tree planting and care is fundamental to the development of economic incentives aimed at sustaining healthy and productive urban forests. Use of benefit-cost analysis to evaluate the economics of urban forestry policies and programs is illustrated with an example from the Chicago Urban Forest Climate Project. The thirty-year annt13l costs and benefits associated with planting 95,000 trees were estimated using the computer model Cost-Benefit Analysis of Trees (C-BA T) and discount rates of 4,7, and 10 percent. Net present values were positive, and projected benefit-cost ratios were greater than 1.0 at all discount rates. Assuming a 7 percent discount rate, a net present value of $38 million, or $402 per planted tree, was projected. Benefit-cost ratios were largest for trees planted in residential yards and public housing sites (3.5), and least for park (2.1) and highway (2.3) sites. Discounted payback periods ranging from nine to fifteen years. Strategies for strengthening connections between city residents and city trees, as well as maximizing return on investment in the urban forest, are presented!
60!7/18/2002 4:07:00 PM!Accounting for benefits and costs of urban greenspace!McPherson, E.G!1992!Landscape and Urban Planning. 22!Articles in Journals!Miscellaneous Benefit-Cost Literature!cufr_60_EM92_8.PDF!PDF!McPherson, E.G. 1992. Accounting for benefits and costs of urban greenspace. Landscape and Urban Planning. 22: 41-51!!Urban greenspace provides many environmental and social services that contribute to the quality of life in cities. Economic approaches used to estimate value of greenspace services include travel cost, willingness to pay, hedonic pricing, and tree valuation. These methods have limited utility for policy-makers, planners, and managers because the underlying values they estimate only indirectly reflect the flow of multiple benefits and costs. A greenspace accounting approach to partially address this deficiency is described using benefit-cost analysis for a proposed tree-planting project in Tucson, AZ. The approach directly connects vegetation structure with the spatial-temporal flow of functional benefits and costs. Prices are assigned to each cost ( i.e. planting, pruning, removal, irrigation) and benefit ( i.e. cooling energy savings, interception of particulates, stormwater runoff reduction) through direct estimation and implied valuation of benefits as environmental externalities. The approach can be used to evaluate net economic benefits associated with capital investments in urban forests vs. other investments in the urban infrastructure or traditional environmental control technologies!
61!7/18/2002 4:08:00 PM!Assessing the benefits and costs of the urban forest!Dwyer, J.F., E.G. McPherson, H.W. Schroeder and R.A. Rowntree!1992!Journal of Arboriculture. 18(5)!Articles in Journals!Miscellaneous Energy Literature!cufr_61_JD92_4.PDF!PDF!Dwyer, J.F., E.G. McPherson, H.W. Schroeder and R.A. Rowntree. 1992. Assessing the benefits and costs of the urban forest. Journal of Arboriculture. 18(5): 227-234!!With effective planning and management, urban trees and forests will provide a wide range of important benefits to urbanites. These include a more pleasant, healthful, and comfortable environment to live, work, and play in, savings in the costs of providing a wide range of urban services, and substantial improvements in individual and community well-being. Urban forestry plans should begin with consideration of the contribution that trees and forests can make to people's needs. Planning and management efforts should focus on how the forest can best meet those needs. Past planning and management efforts have not been as effective as they might have been because planners and managers have underestimated the potential benefits that urban trees and forests can provide, and have not understood the planning and management efforts needed to provide those benefits, particularly the linkages between benefits and characteristics of the urban forest and its management!of urbanites' preferences and behavior confirm the strong contribution that trees and forests make to the quality of life in urban areas. Trees and forests are a prominent component of the landscape in most urban areas. Urban forests provide significant outdoor leisure/recreation opportunities for urbanites. Based on nine visits per year to local parks per person, and $1.00 per visit in value added by the presence of well managed urban forest resources, the total contribution of urban trees and forests in park and recreation areas to the value of recreation experiences provided in the USA could exceed $2 billion (8). These are 230 both conservative estimates based on studies in the Midwest (6,7), and do not include benefits from trees on residential lots and other "non-desig-nated" areas. The Forest Preserve District of Cook County, Illinois provides more than 40 million visits per year from a base of 66,000 acres of urban forests. In addition to parks and preserves, urban greenways provide a wide range of recreational opportunities. Bicycle trails in river corridors in the Chicago Metropolitan area support up to 5,000 bicycles per day passing a given point on a single trail. To the extent that urban trees and forests increase the quality of the urban environment and make spending leisure time there more attractive, there will be substantial savings in fuel consumed because people will not drive to distant recreation sites as often. At $1.25 per gallon, the savings to individuals across the U.S. total $300 million per year if just one gallon per individual is saved by reduced leisure trips. It would seem that the potential savings in fuel costs from an urban environment that is enhanced by well managed trees and forests might be five times that amount or $1.5 billion per year (8). Reduced fuel consumption would substantially reduce air pollution and related problems. Medical. Reduced stress and improved physical health for urban residents have been associated with the presence of urban trees and forests. Studies have shown that landscapes with trees and vegetation produce more relaxed physiological states in humans than landscapes that lack these natural features. Hospital patients with window views oftrees recover significantly faster and with fewer complications than comparable patients without access to such views (27). Future research will identify specific situations (e.g., urban commuting) in which urban forests can offset stress, and measure the amount of stress reduction that occurs. The benefits to public health from using trees to reduce urban stress are potentially very significant. In addition, cleaner air can be expected to improve health. There may be health-related costs as well, such as allergies to plants, pollen, or associated animals and insects. Psychological. Urban forest environments provide esthetic surroundings, increased enjoy- Dwyer et al: Urban Forest Benefits and Costs ment of everyday life, and a greater sense of meaningful connection between people and the natural environment. Trees are among the most important features contributing to the esthetic quality of residential streets and community parks (21). Perceptions of esthetic quality and personal safety are very sensitive to features of the urban forest such as number of trees per acre and view distance (22). Park and arboretum visitors have reported that trees and forests provide settings for significant emotional and spiritual experiences (3,23,24). These experiences are extremely important in people's lives, and can lead to a strong feeling of attachment to particular places and trees (9). An improved understanding of the emotional and symbolic meanings of trees will enable managers to provide the kind of settings that contribute to a meaningful and satisfying sense of place in the urban environment. Costs include fear of trees, forests, and associated environments. Real estate values. The sales value of real estate reflects the benefits that buyers attach to the attributes of that property, including the trees and forest resource found on the property, along the street, and in neighboring parks and greenways. An individual's willingness to pay for a residential property is likely to reflect the value of benefits that they expect from these forest environments, including opportunities for leisure out in the yard or in the neighborhood, reduced heating and cooling costs, privacy, and the lack of a need to construct fences or screens. The variation in sales prices over a large number of residential properties with different forest resources on the property and nearby can be used to infer the willingness of users to pay for those urban forest resources (2). These increases in property values are not a separate category of value that is distinct from the goods and services provided; but rather one means of reflecting or capturing the values of the many important services that urban residents receive from urban forests. The ties between trees and property values provide an incentive for homeowners to invest in trees since increased revenues can be received at the time of sale of that home (i.e., an advertisement mentioning well landscaped yard, shaded patio, close to parks and bicycle trails, and an 231 Journal of Arboriculture 18(5): September 1992 energy efficient home). Economic values of trees and forests that are expressed as increased real estate values also prOduce direct economic gains to local communitieS, through property taxes. Consequently, tree planting and tree care on public and private lands can be viewed as an investment that achieves an annual return in property taxes. A conservative estimate of a 5 percent increase in property values due to trees and forests on residential properties (several studies suggest higher values) represents $25 per year on a conservative property tax bill'of $500, and quickly adds up to $1.5 billion per year over the 62 million single family detached housing units in the USA. A more realistic estimate is two to three times that amount. Parks and greenways have been associated with increments in the value of nearby real estate (5,16). Some of these increments have been substantial and it appears that parks with an "open space character" add most to the value of nearby real estate. We have yet to identify the increments in real estate value associated with urban forest resources in street corridors. Residential properties are not the only real estate that gains in value from urban trees and forests. Shopping centers frequently landscape their surroundings in an effort to provide a pleasing environment that will attract shoppers, thereby increasing the value of businesses and the shopping center. While we are currently unaware of research that documents the increased business and tax receipts that are associated with such efforts, trees and forests may make an important contribution to the economic vitality of these businesses, and the private sector is currently making substantial investments in this area --far in excess of, what is required by local regulations. One neighborhood shopping district in Chicago has concluded that planting trees along the street in front of their establishments increased their business activity. Similarly, employers invest in landscaping, beyond what is required, to enhance worker productivity, and morale. While there is currently no research to document the increased worker productivity in such environments, building owners are generally able to obtain higher rents for offices that overlook well-landscaped areas. In short, trees and forests can make a substantial contribution to property tax revenues, thereby providing annual returns on municipal investments in urban trees and forests. These benefits are offset, in part, by the costs of managing the forests and repairing damages that may be associated with them, such as disruption of sidewalks, sewers, powerlines, etc. Local economic development. Urban forest resources also make a broad contribution to the economic vitality of a city, neighborhood, or subdivision. While this is particularly difficult to quantify, it is apparently no accident that many cities and towns are named after trees and forests (i.e., Elmhurst and Oak Park) as are subdivisions (i.e. Tall Timbers and Timber Trails) and many areas strive to be designated as a "Tree City USA." Many neighborhoods select tree planting as a community improvement project. Trees can dominate the urban environment and contribute much to its character. In the Chicago area, communities such as Evanston, Oak Park, and Elmhurst are well known for their mature forest environments. Atlanta's large investment in downtown tree plantings has paralleled an upswing in convention business and contributed to its image of a progressive, livable city. Community action programs that start with trees and forests often spread to other aspects of the community and result in substantial economic development. Often trees and forests on public lands-- and to some extent those on private lands as well -- are significant "common property" resources that contribute to the economic vitality of an entire area. The substantial efforts that many communities undertake to develop and enforce local ordinances and manage urban forest resources attests to the substantial return that they expect from these investments. Societal. Stronger sense of community, em-powerment of inner city residents to improve neighborhood conditions, and promotion of environmental responsibility and ethics can be attributed to involvement in urban forestry efforts. Active involvement in tree-planting programs has been shown to enhance a community's sense of social identity, self-esteem, and territoriality, and 232 Dwyer et al: Urban Forest Benefits and Costs it teaches residents that they can work together to choose and control the condition of their environment. Community tree planting programs can help alleviate some of the hardships of inner city living, especially for low-income groups. Research on environmental education is exploring ways of teaching children about their responsibility in caring for trees, and can provide badly needed opportunities for inner city children to experience nature. Researchers are examining how such early experiences with nature influence the willingness to adopt an environmental ethic later in life. Summary and Conclusions With effective planning and management, urban trees and forests will provide a wide range of important benefits to urbanites. These include a more pleasant, healthful, and comfortable environment in which to live, work, and play, savings in the-costs of providing a wide range of urban services, and substantial improvements in individual and community well-being. Urban forests can enhance the city environment by influencing temperature, wind, humidity, rainfall, soil erosion, flooding, air quality, scenic quality, and plant and animal diversity. Each of these influences has significant implications for the well-being of urbanites. But there are also environmental problems that may be associated with the urban forest, such as the generation of pollen, hydrocarbons, and green waste;water and energy consumption; obscured views; and displacement of native species of plants. A well planned and managed urban forest can reduce costs for heating and cooling, health care, driving to exurban areas for recreation and leisure,' stormwater management, and damage from flooding, erosion, and polluted air. Substantial i~creases in revenues can also be associated with urban trees and forests, including the sale of real estate (individual gains), real estate and business taxes (government gains), and tourism (individuals and government may gain). Costs associated with urban forests include establishment and care of the forest; repair of forest-induced damage to other parts of the urban infrastructure (particularly sidewalks and utilities); blocked solar collectors, and foregone opportunities for activities such as gardening and sports. Many important benefits and costs of urban forests that contribute significantly to the well-being of urbanites are not easily reflected in dollars and cents. Psychological benefits associated with urban forests include more pleasant environments for a wide range of activities, improvements in the esthetic environment (sights, sounds, smells), relief from stress (which can lead to improved physical health), enhanced feelings and moods, increased enjoyment of everyday life, and a stronger feeling of connection between people and their environment. Psychological costs can include fears of crime, animals, insects, disease (i.e., Lyme disease), darkness, and falling trees or limbs; and the displeasure of messiness and clutter. Benefits attributed to urban trees and forests extend beyond individuals to society. Societal benefits include a stronger sense of community, empowerment to improve neighborhood conditions, promotion of environmental responsibility and ethics, and enhanced economic development (business, commerce, employment). Societal costs include money and other resources that must be diverted from other social programs. The challenge faced by urban forest resource managers and planners is to balance the many benefits and costs that are associated with urban trees and forests. Lack of information about the extent and magnitude of these benefits and the best approaches for prm/iding them often makes that task a very difficult one. Urban forestry plans should begin with consideration of the contribution that trees and forests can make to people's needs. Planning and management efforts should focus on how the forest can best meet those needs. Past planning and management efforts have not been as effective as they might have been because planners andman-agers.have underestimated the potential benefits that urban trees and forests can provide, and have not understood the planning and management efforts needed to provide those benefits, particularly the linkages between benefits and characteristics of the urban forest and its management. Research continues to document new ways in which trees and forests can benefit urbanites, as well as the magnitudes of these benefits. The 233 Journal of Arboriculture 18(5): September 1992 efforts of urbanites to protect and preserve trees as well as their enthusiastic involvement in tree planting programs reflects their high regard for urban forest benefits. Urban trees and forests promise to be even more consequential in the years ahead. Increasing interest in cost-effective and "minimum impact" approaches for improving the quality of the urban environment suggests that trees will play increasingly important roles in efforts to enhance air quality and improve urban hydrologic processes. Worldwide concern for "global warming" suggests increasing interest in trees for sequestering carbon and reducing carbon dioxide emissions. Associated concern for efficient use of energy resources will bring increasing attention to trees as a means of reducing heating and cooling costs as well as for encouraging urbanites to spend leisure time in the urban environment rather than driving to more remote areas. As we learn more about the functioning of the urban ecosystem and the role of trees and forests in that system, it is likely that these resources will assume new roles in efforts to manage the urban environment. With increasing emphasis on improving the quality of life for urbanites and in "wellness" programs overall, increasing attention will be given to trees and forests as a means for enhancing the quality of urban life. This is likely to include efforts aimed specifically at stress reduction and improved public health. As we learn more about the deep psychological ties between urbanites and trees and forests, it is likely that urban trees and forests will assume new roles in efforts to increase the quality of urban life. As we learn more about the contribution of trees and forests to the value of residential and commercial real estate it is likely that owners will make increasing investments in their trees and forests. Local governments and energy utilities will undertake programs to encourage such efforts, due in part to the increased tax revenues that will result, and to avoid energy costs. Education regarding the planting and care of appropriate tree species in desirable locations will be critical to the long term cost-effectiveness of these programs. With increased evidence of the boost that trees and tree planting can give to local economic development and the sense of community, more community organizations will become involved in tree planting and tree care and tree and forest-related projects will be increasingl~ sponsored as a means of enhancing community spirit and organization. These projects will also be increasingly seen as a means of providing a sense of empow-erment of inner city residents to improve neighborhood conditions and for promoting environmental responsibility and ethics. Literature Cited 1. Akbari, H., Huang, J., Martien, P., Rainier, L, Rosenfeld, A., and H. Taha. 1988. The impact of summer heat islands on cooling energy consumption and CO2 emissions. In Proceedings of the 1988 Summer Study in Energy Efficiency in Buildings. American Council for an Energy-Efficient Economy, Washington DC. 2. Anderson, L.M. and H.K. Cordell. 1985. Residential property values improve by landscaping with trees. S. J. Appl. For. 9:162-166. 3. Chenoweth, R.E., and P. H. Gobster. 1990. The nature and ecology of aesthetic experiences in the landscape. Landscape J. 9:1-18. 4. Cook, D.I. 1978. Trees, solid barriers, and combinations: Alternatives for noise control, pp. 330-339. In Hopkins, G. (ed.) Proceedings of the National Urban Forestry Conference, USDA Forest Service, State University of New York College of Environmental Science and Forestry, Syracuse, NY. 5. Corrill, M., Lillydahl, J., and L. Single. 1978. The effects of greenbelts on residential property values: some findings on the political economy of open space. Land Econ. 54:207-217. 6. Dwyer, J.F., Peterson, G.L., and A.J. Darragh. 1983. Estimating the value of urban trees and forests using the travel cost method. J. Arboric. 9:182-195. 7. Dwyer, J.F., Schroeder, H.W., Louviere, J.J., and D.H. Anderson. 1989. Urbanites willingness to pay for trees and forests in recreation areas. J. Arboric. 15:247-252. 8. Dwyer, J.F. 1991. Economic value of urban trees, pp. 27-32. In A National Research Agenda for Urban Forestry in the 1990's. International Society of Arboriculture, Research Trust, Urbana IL. 9. Dwyer, J.F., Schroeder, H.W., and P.H. Gobster. 1991. The significance of urban trees and forests: Toward a deeper understanding of values. J. Arboric. 17:276-284. 10. Johnson, C.W., Barker, F.S. and W.S. Johnson. 1990. Urban and Community Forestry. USDA Forest Service, Ogden UT. 11. McPherson, E.G. 1987. Effects of vegetation on building energy performance. Ph. D. Dissertation, State University of New York College of Environmental Science and Forestry at Syracuse, 245 pp. 12. McPherson, E.G. 1991. Economic modeling for large- 4. J 2:34 Dwyer et al: Urban Forest Benefits and Costs scale tree plantings. In E. Vine, D. Crawley, and P. Centolella (Eds). Energy Efficiency and the Environment: Forging the Link, Chapter 19, American Council for an Energy-Efficient Economy, Washington DC. 13. McPherson, E.G. (in press). Cooling heat islands with sustainable landscapes. In Proceedings of the Sustainable Cities Symposium, Chicago IL. 14. McPherson, E.G. and E. Dougherty. 1989. Selecting trees for shade in the Southwest. J. Arboric. 15:35-43. 15. McPherson, E.G. and R.A. Rowntree. 1991. The environmental benefits of urban forests, pp. 52-57. In A National Research Agenda for Urban Forestry in the 1990's. International Society of Arboriculture, Research Trust, Urbana IL. 16. More, T.A., Stevens, T., and P.G. Allen. 1988. Valuation of urban parks. Landscape and Urban Plan. 15:139-152. 17. Reethof, G. and O.H. McDaniel. 1978. Acoustics and the urban forest, pp. 321-329. In Hopkins, G. (ed.) Proceedings of the National Urban Forestry Conference, USDA Forest Service, State University of New York College of Environmental Science and Forestry, Syracuse, NY. 18. Rich, S. 1971. Effects of trees and forests in reducing air pollution, pp. 29-34. In Little, S and J.H, Noyes (eds) Trees and Forests in an Urbanizing Environment. USDA Cooperative Extension Service, University of Massachusetts, Amherst. 19. Rowntree, R.A. and D.J. Nowak. 1991. Quantifying the role of urban forests in removing atmospheric carbon dioxide. J. Arboric. 17:269-275. ;.~0. Sanders, R.A. 1984. Urban vegetation impacts on the urban hydrology of Dayton Ohio. Urban Ecol. 9:361-376. • 'H. Schroeder, H.W. 1989. Environment, behavior, and design research on urban forests, pp. 87-107. In E.H. Zube and G.T. Moore, eds. Advances in Environment, Behavior, and Design. Plenum, New York. 22. Schroeder, H.W. and L.M. Anderson. 1984. Perception of personal safety in urban recreation sites. J. Leis. Res. 16:178-194. 23. Schroeder, H.W. 1991. Preference and meaning of arboretum landscapes: Combining quantitative and qualitative data. J. Envir. Psych. 11:231-248. :?>4. Schroeder, H.W. 1991. Social values of urban trees, pp. 33-36. In A National Research Agenda for Urban Forestry in the 1990's. International Society of Arboriculture, Research Trust, Urbana IL. 25. Shaw, W.W., Magnum, W.R., and J.R. Lyons. 1985. Residential enjoyment of wildlife resources by Americans. Leis. Sci. 7:361-375. 26. Taha, H. (in press). Effects of urban heat islands. In S. Davis (ed) Urban Heat Island Manual. Washington DC. Environmental Protection Agency and Lawrence Berkeley Laboratory. 27. Ulrich, R.S. 1984. View through a window may influence recovery from surgery. Science 224:420-421. " U.S.D.A. Forest Service North Central and Northeastern Forest Experiment Stations 5801 N. Pulaski Rd. Chicago, IL 60646. An earlier version of this paper was prepared as background for the Fifth National Urban Forest Conference: Forging Alliances for Community Trees, in Los Angeles CA November 12-17, 1991 Resum6. Les arbres et les for~ts urbaines sont des composantes significatives et de grandes valeurs pour I'environnement urbain et peuvent pourvoir un large eventail de benefices pour les citadins. Ceux-ci incluent un environnement plus agreable, sain et confortable dans lequel vivre, travailler et jouer; des economies dans les co~ts de fourniture d'une large gamme de services urbains; et des ameliorations substantielles de laqualite de vie individuelle et communautaire. Ces benefices et co~ts sont analyses en debutant avec I'influence des arbres et des for~ts urbaines sur I'environnement physique et biologique et se poursuit avec I'importance socio-economique des arbres urbains et la multitude d'environnements qu'ils creent pour les individus et les communautes.. Zusammenfassung. Stadtb~ume und Stadtw&lder sind wichtige und wertbestimmende Komponenten der st&dtischen Umwelt und k6nnen zahlreiche Wohlfahrtswirkungen f~r die Stadt haben. Diese beinhalten eine schSnere, gesLindere und komfortablere Umwelt zum Leben, Arbeiten und Spielen, Kostenersparnis auf vielen Gebieten st&dtischer Dienstleistungen und substantielle Verbesserung beim individuellen und gemeinschaftlichen Wohlbefinden. Diese Vorteile und Kosten we~'den diskutiert, angefangen mit dem Einflu B der Stadtb~ume und Stadtw&lder auf die physikalische und biologische Umwelt, und f~hren fort mit der sozioSkonomischen Bedeutung der Stadtb&ume und die Umgebung, die sie schaffen f~r den Printed on Recycled Paper <input type="hidden" name="ProductText" value="227 Journal of Arboriculture 18(5): September 1992 ASSESSING THE BENEFITS AND COSTS OF THE URBAN FOREST by John F. Dwyer, E. Gregory McPherson, Herbert W. Schroeder, and Rowan A. Rowntree Abstract. With effective planning and management, urban trees and forests will provide a wide range of important benefits ;to urbanites. These include a more pleasant, healthful, and ~omfortable environment to live, work, and play in, savings in the costs of providing a wide range of urban services, and substantial improvements in individual and community well-being. Urban forestry plans should begin with consideration of the contribution that trees and forests can make to people's needs. Planning and management efforts should focus on how the forest can best meet those needs. Past planning and management efforts have not been as effective as they might have been because planners and managers have underestimated the potential benefits that urban trees and forests can provide, and have not understood the planning and management efforts needed to provide those benefits, particularly the linkages between benefits and characteristics of the urban forest and its management. Urban forests are a significant and increasingly valuable component of the urban environment. However, with the limited information on the benefits and costs of urban trees and forests currently available to decision makers, management of these valuable assets continues to be inadequate. Urban forest resources are declining in many cities, and the resulting benefits are only a fraction of what they could be. In many instances costs are higher than necessary We are just beginning to learn about the extent and magnitudes of the many benefits and costs associated with urban trees and forests, as well as the many ties between urban forest resources and the quality of urban life. Research in a number of areas suggests that we have vastly underestimated the many ways that the urban forest touches the lives of urbanites, as well as the deep significance that many people attach to trees. Furthermore, we often lack reliable information onlhow to most effectively manage urban forests to provide many of these benefits. A sound understanding of the full range of benefits and costs associated with urban forests, as well as how various management practices, programs, and policies influence those benefits and costs, is essential for action to enhance urban forests and the associated well-being of urbanites. Benefits to consider include the goods and services produced by urban trees and forests that are valuable to people. These benefits vary over space and time according to changes in the urban environment, its inhabitants, and their needs. Some benefits are easily expressed in dollars or other numbers, while others are difficult to quantify using such measures; but in the aggregate they are highly significant to urbanites. The long life of urban trees and forests mandates planning with a view to future needs. Investments in the planting and care of trees represent a long term commitment of scarce dollars, and improper plantings can increase costs and reduce benefits. Therefore, it is important to do it right and plan for future management. The effectiveness of urban trees and forests in providing benefits to people depends on their species composition, diversity, age, and location with respect to people and other elements in the landscape. An ecosystem approach that recognizes people as the central component offers the best means to assess the complex interactions between urban trees and forests and the well-being of urbanites, linking management actions with their effects on urban forests and the associated benefits and costs. The following discussion begins with the influence of urban trees and forests on the physical and biological environment and continues with the socio-economic importance of urban trees and the environments that they create. .228 Physical/Biological Environment and Pro- ,-cesses Urban and community .forests can strongly influence the physical/biological environment and .miti.gaEte many impacts of urban deve.opment by :mode rating Climate, ~c0nserving energy, carbon dioxide, .and water, improving air,quality, con. tr,0l-ling rainfall runoff and flooding, .lowering noise :lev.e.S, harboring wildlife, and enhancing the at,t,ractiy..e#.e.ss .o.f .cit~ies. These ,benefits may b.e partially offset by problems that vegetation can pose Such as pollen production, hydrocarbon emissions, green wastedisposal, water consumption, and displacement of native species by ag-,gressive exotics(15). Urban forests can be,viewed as a "lMng technology," a key component of the urban infrastructure that helps maintain a healthy environment for urban dwellers. Energy and carbon dioxide conservation. Trees can contribute to energy conservation` be-cau.se they help toreduce the cost of heating and cooling buildings. Projections from computer simulations indicate that .00 mi•llien mature trees in U..S.- Cities (three trees for every o`ther single .[.a,,~i y I~#,me) CoU.d .r, edu-ce annua energy u,se by .30 billion kWh, saving about 2 billion '(Jollars in energy costs (.1). Savings associated with avoided i0vestment in new power supplies could augment .he.se savin.gs considerably. A.Is# as,so,c..a,ted w.it, b this energy savings is a 9 .million ton per Year :reduction i0 carbon dioxide em ss ons from power plants. At present U.S. urban forests are estimated il.o S,`tore approximately 800 million tons.of carbon, ,0ear y 5 percent of live tree carbon storage :in all US forests (. 9). Recent studies .by scien[is.ts and energyutilities show that when the costs 0fp.anting, .:ea.te,~og, and mai0ta[ning treesare ,co0si,d.ered :.roe plan..ing is a more cost~effect, ve energy Ao.d, ,carbon dioxide conservation strategy •than manY ,..o.tber .fuel-saving measures .(13). As with most urban .forest benefits, .energy savings.can only be rea[ize.d, thr0ug.h appropriate r#anagement strategies. With poor management, ~,important benef:its can belost ar)d increased costs iincurred. For example, annual space air condition-ii.n.g, and heating costs for a typical hone ].n Madison ,Wisconsin increase from $671 for an energy-efficient planting design, to $700 for no .trees, to J Dwyer et.al: Urban Forest Benefits a, nd c: 9StS $769 ,iortre.es t h.at b.ock winter su.n.l..ght ,and. ~pro, vide little summer shads .(t 1). Cpsts .for water, pruning removal litter clean-up, po.Jen, heal.th- 'relateci problems andliabiiiiy c~n ai:~gofts#t b,en-- efits, pa.(ticularly if the wrong tree isplanted j n the w[e£g pjace. 4ir'q#a.ity. Trees exchange gases with the atmosphere and -capture particulates that £an be harmful to people. The rate at.which tree# remove gaseous pollutants such as ozone, carbon mon- oxide, ia0d sulphur dioxide depellds pfimari.y on the amount of foliage, number an# conditi#n of the stomata, an# meteorological c0nditi0.ns. Re.su.lts f[or;n computer studies indicate that trees can reduce appreciably the amount of ozone in poll.uted air. P.ine'trees in Los Angeles were projected .to remove from t he atmosphere (under 400 meters) ,about 8% of the #zone .and decrease ,the con-cen,- tratiohoar, ound the I.eaves by 49% (. 8). Urban ozone concentrations go UP with in, creases in amb.ent temperatures. Onestudy fou, n d that the incidence of smoggy days increased 1% for each 1°C increase in t.empe.[ature (26)..B.ff" c-ause .U r)an, .fores. ts can reduce ?summe,~ime tem- pe[a.tufe?s.they provide an`oth, er means ,of mprow ing air quality. By extrapolating from studies for .non-urban forests we can in fer that a mature urban ,tree -can Jo.te[c,ept.up to ,5.0 POunds of parti#ul.ates per year. Planting of 500 000 trees in Tucson was projected .to .reduce air-borne particulates by.6,500 t ons. per year..The annual imp.lied value of part iculatemat.ter control was estimated at $4.16 per treeper year£n averageor $1.5 million for all trees eac, h year (t2). Citjzlen`s spend millio.ns Of dollars ar~nua.lly ,to controlgase0us and pa~icu.ate poll.utant,s ~t.h rough pr~ograms for veh c e nspect on and maintenance 0xygefiated fuels, rideshare, and street #ay.ing and sweeping.To the exltent that trees can c0.ntr01 .p,0,[lutants th.ere is p0ten.ial for i.mp.r, .oved air qu.ality a,o..d s.d, bsta.ntj#l `cost savings. Urban for#stscanbe viewed as c.omPonen.ts .of an ,overall strategy to restore air quality in our cities. Improved air qualit'y will,enhancephysical and mental h ea, lth, re~.ulting in substantial savings .in expenditures for .health care. Improvements in air quality also reduce the .. . ,. .' , ,; , ,.. . ., , costs ofrepairing damage to buildings statuarY, etc. that po.or air quality causes. Journal of Arboriculture 18(5): September 1992 229 ~ Urban hydrology. Urban forests can play an important role in urban hydrologic processes by reducing the rate and volume of stormwater runoff,flooding damage, stormwater treatment costs, and water quality problems. Runoff estimates for an intensive storm event in Dayton, Ohio showed that the existing tree canopy reduced potential runoff by 7% and a modest increase in canopy cover would reduce runoff by nearly 12% (20). Runoff reductions could be further enhanced by directing runoff to landscape plantings. By reducing runoff, trees function like retention/ detention structures that are essential to many communities. Savings in stormwater management costs from trees in Tucson were calculated at $0.18 per tree per year or $600,000 over 500,000 trees and 40 years (12). Reduced runoff due to rainfall interception can also reduce stormwater treatment costs in many communities. Water use by landscape vegetation is an important issue in arid and semi-arid regions where water resources are increasingly scarce; but also in other ,~reas where drought can bring about restrictions on watering. We know that annual water costs can be twice as great as cooling energy savings from shade for high water use species such as mulberry (14). However, energy savings have the indirect effect of conserving water at power plants. In Tucson, 16% of the annual irrigation requirement for each tree was offset by water conserved at the power plant due to energy savings provided by the tree. Because of recent regulations by the Environmental Protection Agency aimed at improving the quality of urban runoff and growing interest in water conservation, these hydrologic benefits will increase in importance over time. Noise reduction. Field tests have shown that properly designed plantings of trees and shrubs significantly reduce noise. Wide belts of tall dense trees combined with soft ground surfaces can reduce apparent loudness by 50% or more (4,17). Noise reduction from plantings along roadsides in urbanized areas is often limited due to narrow roadsideplanting space. Buffer plantings in these circumstances are typically more effective at screening views than reducing noise. Ecological benefits. Urban forests promote ecological stability by providing habitat for wildlife, conserving soil, and enhancing biodiversity. Although the value of these benefits is seldom quantified, they are important to many urban dwellers and to the long term stability of urban ecosystems. Surveys have found that most city-dwellers enjoy and appreciate wildlife in their day-to-day lives (25). To enhance wildlife habitat, numerous communities have developed programs to preserve valuable existing natural areas and to restore the habitat on degraded lands. For example, restoration of urban riparian corridors and their linkages to surrounding natural areas have facilitated the movement of wildlife and dispersal of flora. Usually habitat creation and enhancement increases biodiversity and complements many other beneficial functions of the urban forest (10). Because of the growing environmental awareness and concern for quality of life in our cities, ecological benefits such as these will increase in significance over time. There can also be problems or costs associated with urban wildlife, including damage to plants and structures, droppings, threats to domestic pets, disease, etc. Social Dimensions All of the benefits associated with the physical/ biological environment and processes discussed above have significant implications for people who live in urban areas. We now turn our attention to critical people/forest interactions. Desirable environments. The presence of urban trees and forests can make the urban environment a more pleasant place to live, work, and spend leisure time. Studies of urbanites' preferences and behavior confirm the strong contribution that trees and forests make to the quality of life in urban areas. Trees and forests are a prominent component of the landscape in most urban areas. Urban forests provide significant outdoor leisure/recreation opportunities for urbanites. Based on nine visits per year to local parks per person, and $1.00 per visit in value added by the presence of well managed urban forest resources, the total contribution of urban trees and forests in park and recreation areas to the value of recreation experiences provided in the USA could exceed $2 billion (8). These are 230 both conservative estimates based on studies in the Midwest (6,7), and do not include benefits from trees on residential lots and other "non-desig-nated" areas. The Forest Preserve District of Cook County, Illinois provides more than 40 million visits per year from a base of 66,000 acres of urban forests. In addition to parks and preserves, urban greenways provide a wide range of recreational opportunities. Bicycle trails in river corridors in the Chicago Metropolitan area support up to 5,000 bicycles per day passing a given point on a single trail. To the extent that urban trees and forests increase the quality of the urban environment and make spending leisure time there more attractive, there will be substantial savings in fuel consumed because people will not drive to distant recreation sites as often. At $1.25 per gallon, the savings to individuals across the U.S. total $300 million per year if just one gallon per individual is saved by reduced leisure trips. It would seem that the potential savings in fuel costs from an urban environment that is enhanced by well managed trees and forests might be five times that amount or $1.5 billion per year (8). Reduced fuel consumption would substantially reduce air pollution and related problems. Medical. Reduced stress and improved physical health for urban residents have been associated with the presence of urban trees and forests. Studies have shown that landscapes with trees and vegetation produce more relaxed physiological states in humans than landscapes that lack these natural features. Hospital patients with window views oftrees recover significantly faster and with fewer complications than comparable patients without access to such views (27). Future research will identify specific situations (e.g., urban commuting) in which urban forests can offset stress, and measure the amount of stress reduction that occurs. The benefits to public health from using trees to reduce urban stress are potentially very significant. In addition, cleaner air can be expected to improve health. There may be health-related costs as well, such as allergies to plants, pollen, or associated animals and insects. Psychological. Urban forest environments provide esthetic surroundings, increased enjoy- Dwyer et al: Urban Forest Benefits and Costs ment of everyday life, and a greater sense of meaningful connection between people and the natural environment. Trees are among the most important features contributing to the esthetic quality of residential streets and community parks (21). Perceptions of esthetic quality and personal safety are very sensitive to features of the urban forest such as number of trees per acre and view distance (22). Park and arboretum visitors have reported that trees and forests provide settings for significant emotional and spiritual experiences (3,23,24). These experiences are extremely important in people's lives, and can lead to a strong feeling of attachment to particular places and trees (9). An improved understanding of the emotional and symbolic meanings of trees will enable managers to provide the kind of settings that contribute to a meaningful and satisfying sense of place in the urban environment. Costs include fear of trees, forests, and associated environments. Real estate values. The sales value of real estate reflects the benefits that buyers attach to the attributes of that property, including the trees and forest resource found on the property, along the street, and in neighboring parks and greenways. An individual's willingness to pay for a residential property is likely to reflect the value of benefits that they expect from these forest environments, including opportunities for leisure out in the yard or in the neighborhood, reduced heating and cooling costs, privacy, and the lack of a need to construct fences or screens. The variation in sales prices over a large number of residential properties with different forest resources on the property and nearby can be used to infer the willingness of users to pay for those urban forest resources (2). These increases in property values are not a separate category of value that is distinct from the goods and services provided; but rather one means of reflecting or capturing the values of the many important services that urban residents receive from urban forests. The ties between trees and property values provide an incentive for homeowners to invest in trees since increased revenues can be received at the time of sale of that home (i.e., an advertisement mentioning well landscaped yard, shaded patio, close to parks and bicycle trails, and an 231 Journal of Arboriculture 18(5): September 1992 energy efficient home). Economic values of trees and forests that are expressed as increased real estate values also prOduce direct economic gains to local communitieS, through property taxes. Consequently, tree planting and tree care on public and private lands can be viewed as an investment that achieves an annual return in property taxes. A conservative estimate of a 5 percent increase in property values due to trees and forests on residential properties (several studies suggest higher values) represents $25 per year on a conservative property tax bill'of $500, and quickly adds up to $1.5 billion per year over the 62 million single family detached housing units in the USA. A more realistic estimate is two to three times that amount. Parks and greenways have been associated with increments in the value of nearby real estate (5,16). Some of these increments have been substantial and it appears that parks with an "open space character" add most to the value of nearby real estate. We have yet to identify the increments in real estate value associated with urban forest resources in street corridors. Residential properties are not the only real estate that gains in value from urban trees and forests. Shopping centers frequently landscape their surroundings in an effort to provide a pleasing environment that will attract shoppers, thereby increasing the value of businesses and the shopping center. While we are currently unaware of research that documents the increased business and tax receipts that are associated with such efforts, trees and forests may make an important contribution to the economic vitality of these businesses, and the private sector is currently making substantial investments in this area --far in excess of, what is required by local regulations. One neighborhood shopping district in Chicago has concluded that planting trees along the street in front of their establishments increased their business activity. Similarly, employers invest in landscaping, beyond what is required, to enhance worker productivity, and morale. While there is currently no research to document the increased worker productivity in such environments, building owners are generally able to obtain higher rents for offices that overlook well-landscaped areas. In short, trees and forests can make a substantial contribution to property tax revenues, thereby providing annual returns on municipal investments in urban trees and forests. These benefits are offset, in part, by the costs of managing the forests and repairing damages that may be associated with them, such as disruption of sidewalks, sewers, powerlines, etc. Local economic development. Urban forest resources also make a broad contribution to the economic vitality of a city, neighborhood, or subdivision. While this is particularly difficult to quantify, it is apparently no accident that many cities and towns are named after trees and forests (i.e., Elmhurst and Oak Park) as are subdivisions (i.e. Tall Timbers and Timber Trails) and many areas strive to be designated as a "Tree City USA." Many neighborhoods select tree planting as a community improvement project. Trees can dominate the urban environment and contribute much to its character. In the Chicago area, communities such as Evanston, Oak Park, and Elmhurst are well known for their mature forest environments. Atlanta's large investment in downtown tree plantings has paralleled an upswing in convention business and contributed to its image of a progressive, livable city. Community action programs that start with trees and forests often spread to other aspects of the community and result in substantial economic development. Often trees and forests on public lands-- and to some extent those on private lands as well -- are significant "common property" resources that contribute to the economic vitality of an entire area. The substantial efforts that many communities undertake to develop and enforce local ordinances and manage urban forest resources attests to the substantial return that they expect from these investments. Societal. Stronger sense of community, em-powerment of inner city residents to improve neighborhood conditions, and promotion of environmental responsibility and ethics can be attributed to involvement in urban forestry efforts. Active involvement in tree-planting programs has been shown to enhance a community's sense of social identity, self-esteem, and territoriality, and 232 Dwyer et al: Urban Forest Benefits and Costs it teaches residents that they can work together to choose and control the condition of their environment. Community tree planting programs can help alleviate some of the hardships of inner city living, especially for low-income groups. Research on environmental education is exploring ways of teaching children about their responsibility in caring for trees, and can provide badly needed opportunities for inner city children to experience nature. Researchers are examining how such early experiences with nature influence the willingness to adopt an environmental ethic later in life. Summary and Conclusions With effective planning and management, urban trees and forests will provide a wide range of important benefits to urbanites. These include a more pleasant, healthful, and comfortable environment in which to live, work, and play, savings in the-costs of providing a wide range of urban services, and substantial improvements in individual and community well-being. Urban forests can enhance the city environment by influencing temperature, wind, humidity, rainfall, soil erosion, flooding, air quality, scenic quality, and plant and animal diversity. Each of these influences has significant implications for the well-being of urbanites. But there are also environmental problems that may be associated with the urban forest, such as the generation of pollen, hydrocarbons, and green waste;water and energy consumption; obscured views; and displacement of native species of plants. A well planned and managed urban forest can reduce costs for heating and cooling, health care, driving to exurban areas for recreation and leisure,' stormwater management, and damage from flooding, erosion, and polluted air. Substantial i~creases in revenues can also be associated with urban trees and forests, including the sale of real estate (individual gains), real estate and business taxes (government gains), and tourism (individuals and government may gain). Costs associated with urban forests include establishment and care of the forest; repair of forest-induced damage to other parts of the urban infrastructure (particularly sidewalks and utilities); blocked solar collectors, and foregone opportunities for activities such as gardening and sports. Many important benefits and costs of urban forests that contribute significantly to the well-being of urbanites are not easily reflected in dollars and cents. Psychological benefits associated with urban forests include more pleasant environments for a wide range of activities, improvements in the esthetic environment (sights, sounds, smells), relief from stress (which can lead to improved physical health), enhanced feelings and moods, increased enjoyment of everyday life, and a stronger feeling of connection between people and their environment. Psychological costs can include fears of crime, animals, insects, disease (i.e., Lyme disease), darkness, and falling trees or limbs; and the displeasure of messiness and clutter. Benefits attributed to urban trees and forests extend beyond individuals to society. Societal benefits include a stronger sense of community, empowerment to improve neighborhood conditions, promotion of environmental responsibility and ethics, and enhanced economic development (business, commerce, employment). Societal costs include money and other resources that must be diverted from other social programs. The challenge faced by urban forest resource managers and planners is to balance the many benefits and costs that are associated with urban trees and forests. Lack of information about the extent and magnitude of these benefits and the best approaches for prm/iding them often makes that task a very difficult one. Urban forestry plans should begin with consideration of the contribution that trees and forests can make to people's needs. Planning and management efforts should focus on how the forest can best meet those needs. Past planning and management efforts have not been as effective as they might have been because planners andman-agers.have underestimated the potential benefits that urban trees and forests can provide, and have not understood the planning and management efforts needed to provide those benefits, particularly the linkages between benefits and characteristics of the urban forest and its management. Research continues to document new ways in which trees and forests can benefit urbanites, as well as the magnitudes of these benefits. The 233 Journal of Arboriculture 18(5): September 1992 efforts of urbanites to protect and preserve trees as well as their enthusiastic involvement in tree planting programs reflects their high regard for urban forest benefits. Urban trees and forests promise to be even more consequential in the years ahead. Increasing interest in cost-effective and "minimum impact" approaches for improving the quality of the urban environment suggests that trees will play increasingly important roles in efforts to enhance air quality and improve urban hydrologic processes. Worldwide concern for "global warming" suggests increasing interest in trees for sequestering carbon and reducing carbon dioxide emissions. Associated concern for efficient use of energy resources will bring increasing attention to trees as a means of reducing heating and cooling costs as well as for encouraging urbanites to spend leisure time in the urban environment rather than driving to more remote areas. As we learn more about the functioning of the urban ecosystem and the role of trees and forests in that system, it is likely that these resources will assume new roles in efforts to manage the urban environment. With increasing emphasis on improving the quality of life for urbanites and in "wellness" programs overall, increasing attention will be given to trees and forests as a means for enhancing the quality of urban life. This is likely to include efforts aimed specifically at stress reduction and improved public health. As we learn more about the deep psychological ties between urbanites and trees and forests, it is likely that urban trees and forests will assume new roles in efforts to increase the quality of urban life. As we learn more about the contribution of trees and forests to the value of residential and commercial real estate it is likely that owners will make increasing investments in their trees and forests. Local governments and energy utilities will undertake programs to encourage such efforts, due in part to the increased tax revenues that will result, and to avoid energy costs. Education regarding the planting and care of appropriate tree species in desirable locations will be critical to the long term cost-effectiveness of these programs. With increased evidence of the boost that trees and tree planting can give to local economic development and the sense of community, more community organizations will become involved in tree planting and tree care and tree and forest-related projects will be increasingl~ sponsored as a means of enhancing community spirit and organization. These projects will also be increasingly seen as a means of providing a sense of empow-erment of inner city residents to improve neighborhood conditions and for promoting environmental responsibility and ethics. Literature Cited 1. Akbari, H., Huang, J., Martien, P., Rainier, L, Rosenfeld, A., and H. Taha. 1988. The impact of summer heat islands on cooling energy consumption and CO2 emissions. In Proceedings of the 1988 Summer Study in Energy Efficiency in Buildings. American Council for an Energy-Efficient Economy, Washington DC. 2. Anderson, L.M. and H.K. Cordell. 1985. Residential property values improve by landscaping with trees. S. J. Appl. For. 9:162-166. 3. Chenoweth, R.E., and P. H. Gobster. 1990. The nature and ecology of aesthetic experiences in the landscape. Landscape J. 9:1-18. 4. Cook, D.I. 1978. Trees, solid barriers, and combinations: Alternatives for noise control, pp. 330-339. In Hopkins, G. (ed.) Proceedings of the National Urban Forestry Conference, USDA Forest Service, State University of New York College of Environmental Science and Forestry, Syracuse, NY. 5. Corrill, M., Lillydahl, J., and L. Single. 1978. The effects of greenbelts on residential property values: some findings on the political economy of open space. Land Econ. 54:207-217. 6. Dwyer, J.F., Peterson, G.L., and A.J. Darragh. 1983. Estimating the value of urban trees and forests using the travel cost method. J. Arboric. 9:182-195. 7. Dwyer, J.F., Schroeder, H.W., Louviere, J.J., and D.H. Anderson. 1989. Urbanites willingness to pay for trees and forests in recreation areas. J. Arboric. 15:247-252. 8. Dwyer, J.F. 1991. Economic value of urban trees, pp. 27-32. In A National Research Agenda for Urban Forestry in the 1990's. International Society of Arboriculture, Research Trust, Urbana IL. 9. Dwyer, J.F., Schroeder, H.W., and P.H. Gobster. 1991. The significance of urban trees and forests: Toward a deeper understanding of values. J. Arboric. 17:276-284. 10. Johnson, C.W., Barker, F.S. and W.S. Johnson. 1990. Urban and Community Forestry. USDA Forest Service, Ogden UT. 11. McPherson, E.G. 1987. Effects of vegetation on building energy performance. Ph. D. Dissertation, State University of New York College of Environmental Science and Forestry at Syracuse, 245 pp. 12. McPherson, E.G. 1991. Economic modeling for large- 4. J 2:34 Dwyer et al: Urban Forest Benefits and Costs scale tree plantings. In E. Vine, D. Crawley, and P. Centolella (Eds). Energy Efficiency and the Environment: Forging the Link, Chapter 19, American Council for an Energy-Efficient Economy, Washington DC. 13. McPherson, E.G. (in press). Cooling heat islands with sustainable landscapes. In Proceedings of the Sustainable Cities Symposium, Chicago IL. 14. McPherson, E.G. and E. Dougherty. 1989. Selecting trees for shade in the Southwest. J. Arboric. 15:35-43. 15. McPherson, E.G. and R.A. Rowntree. 1991. The environmental benefits of urban forests, pp. 52-57. In A National Research Agenda for Urban Forestry in the 1990's. International Society of Arboriculture, Research Trust, Urbana IL. 16. More, T.A., Stevens, T., and P.G. Allen. 1988. Valuation of urban parks. Landscape and Urban Plan. 15:139-152. 17. Reethof, G. and O.H. McDaniel. 1978. Acoustics and the urban forest, pp. 321-329. In Hopkins, G. (ed.) Proceedings of the National Urban Forestry Conference, USDA Forest Service, State University of New York College of Environmental Science and Forestry, Syracuse, NY. 18. Rich, S. 1971. Effects of trees and forests in reducing air pollution, pp. 29-34. In Little, S and J.H, Noyes (eds) Trees and Forests in an Urbanizing Environment. USDA Cooperative Extension Service, University of Massachusetts, Amherst. 19. Rowntree, R.A. and D.J. Nowak. 1991. Quantifying the role of urban forests in removing atmospheric carbon dioxide. J. Arboric. 17:269-275. ;.~0. Sanders, R.A. 1984. Urban vegetation impacts on the urban hydrology of Dayton Ohio. Urban Ecol. 9:361-376. • 'H. Schroeder, H.W. 1989. Environment, behavior, and design research on urban forests, pp. 87-107. In E.H. Zube and G.T. Moore, eds. Advances in Environment, Behavior, and Design. Plenum, New York. 22. Schroeder, H.W. and L.M. Anderson. 1984. Perception of personal safety in urban recreation sites. J. Leis. Res. 16:178-194. 23. Schroeder, H.W. 1991. Preference and meaning of arboretum landscapes: Combining quantitative and qualitative data. J. Envir. Psych. 11:231-248. :?>4. Schroeder, H.W. 1991. Social values of urban trees, pp. 33-36. In A National Research Agenda for Urban Forestry in the 1990's. International Society of Arboriculture, Research Trust, Urbana IL. 25. Shaw, W.W., Magnum, W.R., and J.R. Lyons. 1985. Residential enjoyment of wildlife resources by Americans. Leis. Sci. 7:361-375. 26. Taha, H. (in press). Effects of urban heat islands. In S. Davis (ed) Urban Heat Island Manual. Washington DC. Environmental Protection Agency and Lawrence Berkeley Laboratory. 27. Ulrich, R.S. 1984. View through a window may influence recovery from surgery. Science 224:420-421. " U.S.D.A. Forest Service North Central and Northeastern Forest Experiment Stations 5801 N. Pulaski Rd. Chicago, IL 60646. An earlier version of this paper was prepared as background for the Fifth National Urban Forest Conference: Forging Alliances for Community Trees, in Los Angeles CA November 12-17, 1991 Resum6. Les arbres et les for~ts urbaines sont des composantes significatives et de grandes valeurs pour I'environnement urbain et peuvent pourvoir un large eventail de benefices pour les citadins. Ceux-ci incluent un environnement plus agreable, sain et confortable dans lequel vivre, travailler et jouer; des economies dans les co~ts de fourniture d'une large gamme de services urbains; et des ameliorations substantielles de laqualite de vie individuelle et communautaire. Ces benefices et co~ts sont analyses en debutant avec I'influence des arbres et des for~ts urbaines sur I'environnement physique et biologique et se poursuit avec I'importance socio-economique des arbres urbains et la multitude d'environnements qu'ils creent pour les individus et les communautes.. Zusammenfassung. Stadtb~ume und Stadtw&lder sind wichtige und wertbestimmende Komponenten der st&dtischen Umwelt und k6nnen zahlreiche Wohlfahrtswirkungen f~r die Stadt haben. Diese beinhalten eine schSnere, gesLindere und komfortablere Umwelt zum Leben, Arbeiten und Spielen, Kostenersparnis auf vielen Gebieten st&dtischer Dienstleistungen und substantielle Verbesserung beim individuellen und gemeinschaftlichen Wohlbefinden. Diese Vorteile und Kosten we~'den diskutiert, angefangen mit dem Einflu B der Stadtb~ume und Stadtw&lder auf die physikalische und biologische Umwelt, und f~hren fort mit der sozioSkonomischen Bedeutung der Stadtb&ume und die Umgebung, die sie schaffen f~r den Printed on Recycled Paper ">!
62!7/18/2002 4:09:00 PM!The cost of shade: cost-effectiveness of trees versus bus shelters!McPherson, E.G. and S. Biedenbender!1991!Journal of Arboriculture. 17(9)!Articles in Journals!Miscellaneous Benefit-Cost Literature!cufr_62_EM91_23.PDF!PDF!McPherson, E.G. and S. Biedenbender. 1991. The cost of shade: cost-effectiveness of trees versus bus shelters. Journal of Arboriculture. 17(9): 233-242!!Shade at bus stops can enhance the thermal comfort of waiting riders and can encourage new passengers, thereby reducing air pollution and traffic congestion. This study used computer simulation to compare the cost-effectiveness of shade provided by metal shelters versus trees at 64 bus stops in Tucson, Arizona. The 40-year projected total future and present values of costs were over 50% greater for shelters than for trees. When differences in the amount of shade provided over time were considered, a 20% cost savings was projected for trees. Expenses for irrigation and pruning accounted for about 95% of all projected tree costs. These findings suggest that trees can be a cost-effective substitute for shelters at bus stops in mid-latitude cities where shade is useful!
63!7/18/2002 4:12:00 PM!The effects of roof albedo modification on cooling loads of scale model residences in Tucson, Arizona!Simpson, J.R. and E.G. McPherson!1997!Energy and Buildings. 25(2)!Articles in Journals!Impact of Roof Materials on Residential Cooli!cufr_63_JS97_51.PDF!PDF!Simpson, J.R. and E.G. McPherson. 1997. The effects of roof albedo modification on cooling loads of scale model residences in Tucson, Arizona. Energy and Buildings. 25(2): 127-137!Roof albedo, scale model residences, roof color, computer simulation, Arizona!Data supporting reductions in cooling load and related demand for electric power possible from increasing building surface albedo are limited. Electrical use of wall-mounted air conditioners, roof temperatures, and related environmental factors were monitored during the summer of 1990 on three initially identical 1/ 4-scale model buildings situated in rock mulch landscapes in Tucson, Arizona. Model thermodynamic properties were scaled to approximate thermodynamic similarity with full-size buildings. With ceiling insulation of R value 5.28 m2 K W-1 (R-30) installed, increasing roof albedo of the gray composition shingles (0.30 albedo, 0.94 emissivity) by painting one roof silver and another white (0.49 and 0.75 albedos, 0.70 and 0.98 emissivities, respectively) reduced daily total and hourly peak electrical use for air conditioning approximately 5% for the house with white-colored roof compared to either gray or silver-colored roofs. Larger differences were found without ceiling insulation, with daily total and peak hourly demand for houses with white compared to dark brown roofing ( 0.9 albedo, 0.98 emissivity) reduced 28 and 18%, respectively. Computer simulations of daily total energy use confirmed comparable savings for similar full-sized buildings. White roofs were 20 to 30°C cooler than either silver or dark-colored roofs on hot, sunny days, indicating that expected cooling due to an increase in albedo may not be realized if it is accompanied by a decrease in emissivity. Light-colored roofs, by maintaining cooler attic temperatures, may provide savings in addition to those presented here by reducing heat gain to air distribution systems located in the attic space!energy !
66!7/18/2002 4:26:00 PM!Parking lot shade study: a critical examination of Davis parking lot tree shade!Wong, T.W!1996!Senior thesis project. Davis, CA. University of California and USDA Forest Service, Western Center for Urban Forest Research!Dissertations/Thesis!Impacts of Shade Trees in Parking Lots in Dav!cufr_66_TW96_80.PDF!PDF!Wong, T.W. 1996. Parking lot shade study: a critical examination of Davis parking lot tree shade. Senior thesis project. Davis, CA. University of California and USDA Forest Service, Western Center for Urban Forest Research: 75!!!
68!7/18/2002 4:32:00 PM!Effects of tree cover on parking lot microclimate and vehicle emissions!Scott, K.I., J.R. Simpson, E.G. McPherson!1999!Journal of Arboriculture. 25(3)!Articles in Journals!Effects of Tree Cover on Parking Lot Microcli!11/cufr_68.pdf!PDF!Scott, K.I., J.R. Simpson, E.G. McPherson. 1999. Effects of tree cover on parking lot microclimate and vehicle emissions. Journal of Arboriculture. 25(3): 129-142!Parking lot; microclimate; vehicle emissions!A pilot study was performed to measure the difference in parking lot microclimate resulting from the presence or absence of shade tree cover. Microclimate data from contrasting shade regimes were then used as input to a motor-vehicle emissions model. Model results were used to estimate the potential for regional increases in parking lot tree cover to reduce motor-vehicle hydrocarbon and nitrogen oxide (NOx) emissions!air !
69!7/18/2002 4:35:00 PM!Actualizing microclimate and air quality benefits with parking lot tree shade ordinances!McPherson, E.G., J.R. Simpson and K.I. Scott!2001!Wetter und Leben. 4(98)!Articles in Journals!Effects of Tree Cover on Parking Lot Microcli!11/cufr_69.pdf!PDF!McPherson, E.G., J.R. Simpson and K.I. Scott. 2001. Actualizing microclimate and air quality benefits with parking lot tree shade ordinances. Wetter und Leben. 4(98): 353-369!!Parking lots have been recognized as thermal "hot-spots" and many California cities have implemented ordinances that require shading of 50 percent of paved areas by trees. Although these regulations have been in effect for over 15 years, relatively few lots achieve this level of canopy cover. Inadequate shade can increase air temperatures and pollutants emitted from parked cars. Parked cars emit evaporative hydrocarbons (HC) that contribute to the formation of ground level ozone. The hotter the car the higher the rate of evaporation from fuel tanks, hoses, and carbon canisters. A pilot study was performed to measure the difference in parking lot microclimate resulting from the presence or absence of shade tree cover in Davis, CA. A very modest level of shading resulted in an air temperature reduction of approximately 1 to 2 C (1.8-3.6 F), compared to an unshaded lot. The fuel tank in a shaded vehicle was 2 to 4 C (3.6-7.2 F) cooler than the tank in an unshaded vehicle, which suggests that irradiance and temperature reduction have approximately equivalent effects. Measured microclimate data were then used as input to a motor vehicle emissions model. Results indicate that increasing parking lot canopy cover from 8% to 50% would reduce Sacramento County's light-duty vehicle ROO evaporative emissions by 2% (0.85 tpd) and NOx start emissions by less than 1% (0.1 tpd). Though modest, these reductions are equivalent to projected emission reductions for existing air quality management district control measures for HCs and NOx (e.g., graphic arts, alternative fuel stations and waste burning, vehicle scrappage program). Measures to strengthen and more effectively implement Davis's Parking Lot Tree Shading Ordinance are described!air !
70!7/18/2002 4:36:00 PM!The impact of shade trees on reducing heat island effect in parking lots!McPherson, E.G!1998!Arid Zone Times. February!Articles in Periodicals!Effects of Tree Cover on Parking Lot Microcli!cufr_70_EM98_65.PDF!PDF!McPherson, E.G. 1998. The impact of shade trees on reducing heat island effect in parking lots. Arid Zone Times. February: 1-2!!!
71!7/18/2002 4:38:00 PM!Green parking lots: can trees improve air quality?!Scott, K.I., J.R. Simpson and E.G. McPherson!1998!California Urban Forests Council Newsletter: CUF Link. Spring!Articles in Periodicals!Effects of Tree Cover on Parking Lot Microcli!cufr_71_SK98_77.PDF!PDF!Scott, K.I., J.R. Simpson and E.G. McPherson. 1998. Green parking lots: can trees improve air quality?. California Urban Forests Council Newsletter: CUF Link. Spring: 1-2!!!air !
73!7/18/2002 4:42:00 PM!Reducing air pollution through urban forestry!McPherson, E.G. and J.R. Simpson!2000!In: Adams, D., (ed). Proceedings of the 48th annual meeting of the California Forest Pest Council; 1999 November 18-19; Sacramento. Sacramento: California Forest Pest Council!Articles in Conference Proceedings!Effects of Tree Cover on Parking Lot Microcli!11/cufr_73.pdf!PDF!McPherson, E.G. and J.R. Simpson. 2000. Reducing air pollution through urban forestry. In: Adams, D., (ed). Proceedings of the 48th annual meeting of the California Forest Pest Council; 1999 November 18-19; Sacramento. Sacramento: California Forest Pest Council: 18-21!!This paper presents a brief review of ways that urban forests positively and negatively impact air quality .It provides an overview of our research on air quality effects from parking lot shade and guidelines to estimate atmospheric carbon dioxide reductions through urban forestry!air !
74!7/18/2002 4:45:00 PM!Sacramento's parking lot shading ordinance: environmental and economic costs of compliance!McPherson, E.G!2001!Landscape and Urban Planning. 57!Articles in Journals!Sacramento Parking Lot Tree Shade Ordinance!cufr_74_EM01_62.PDF!PDF!McPherson, E.G. 2001. Sacramento's parking lot shading ordinance: environmental and economic costs of compliance. Landscape and Urban Planning. 57: 105-123!Tree shade; Natural resource valuation!A survey of 15 Sacramento parking lots and computer modeling were used to evaluate parking capacity and compliance with the 1983 ordinance requiring 50% shade of paved areas (PA) 15 years after development. There were 6% more parking spaces than required by ordinance, and 36% were vacant during peak use periods. Current shade was 14% with 44% of this amount provided by covered parking. Shade was projected to increase to 27% (95% CI 24-37%) when all lots in the sample were 15-year-old. Annual benefits associated with the corresponding level of tree shade were estimated to be US$ 1.8 million (CI US$ 1.5-2.6 million) annually citywide, or US$ 2.2 million less than benefits from 50% shade (CI US$ 1.4-2.5 million). The cost of replacing dying trees and addressing other health issues was US$ 1.1 million. Planting 116,000 trees needed to achieve 50% shade was estimated to cost approximately US$ 20 million. Strategies for revising parking ordinances to enhance their effectiveness are presented!
75!7/18/2002 4:49:00 PM!Green plants or power plants?!Geiger, J.R!2002!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 4p. Research summary!Research Summaries!Energy Effects of Urban Forests in California!3/cufr_148.pdf!PDF!Geiger, J.R. 2002. Green plants or power plants?. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 4p. Research summary!shade, planting trees, locations, energy, utilities, savings!Researchers at the Center for Urban Forest Research in Davis, California found that planting shade trees can reduce the need for power plants. The study shows that 50 million shade trees planted in strategic, energy-saving locations could eliminate the need for seven 100-megawatt (MW) power plants!
76!7/18/2002 4:52:00 PM!Trees are good, but can they solve the energy crisis?!Geiger, J.R!2001!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 1p. Briefing paper!News Briefs!Energy Effects of Urban Forests in California!!PDF!Geiger, J.R. 2001. Trees are good, but can they solve the energy crisis?. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 1p. Briefing paper!!!
77!7/18/2002 4:53:00 PM!California Energy Study: Frequently Asked Questions!Geiger, J.R!2001!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 1p!Frequently Asked Questions!Energy Effects of Urban Forests in California!CUFR_77_ENERGY_QandA.pdf!PDF!Geiger, J.R. 2001. California Energy Study: Frequently Asked Questions. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 1p!energy, crisis, smog, shade, water!!
78!7/18/2002 4:53:00 PM!Effects of California's urban forests on energy use and potential savings from large-scale tree planting!McPherson, E.G. and J.R. Simpson!2001!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!Published Reports!Energy Effects of Urban Forests in California!cufr_78_EM01_68.PDF!PDF!McPherson, E.G. and J.R. Simpson. 2001. Effects of California's urban forests on energy use and potential savings from large-scale tree planting. Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research. 35!!!
79!7/18/2002 4:56:00 PM!Indirect carbon reduction by residential vegetation and planting strategies in Chicago, USA!Jo, H.-K. and E.G. McPherson!2001!Journal of Environmental Management. 61!Articles in Journals!Miscellaneous Air Literature!cufr_79_HJ01_6.PDF!PDF!Jo, H.-K. and E.G. McPherson. 2001. Indirect carbon reduction by residential vegetation and planting strategies in Chicago, USA. Journal of Environmental Management. 61: 165-177!climate change, carbon dioxide, urban vegetation, building energy savings, proper planting!Concern about climate change has evoked interest in the potential for urban vegetation to help reduce the levels of atmospheric carbon. This study applied computer simulations to try to quantify the modifying effects of existing vegetation on the indirect reduction of atmospheric carbon for two residential neighborhoods in north-west Chicago. The effects of shading, evapotranspiration, and windspeed reduction were considered and were found to have decreased carbon emissions by 3.2 to 3.9% per year for building types in study block 1 where tree cover was 33%, and -0.2 to 3.8% in block 2 where tree cover was 11%. This resulted in a total annual reduction of carbon emission averaging 158.7 (+/-12.8) kg per residence in block 1 and 18.1 (+/-5.4) kg per residence in block 2. Windspeed reduction greatly contributed to the decrease of carbon emission. However, shading increased annual carbon emission from the combined change in heating and cooling energy use due to many trees in the wrong locations, which increase heating energy use during the winter. The increase of carbon emission from shading is somewhat specific to Chicago, due in part to the large amount of clean, nuclear-generated cooling energy and the long heating season. In Chicago, heating energy is required for about eight months from October to May and cooling energy is used for the remaining 4 months from June to September. If fossil fuels had been the primary source for cooling energy and the heating season had been shorter, the shading effects on the reduction of carbon emission would be greater. Planting of large trees close to the west wall of buildings, dense planting on the north, and avoidance of planting on the south are recommended to maximize indirect carbon reduction by residential vegetation, in Chicago and other mid and high-latitude cities with long heating seasons!three-dimensional model. Journal of Geophysical Resecirch 93, 9341-9364. Heisler, G. M. (i990). Mean wind speed below building height in residential neighborhoods 176 H.-K. Jo and E. G. McPherson part to a relatively long heating season and clean, nuclear-generated cooling energy. Carbon emission reduction from shading is likely to be substantial in regions where the cooling season is long and coal is? the main source for cooling energy. Planting in optimum locations and proper selection of tree species are :essential in avoiding a-negative shading effect. This study suggested appropriate planting strategies to minimize energy consumption and Carbon emissions to the-atmosphere. The planti.ng strategies based on simulations of indirect carbon reduction can: be used for landscape designers, greenspace planners, and residents. Computer simulations of building energy-performance to quantify-indirect carbon: reduction were based on an actual survey of tree and building parameters, although the sample size for some data (i.e. metered: energy use) Was not large due to limite& cooperation. This study pioneers in tackling the complexities associated with simulatingl actual neighborhoods instead of single building and landscape prototypes. The two resi-~ Acknowledgements This study would not have been possible without assistance and information provided by homeowners in the study area, Paul Rocks, Paul Sacamano, Claire Saddler of Commonwealth Edison, and L. Guzy of Peoples Gas. We are very grateful to Dr Donovan Wilkin of the University of Arizona for his helpful advice and review in fulfilling this study. This research was supported by funds provided by the US Department of Agriculture, Forest Service, North Eastern Forest Experiment Station. References Akbari, H., Huang, J., Martien, P., Rainer, L., Rosenfeld, A. and Taha, H. (1988). The impact of summer heat islands oncoming energy consumption and global COs concentratidn. In Proceedings of ACEEE 1988 Summer Study on Energy Efficiency in Buildings, 5, pp. 11-23. Asilomar, CA: American Council for an Energy-Efficient Economy. Ames, M. J. (1987). Solar Friendly Trees Report. Technical Report. Portland, OR: City of Portland Energy Office. dentialneighborhoodscontainedasurprising.- Atkinson, B., Barnaby, C., Wexler, A. and amount of building- and tree diversity. For Wilcox, B. (1983). Validation of Calpas3 corn- example, it was necessary to account for var- purer simulation program. In Progress in Pas- ious: (1) building types and sizes; (2) tree~ species and sizes; (3) tree-building juxta-pSsitions; and (4) tree-climate interactions.~ Capturing this diversity both in the field and: within the existing modeling system was a challenge. This study went beyond estimating annual i carbon reduction based on the existing tree distribution and projected potential carbon reduction obtained by planting additional: trees in vacant sites. This information could be useful for evaluating the cost effectiveness of a utility-sponsored retrofit program that plants trees in strategic locations to obtain: carbon offset credits. The amount of indirect carbOn reduction could be regionally variable with differences in tree plantings around buildings, length in the heating and cooling season, and carbon contents of energy sup-: plied. Therefore, the carbon-estimates from: this study cannot be directly transferred to other cities with even similar building structures. More studies at a regional or national scale, including multi-family residential set=~ tings, are required to deepen our understand-÷ ing of effects of urban vegetation on indirect carbon reduction. F Indirect carbon reduction and planting strategies 177 with different tree densities. ASHRAE Transactions 96, 1389-1396. Huang, J., Akbari, H., Taha, H. and Rosenfeld, A. (1987). The potential of vegetation in reducing summer cooling loads in residential buildings. Journal of Climate and Applied Meteorology 26, 1103-1116. Huang, J., Akbari, H. and Taha, H. (1990). The wind shielding and shading effects of trees on residential heating and cooling requirements. ASHRAE Transactions 96, 1403-1411. Huang, J., Ritschard, R., Sampson, N. and Taha, H. (1992). The benefits of urban trees. In Cooling Our Communities (H. Akbari, S. Davis, S. Dorsano, J. Huang and S. Winnett, eds), pp. 27-42. Washington, DC: US Environmental Protection Agency. Mahajan, S., Newcomb, M., Shea, M., Pond, B., Morandi, P., Jones, M. et al. (1983). Class C survey data versus computer predictions-a comparison between field data and simulations. In Progress in Passive Solar Energy Systems, pp. 311-315. Boulder, CO: American Solar Energy Society. McPherson, E. G. (1984). Planting design for solar control. In Energy-Conserving Site Design (E. G. McPherson, ed.), pp. 141-164. Washington, DC: ASLA. McPherson, E. G. (1990). Modeling residential landscape energy and water use to evaluate water conservation policies. Landscape Journal 9, 122-134. McPherson, E. G. (1994). Energy-saving potential of trees in Chicago. In Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project (E. G. McPherson, D. J. Nowak and R. A. Rowntree, eds), General Technical Report NE-186, pp. 95-113. Radnor, PA: U.S.D.A. Forest Service, Northeastern Forest Experiment Station. McPherson, E. G., Brown, R. and Rowntree, R. A. (1985). Simulating tree shadow patterns for building energy analysis. In Solar 85-Proceed-ings of the National Passive Solar Conference (A. T. Wilson and W. Glennie, eds), pp. 378-382. Boulder, CO: American Solar Energy Society. McPherson, E. G., Herrington, L. P. and Heisler, G. M. (1988). Impacts of vegetation on residential heating and cooling. Energy and Buildings 12, 41-51. McPherson, E. G., Nowak, D. J., Sacamano, P. L., Prichard, S. E. and Makra, E. M. (1993a). Chicago's Evolving Urban Forest: Initial Report of the Chicago Urban Forest Climate Project, General Technical Report NE-169. Radnor, PA: U.S.D.A. Forest Service, Northeastern Forest Experiment Station. McPherson, E. G., Sacamano, P. L., Wensman, S., Ratliff, J. and Jo, H.-K. (1993b). Modeling Benefits and Costs of Community Tree Plantings: A Demonstration Project. Final Report to American Forests, US Environmental Protection Agency, US Department of Energy and U.S.D.A. Forest Service. Melillo, J. M., Callaghan, T. V., Woodward, F. I., Salati, E. and Sinha, S. K. (1990). Effects on ecosystems. In Climate Change (J. T. Houghton, G. J. Jenkins and J. J. Ephraums, eds), pp. 285-310. Cambridge: Cambridge University Press. Minnesota Department of Natural Resources (1991). Carbon Dioxide Budgets in Minnesota and Recommendations on Reducing Net Emissions with Trees. Report to the Minnesota Legislature. Mitchell, J. F. B., Manabe, S., Meleshko, V. and Tokioka, T. (1990). Equilibrium climate change and its implications for the future. In Climate Change (J. T. Houghton, G. J. Jenkins and J. J. Ephraums, eds), pp. 134-164. Cambridge: Cambridge University Press. Myrup, L. O., McGinn, C. E. and Flocchini, R. G. (1993). An analysis of microclimatic variation in a suburban environment. Atmospheric Environment 27B, 129-156. Nittler, K. B. and Novotny, R. E. (1983). MICROPAS, an annual hourly heating and cooling building simulation for microcomputers. In Progress in Passive Solar Energy Systems. Boulder, CO: American Solar Energy Society. National Oceanic and Atmospheric Administration (NOAA) (1993). Local Climatological Data. Parker, J. H. (1989). The impact of vegetation on air conditioning consumption. In Proceedings of the Workshop on Saving Energy and Reducing Atmospheric Pollution by Controlling Summer Heat Islands (K. Garbesi, H. Akbari and P. Martien, eds), pp. 45-51. Berkeley, CA: University of California, Lawrence Berkeley Laboratory. Pastor, J. and Post, W. M. (1988). Response of northern forests to CO2-induced climate change. Nature 334, 55-58. Post, W. M., Peng, T. H., Emanuel, W. R., King, A. W., Dale, V. H. and DeAngelis, D. L. (1990). The global carbon cycle. American Scientist 78, 310-326. Profous, G. V. (1992). Trees and urban forestry in Beijing, China. Journal of Arboriculture 18, 145-153. Rodhe, H. (1990). A comparison of the contributions of various gases to the greenhouse effect. Science 248, 1217-1219. Schlesinger, W. H. (1991). Climate, environment and ecology. In Climate Change: Science, Impacts and Policy (J. Jager and H. L. Fergu-son, eds), pp. 371-378. Cambridge: Cambridge University Press. Smith, J. B. and Tirpak, D. A. (1988). The Potential Effects of Global Climate Change on the United States. Report to Congress. Washington, DC: US Environmental Protection Agency. US Department of Energy (1993). Household Energy Consumption and Expenditures. DOE/ EIA-0321(90), Washington, DC: Energy Information Administration. Washington, W. M. and Meehl, G. A. (1989). Climate sensitivity due to increased CO2: experiments with a coupled atmosphere and ocean general circulation model. Climate Dynamics 4, 1-38. Watson, G. W. (ed.). (1991). Selecting and Planting Trees. Lisle, IL: The Morton Arboretum!
80!7/18/2002 4:58:00 PM!Carbon storage and flux in urban residential greenspace!Jo, H.-K. and E.G. McPherson!1995!Journal of Environmental Management. 45!Articles in Journals!Miscellaneous Air Literature!cufr_80_HJ95_5.PDF!PDF!Jo, H.-K. and E.G. McPherson. 1995. Carbon storage and flux in urban residential greenspace. Journal of Environmental Management. 45: 109-133!climate change, carbon budget, greenspace planning, residential landscape, northwest Chicago!There is increasing concern about the predicted negative effects of the future doubling of carbon dioxide on the earth. This concern has evoked interest in the potential for urban greenspace to help reduce the levels of atmospheric carbon. This study quantifies greenspace-related carbon storage and annual carbon fluxes for urban residential landscapes. For detailed quantification, the scale of this study was limited to two residential blocks in northwest Chicago which had a significant difference in vegetation cover. Differences between the two blocks in the size of greenspace area and vegetation cover resulted in considerable differences in total carbon storage and annual carbon uptake. Total carbon storage in greenspace was about 26.15 kg/m2 of greenspace in study block 1, and 23.20 kg/m2 of greenspace in block 2. Of the total, soil carbon accounted for approximately 78.7% in block 1 and 88.7% in block 2. Trees and shrubs in block 1 and block 2 accounted for 20.8% and 10.6%, respectively. The carbon storage in grass and other herbaceous plants was approximately 0.5-0.7% in both blocks. Total net annual carbon input to the study blocks by all the greenspace components was in the region of 0.49 kg/m2 of greenspace in block 1 and 0.32 kg/m2 of greenspace in block 2. The principal net carbon release from greenspaces of the two residential landscapes was from grass maintenance. Greenspace planning and management strategies were explored to minimize carbon release and maximize carbon uptake!air !
81!7/18/2002 5:00:00 PM!Energy-efficient landscapes!McPherson, E.G., R.A. Rowntree and J.A. Wagar!1995!In: Bradley, G.A., (ed). Urban forest landscapes: integrating multidisciplinary perspectives. Seattle: University of Washington Press!Articles in Conference Proceedings!Miscellaneous Energy Literature!cufr_81_EM95_30.PDF!PDF!McPherson, E.G., R.A. Rowntree and J.A. Wagar. 1995. Energy-efficient landscapes. In: Bradley, G.A., (ed). Urban forest landscapes: integrating multidisciplinary perspectives. Seattle: University of Washington Press: 150-160!!A 25-foot tree reduces annual heating and cooling costs of a typical residence by about 8 to 12 percent ($10-$25). Assuming savings of $10 per household, a nationwide residential tree planting program could eventually save about $1 billion each year. Direct shade on the building will account for most of these savings in hot climates, while heating and cooling savings from reduced wind speeds and evapotranspirational cooling will be relatively more important in cooler climates. The energy conservation potential of landscapes is greatest in residential and commercial land uses, where planting space is most available and buildings consume large amounts of energy for heating and cooling. The greatest cooling savings can be obtained by shading the west side of air-conditioned buildings located in areas with the hottest climates. In cool climates the need for wind protection tends to result in a more "closed" landscape structure than in hot climates, where an "open" landscape enhances cooling breezes. The structure of energy-efficient landscapes can complement landscapes designed for wildlife, visual quality, sustainability, and buffering. Careful desigt1 can minimize potential conflicts with fire-safe and water conserving landscapes. Tree plantings for energy conservation are likely to become more commonplace due to their relatively flexible structural requirements, cost-effectiveness, and growing support from utilities and federal agencies!dating back to the 1930s have monitored heating savings from windbreaks and more recently have measured wind speed reductions in residential neighborhoods resulting from the combined effects of buildings and landscapes (Heisler 1990). Reported heating savings from windbreaks have ranged from 3 to 40 percent (Heisler 1986), with 10 to 12 percent savings found for a mobile home and detached houses in Pennsylvania and New Jersey, respectively. Simulated Savings The effects of landscapes• on energy use in buildings are easier to-.simulate than to measure because all variables can be kept constant except the landscape. To date, most simulation studies have assumed mature trees and near optimum locations of vegetation around a limited number of building types. In reality, it may take five to fifteen years before trees grow large enough to provide the savings reported, or else additional expense is incurred by planting larger trees. And the opportunity to plant trees in optimal locations is constrained by the presence of utilities, narrow sideyards, paving, buildings, and existing vegetation. Therefore, the assumptions used in simulation studies should be as carefully scrutinized as the results. Simulations are best used to compare the relative impacts of different landscape treatments. Recent simulation studies have used shading models and empirical data to incorporate effects of trees on solar gains, wind speed reductions, and air temperatures in building energy analysis (Wagar 1984; Huang et al. 1987, 1990; McPherson and Dougherty 1989; Akbari et al. 1990; Heisler 1991; Sand 1991; McPherson andSacamano 1992). Results vary because of different assumptions regarding tree numbers, size, and locations; building insulation levels; and local climate. Generally, annual air-conditioning savings from a deciduous tree (25 feet tall and wide), near a well-insulated home, ranged from 10 to 15 percent (200-400 kWh, $15-$25)'(McPhers0n and Rowntree 1993). Savings during peak cooling periods ranged from about 8 to 12 percent (0.4-0.5 kW). 152 / Mc?Pherson, Rowntree, and Wagar .... i• • i • -,t ~ .. ~T-~ Higher percentage air-conditioning savings for cities in cool climates compared to those in warm climates can be misleading, since estimated annual cooling energy (kWh) and dollar savings are greatest in warm climate cities. Reduced solar gains from tree shade account for most of the cooling savings in warm climate cities. The effect of ET cooling on air-conditioning is poorly understood. It was estimated to account for 25 to 50 percent of total cooling savings in one study (McPherson and Rowntree 1993), but found to be 60 to 80 percent in another (Huang et al. 1987). For both heating and cooling, annual residential, energy savings from a single 25 foot yard tree generally ranged from 2 to 8 percent, with the greatest dollar savings ($10 to $25 per year) in warm climates. As expected, reduced wind speeds from increased tree cover resulted in greatest heating savings in cool climate cities. For instance, in Boston and Minneapolis heating savings that were attributed to reduced wind speeds.accounted for over 50 percent of the total annual energy savings (McPherson and Rowntree 1993). However, deciduous trees located to shade east ;and south walls can obstruct winter irradiance and provide little sumrher shade in cool climate cities. The result is increased energy costs compared to an unshaded condition (Thayer and Maeda 1985; Heisler 1986; Sand 1991). Therefore, the potential energy costs of trees improperly located near buildings are gTeatest in cooiclimates, while their potential energy savings are greatest in warm climates. In all climate zones, a tree shading the west-facing wall provides about twice the energy, savings of the same tree shading a similar east-facing wall (McPherson and Rowntree 1993). These monitoring and simulation studies suggest that landscape vegetation around individual buildings can provide heating savings of 5 to 15 percent and cooling savings of 10 to 50 percent. Despite our incomplete understanding of the aggregate effects of neighborhood trees on air temperature and wind speed, these indirect effects appear to be just as important as direct shading effects. COST-EFFECTIVENESS OF ENERGY-EFFICIENT LANDSCAPES Studiesby scientists and electric utilities have reported that proper planting and care of trees to maximize building energy savings and mitigate heat islands can be more economical than other methods of reducing electrical demand, carbon dioxide emissions, and heat islands (e.g., light-colored surfaces; modifying urban geometry) (McPherson 1994). An increasing number of utility-sponsored tree planting programs for energy conservation indicate their cost-effectiveness. The Arizona Corporation Commission (1990) staff recommended that utilities fund the development of consumer guides on energy-efficient landscaping and tree planting rebate programs. These recommendations were based on the results of a benefit-cost analysis that found the present value of net benefiits for planting 180,000 trees to be $2.9 million. The analysis assumed planting costs of $45 per tree, •annual water costs of $4 to $6 per tree, a 7 percent discount rate, and a 20 year planning horizon. Each tree was assumed to shade the west-facing wall and provide annual and peak savings of 250 kWh and 0.33 kW, respectively, after the fifth year. Trees were found to be an economical conservation measure because they met the need for cooling energy services at a lower cost than generation of electricity. Arizona utilities now support tree planting programs that are delivered through nonprofit groups such as Trees for Tucson/Global ReLeaf. American Forests and the U.S. Environmental Protection Agency have implemented 2;,, L-.;?-?: ': , ~" i.;i Y ;i' Energy-Efficient Landscapes / 153 i:.. ,' 'if .i L - a Cool Communities Program to capture the potential of volunteerism with the goal of improving energy conservation through community tree planting and light-colored surfacing. Currently there are seven Model Cool Communities, with possible expansion to 250 cities as part of the Clinton administration's Global Change Action Plan. The Energy Policy Act of 1992 requires utilities to include environmental externalities and other social costs associated with different energy supplies when evaluating the costs of alternative energy sources. Because energy-efficient landscapes can be cost-ef-fective energy conservation measures and provide other economic, environmental, and aesthetic benefits that extend beyond the site where each tree is planted, utility and public sector investment in tree planting is likely tO grow (Dwyer et al. 1992). STRUCTURE OF ENERGY-EFHCIENT LANDSCAPES WITHIN A CITY The physical structure of energy-efficient landscapes will differ within a city due largely to different land use characteristics. For instance, windbreaks are more suitable in low-density suburban residential areas than in high-density residential zones near the city center. This section examines how the potential for energy-conserving landscapes changes with land use and existing tree cover. A strategy is presented for identifying locations that are likely to provide the greatest return on investment in new tree planting for energy conservation. Energy Conservation Potential of Different Land Uses Land use is perhaps the single most important variable related to urban forest cover, because different land uses have characteristic development patterns that influence tree planting and survival (Rowntree 1984). Land use refers to the primary activity occurring on the la~d (e.g., commerc.al, residential, industrial), while land cover refers to the physical surface material covering an area (e.g., tree, building, paving, grass). Many city and county planning agencies map land use, bu t few map land cover. Both land use and land cover can be interpreted from aerial photographs and other remotely sensed imagery. The potential of new tree plantings to conserve energy dePends on the amount of plantable space within land uses. The amount of available growing space (AGS) is defined• as land covered by grass, bare soil, shrub, and tree cover. Canopy stocking level (CSL) is defined as the percentage of AGS covered by trees and reflects the degree to which potential tree planting spaces have been filled (McPherson and Rowntree 1989). Areas with low CSLindicate relatively high tree planting potential. This definition is an approximate indicator of plantable space because some areas without tree cover are not suitable for trees due to other incompatible uses (e.g., ball fields, utilities, vehicular use), while some paved areas excluded from the indexare actually plantable (e.g., sidewalks, parking 10ts, playgrounds). To evaluate citywide tree planting potential it is necessary to consider the relative magnitude of land use types across a City, as well as CSL associated with each land use. A poorly stocked area occupying half of the city's land should supportmore new plantings than a similarly stocked area oc4upying only 10 percent of city land. A simple indicator of tree planting potential (TPP) by land use Car/be calculated, if percentages of CSL and area (A) are known, using the equation: 154 / McPherson, Rowntree, and Wagar ii- . ~. ilir" i - .?iii.i (1 - CSL) x A = TPP. Tree planting potentials have been estimated for one region based on data obtained from the Chicago Urban Forest Climate Project (McPherson et al. 1993). Differences in TPP span the urban-to-rural gradient: from densely populated Chicago, to the older suburban communities of Cook County, to the rapidly urbanizing farmlands of DuPage County. In all three sectors, TPP is greatest in the one-to-three-family residential land use category. Large commercial land uses are a second potential planting location. In Chicago, significant opportunities for tree planting; exist in higher density residential, small commercial, and park land uses. The conversion of vacant and agricultural land to urban• land uses provides substantial potential for tree planting in Cook and DuPage counties. Parks and forest preserves also have potential for increased tree numbers in suburban communities near Chicago. Although the values for CSL and area will differ for land uses across cities of varying size, age, and location, the relative ranking of tree planting potential will probably .remain relatively constant. Prioritizing New Planting Locations for Energy Conservation The potential for tree planting in residential and commercial land uses is especially significant because buildings in these areas consume most of the heating and cooling energy used in a city. Therefore, adding vegetation is likely to provide the greatest net benefits when planting and maintenance costs and energy savings are calculated. At least two other factors need to be considered to further specify areas within these land uses where new tree plantings can achieve the greatest energy savings. First, energy savings are likely to be greatest in areas where climate is most extreme. For example, cooling savings will be greater from trees shading homes in the hot interior valley of Los Angeles than from trees near homes in. the clement coastal zone. Second, greater cooling savings will come from shaded buildings with air-conditioners or heat pumps than from shaded buildings with evaporative coolers or no mechanical cooling. Other build.ng-related factoi's that influence potential energy savings include construction type (e.g., wood frame, masonry., slab, basement), floor area, building orientation, and the thermophysical properties of walls, windows, and roof. Also, setback distances ~ of buildings from the street and other buildings influence the potential space for addition ,~ ~ of new trees, as well as their shading impact, ~,.~ ;*' ~.: Greater absolute energy savings can be obtained from older homes that are poorly ~h~ . -* insulated or loosely constructed than from new homes that are energy efficient. How- ~ ~ g'. ever, traditional energy conservation measures (e.g., double pane windows, insulation) ~2. .may be more cost-effective than tree planting for older homes. Energy-efficient land~ scapes are likely to be more cost-effective for new construction, because most traditional • conservation measures are already installed and the marginal costs of additional meas- i ure's are relatively high compared to trees. ~- Finally, it is important to reiterate that sizable energy savings can be obtained from ~i vegetation that does not directly shade buildings. The magnitude of indirect effects on -:,~-•~ air temperature, airflow, and radiation generally increases, with in cr, easing leaf surface ~= area. Forest belts, riparian corridors, woodlots, and other natural landscapes contain ~ large amounts of leaf surface area per unit land area. The salubrious influence of these ~. vegetated masses on climate can extend well into the adjacent built environment, I although further research is needed to document this impact on energy use. ~-i i Energy-Efficient Landscapes / 155 ~i,.¸ • -i ~v - ~;.. ..~,v 2- • N2 b ilia• i. i >; ~-;:X .ii~ -.i To summarize planting priorities, residential and commercial land uses offer the greatest potential for new tree planting, and, coincidentally, these buildings consume the largest percentage of energy for heating and cooling. As a first priority, energy-effident landscapes should be targeted to shade buildings and paved surfaces within these areas, while providing solar access and wind protection during winter. A more refined approach to maximize energy savings will further subdivide these areas based on factors such as local climate and pertinent characteristics of the building stock. Secondary opportunities for energy-efficient tree plantings are more likely to vary from city to city depending on land use patterns and canopy stocking levels. STRUCTURE OF ENERGY-EFFICIENT LANDSCAPES IN DIFFERENT CLIMATIC ZONES The ideal structure of energy-efficient landscapes in different climatic regions of the United States follows from principles of bioclimatic architectural design (Olgyay 1973). For instance, tree shade on the east side of buildings is a net benefit in warm climates but often a net cost in cold climates because of reduced winter solar heat gain, even from deciduous trees and sl~rubs. Generally, requirements for winter wind protection and solar access in cold climates result in residential landscapes with the following structural characteristics: • Dense evergreen foundation plantings. • Tall, dense evergreen and deciduous windbreaks, hedges, and buffers. • Deciduous shade trees, shrubs, and vines shading west walls and air-conditioners (and in more temperate zones, east walls). • Unobstructed sky space to the south for solar access. • Deciduous trees shading sidewalks, parking lots, streets, and other paved surfaces. • Multistory buffer plantings between neighborhoods. Usually, energy-efficient landscapes in hot climates are more "open" than landscapes in cold climates, because airflow cools building surfaces, thereby minimizing air-conditioning use when temperatures are below 90°F (Givoni 1981). Structural characteristics of landscapes in hot climates can be generalized as follows: • Evergreen shade trees, shrubs, and vines shading west and east (deciduous trees for south shade in areas without heating loads and solar collectors) building surfaces and air-conditioners. • Open understory for natural ventilation. • Trees sl~ading sidewalks, parking lots, streets, and other paved heat sinks. • Dispersed vegetated parklike oases for local climatic amelioration. Of course, desert areas subject to extreme winds and dust storms will benefit from shelterbelts and a more "closed" landscapestructure. Extensive damage to homes from trees felled by recent tropical storms suggests the need for more judicious selection and location of shade trees in hurricane-prone regions. Landscapes designed for energy conservation in temperate climate zones combine :7 principles listed above depending on the relative need for heating and cooling. The greatest challenge in temperate zones lies in resolving sometimes conflicting needs for - < 156 / McPherson, Rowntree, and Wagar i/f~ : Ik4| .. wind protection and solar access (Oke 1988) or shading and cooling breezes (Westerberg and Glaumann 1990-91). CONFLICTING AND COMPLEMENTARY USES WITH OTHER URBAN LANDSCAPES ]Landscapes are seldom designed to optimize a particular function such as energy efficiency. The extent to which new landscapes will be devoted to conserving energy will ]3 related to how well they can provide other functions required by city dwellers. This section notes some of the ways that energy-efficient landscapes complement or conflict with other landscapes. The structure of energy-efficient residential landscapes can conflict with design recommendations for fire-safe landscapes, Shading geometry is such that plants close to a building provide greater shade than similar plants away from the building. However, plants near buildings can carry fire to the Structure, thereby increasing the fire hazard. Application of the following guidelines can reduce conflicts between energy-efficient and fire-safe landscapes~i • Do not s.~ade roof surfaces (most attics are well insulated anyway, so little is saved). • Use fire-resistant species to shade wails. • Irrigate plants near the structure on a regular basis (this mini-oasis also enhances ET cooling). • Avoid continuous vegetation from property boundaries to the buildings. A conflict between energy and water conserving landscapes is possible because reduced landscape irrigation results in reduced ET cooling. Also, as overall leaf area is reduced to conserve water, direct and indirect ener:gy benefits diminish. Research to evaluate energy and water tradeoffs has shown that lowering city temperatures can reduce landscape water Consumption, and cooling energy savings can reduce water consumed at power plants (McPherson 1991). However, the cost of irrigation water for high water use trees such as mulberry can offset the energy savings from shade (McPher-son and Dougherty 1989). The following guidelines can be applied to promote the conservation of both water and energy: • Create a mini-oasis near the building to provide wind protection, ET cooling, and strategically located plants for shading windows, walls, and air-conditioners. • Shift to more xeric plant associations away from the building. • Use water-efficient irrigation systems and landscape management practices. • Plan a citywide system of water-efficient oases designed to mitigate urban heat islands (e.g., some parks, cemeteries, golf courses, riparian areas). • Shade streets, parking lots, and public buildings with low water use tree species to mitigate the Urban heat island and demonstrate xeriscape design principles. Energy-efficient landscapes have potential to complement other functions required of landscapes. Although the "open" character of energy-efficient residential landscapes in warm climates can conflict with the multilayered structure of landscapes valued by certain types of wildlife, community-scale greenbelts that provide important wildlife habitat can simultaneously contribute to energy conservation. Through judicious design, energy-efficient landscapes can increase species, age, and genetic diversity of the urban ;i/ -}. • - -~-I : • i .;IJ- ;F. 2 ~F~ ".@, g , ~ .7 ". ;.:~L: .I Energy-Efficient Landscapes / 157 i•... i~/•. "4..'. forest, thus enhancing the sustainability of natural organisms and processes v¢ithin our cities. Residential landscapes can express individual aesthetic preferences while conserving energy. Energy-efficient landscapes on public land can be designed to reflect "sense of place" within a city, as well as the city's overall identity. CONCLUSION As the need for cost-effective urban forest management grows, multipurpose landscapes will expand because they produce more net benefits than single-purpose landscapes. The structure of energy-efficient landscapes can complement the structure of most other urban forest landscapes. Careful planning and design will minimize structural conflicts when fire safety, water conservation, and other functions are high priority. Given the ease with which energy-efficient landscapes can be integrated with other landscapes; and the burgeoning support of tree planting programs that is coming from utilities and government agencies, their future looks bright. In this chapter we have described methods for planning energy-efficient landscapes ata citywide scale. What is needed now are examples that apply and evaluate these ideas. With research findings and demonstration results in hand, citizens, policy makers, pianners, and utilities will be better equipped to create more energy-efficient landscapes and more sustainable cities. LITERATURE CITED Akbari, H., S. Davis, S. Dorsano, J. Huang, and S. Wim:ett, eds. 1992. Cooling our communities: A guidebook on tree planting and light-c01ored surfacing. U.S. Environmental Protection Agency, Washington, D.C. Akbari, H., A.H. Rosenfeld, and H. Taha. 1990. Summer heat islands,• urban trees, and white surfaces. ASHRAE Transac~ol:s 96(1):1381-1388. Arizona Corporation •Commission. 1990. Resource Planning Staff Report. Utilities Division, Arizona Corporation Commission, Phoenix. Bartag, A., and W. Kuttler. 1990-91. The significance of country breezes for urban planning. Energy and Buildings 15116:291-297. DeWalle, D.R., and G.M. Heisler. 1988. Use of windbreaks for home energy conservation. Agriculture, Ecosystems, and Eiwironment 22-23:243-260. DeWalle, D.R., G.M. Heisler, and R'.E. Jacobs. 1983. Forest home sites influence heating and cooling energy. Journal of Forestry 81:84-88. Dwyer, J.F., E.G. McPherson, H.W. Schroeder, and R.A. Rowntree. 1992. Assessing the benefits and costs of the urban forest. Journal of Arboriculture 18:227-234. Energy Information Administration. 1989. EIA household energy consumption and expenditures, 1987, vol. 1. Energy Information Administration, Washington, D.C. Givoni, B. 1981. Man, climate, architecture. 2nd ed. Van Nostrand Reinhold, New York. 158 / Mc?Pherson, Rowntree, and Wagar 2 Heisler, G.M. 1986. Energy savings with trees. Journal of Arboriculture 12:113-125. • 1990. •Mean wind speed below building height in residential neigl~borhoods with different tree densities. ASHRAE Transactions 96, part 1:1389-1396• • 1991. Computer simulation for optimizing windbreak placement to save energy for heating and cooling buildings~ In Trees and Sustainable Development:The Third National Windbreaks and Agroforestry Symposium Proceedings, pp. 101)-104. Ridgetown College, Ridge-town, Ontario. Honjo, T., and T. Takakura. 1990-91. Simulation of thermal effects of urban green areas on their surrounding areas. Energy and Buildings 15-16:433446. Huang, J., H. Akbari, H. Taha, and A. Rosenfeld. 1987. The ]potential of vegetation in reducing summer cooling loads in residential buildings. Journal of Climate and Applied Meteorology 26:1103-1116. ' Huang, Y.J., H. Akbari, and H. Taha. 1990. The wind-shielding and shading effects of trees on residential heating and cooling requirements. ASHRAE Transactions 96, part 1:1403-1411. McPherson, E.G. 1991. Economic modeling for large-scale tree planting. In E. Vine, D. Crawley, and P. Centolella, eds., Energy efficiency and the environment: Forging the link, pp. 349-369. American Council for an Energy Efficient Economy, Washington, D.C. McPherson, E.G. 1994• Cooling urban heat islands with sustainable landscapes. In R. Platt, R.A. Rowntree, and P.C. Muick, eds., The ecological city: Preserving and restoring urban biodiver-sity, pp. 151-171. University of Massachusetts Press, Amherst. McPherson, E.G., and E. Dougherty. 1989. Selecting trees for shade in the Southwest. Journal of Arboriculture 15:35-43. McPherson, E.G., D.J. Nowak, P.L. Sacamano, SIE. Prichard, and E.M. Makra. 1993. Chicago's evolving urban forest. General Technical Report NE-16Q. USDA Forest Service Northeastern Forest Experiment Station, Radnor, Pennsylvania. McPherson, E.G., and R.A. Rowntree. 1989. Using structural measures to compare twenty-two street tree populations. Landscape Journal 8:13-23• 1993. Energy conservation-potential of urban tree planting. Journal of Arboriculture 19:321-331. McPherson, E.G., and P.L. Sacamano. 1992. Energy savings with trees in Southern California. Research Report• USDA Forest Service Western Center for Urban Forest Research, Davis, California. McPherson, E.G., J.R. Simpson, and M. Livingston. 1988. Effects of three landscape treatments On residential energy and water use in Tucson, Arizona. Energy and Buildings 13:127-138. Meier, A. 1990-91. Strategic landscaping and air-conditioning savings: A literature review. Energy and Buildings 15-16:479-486. Mizuno, M., M. Nakamura, H. Murakami, and S. Yamamoto. 1990-91. Effects of land use on urban horizontal atrnospheric temperature distributions. Energy and Buildings 15-16:165-176. Energy-Efficient Landscapes / 159 6- •. Oke, T.R. 1988. Street design and urban canopy layer climate. Energy and Buildings 11:103-113. • 1989. The micrometeorology of the urban forest. Philosophical Transactions of the Royal Society of London 324:335-349. Olgyay, V. I973. Design with climate. Princeton University Press, Princeton, New Jersey. Parker, J.H. 1983. Landscaping to reduce the energy used in cooling buildings. Journal of Forestry 81(2):82-84. Rowntree, R.A. 1984. Forest canopy cover and land use in four eastern United States cities. Urban Ecology 8:55-67. Saito, I., O. Ishihara, and T. Katayama. 1990-91. Study of the effect of green areas on the thermal environment in an urban area. Energy and Buildings 15-16:493-498. Sand, M.A.P. 1991. Planting for energy conservation in the North: Modeling the impact of tree shade on home energy use in Minnesota and development of planting guidelines. Master's thesis, University of Mi1~esota. 111 p. Simpson, J.R. 1991. Simulating effects of turf landscaping on building energy use. in E. Vine, D. Crawley, and P. Centolella, eds. Energy efficiency and the environment: Forgi.ng the link, pp. 335-347. American Council for an Energy Efficient Economy, Washington, D.C. Thayer, R.L., and B. Maeda. 1985. Measuring street tree impact on solar performance: A five climate computer modeling study. Journal of Arboriculture 11:1-12. Wagar, J.A. 1984. Using vegetation to control sunlight and shadeon windows. Landscape Journal 3:235-245. Westerberg, U., and M. Glaumann. 1990-91• Design criteria for solar access and wind shelter in the outdoor environment. Energy and Buildings 15-16:425-431. Wilmers, F. 1990-91. Effects of vegetation on urban climate and buildings. Energy and Buildings 15-16:507-514. Portions of an earlier version of this chapter were published in the November 1993 issue of the Journal of ArboricultT~re. 160 / McPherson, Rowntree, and Wagar ; ~-;:X .ii~ -.i To summarize planting priorities, residential and commercial land uses offer the greatest potential for new tree planting, and, coincidentally, these buildings consume the largest percentage of energy for heating and cooling. As a first priority, energy-effident landscapes should be targeted to shade buildings and paved surfaces within these areas, while providing solar access and wind protection during winter. A more refined approach to maximize energy savings will further subdivide these areas based on factors such as local climate and pertinent characteristics of the building stock. Secondary opportunities for energy-efficient tree plantings are more likely to vary from city to city depending on land use patterns and canopy stocking levels. STRUCTURE OF ENERGY-EFFICIENT LANDSCAPES IN DIFFERENT CLIMATIC ZONES The ideal structure of energy-efficient landscapes in different climatic regions of the United States follows from principles of bioclimatic architectural design (Olgyay 1973). For instance, tree shade on the east side of buildings is a net benefit in warm climates but often a net cost in cold climates because of reduced winter solar heat gain, even from deciduous trees and sl~rubs. Generally, requirements for winter wind protection and solar access in cold climates result in residential landscapes with the following structural characteristics: • Dense evergreen foundation plantings. • Tall, dense evergreen and deciduous windbreaks, hedges, and buffers. • Deciduous shade trees, shrubs, and vines shading west walls and air-conditioners (and in more temperate zones, east walls). • Unobstructed sky space to the south for solar access. • Deciduous trees shading sidewalks, parking lots, streets, and other paved surfaces. • Multistory buffer plantings between neighborhoods. Usually, energy-efficient landscapes in hot climates are more "open" than landscapes in cold climates, because airflow cools building surfaces, thereby minimizing air-conditioning use when temperatures are below 90°F (Givoni 1981). Structural characteristics of landscapes in hot climates can be generalized as follows: • Evergreen shade trees, shrubs, and vines shading west and east (deciduous trees for south shade in areas without heating loads and solar collectors) building surfaces and air-conditioners. • Open understory for natural ventilation. • Trees sl~ading sidewalks, parking lots, streets, and other paved heat sinks. • Dispersed vegetated parklike oases for local climatic amelioration. Of course, desert areas subject to extreme winds and dust storms will benefit from shelterbelts and a more "closed" landscapestructure. Extensive damage to homes from trees felled by recent tropical storms suggests the need for more judicious selection and location of shade trees in hurricane-prone regions. Landscapes designed for energy conservation in temperate climate zones combine :7 principles listed above depending on the relative need for heating and cooling. The greatest challenge in temperate zones lies in resolving sometimes conflicting needs for - < 156 / McPherson, Rowntree, and Wagar i/f~ : Ik4| .. wind protection and solar access (Oke 1988) or shading and cooling breezes (Westerberg and Glaumann 1990-91). CONFLICTING AND COMPLEMENTARY USES WITH OTHER URBAN LANDSCAPES ]Landscapes are seldom designed to optimize a particular function such as energy efficiency. The extent to which new landscapes will be devoted to conserving energy will ]3 related to how well they can provide other functions required by city dwellers. This section notes some of the ways that energy-efficient landscapes complement or conflict with other landscapes. The structure of energy-efficient residential landscapes can conflict with design recommendations for fire-safe landscapes, Shading geometry is such that plants close to a building provide greater shade than similar plants away from the building. However, plants near buildings can carry fire to the Structure, thereby increasing the fire hazard. Application of the following guidelines can reduce conflicts between energy-efficient and fire-safe landscapes~i • Do not s.~ade roof surfaces (most attics are well insulated anyway, so little is saved). • Use fire-resistant species to shade wails. • Irrigate plants near the structure on a regular basis (this mini-oasis also enhances ET cooling). • Avoid continuous vegetation from property boundaries to the buildings. A conflict between energy and water conserving landscapes is possible because reduced landscape irrigation results in reduced ET cooling. Also, as overall leaf area is reduced to conserve water, direct and indirect ener:gy benefits diminish. Research to evaluate energy and water tradeoffs has shown that lowering city temperatures can reduce landscape water Consumption, and cooling energy savings can reduce water consumed at power plants (McPherson 1991). However, the cost of irrigation water for high water use trees such as mulberry can offset the energy savings from shade (McPher-son and Dougherty 1989). The following guidelines can be applied to promote the conservation of both water and energy: • Create a mini-oasis near the building to provide wind protection, ET cooling, and strategically located plants for shading windows, walls, and air-conditioners. • Shift to more xeric plant associations away from the building. • Use water-efficient irrigation systems and landscape management practices. • Plan a citywide system of water-efficient oases designed to mitigate urban heat islands (e.g., some parks, cemeteries, golf courses, riparian areas). • Shade streets, parking lots, and public buildings with low water use tree species to mitigate the Urban heat island and demonstrate xeriscape design principles. Energy-efficient landscapes have potential to complement other functions required of landscapes. Although the "open" character of energy-efficient residential landscapes in warm climates can conflict with the multilayered structure of landscapes valued by certain types of wildlife, community-scale greenbelts that provide important wildlife habitat can simultaneously contribute to energy conservation. Through judicious design, energy-efficient landscapes can increase species, age, and genetic diversity of the urban ;i/ -}. • - -~-I : • i .;IJ- ;F. 2 ~F~ ".@, g , ~ .7 ". ;.:~L: .I Energy-Efficient Landscapes / 157 i•... i~/•. "4..'. forest, thus enhancing the sustainability of natural organisms and processes v¢ithin our cities. Residential landscapes can express individual aesthetic preferences while conserving energy. Energy-efficient landscapes on public land can be designed to reflect "sense of place" within a city, as well as the city's overall identity. CONCLUSION As the need for cost-effective urban forest management grows, multipurpose landscapes will expand because they produce more net benefits than single-purpose landscapes. The structure of energy-efficient landscapes can complement the structure of most other urban forest landscapes. Careful planning and design will minimize structural conflicts when fire safety, water conservation, and other functions are high priority. Given the ease with which energy-efficient landscapes can be integrated with other landscapes; and the burgeoning support of tree planting programs that is coming from utilities and government agencies, their future looks bright. In this chapter we have described methods for planning energy-efficient landscapes ata citywide scale. What is needed now are examples that apply and evaluate these ideas. With research findings and demonstration results in hand, citizens, policy makers, pianners, and utilities will be better equipped to create more energy-efficient landscapes and more sustainable cities. LITERATURE CITED Akbari, H., S. Davis, S. Dorsano, J. Huang, and S. Wim:ett, eds. 1992. Cooling our communities: A guidebook on tree planting and light-c01ored surfacing. U.S. Environmental Protection Agency, Washington, D.C. Akbari, H., A.H. Rosenfeld, and H. Taha. 1990. Summer heat islands,• urban trees, and white surfaces. ASHRAE Transac~ol:s 96(1):1381-1388. Arizona Corporation •Commission. 1990. Resource Planning Staff Report. Utilities Division, Arizona Corporation Commission, Phoenix. Bartag, A., and W. Kuttler. 1990-91. The significance of country breezes for urban planning. Energy and Buildings 15116:291-297. DeWalle, D.R., and G.M. Heisler. 1988. Use of windbreaks for home energy conservation. Agriculture, Ecosystems, and Eiwironment 22-23:243-260. DeWalle, D.R., G.M. Heisler, and R'.E. Jacobs. 1983. Forest home sites influence heating and cooling energy. Journal of Forestry 81:84-88. Dwyer, J.F., E.G. McPherson, H.W. Schroeder, and R.A. Rowntree. 1992. Assessing the benefits and costs of the urban forest. Journal of Arboriculture 18:227-234. Energy Information Administration. 1989. EIA household energy consumption and expenditures, 1987, vol. 1. Energy Information Administration, Washington, D.C. Givoni, B. 1981. Man, climate, architecture. 2nd ed. Van Nostrand Reinhold, New York. 158 / Mc?Pherson, Rowntree, and Wagar 2 Heisler, G.M. 1986. Energy savings with trees. Journal of Arboriculture 12:113-125. • 1990. •Mean wind speed below building height in residential neigl~borhoods with different tree densities. ASHRAE Transactions 96, part 1:1389-1396• • 1991. Computer simulation for optimizing windbreak placement to save energy for heating and cooling buildings~ In Trees and Sustainable Development:The Third National Windbreaks and Agroforestry Symposium Proceedings, pp. 101)-104. Ridgetown College, Ridge-town, Ontario. Honjo, T., and T. Takakura. 1990-91. Simulation of thermal effects of urban green areas on their surrounding areas. Energy and Buildings 15-16:433446. Huang, J., H. Akbari, H. Taha, and A. Rosenfeld. 1987. The ]potential of vegetation in reducing summer cooling loads in residential buildings. Journal of Climate and Applied Meteorology 26:1103-1116. ' Huang, Y.J., H. Akbari, and H. Taha. 1990. The wind-shielding and shading effects of trees on residential heating and cooling requirements. ASHRAE Transactions 96, part 1:1403-1411. McPherson, E.G. 1991. Economic modeling for large-scale tree planting. In E. Vine, D. Crawley, and P. Centolella, eds., Energy efficiency and the environment: Forging the link, pp. 349-369. American Council for an Energy Efficient Economy, Washington, D.C. McPherson, E.G. 1994• Cooling urban heat islands with sustainable landscapes. In R. Platt, R.A. Rowntree, and P.C. Muick, eds., The ecological city: Preserving and restoring urban biodiver-sity, pp. 151-171. University of Massachusetts Press, Amherst. McPherson, E.G., and E. Dougherty. 1989. Selecting trees for shade in the Southwest. Journal of Arboriculture 15:35-43. McPherson, E.G., D.J. Nowak, P.L. Sacamano, SIE. Prichard, and E.M. Makra. 1993. Chicago's evolving urban forest. General Technical Report NE-16Q. USDA Forest Service Northeastern Forest Experiment Station, Radnor, Pennsylvania. McPherson, E.G., and R.A. Rowntree. 1989. Using structural measures to compare twenty-two street tree populations. Landscape Journal 8:13-23• 1993. Energy conservation-potential of urban tree planting. Journal of Arboriculture 19:321-331. McPherson, E.G., and P.L. Sacamano. 1992. Energy savings with trees in Southern California. Research Report• USDA Forest Service Western Center for Urban Forest Research, Davis, California. McPherson, E.G., J.R. Simpson, and M. Livingston. 1988. Effects of three landscape treatments On residential energy and water use in Tucson, Arizona. Energy and Buildings 13:127-138. Meier, A. 1990-91. Strategic landscaping and air-conditioning savings: A literature review. Energy and Buildings 15-16:479-486. Mizuno, M., M. Nakamura, H. Murakami, and S. Yamamoto. 1990-91. Effects of land use on urban horizontal atrnospheric temperature distributions. Energy and Buildings 15-16:165-176. Energy-Efficient Landscapes / 159 6- •. Oke, T.R. 1988. Street design and urban canopy layer climate. Energy and Buildings 11:103-113. • 1989. The micrometeorology of the urban forest. Philosophical Transactions of the Royal Society of London 324:335-349. Olgyay, V. I973. Design with climate. Princeton University Press, Princeton, New Jersey. Parker, J.H. 1983. Landscaping to reduce the energy used in cooling buildings. Journal of Forestry 81(2):82-84. Rowntree, R.A. 1984. Forest canopy cover and land use in four eastern United States cities. Urban Ecology 8:55-67. Saito, I., O. Ishihara, and T. Katayama. 1990-91. Study of the effect of green areas on the thermal environment in an urban area. Energy and Buildings 15-16:493-498. Sand, M.A.P. 1991. Planting for energy conservation in the North: Modeling the impact of tree shade on home energy use in Minnesota and development of planting guidelines. Master's thesis, University of Mi1~esota. 111 p. Simpson, J.R. 1991. Simulating effects of turf landscaping on building energy use. in E. Vine, D. Crawley, and P. Centolella, eds. Energy efficiency and the environment: Forgi.ng the link, pp. 335-347. American Council for an Energy Efficient Economy, Washington, D.C. Thayer, R.L., and B. Maeda. 1985. Measuring street tree impact on solar performance: A five climate computer modeling study. Journal of Arboriculture 11:1-12. Wagar, J.A. 1984. Using vegetation to control sunlight and shadeon windows. Landscape Journal 3:235-245. Westerberg, U., and M. Glaumann. 1990-91• Design criteria for solar access and wind shelter in the outdoor environment. Energy and Buildings 15-16:425-431. Wilmers, F. 1990-91. Effects of vegetation on urban climate and buildings. Energy and Buildings 15-16:507-514. Portions of an earlier version of this chapter were published in the November 1993 issue of the Journal of ArboricultT~re. 160 / McPherson, Rowntree, and Wagar ">!
82!7/18/2002 5:02:00 PM!Cooling urban heat islands with sustainable landscapes!McPherson, E.G!1994!In: Rutherford, H.P., R.A. Rowntree and P.C. Muick (eds.). The ecological city: preserving and restoring urban biodiversity. Amherst: University of Massachusetts Press!Published Reports!Miscellaneous Energy Literature!cufr_82_EM94_59.PDF!PDF!McPherson, E.G. 1994. Cooling urban heat islands with sustainable landscapes. In: Rutherford, H.P., R.A. Rowntree and P.C. Muick (eds.). The ecological city: preserving and restoring urban biodiversity. Amherst: University of Massachusetts Press: 151-171!!This paper is directed to the policy-makers who are responsible for urban design and its climatological consequences. It summarizes our current knowledge on the structure, energetics, and mitigation of the urban heat island. Special attention is given to physical features of the environment that can be easily manipulated, particularly vegetation. Prototypical designs illustrate how concepts of sustainable landscapes and urban climatology can be applied to counteract urban warming in street canyons, parking lots, urban parks, and residential streets. In a previous study (McPherson 199Oa), sustainable landscapes were defined as multifunctional, low maintenance, biologically diverse, and expressive of "place." Mitigation of urban heat-islands by landscapes can contribute to the sustainability of our cities. Because most electric utilities experience peak demands during summer because of air-conditioning loads, this paper addresses mitigation of summertime heat islands, while recognizing that winter heat islands can be beneficial in cities with cool climates!are needed to determine the most cost-effective method for obtaining land-surface information for modeling purposes. Remotely sensed information seems appropriate for mesoscale modeling but may not provide the resolution needed for microscale simulation. Field surveys might be needed to identify plant species and size as well as building construction types, and to collect other detailed information. This will require the development of appropriate sampling and sur- vey techniques. ..... • ~: : Environmental planners are asking many practical questions related to urban ~ ...... heat-island mitigation that we cannot answer now. For instance, policy-makers in Arizona want to know the trade-offs between F.T cooling and water demand. Elsewhere, utility and urban planners want to know how much savings in cooling energy can be achieved by increasing the amount of urban vegetation by a spec- ified amount. Designers are asking how best to locate and manage vegetation in parks, streets, and residential areas to improve urban climate. Urban foresters want to know which tree species will provide the greatest long-term net benefits. Clearly, there is a need for further development of urban dimate models, as well as for climatological and urban forestry research that can be used to validate and verify the models. Equally important is the development and application of "user.• friendly" planning and design tools. The cooling of our urban heat islands de- pends on the timely development and implementation of reliable predictive mod- els, and the guidelines, regulations, and incentives that can be generated from the information they provide. t i.~•. :~ i Acknowledgments I appreciate reviews of earlier versions of this manuscript by Sue Grimmond (Indiana University), Hashem Akbari (Lawrence Berkeley Laboratory), Rich Grant (Purdue University), and Craig Johnson (Utah State University). Steve Wensman provided assistance with the illustrations. i ~J Cooling Urban Heat Islands 169 References Akbari, H., H. Taha, P. Martien, and J. Huang. 1987. Strategies for reducing urban heat islands: Savings, conflicts, and city's role. In Proceedings of the First National Conference on Energy Efficient Cooling. San Jose, CA. Akbari, H., J. Huang, P. Martien, L. Ranier, A. Rosenfeld, and H. Taha. 1988. The impact of summer heat islands on cooling energy consumption and COz emissions. In Proceedings of the 1988 ACBEB summer study On energy efficiency in buildings. Washington: American Council for an Energy Efficient Economy. " Akbari, H., A. Rosenfeld, and H. Taha. i99o. Recent developments in heat island studies: Technical and policy. In ControllingSummerHeat Islands, ed. K. Garbesi et al. Berkeley: Lawrence Berkeley Laboratory. Akbari, H., S. Davis, S. Dorsano, J. Huang, and S. Winnett. 1992. Cooling our communities: A guidebook on tree planting and light-colored surfacing. Washington: U.S. Environmental Protection Agency. Arizona Corporation Commission. 199o. Resource planning staff report. Phoenix: Utilities Division, Arizona Corporation Commission. Arnfield, A. J. 199o. Street design and urban canyon solar access. Energy and Buildings 14(2): 117-31. Beatty, R. A. 199o. Planting guidelines for heat island mitigation and energy conservation. In Control- ling summer heat islands, ed. K. Garbesi, H. Akbari, and P. Martien. Berkeley:. Lawrence Berkeley ~. Laboratory. Cardelino, C. A., and W. L. Chameides. 199o. Natural hydrocarbons, urbanization, and urban ozone. ]ournal of Geophysical Research 95(D9): 13971-79. Chandler, T. J. 1965. The climate of London. London: Hutchinson. Duckworth, F. S., and J. S. Sandberg. 1954. The effect of cities upon horizontal and vertical temperature gradients. Bulletin of the American Meteorological Society 35:198-2o7. Goward, S. N. 1981. Thermal behavior of urban landscapes and the urban heat island. Physical Geogra- phy z(*): 19-33. Grimmond, C. S., and T. IL Oke. 1986. Urban water balance z: Results from a suburb in Vancouver, B.C. Water Resources Research zz:14o4-12. . Preliminary comparisons of measured summer suburban and rural energy balances for a hot dry city, Tucson, Arizona. Proceedings of the International Symposium on Urban Climatology, Air Pollution and Planning in TroPical Cities, 25-3o November, 199o. Guadalajara, Mexico. Heisler, G. 1986. Energy savings with trees, lournal of Arboriculture 12(5): 125. Herrington, L. P., G. E. Bertolin, and R. E. Leonard. 1972. Microclimates of a suburban parL In Proceedings of a Conference on Urban Environment and the Second Conference On Biometeorology, Boston: American Meteorological Society. Huang, J., H. Akbari, H. Taha, and A. Rosenfeld. 1987. The potential of vegetation in reducing summer cooling loads in residential buildings. Journal of Climate and Applied Meteorology 26:no3-6. Landsberg, H. E. 1981. The urban climate. New York: Academic Press. Lowry, W. P. 1988. Atmospheric ecology for designers and planners: McMinnville, OR: Peavine Publica- tions. 17o Urbanization and Terrestrial Ecosystems Martien, P, H. Akbari, A. Rosenfeld, and I. Duchesne. 199o. Approaches to using models of urban climate in build.ing energy simulation. In Controlling Summer Heat Islands, ed. Garbesi et al. Berkeley: Lawrence Berkeley Laboratory. McPherson, E. G., L. P. Herrington, and G. Heisler. 1988. Impacts of vegetation on residentialheating and cooling. Energy and Buildings 12:41-51. McPherson, E. G. and E. Dougherty. 1989. Selecting trees for shade in the Southwest. Journal of : Arboriculture 15(2): 35-43. McPherson, E. G., J. R. Simpson, and M. Livingston. 1989. Effects of three landscape treatments on residential energy and water use in Tucson, Arizona. Energy and Buildings 13:.27-38. McPherson, E. G. 199oa. Creating an ecological landscape. In Proceedings of the Fourth Urban Forestry , ~ Conference, ed. P. Rodbell. Washington: American Forestry Association. ~. 199ob. Modeling residential landscape water and energy use to evaluate water conservation policies. Landscape]ournal9(z): 12-34. : ~. 1991. Economic modeling for large-scale urban tree plantings. In Energy Efficiency and the Environment: Forging the link. Washington: American Council for an Energy Efficient Economy. McPherson, E. G. and G. C. Woodardl 199o. Cooling the urban heat island with water-and-energy efficient landscapes. Arizona Review, (Spring)a-8. Meier, A. K. 1991. Measured cooling savings from vegetative landscaping. In Energy Efficiency and the~ i i Environment: Forging the link. Washington: American Council for an Energy Efficient Economy. "~ Oke, T. R. 1982. The energetic basis of the urban heat island. Quarterly]ournal of the Royal Meteorologi- cal Society 188(455): 1-z4. Oke, T. R., ed. 1986. Urban climatology and its application with special regard to tropical areas. Geneva: World Meteorological Organization. Oke, T. R. 1987a. Boundary layer climates. New York: Methuen. Oke, T. R., ed. 1987b. Modeling the urban boundary layer. Boston: American Meteorological Society. Oke, T. R. 1988a. The urban energy balance. Progress in Physical Geography lz:471-5o8. .1988b. Street design and urban canopy layer climate. Energy and Buildings 11: lo3-13. .. 1989. The micrometeorology of the urban forest. Philosophical Transactions ofthe Royal Societ7 of London 324: 335-49- O'Rourke, P. A. and W. H. Terjung. 1981. Urban parks, energy budgets, and surface temperatures. Archives for Meteorology, Geophysics and Biodimatology a9: 3z7-44. Parker, J. H. 1987. The use of shrubs in energy conservation plantings. Landscape Journal 6(z): 13z-9. • . 199o. The impact of vegetation on air conditioning consumption. In Controlling Summer Heat Islands, ed. Garbesi et al. Berkeley: Lawrence Berkeley Laboratory. Rowntree, R. A. 1984. Forest canopy cover and land use in four eastern United States cities. Urban Ecology 8:55-67. Swaid, H. and M. E. Hoffman. 199o. Climatic impacts of urban design features for high- and mid- latitude cities. Energy and Buildings 15(4): 325-36. Cooling Urban Heat Islands 171 Taha, HI, H. Akbari, A. Rosenfeld, and I. Huang. 1988. Residential cooling loads and the urban heat island-the effects of albedo. Building and Environment 23(4): 271-83. Thayer, R. L and B. Maeda. t985. Measuring street tree impact on solar performance: A five dimate computer modeling study. ]ournal of Arboriculture ha-t2. Tuller, S. E. 1973. Microdimatic variations in a downtown urban environment. Geograf~ka Annaler 54(3-4)" 123-35. . • Tyson, P. D., M. Garstang, and G. D. Emmitt. 1973. The structure of heat islands. Occasional paper no. m, Department of Geography and Environmental Studies, University of Witwatersrand. Johannesburg. Weihe, W. H. 1986. Life expectancy in tropical climates and urbanizati0n. In Urban Climatology and its Applications with Special Regard to Tropical Areas, ed. "1". R. Oke. Geneva: World Meteorological Organization .... I • '] ii <input type="hidden" name="ProductText" value="m Cooling Urban Heat Islands with Sustainable Landscapes E. Gregory McPherson Introduction The rapid urbanization of U.S. cities during the past fifty years has been associated with a steady increase in downtown temperatures of about o.1° to m°C (0.25°. to 2°F) per decade. Because the demand of cities for electricity'increases by about 3 to 4 percent for every increase of one degree Celsius (1.5 to 2 percent per degree Fahrenheit), about 3 to 8 percent of current electric demand for Cooling is used just tO compensate f0r :this urban heat-island effect (Akbari et al~ x99o). Other implications of growing urban heat islands include .increases in carbon dioxide emissions from power plants, municipal water demand, concentrations of smog, and human discomfort and disease. Global warming, which may double the rate of urban temperature rise, could accentuate these environmental problems. Moreover, the accelerating world trend toward urbanization may expand the local influence of urban heat islands, as megalopolises begin to modify regional dimate and airflow (Tyson et ai. 1973). This paper is directed to the policy-makers who are responsible •for urban design and its climatological consequences. It summarizes our current knowledge on the structure, energetics, and mitigation of the urban heat island. Special attention is given to physical features of the environment that can be easily manipulated, particularly vegetation. Prototypical designs illustrate how concepts of sustainable landscapes and urban climatology can be applied to counteract urban warming in street canyons, parking lots, urban parks, and residential streets. In a previous study (McPherson 199oa), sustainable landscapes were defined as multi-functional, low maintenance, biologically diverse, and expressive of "place." Mitigation of urban heat-islands by landscapes can contribute to the sustainability of our cities. Because most electric utilities experience peak demands during summer because of air-conditioning loads, this paper addresses mitigation of summertime heat islands, while recognizing that winter heat islands can be beneficial in cities with cool dimates. 152 Urbanization and Terrestrial Ecosystems Urban Heat Islands Warmer air temperatures in cities compared to air temperatures in surrounding rural areas is the principal diagnostic feature of the urban heat island. Alterations of the urban surface by people result in diverse microdimates whose aggregate effect is reflected by the heat island (Landsberg 1981). Buildings, paving, vegetation, and other physical elements of the urban fabric are the active thermal interfaces between the atmosphere and land surface. Their composition and structure within the urban canopy layer, which extends from the ground to about roof level, largely determine the thermal behavior of different sites within a city (Goward 1981; Oke 1987a). Thus, Urban heat islands can be detected at a range of scales, from the microscale of a shopping center parking lot to the mesoscale of an urbanized region. Structure of Urban Heat Islands The structure of urban heat-islands has been well documented from climatological studies of cities around the world (see Chandler 1965; Landsberg 1981; Oke 1986). Urban and rural temperature differences are greatest and the spatial and temporal qualities of these anomalies most apparent during clear and calm summertime conditions. The horizontal structure of a hypothetical heat island is characterized by a "diff" that follows the city's perimeter and is steepest along the windward boundary (Oke 1982). This sharp temperature gradient leads to pulses of cool air flowing into the city at night. Intraurban heat islands and "cool islands" reflect localized effects of differences in building density and surface cover. Temperatures in mid-latitude parks can be 1° to 3°C (1.8° to 5.4°F) cooler than outside, and their influence can extend several hundred meters beyond the park boundary" (Chandler 1965; Herrington et al. 1972; Oke 1989). Differences in urban and rural temperatures usually are greatest (3° to 8°C) in early evening near the city core. However, daytime temperatures often are warmest outside the core in a zone with lower buildings and more exposed pavement (Tuller 1973). Winds carry the warmth of the city downwind. Analysis of temporal differences shows that the intensity of the Urban heat-island is greatest at night, primarily due to differences in urban-rural cooling (Oke 1982). Nocturnal urban air-temperature anomalies of 3° to 50C are typical, as compared with 1°C daytime anomalies (Goward 1981). At sunset, rural areas begin to cool rapidly while urban areas remain warm and then cool at a slower rate. Different urban-rural cooling rates at sunset produce maximum heat-island intensities three to five hours later. At sunrise, urban areas begin to warm relatively slowly, sometimes producing urban "cool islands" during the morning. Cooling Urban Heat Islands 153 Under calm conditions, a rural/urban breeze system develops at night that modifies the heat island's vertical structure by creating an urban heat dome. Downwind heat plumes• can extend over rural areas for considerable distances. The vertical extent of air temperature anomalies at night is only two to three times building height, compared with more than 1 kilometer during the day. Increased turbulent mixing of the atmosphere during daytime is primarily responsible for this urban impact on the atmosphere (Duckworth and Sandberg 1954). Energetics of Urban Heat Islands Radiation and anthropogenic sources of energy are partitioned into latent, sensible, and stored energy within the urban environment. Flows (or fluxes) of energy for each of these terms are expressed in the energy balance equation for an urban surface as: Qr+ K" + L'= QF+ Q" = Q~ + 0N + Qs where QF is afitil~ro'p~g~enic heat release, K" is net shortwave radiation (direct, diffuse,and reflected), L" is net longwave radiation, Q" is the net allwave radiation, QE is latent heat-flux density, Q~ is sensible heat-flux density, and Qs is net storage heat-flux density. The magnitude of these energy fluxes ranges widely within and among cities depending on factors such as city size, population, latitude, urban morphology, and land cover characteristics. As a general guide for assessing the relative impor-• tance of each flux along the urban-rural gradient, Oke (1988a) listed hypothetical flux densities based on existing observations. These data, reproduced in table 1, refer to dear summer conditions at noon for a mid-latitude city with 1 million inhabitants. Unfortunately, typical values for nocturnal conditionsl when the urban heat island is most intense are unavailable. The relative importance of anthropogenic heat is small except during winter in high-latitude cities. At noon during summer, anthropogenic heat-flux densities typically range from twenty to fifty watts per square meter (table 1), depending on population density and energy use per capita (Oke 1988a). Surprisingly, differences in net all-wave radiation (Q') bet~yeen rural and urban environments are relatively small because of offsetting the effects of urban atmosphere, albedo, and geometry (table 1). On average, smog attenuates urbanshort- x54 Urbanization and Terrestrial Ecosystems Table 1 Radiation and Energy Balances for Hypothetical Midlatitude City at Noon During Clear Summer Conditions. All Values in W m-~ (after Oke, x988a). Available Energy Rural Suburban Urban K~ 800 776• KT . -160 -116 L$ 350 t 357 LT -455 -478 Q* 535 539 QF " 0 15 Total 535 554 760 --106 365 -503 516 30 546 Panifioned Energy Rural Qs 80 QH 150 QE 305 Total 535 96 Suburban 15 122 28 216 57 216 100 554 96• 22 39 39 100 Urban 148 240 158 • 546 96 27 44 29 I00 wave radiation by about lo percent, but a lower urban albedo (15 percent versus a rural albedo ofzo to 25 Percent) results in relatively more absorption than in rural surroundings. Longwave radiation is primarily a function of surface temperature and exposure to the sky. Warmer air temperatures above Cities result in greater incoming longwave radiation, but this is offset by increased outgoing longwave radiation due to warmer urban surface temperatures. However, it is important to recognize that urban heat-island intensity is greatest in urban canyons, par@ because of the effect of tall buildings on radiation exchange. These buildings shade the street and wall surfaces during the day, reducing absorption of shortwave radiation and in some cases creating daytime "cool islands" However, the rate of heat loss to the sky at night is reduced because the sky in the city core is a less accessible sink for longwave heat loss compared with the sky in more open rural or suburban settings. Thus, although net allwave radiation in urban and rural environments is similar when averaged over a day, the geometry of cities results in diurnal differences in flux densities that Can have important effects on the timing and intensity of the heat island. Available energy (QF + Q') is partitioned into three fluxes, Qs, QH, and Qe. Net storage heat flux (Qs) depends on thethermal properties and arrangement of elements within the urban canopy layer. The thermal properties of typical urban materials such as asphalt, brick, and concrete are similar to those of iural materials such as bare soils. Higher urban net storage heat-flux densities are attributed to Cooling Urban Heat Islands 155 differences in the composition and structure of these materials rather than• their thermal properties per se (Goward 1981). For instance, unshaded, vertical building walls in the urban core can absorb larger amounts of radiant energy per unit of ground surface area than flatter rural surfaces can. Much of this energy is returned to the air as sensible heat because the low thermal mass of honeycomb-structured buildings results in relatively( little heat storage. Paving materials have high thermal inertias that delay the time of peak surface temperature and reduce temperature ranges compared with those for surfaces of unshaded buildings with similar al-bedos. For the hypothetical mid-latitude city at noon, net storage heat flux :typically accounts for about 15 and 27 percent (80 and 148 watts per square meter) of the available energy in rural and urban areas, respectively (Oke 1988a). Most importantly, daytime heat storage by the urban fabric delays the onset and retards the rate of nocturnal cooling. Partitioning of the remaining energy into sensible (QH) and latent energy (QE) fluxes depends largely on available atmospheric, surface, and soil moisture. Moisture availability in urban environments exhibits great diversity in both space and time, whereas spatial diversity is less in rural areas (Oke .988a). Lakes, irrigated fields, and foresfs 0f rural areas transform incoming energy into latent energy through evapotranspiration. Because less energy remains as sensible heat, air temperatures are lower. Hence, at noon in rural areas, 50 to 60 percent of the available energy is consumed as latent heat flux, and about 30 and 15 percent becOme sensible and subsurface heat fluxes (table 1). Vegetation cover accounts for from 5 to 20 percent of the surfaces in cities, "15 to 50 percent in suburbs, and 75 percent or more in rural areas (Rowntree 1984). Because cities have less vegetation and more impervious surfaces than rural areas, more energy is available to warm the air. Latent heat flux typically consumes only 30 percent of the incoming energy in the irrigated hypothetical city at noon, about half that consumed in the country. Hence, in urban areas, nearly 45 percent of the incoming energy warms the air as sensible heat (table 1). It should be recognized that in the previous discussion "ideal" conditions were assumed. When conditions are calm and dear, microdimatic differences are en-• hanced and the relative importance of radiation and heat storage is increased. As windspeed and cloud cover increase, convection becomes relatively more important and net radiation and storage heat fluxes are dampened. Implications of Urban Heat Islands • Urban temperatures have been increasing in cities around the world. Comparisons of temperature data from paired urban and rural weather stations suggest that the 156 Urbanization and Terrestrial Ecosystems recent warming trends are due to the urban heat island effect rather than to changes in regional weather. For example, data from thirty-one California cities show a warming rate of o.4°C (o.7°F) per decade since 1965 (Akbari et al. 1992). Additionally, scientists project a "greenhouse" warming rate of about o.3°C (o.5°F) per decade, which could exacerbate urban heat-island effects. This section reviews some of the significant economic and social implications of continued urban warming. Peak cooling loads occur on the warmest days when air conditioning demandis greatest. They increase by about t percent for every increase in temperature of lo°C in U.S. cities with populations larger than one hundred thousand. Approximately 3 to 8 percent of the current U.S. electricity used for air conditioning is neededto compensate for the heat island effect caused by an increase in city temperatures of about 1° to 2°C since 195o. Scientists at the Lawrence Berkeley Laboratory (Akbari et al. 1988) estimate total national costs for offsetting the effects of summer heat islands on electricity at about $1 million per hour or more than $1 billion per year (5 percent of total air-conditioning costs). Urban heat islands can contribute to global warming because warmer temperatures result in greater demands for cooling. Coal-burning power plants release about o.45 ldlograms (1 pound) of carbon per kilowatt-hour of electricity they generate. Therefore, mitigating urban heat islands can indirectly reduce carbon dioxide emissions at power plants and concentrations of atmospheric CO2. Large-scale plantings of urban trees and the use of light-colored surfaces can conserve about 2 percent of the total U.S. carbon production (Akbari et al. 1988). Concentrations of urban Ozone are increased by increases in ambient temperature (Cardelino and Chameides 199o). One study found that the incidence of smoggy days increased by I percent for each degree Celsius increase in temperature (Akbari et al. 1992). Because many large cities have smog problems and smog concentrations are sensitive to small increases in temperature, controlling urban heat islands is one means of improving air quality. Urban heat islands can have numerous other adverse effects on the physical and psychological well-being of city dwellers. Heat-aggravated illness and death are related to increased cardiovascular diseases that weaken resistance to heat. Unnaturally high heat loads can directly and indirectly reduce life expectancy (Weihe 1986). Mitigation of Urban Heat Islands The thermal behavior of cities is largely a by-product of urban morphology or, more specifically, the composition and three-dimensional structure of materials , , "..'i.. Cooling Urban Heat Islands 157 that constitute the urban canopy layer. This section reviews mitigation potential and the problems associated with urban geometry, surface color, and vegetation, elements that are commonly manipulated during the development process. Urban geometry. Oke (1988b) stated that designs for street canyons in high- and mid-latitude cities should (1) maximize shelter from wind for pedestrian comfort, (z) maximize dispersion of air pollutants, (3) maximize urban warmth to reduce the need for space heating, and (4) maximize solar access.For warm-dimate cities, objective 3 could be modified to read: minimize urban warming to reduce the need for space cooling. In either case, there can be a conflict between objectives promoting shelter, which imply narrow streets and compact forms, and objectives promoting dispersion, which imply separation and low building density. No design can maximize all objectives but it is possible to meet all objectives to a degree that is minimally acceptable. Oke's analysis of urban geometry in relation to air-flow patterns, radiation exchange, and thermal behavior resulted in a range of canyon geometries and building densities that achieve a "zone of Compatibility" wherein the worst aspects of not providing shelter, dispersion, warmth, or solar access are avoided. For instance, aspeCt:ratios (building height/canyon width) of 0.4 to 0.6 and building densities (roof area/total surface area) ofo.2 to 0.4 satisfied all four objectives. The deep canyons and high building densities of many European cities result in geometries that more frequently fall within Oke's zones of compatibility compared to those many North American cities whose settlement patterns are more dispersed (Oke 1988b). Numerical models and computer simulations have been used to evaluate the climatic impacts of urban design features. Arnfield's (199o)" calculations of irra-diances on urban canyon walls and floors provide quantitative guidelines on street geometry. He found that irradiance values generally were smaller for canyon walls than for floors, and that controlling canyon-floor irradiance was more critical at lower latitudes because of higher solar angles. North-south street orientation provided less summer and more winter canyon-floor irradiance than east-west street orientation, though the latter provided more favorable seasonal irradiance on canyon walls. Using their Cluster Thermal Time Constant model, Swaid and Hoffman (199o) found that in hot regions, cities with north-south streets have weaker urban heat4sland intensities (o.8°C) than cities with east-west streets. Their sensitivity analysis illustrated how increasing aspect ratios (canyon height to width) results in a stronger daytime "cool island" due to increased shade, and a weaker nocturnal heat island due to appreciably reduced maximum temperature. Although manipulation of aspect ratio, building density, and street orientation might reduce urban heat island effects substantially, the opportunity to exercise 158 Urbanization and Terrestrial Ecosystems this control is limited to new town planning and redevelopment projects. The urban geometry of most cities is well established and large-scale change is unlikely. In these circumstances, the use of vegetation and light-colored surfaces are more feasible mitigation options. Light-colored surfaces. Increasing the albedo of building Surfaces by whitewashing reduces solar heat gain and resulting heat storage. Additionally, increasing the albedo of large areas of the city by using light-colored dyes or sand in paving materials will lower air temperature by reducing the absorption of shortwave radiation. According to data from computer simulations for Sacramento, California, a temperature drop of one to four degrees Celsius can be achieved by "increasing citywide albedo from 25 to 40 percent (Taha et al. 1988). Whitewashing residential buildings (albedo change from 9 to 70 percent) reduced annual cooling energy 19 percent and peak cooling demand by 14 percent (Taha et al. 1988). The combined effects of modifications in urban and building albedo resulted in savings of up to 62 percent for annual cooling and 35 percent for peak cooling. However, because the effect of the increased solar load on buildings from lighter surroundings was not incorporated in the model, predicted savings may exceed actual savings. Albedo modification is a promising strategy for heat island mitigation because of the relatively quick payback period. Once.light surfaces are applied, benefits begin to accrue. Many surfaces need to be recoated, so there is the opportunity for large-scale implementation. Using data for Sacramento, Akbari and others (1987) calculated that urban albedo could be increased from 2o to 30 percent by changing the albedo of rooftops (15 to 4o percent) and streets (14 to 3o percent). Increased glare and the desire of some designers and property owners for unrestricted color selection are potential obstacles to implementation. Also, some materials (e.g., tar roofing) do not lend themselves to painting and others may require regular recoating and deaning (Akbari et al. 1987). Large-scale tree planting could counteract the effectiveness of color change by shading light surfaces and reducing citywide albedo. The extent to which the energy absorbed in this way would influence urban warming depends on its partitioning into latent and sensible heat fluxes. • Vegetated surfaces. The energy-saving potential of trees and other landscape vegetation has been documented (Heisler 1986; Meier 1991; Parker 199o). Vegetation can mitigate urban heat islands directly by shading heat-absorbing surfaces, and indirectly through evapotranspirational (P-T) cooling. In a review of studies that measured temperature reductions, Meier (1991) reported that vegetation consistently lowered wall surface temperatures by about seventeen degrees Celsius and reduced air-conditioning costs by 25 to 80 percent. The extent to which measured reductions in surface temperature and savings in cooling costs can be attributed to Cooling Urban Heat Islands 159 direct building shade versus ET cooling is not dear. In most circumstances, the impact of one or Several trees on ambient temperatures and cooling load are small compared to the shading effect. Cool air produced in the tree crown is dissipated by the much larger volume of air moving through the tree. However, large num' bers of trees and expansive greenspaces can reduce local air temperatures by one to five degrees Celsius, and the advection of this cool air can lower the demand for air conditioning (O'Rourke and Terjung 1981; Oke 1989). • Computer simulations (Huang et al. 1987) of the cooling effects of three trees around a residential home in Sacramento showed that shade alone reduced annual and peak cooling energy use by 16 and 11 percent, respectively. The combined ~ effects of shade and ET cooling resulted in savings of 53 and 34 percent, respectively. Thus, ET cooling accounted for 70 percent of the annual energy savings and 68 percent of the peaksavings. This finding may reflect the modeling assumption that Ea- isnot limited by soil moisture. Trees in urban environments can experience drought stress due to limited soil moisture and large heat gains from absorbed and reflected radiation (Oke 1989). Theoretically, for stressed plants ET cooling is least during mid- to late afternoon when water vapor deficits are greatest and stomata -~ ~..-. ~ are closed..Therefore, actual ~T cooling effects may be less than projected,:espe~::: .~: .......... ........ cially with regard to peak savings. The relative importance of mr cooling has been disputed by Lowry (1988), who calculated an ~-w cooling rate of o.3°C per hour and a sensible heating rate of 1.o°C per hour along ten meters of street canyon contain- ing six mature trees. The selection and location• of trees around buildings to minimize the peak dema.nd for air conditioning is particularly important to electric utilities because the marginal cost of peak power is generally 2o to 30 percent greater than the cost of base load power (about $O.lO versus $o.o75 per kilowatt-hour). Parker (1987) described a methodology for determining the optimal location of vegetation to' reduce peak loads. "Peak load landscaping" requires that plants be positioned to provide maximum shade several hours before the time when the local utility • typically experiences peak demand. In south Florida peak demand usually occurs. between 5 and 6 P.M.in early August when temperatures are warmest. To account for the delay before heat on the exterior walls transfers inside and affects the air-conditioning load, Parker recommended plantings for maximum shading of south- and west-facing surfaces between 3 and 4 P.~. in early August. Large-scale implementation of "peak load" landscaping also could reduce urban heat-island intensity because this intensity often is greatest (6 to n P.M.) during the period of peak demand for most summer-peaking electric utilities (3 to lO P.M0. How effectively this landscaping can "shave" and shift peak demand for. electricity depends on factors such as the utility's demand profile and regional climate. McPherson 1673 0.97 0.12 1990b 1353 0.94 0.12 McPherson 500,000 61 - 338 1991 mesquite 16o Urbanization and Terrestrial Ecosystems 1"able 2 Summary of Impacts of Vegetation on Electricity Use in Arizona Annual Cooling Savings (kWh) and Peak Demand Savings (kW) House Planting Shade ET Cool Total~Tree Study Type Type kWh kW kWh kW kwh kW Huang et al. 143 m' 1987 wood Phoenix McPherson & 137 mz Dougherty wood 1989 Tucson 137 mz wood Phoenix and Tucson Tucson I tree west side 50 m2 1 olive tree west side 46 m2 xeriscape 8 trees 50 shrubs 208 0.47 665 0.33 873 0.80 292 0.39 - - 292 0.39 (Phoenix) (Tucson) 277 : - 209 169 Additional measurements and modeling studies are needed to quantify the potential savings in annual and peak load electricity to be gained through landscaping. Water is becoming increasingly expensive in many cities, and the cooling value of trees that use little water has been questioned in desert cities. Shading with little ~T cooling, as with desert trees, results in the conversion of most absorbed radiant energy info sensible heat that warms the air. However, because net storage heat flux can be substantial in hot, arid cities (Grimmond & Oke 199o), shading alone can reduce urban heat-island intensity by reducing surface temperatures and the amount of energy stored and later reradiated from paving and buildings (Swaid and Hoff-man 199o). Findings from a study using quarter-scale buildings (McPherson et al. 1989) suggest that ~T cooling from turf can provide cooling savings equivalent to the savings gained from the dense shade of shrubs and trees requiring little water. These results indicate that the microscale effects of vegetation in hot, arid regions can be more significant than was commonly thought. Landscaped mini-oases with small turf areas that provide ST cooling and desert trees that shade buildings can effectively balance the need to conserve energy and water (McPherson 199ob). Results of several field studies and computer simulations designed to quantify the effects of trees on electric use in Arizona are summarized in table ~-. Annual cooling energy and peak demand savings ranged from 169 to 873 kilowatt-hours and o.xz to 0.80 kilowatts, respectively. Other findings suggest that: Cooling Urban Heat Islands 161 (1) Shading of windows and west-facing walls provides the most savings in cooling energy (McPherson and Dougherty 1989). (z) On trees selected for shade, crown shape can be more important than crown density (McPherson and Dougherty 1989). (3) Annual water costs for certain tree species can be twice as much as the energy savings from their shade (McPherson and Dougherty 1989). (4) Energy and water prices determine the extent to which it is economical to substitute ua" cooling for electric air conditioning (McPherson and Woodard 199o). (5) Effects of tree shade on Winter heating demand can be substantial (Thayer and Maeda 1985; Heisler 1986; McPherson et al. 1988). The Arizona Corporation Commission (199o) recommended that utilities fund the development of consumer guides on energy-efficient landscaping and pro, grams offering rebates for tree planting. These recommendations were based upon the results of a benefit-cost analysis that found that the present value of net benefits for planting 18o,ooo trees is $2.9 million. The analysis assumed planting costs of $45 per:tree, annual water costs of $4 to $6 per tree, a 7 percent discount rate, and a twenty-year planning horizon. Each tree was assumed to shade the west-facing wall and provide annual and peak savings of 250 kilowatt-hours and 0.33 kilowatts, respectively, after the fifth year. The study showed that trees were an economical conservation measure because they met the need for electric energy services at a cost lower than the cost of generating electricity. A benefit-cost analysis (fig. 1) for the planting of 500,000 trees in Tucson, Arizona, projected net benefits of $~36.5 million for the forty-year planning horizon (McPherson 1991). The benefit-cost ratio and the internal rate of return for all trees were 2.6 and 7.11, respectively. Yard trees provided the highest rate of return (14 percent) and street trees the lowest (z percent). Average annual costs and benefitsper tree were estimated as $9.61 and $25.09, respectively. Cooling savings provided the greatest benefits, and removal costs were the largest management expense. Projected average annual benefits in cooling energy per tree were 61 kilowatt-hours ($4.39) for shade and 227 kilowatt-hours ($16.34) for ET cooling. Carbon savings averaged 185 kilograms (408 pounds) annually per tree. An important conclusion was that investment in tree planting by the public sector may be warranted because economic, environmental, and aesthetic benefits extend beyond the site where individual trees are planted. The value of trees for energy conservation has also been evaluated at the national level. Projections from computer simulations indicate that lOO million mature trees in U.S. cities (three trees for every other single-family home) could •:I . . / 162 Urbanization and Terrestrial Ecosystems reduce energy use for heating and cooling by 30 billion kilowatt-hours and reduce CO2 emissions by as much as 8 billion kilograms (9 million tons) per year (Akbari et al. 1988). Increasing vegetation was more cost-effective in mitigating heat island effects than other fuel-saving measures such as using energy-efficient appliances and cars ..... Although the potential for planting trees in U.S. cities is great and considerable mitigation of urban heat-island effects is possible, there are problems associated with tree planting. First, trees can be a serious liability if they become a publ.c hazard, interfere with aboveground or belowground utilities, or require excessive maintenance. Second, trees can adversely affect the urban climate by blocking solar access in winter, by trapping pollutants within the urban canopy layer and by • increasing aerodynamic roughness, thereby reducing country-city air flow and convective heat loss. Third, trees can be relatively expensive to plant and slow to provide a return on investment. Fourth, increased tree planting can increase the amount of pollen that affects allergy sufferers, the use of scarce water supplies, and the amount of solid waste that goes into landfills. However, these problems can be minimized through careful planning, wise selection of species, and designs that fully use the hydrologic, ecologic, atmospheric, restorative, and aesthetic benefits: that vegetation can provide. Figure 1 Projected average annual costs and benefits from proposed planting ofsoo,ooo desert trees during 199o to x995 in parks, yards, and streets of Tucson, Arizona (from McPherson 1991) • ' • I'B Park Costs Icl Yard Costs El Street Costs • Park Benefits . mYard Benefits [] Street Benefits $ in Millions II 15 " / . oj 1993 1998 2003 2008 .013 2018 2023 2028 i Cooling Urban Heat Islands 163 Figure Z Tall, narrow deciduous street trees shade the canyon walls and sidewalks, reduce downdrafts, and provide ET cooling. Pollution dispersion by down-canyon breezes and vertical mixing of buoyant air is achieved because the crowns do not cover the entire canyon. Bare branches in winter enhance solar heat gain. Design Examples Several design examples illustrate how climatological information is applied to urban.heat:island mitigation in a northern hemisphere city (approximately thirty. ~ : .... degrees north latitude) with a hot climate. These examples focus on the use of vegetation in situations that are typical of urban canyons, parking lots,• parks, and single-family residential neighborhoods. Each design addresses objectives defined for street canyons and restated here for hot-climate cities. 1) Promote summertime cooling and the conservation of air-conditioning energy by reducing irradiance and increasing heat loss through latent heat flux, convection, and longwave radiation. • 2) Allow for the dispersion of air pollutants by promoting down- and cross-canyon circulation and mixing with air moving above the city. 3) Provide for solar access during the winter by increasing irradiance. 4) Shelter pedestrian; from extreme winds, turbulence, and downdrafts near buildings. Street Canyons Various techniques have provided a salubrious street-canyon environment by balancing the needs for solar protection and atmospheric dispersion (fig. z). A high aspect ratio reflects the importance of reducing the irradiance of canyon floors at lower latitudes. Light-colored roof, wall, and paving surfaces further reduce the amount of absorbed radiation. Tall, narrow trees reduce canyon wall irradiance, shade sidewalks, and lessen downdrafts at the base of buildings. Down-canyon ~64 Urbanization and Terrestrial Ecosystems ventilation is not entirely obstructed since the trees do not cover the street. This arrangement also allows for some longwave heat loss from street to sky and perhaps for pollution dispersion through the ascension of hot air parcels. Amply irrigated deciduous trees lower summertime temperatures through ET cooling and provide increased winter irradiance when they drop their leaves. The trees also furnish other benefits such as absorbing gaseous pollutants and carbon dioxide, emitting oxygen, intercepting particulates, .reducing noise, and enhancing scenic beauty. On the negative side, the trees reduce convective heat loss from the building skin and pollution dispersion from cross-canyon circulation. Parking Lots Parking 10ts are ubiquitous features of commercial strips and shopping malls that surround the urban core. Issues of visibility, safety, screening, and access are central to traditional parking-lot design. The design in figure 3 incorporates these concerns as well as the needs for shade, buffering, and water harvesting (Beatty 199o). Trees are aligned in north-south rows to shade as much pavement as possible during the summer. Dense, broad-spreading treecrowns increasethe amount of shade. Ample growing space and soil moisture enhance tree survival, growth, and ET cooling effects. Trees are pruned high enough for safe visibility and truck clearance. Pruning also promotes subcanopy circulation for cooling and pollution dispersion. Rainfall runoff drains into the buffer plantings along the perimeter, where it is detained. These buffer plantings exhibit structural diversity, with a variety of species in several strata. Harvested rainfall supplements irrigation, and the plantings function to reduce sound, particulates, and gaseous pollutants. Vertical accents articulate entryways to enhance the safety and legibility of the parking lot. Urban Parks Parks can be important sources of fresh cool air in the city. The park in figure 4 is designed to increase nocturnal cooling and the advection of cool air into the warmer surrounding neighborhood. Much of the park is well-irrigated turf without trees. Transpiring turf shades the ground and cools the air. Although trees in turf can increase the ~.r cooling effect, they also can reduce radiant heat loss to the sky and convection/advection. This trade-off has not been studied sufficiently to permit us to know whether the addition of trees provides net benefits. Multi-layered plantings of drought-tolerant species create a buffer along berms that define the park perimeter. The use of native-looking plants in forms that reflect the • Figure 3 . Cooling Urban Heat Islands x65 Trees in the parking lot are arranged in north-south rows to provide maximum shade on pavement during the summer. Sufficient soil volumes and irrigation promote rapid growth and ET cooling. Stormwater runoffis harvested in basins along the periphery, where structurally diverse plantings filter particulates, intercept rainfall, and screen the parking lot. i I i 166 Urbanization and Terrestrial Ecosystems i: i' Figure 4 The ripen turf area in this urban park is a source of cool air that is carried into the surrounding area by prevailing breezes. Buffer plantings along the park boundary reflect the complex structure of the region's native plant associations. structure of native plant communities promotes a sense of place. The buffer planting is multifunctional and an important symbol of "naturalness" in the heart of the city. The berms and buffer plantings disappear at street intersections to facilitate the flow of cool air through downwind openings and into adjacent street canyons. Residential Streets Most residential streets in the United States have paving that is too wide and planting strips that are too narrow. The design in figure 5 "reclaims" the right-of-way for people, plants, and animals. Narrowed traffic lanes force cars to travel Cooling Urban Heat Islands 167 slowly through residential neighborhoods yet allow access for emergency vehides. Parking for residents and guests is provided along intrablock alleys. Large roadside trees shade the pavement and promote pedestrian travel within a more" comfortable microclimate. Reclaimed irrigation water and stormwater harvested Off the surrounding areas nourish a complex association of plants and animals. Smaller drought-tolerant trees shade adjacent residences, conserving energy and water. Conclusion ' Although urban climatologists have made many measurements of urbanheat- island effects, there are relatively few predictive models for use by those who design r Figure "5 Redaimed greenspaces along residential streets provide areas for naturalistic plantings that enhance biodiversity by creating riparianlike habitats. Runoff harvested from streets and sidewalks reduces flooding downstream and conserves irrigation water. Small trees that use little water shade nearby buildings. . .................... r i , ii . . • I I x68 Urbanization and Terrestrial Ecosystems our cities (Oke 1988a). Most existing models do not adequately consider all fluxes of energy and matter or in.corporate the spatial and temporal variability within the urban canopy layer (Martien et al. 199o). There is need for numerical models that are based on the physical processes at work in cities (Grimmond and Oke 1986). The output from microdimatic or canopy layer models that function at the scale of a homesite could be input for mesoclimatic models that integrate microscale effects over the area of a neighborhood or city. Once these models have been validated in different climatic regions, they should be simplified and integrated with existing geographic information systems to facilitate implementation by ur- ban planners. Studies are needed to determine the most cost-effective method for obtaining land-surface information for modeling purposes. Remotely sensed information seems appropriate for mesoscale modeling but may not provide the resolution needed for microscale simulation. Field surveys might be needed to identify plant species and size as well as building construction types, and to collect other detailed information. This will require the development of appropriate sampling and sur- vey techniques. ..... • ~: : Environmental planners are asking many practical questions related to urban ~ ...... heat-island mitigation that we cannot answer now. For instance, policy-makers in Arizona want to know the trade-offs between F.T cooling and water demand. Elsewhere, utility and urban planners want to know how much savings in cooling energy can be achieved by increasing the amount of urban vegetation by a spec- ified amount. Designers are asking how best to locate and manage vegetation in parks, streets, and residential areas to improve urban climate. Urban foresters want to know which tree species will provide the greatest long-term net benefits. Clearly, there is a need for further development of urban dimate models, as well as for climatological and urban forestry research that can be used to validate and verify the models. Equally important is the development and application of "user.• friendly" planning and design tools. The cooling of our urban heat islands de- pends on the timely development and implementation of reliable predictive mod- els, and the guidelines, regulations, and incentives that can be generated from the information they provide. t i.~•. :~ i Acknowledgments I appreciate reviews of earlier versions of this manuscript by Sue Grimmond (Indiana University), Hashem Akbari (Lawrence Berkeley Laboratory), Rich Grant (Purdue University), and Craig Johnson (Utah State University). Steve Wensman provided assistance with the illustrations. i ~J Cooling Urban Heat Islands 169 References Akbari, H., H. Taha, P. Martien, and J. Huang. 1987. Strategies for reducing urban heat islands: Savings, conflicts, and city's role. In Proceedings of the First National Conference on Energy Efficient Cooling. San Jose, CA. Akbari, H., J. Huang, P. Martien, L. Ranier, A. Rosenfeld, and H. Taha. 1988. The impact of summer heat islands on cooling energy consumption and COz emissions. In Proceedings of the 1988 ACBEB summer study On energy efficiency in buildings. Washington: American Council for an Energy Efficient Economy. " Akbari, H., A. Rosenfeld, and H. Taha. i99o. Recent developments in heat island studies: Technical and policy. In ControllingSummerHeat Islands, ed. K. Garbesi et al. Berkeley: Lawrence Berkeley Laboratory. Akbari, H., S. Davis, S. Dorsano, J. Huang, and S. Winnett. 1992. Cooling our communities: A guidebook on tree planting and light-colored surfacing. Washington: U.S. Environmental Protection Agency. Arizona Corporation Commission. 199o. Resource planning staff report. Phoenix: Utilities Division, Arizona Corporation Commission. Arnfield, A. J. 199o. Street design and urban canyon solar access. Energy and Buildings 14(2): 117-31. Beatty, R. A. 199o. Planting guidelines for heat island mitigation and energy conservation. In Control- ling summer heat islands, ed. K. Garbesi, H. Akbari, and P. Martien. Berkeley:. Lawrence Berkeley ~. Laboratory. Cardelino, C. A., and W. L. Chameides. 199o. Natural hydrocarbons, urbanization, and urban ozone. ]ournal of Geophysical Research 95(D9): 13971-79. Chandler, T. J. 1965. The climate of London. London: Hutchinson. Duckworth, F. S., and J. S. Sandberg. 1954. The effect of cities upon horizontal and vertical temperature gradients. Bulletin of the American Meteorological Society 35:198-2o7. Goward, S. N. 1981. Thermal behavior of urban landscapes and the urban heat island. Physical Geogra- phy z(*): 19-33. Grimmond, C. S., and T. IL Oke. 1986. Urban water balance z: Results from a suburb in Vancouver, B.C. Water Resources Research zz:14o4-12. . Preliminary comparisons of measured summer suburban and rural energy balances for a hot dry city, Tucson, Arizona. Proceedings of the International Symposium on Urban Climatology, Air Pollution and Planning in TroPical Cities, 25-3o November, 199o. Guadalajara, Mexico. Heisler, G. 1986. Energy savings with trees, lournal of Arboriculture 12(5): 125. Herrington, L. P., G. E. Bertolin, and R. E. Leonard. 1972. Microclimates of a suburban parL In Proceedings of a Conference on Urban Environment and the Second Conference On Biometeorology, Boston: American Meteorological Society. Huang, J., H. Akbari, H. Taha, and A. Rosenfeld. 1987. The potential of vegetation in reducing summer cooling loads in residential buildings. Journal of Climate and Applied Meteorology 26:no3-6. Landsberg, H. E. 1981. The urban climate. New York: Academic Press. Lowry, W. P. 1988. Atmospheric ecology for designers and planners: McMinnville, OR: Peavine Publica- tions. 17o Urbanization and Terrestrial Ecosystems Martien, P, H. Akbari, A. Rosenfeld, and I. Duchesne. 199o. Approaches to using models of urban climate in build.ing energy simulation. In Controlling Summer Heat Islands, ed. Garbesi et al. Berkeley: Lawrence Berkeley Laboratory. McPherson, E. G., L. P. Herrington, and G. Heisler. 1988. Impacts of vegetation on residentialheating and cooling. Energy and Buildings 12:41-51. McPherson, E. G. and E. Dougherty. 1989. Selecting trees for shade in the Southwest. Journal of : Arboriculture 15(2): 35-43. McPherson, E. G., J. R. Simpson, and M. Livingston. 1989. Effects of three landscape treatments on residential energy and water use in Tucson, Arizona. Energy and Buildings 13:.27-38. McPherson, E. G. 199oa. Creating an ecological landscape. In Proceedings of the Fourth Urban Forestry , ~ Conference, ed. P. Rodbell. Washington: American Forestry Association. ~. 199ob. Modeling residential landscape water and energy use to evaluate water conservation policies. Landscape]ournal9(z): 12-34. : ~. 1991. Economic modeling for large-scale urban tree plantings. In Energy Efficiency and the Environment: Forging the link. Washington: American Council for an Energy Efficient Economy. McPherson, E. G. and G. C. Woodardl 199o. Cooling the urban heat island with water-and-energy efficient landscapes. Arizona Review, (Spring)a-8. Meier, A. K. 1991. Measured cooling savings from vegetative landscaping. In Energy Efficiency and the~ i i Environment: Forging the link. Washington: American Council for an Energy Efficient Economy. "~ Oke, T. R. 1982. The energetic basis of the urban heat island. Quarterly]ournal of the Royal Meteorologi- cal Society 188(455): 1-z4. Oke, T. R., ed. 1986. Urban climatology and its application with special regard to tropical areas. Geneva: World Meteorological Organization. Oke, T. R. 1987a. Boundary layer climates. New York: Methuen. Oke, T. R., ed. 1987b. Modeling the urban boundary layer. Boston: American Meteorological Society. Oke, T. R. 1988a. The urban energy balance. Progress in Physical Geography lz:471-5o8. .1988b. Street design and urban canopy layer climate. Energy and Buildings 11: lo3-13. .. 1989. The micrometeorology of the urban forest. Philosophical Transactions ofthe Royal Societ7 of London 324: 335-49- O'Rourke, P. A. and W. H. Terjung. 1981. Urban parks, energy budgets, and surface temperatures. Archives for Meteorology, Geophysics and Biodimatology a9: 3z7-44. Parker, J. H. 1987. The use of shrubs in energy conservation plantings. Landscape Journal 6(z): 13z-9. • . 199o. The impact of vegetation on air conditioning consumption. In Controlling Summer Heat Islands, ed. Garbesi et al. Berkeley: Lawrence Berkeley Laboratory. Rowntree, R. A. 1984. Forest canopy cover and land use in four eastern United States cities. Urban Ecology 8:55-67. Swaid, H. and M. E. Hoffman. 199o. Climatic impacts of urban design features for high- and mid- latitude cities. Energy and Buildings 15(4): 325-36. Cooling Urban Heat Islands 171 Taha, HI, H. Akbari, A. Rosenfeld, and I. Huang. 1988. Residential cooling loads and the urban heat island-the effects of albedo. Building and Environment 23(4): 271-83. Thayer, R. L and B. Maeda. t985. Measuring street tree impact on solar performance: A five dimate computer modeling study. ]ournal of Arboriculture ha-t2. Tuller, S. E. 1973. Microdimatic variations in a downtown urban environment. Geograf~ka Annaler 54(3-4)" 123-35. . • Tyson, P. D., M. Garstang, and G. D. Emmitt. 1973. The structure of heat islands. Occasional paper no. m, Department of Geography and Environmental Studies, University of Witwatersrand. Johannesburg. Weihe, W. H. 1986. Life expectancy in tropical climates and urbanizati0n. In Urban Climatology and its Applications with Special Regard to Tropical Areas, ed. "1". R. Oke. Geneva: World Meteorological Organization .... I • '] ii ">!
83!7/18/2002 5:04:00 PM!Neighborhood-scale temperature variation related to canopy cover differences in southern California!Levitt, D.G., J.R. Simpson, C.S. Grimmond, E.G. McPherson and R. Rowntree!1994!In: 11th Conference on biometeorology and aerobiology: 1994 March 7-11; San Diego. Boston: American Meteorological Society!!Miscellaneous Energy Literature!cufr_83_DL94_7.PDF!PDF!Levitt, D.G., J.R. Simpson, C.S. Grimmond, E.G. McPherson and R. Rowntree. 1994. Neighborhood-scale temperature variation related to canopy cover differences in southern California. In: 11th Conference on biometeorology and aerobiology: 1994 March 7-11; San Diego. Boston: American Meteorological Society: 349-352!!The effects of vegetative cover on neighborhood-scale climate in southern California are being studied as part of a larger project in urban forest climate research. A comparison of microclimate between two similar urban neighborhoods in Los Angeles County, with different vegetation densities is presented. Previous studies indicate temperature reductions of 1 to 2 °C can be expected for an increase in vegetation of 10% (Huang et al., 1987). Preliminary tree cover differences between the two areas of this Study are approximately 18 percent (Simpson et al., 1994). The higher-cover area is in Arcadia and Pasadena, CA, and the lower-cover area is in San Gabriel and Alhambra, CA. Measurements were taken in each of the areas using fixed weather stations, augmented with mobile transects. Measurements taken at the field weather stations are described in a companion paper (Simpson et al., 1994). The mobile transect, car-mounted sampling approach has been used in a number of studies as an inexpensive and reliable land-climate sampling strategy (Brazel and Johnson, 1980; Duckworth and Sandberg, 1954). Measurements were made using the mobile transect Strategy as an independent verification of the results presented by Simpson et al., 1994. The objective of this paper is to present the results found during the mobile transects and compare them to the results found at the fixed stations!
84!7/18/2002 5:06:00 PM!Evaluating the cost effectiveness of shade trees for demand-side management!McPherson, E.G!1993!The Electricity Journal. 6(9)!Articles in Journals!Miscellaneous Benefit-Cost Literature!cufr_84_EM93_10.PDF!PDF!McPherson, E.G. 1993. Evaluating the cost effectiveness of shade trees for demand-side management. The Electricity Journal. 6(9): 57-65!!Proper planning and placement of trees as part of a utility DSM strategy offers a number of benefits to utilities and their customers in certain markets. When all of the benefits – including those not easily quantified – are counted, trees may be a resource and customer service tool your utility should consider!are underway to investigate how the age structure, mature sizes, and growth rates of tree species occupying energy conserving sites influence annual penetration and future saturation. This shade tree market analysis suggested that there was ample opportunity for a DSM shade tree program to conserve cooling energy via tree planting around these types of San Diego residences. There was space for planting trees opposite the west wails of more than half of the 6,610 houses surveyed. On average, only one in five of the residences with technical potential has trees that occupy the targeted planting space. Thus, over 40% of all houses surveyed have space available for a shade tree opposite their west wall. Because the NAR is only 2 to 3% each year, a DSM program could substantially increase the amount of tree shade on west wails. III. Cost Effectiveness Shade trees require large initial investments for planting, while energy benefits are relatively small until the tree crowns have grown large and dense. Other DSM options usually provide immediate energy savings upon implementation, and those benefits usually diminish as equipment ages. Cost/benefit analyses used to compare DSM options usually discount future benefits and costs to determine net present values. Shade trees could be expected to perform poorly in these analyses because the present values of large up-front planting and establishment costs are relatively great while the present values of future energy savings become relatively small. Despite this disadvantage, shade trees have been found to be cost effective. In a cost/benefit analysis of six conservation treatments conducted by Arizona Corporation Commission staff,13 small shade trees were second to increased at-fic insulation in cost effectiveness. The present value in 1993 of three small shade trees was $50 for the target home cooled by air conditioner or heat pump onl)~ and $200 for the same home assuming dual cooling. The analysis assumed planting costs of $45 per tree and annual maintenance costs of $6.67 during the first 5 years, increasing to $10 during each of the remaining 25 years. Expected annual cooling savings were assumed to be negligible during the first five years, then 0.48 kW and 717 kWh for the home with air conditioning or heat pump and 0.24 kW and 1,600 kWh for the home with dual cooling. A real discount rate of 7% was assumed. Installation of large shade trees ($382 to plant each) was not cost effective due to greater initial costs than for smaller trees. S DG&E has proposed a pilot shade tree program for 1993 aimed at doubling the NAR by planting about 5,000 trees (15 gallon) in neighborhoods where most households have air conditioning and tree saturation is low. A total budget of $237,800 is projected (about $48 per tree), with participants contributing an additional $10 per tree. The program is estimated to reduce demand at least 0.07 MW within the first six years and nearly 1 MW over a 20-year period. An average annual cooling savings of about 80 kWh per tree is anticipated. Annual avoided capacity and energy benefits are projected to average $62 and $53 per tree, respectively. The overall cost-benefit ratio for the 1993 pilot is 1.54. The program is likely to be a joint effort between SDG&E and a local non-profit tree planting group. Similar arrangements have proven successful in Sacramento, where the Sacramento Municipal Utility District and the Sacramento Tree Foundation are planting 1,000 trees per week, as well as in Iowa, where utilities are supporting planting of trees for energy conservation in over 200 communities under the direction of Trees Forever. November 1993 61 I Our cost/benefit study of proposed yard tree plantings in 12 U.S. cities assumed a 10% cost of capital and 30-year planning period. The following traits were characteristic of the most cost-ef-fective programs:14 • Low unit planting and establishment costs that cut up-front investment: Use of trained volunteers, smaller tree sizes, and follow-up care to insure high survival rates are successful strategies. • Regular maintenance ofma-turing trees: The loss of maturing trees is costly in terms of benefits foregone. The costs of regular tree care during the later years of a project are small compared to benefits received. • Plantings targeted to markets where high levels of net benefits wilt be sustained: Investment in shade trees as a DSM measure should match costs with benefits by considering factors such as local climate, air-conditioning saturation, potential impact of trees on energy, environment, and human health, need for trees, and willingness of participants to maintain trees. IV. Achieving Expected Performance To provide the expected return on investment, shade trees should be: (1) properly planted and strategically located to achieve expected performance, (2) carefully selected to grow vigorously, cast dense shade, and maintain foliage throughout the cooling season, and (3) maintained in a healthy state. Judicious tree selection, lo- cation, and planting can be achieved through workshops and training sessions that provide hands-on education to all participants. Information on request, as is provided through the SMUD/ Sacramento Tree Foundation shade tree hot line, improves the likelihood that participants will make informed tree care decisions. Once planted, tree maintenance usually becomes the customer's responsibility. High loss rates and unhealthy trees will reduce techni- cal performance and expected return on investment. Although yard tree mortality rates have not been studied systematically, our interviews with landscape contractors and arborists suggest that about 15 to 30% of the trees may die during the first five years and 0.2 to 2% will die each year thereafter,is Once established, the life span of healthy yard trees generally exceeds 30 years. Loss rates may be reduced if there is follow-up during the first years of establishment. Follow-up may consist of a mailed questionnaire used to track tree survival and health, invitations to tree care workshops, or site visits. The economics of utility investment in follow-up after planting and long-term tree care needs further investigation. For instance, street tree data suggest that about one-third to one-half of all tree losses occur during the first two years after planting.16 The price of guaranteeing two years' survival after planting may be less than benefits forgone due to estab-lishment-related mortality. V. Externalities and Other Benefits and Costs The Energy Policy Act of 1992 calls for integrated resource planning, and utilities are increasingly incorporating environmental externalities into their planning process. Cost-Benefit Analysis of Trees (C-BAT) is a computer model that complements cost-effectiveness analysis by providing a broader accounting of social benefits and costs. C-BAT calculates the annual present value of benefits and costs over 30 years associated with tree planting. The model uses input regarding the numbers, locations, and species of trees to be planted, as well as expected costs for planting, pruning, removal, irrigation, pest/disease control, green waste disposal, litigation/liability, inspection, administration, and infrastructure repair. Growth and mortality rates are assigned, then tree population numbers and size are simulated. Benefits are projected using a variety of sub- 62 The Electricity Journal I 226 383 175 0 175 94 0 0 5 56 43 99 38 201 1,222 22,30S 19.3 models for energy and carbon savings, air pollution interception/absorption, stormwater runoff reduction, salvage value, property value increases and other aesthetic, social, and ecological benefits. C-BAT was applied in 12 U.S. cities to project 30-year net present values and benefit-cost ratios associated with proposed tree plantings in parks/schools, yards, streets, and unimproved lands. Discounted benefit-cost ratios for yard tree plantings were among the highest found. An example is provided here for yard tree plantings associated with Pacific Gas and Electric's Shade Tree Program in Fresno. F IG&E began a Shade Tree Program in Fresno during 1991 and has developed a program for new customers who purchase energy efficient houses. The current program is delivered through a local non-profit tree planting group, Tree Fresno. A $10 rebate coupon is offered to customers who plant approved trees where they will shade residential buildings. The C-BAT simulations assumed planting of 3,300 (5 gal and 3 ft tall) trees annually from 1991 to 1995 at an average cost of $15 per tree. Chinese pistache, a deciduous tree which grows rapidly to 50 ft tall, was selected as the representative species. Of the 16,500 trees planted, 3,399 (21%) were projected to die during the 30-year period. Mature tree pruning and removal costs were assumed to be $196 and $644, respectively. Dead trees were assumed to be removed but not replaced. Program administration costs were assumed to be $6.50 per mature tree. A 10% cost of capital was assumed and a consumer price index was applied to account for projected effects of inflation on prices. The 30-year net present value of PG&E-sponsored yard tree planb ings in Fresno was estimated to be $22.3 million and the overall bene-fit-cost ratio was .9.3 (Table 2). Most dollars were projected to be spent for pruning, planting, program administration, and dead tree removal. Largest benefits were projected from property value enhancement, energy savings, and avoided stormwater run-off. The 30-year present values of all benefits and costs per planted tree were $1,426 and $74, respectively.17 About 70% of the single-family homes in Fresno are air conditioned. Also, assuming that less than optimal tree selection and location cuts cooling energy savings to about half of the maximum, a healthy; 40-ft tall yard tree (about 25 years old) was projected to save 347 kWh per year. This energy savings translated into about 208 gallons of water saved at the power plant, since approximately six-tenths of a gallon is used for each kilowatt-hour of electricity produced. Table 2: Projected Present Value of Benefits and Costs for Yard Tree Plantings in Fresno (16,500 trees planted, 21% mortality for 30 years, 10% cost of capital) Present Value Benefit Category (in $1,000s) Cost Category Present Value (in $1,000s) Energy: Planting: Shade 3,949 Pruning: ET Cooling 1,484 Removal: Wind Reduction 303 Tree Subtotal 5,736 Stump Air Quality: Subtotal PM10 167 Irrigation: Ozone 26 Landfill: Nitrogen Dioxide 174 Inspection: Sulfur Dioxide 17 Pest/Disease: Carbon Monoxide 13 Infrastructure Repair: Subtotal 397 Water/Sewer Carbon Dioxide: Sidewalk/Curb Sequestered 151 Subtotal Avoided 267 Liability: Subtotal 418 Administration: Hydrologic: Total Costs: Runoff Avoided 614 Saved at Power Plant 11 Subtotal 625 Property/Other: 16,351 Net Present Value: Total Benefits: 23,527 Benetit/Cost Ratio: November 1993 6~ 64 Table 3: Projected Annual Air Pollution Uptake and Avoided Power Plant Emission Rates From A Healthy 40 ft Deciduous Yard Tree in Fresno Depostion Emission Control Annual AnnUal Implied Air Velocity Factor Cost Uptake Avoided Value Pollutant (cm/sec) (Ib/MWh) (~on) (Ib/tree) 0b/tree) ($/tree/yr) PM10 0.6 0.09 1,307 2.02 0.03 1.33 Ozone (VOC) 0.45 0.03 490 0.84 0.01 0.21 NO2 0.4 0.45 4,412 0.50 0.16 1.45 SOz 0.66 0.02 1,634 0.16 0.01 0.14 CO 0.001 0.68 920 0.03 0.23 0.12 CO2 NA 0.0004 22 102.82 153.13 2.81 I Avoided power plant emissions can result from energy savings provided by shade trees. Also, because trees intercept particulates and'absorb gaseous pollutants they can offset power plant emissions. Uptake rates were estimated assuming average deposb tion velocities to vegetation from limited literature on this subject and monthly pollution~concentrations from monitoring stations in Fresno2s Power plant emission rates were linked to fuel mix (primarily natural gas) and implied valuation was used to estimate the societal value of reducing air pollutants through tree planting. Assumptions regarding air pollution control costs, emission factors, and deposition velocities are listed in Table 3. The 40-ft tree was projected to remove atmospheric carbon by sequestering 103 lb in tree biomass and reducing power plant emissions by 153 lb during one year (Table 3). The impled value of carbon removal was projected to be $2.81. With the exception of carbon dioxide, implied values for the pollution uptake by trees were several times greater than values for emissions avoided. The value of avoided emissions will be relatively greater in areas where coal is a primary fuel and. uptake rates are lower due to cleaner air. In this example, total implied values were largest for nitrogen dioxide ($1.45) and particulates ($1.33). The Environmental Protection Agency is considering the concept of using trees as biomass pollution sheds to generate emission reduction credits. U 'rbanization increases the land area that is paved or covered with roofs and other impermeable surfaces, which can increase the incidence and severity of flooding. One means for controlling storm ran-off is to construct basins that detain run-off and thus reduce stream flows and flooding potential. Many jurisdictions require construction of on-site detention basins for new development to insure that off-site flow does not exceed pre-develop-ment rates. To purchase land, construct, and landscape a basin costs approximately $0.02 per gallon of capaci~. The crown of the mature yard tree in Fresno was estimated to intercept 182 gallons of rainfall per year, which ultimately evaporates. The annual implied value of this run-off storage was projected to be $3.64. VI. Summary and Conclusions Cost-effectiveness studies conducted by several utilities suggest that shade tree programs can be viable energy conservation measures in certain markets. When direct and indirect effects are considered, annual air-conditioning savings from a 25-ft tall deciduous tree (about 15 years after planting) were projected to range from 100 to 400 kilowatt-hours (10-15%), and peak cooling demand savings ranged from 0.3 to 0.6 kilowatts (8-10%) in most cities. In a study of over 6,000 sin-gle-family residences in San Diego, over 40% were found to have space available for tree planting to shade west-facing walls. The natural adoption rate of trees for energy conservation was 2 to 3% per year for neighborhoods ranging from 5 to 20 years old. SDG&E is implementing a pilot shade tree program targeted to markets characterized by low NARs and tree cover, but relatively high air-conditioning saturation. Results from the computer model Cost-Benefit Analysis of Trees suggest that benefits from energy savings, air pollution mitigation, avoided run-off, and increased property values associated with yard trees can outweigh planting and maintenance costs. Although the resident can obtain substantial cooling energy say- The Electricity Journal E I I I I1[ ings from direct building shade, benefits accrue to the community as well, due to the aggregate effect of trees on urban climate. Shade tree programs can promote revitalization of our cities by creating new jobs, healthier environments, and positive community interactions.19 Finally the ability of urban trees to remove atmospheric carbon dioxide is far from irrelevant. Carbon emissions avoided due to energy conservation from shade trees usually exceed the amount of carbon sequestered and stored in tree biota?ass.2° This suggests that, despite the expense of planting and maintaining trees in urban areas, such a program may be a very cost-effective component of U.S electric utilities' carbon offset programs. • Acknowledgments: The author wishes to thank Drs. Rowan Rowntree, Jim Simpson, Gordon Heisler and Alan Wagar for their helpful reviews of an earlier version of this article. Ion Vencil, Robert Lad-ner, Rich Jarvinen, Sharon Dezurick, Roger Snow, Gerry Bird, Susan Stilz, Esther Kerkmann and Paul Sacamano also provided valuable assistance. Endnotes: 1. In a process similar to sweating, trees use heat to evaporate water from their leaves before it can heat the air, thus cooling the air immediately around the leaves. The cumulative effect of many leaves and trees can cool the air in a large area. See Cooling Our Communities: A Guidebook on Tree Planting and Light-colored Surfacing (H. Akbari, S. Davis, S. Dorsano, J. Huang and S. Winnett, eds. U.S. Environmental Protection Agency 1992). ' Ill I I I 2. E.G. MCPHEKSON, ENERGY EFFI- CIENCY AND THE ENVIRONMENT: FORG- ING THE LINK 349-369 (E. Vine, D. Crawley, and P. Centolella eds., Ameri- can Council for an Energy Efficient Economy 1991). 3. E.G. McPherson, R. Brown, and R.A. Rowntree, Simulating Tree Shadow Patterns for Building Energy Analysis, PROCEEDINGS OF SOLAR 85 CONFER- ENCE, AMERICAN SOLAR ENERGY SOCI- ETY at 378 (1985). 4. Enercomp Inc., Micropas4 Users Manual (1992). 5. E.G. McPherson, P.L. Sacamano and S. Wensman, Modeling Benefits and Costs of Community Tree Plantings, USDA Forest Service, Western Center for Urban Forest Research, technical report (1993). 6. E.G. McPherson, Solar Control Planting Design, ENERGY-CONSERVING SITE DESIGN at 141-64 (E.G. McPherson ed., American Society of Landscape Architects) (1984). 7. J. Huang, H. Akbari, H. Taha & A. Rosenfeld, The Potential of Vegetation in Reducing Summer Cooling Loads in Resi- dential Buildings, 26 J. CLIM. & APPL. METEOROL. at 1103-06 (1987). 8- G. M. Heisler, Mean Wind Speed Below Building Height in Residential Neighborhoods with Different Tree Densities, 96 ASHRAE TRANSACTIONS, PART I at 1389-96 (1990); T. Honjo & T. Takakura, Simulation of Thermal Effects of Urban Green Areas on Their Surrounding Areas, 15-16 ENERGY AND BUILDINGS at 433-46 (1990/91). 9. G.M. Heisler, Effects of Individual Trees on the Solar Radiation Climate of Small Buildings, ECOLOGYOF THE URBAN FOREST PART [I: FUNCTION, URBAN ECOLOGY at 337-59 (R. Rowntree, ed., 1986); M.A.P. Sand, Planting for Energy Conservation in the North: Modeling the Impact of Tree Shade on Home Energy Use in Minnesota and Development of Planting Guidelines, Master's thesis, University of Minne-. sota (1991). 10. Supra note5. 11. See A. Meier, Strategic Landscaping and Air Conditioning Savings: A Litera ture Review, 15-16 ENERGY AND BUILDINGS at 479-86 (1990/91) for a review of most studies. 12. E.G. McPherson and EL. Sa-camano, Energy Savings With Trees i Southern California, USDA Forest Service, Western Center for Urban F~ est Research, technical report (1992). 13. K.E. Clarkand D. Berry, Targetir Residential Energy Conservation Measures in the Desert Southwest, ;-zona Corporation Commission, Resource Planning Staff Report (1993). 14. Supra, note 5. 15. ld. 16. R.H. Miller and R.W. Miller, Pla ing Survival of Selected Street Trees, 1" ARBOR. at 185-91 (1992). 17. Supra, note 5. 18. E.G. McPherson, D.J. Nowak, F Sacamano, S.E. Prichard and E.M. Makra, Chicago's Evolving Urban est, USDA Forest Service, Northeastern Forest Experiment Station, General Technical Report NE-169 (1993). 19. J.E Dwyer, E.G. McPherson, H Schroeder & R.A. Rowntree, Asses: the Benefits and Costs of the Urban F est, 18 J. ARBOR. at 227-34 (1992). 20. D.J. Nowak, Atmospheric Carb Reduction by Urban Trees, 37 J. OF E VIR. MANAGEMENT, at 207-17 (1992 R.A. Rowntree & D. J. Nowak, Qu lying the Role of Urban Forests in R~ ing Atmospheric Carbon Dioxide, 17 ARBOR, at 269-75 (1991)!
85!7/18/2002 5:09:00 PM!Investigation into hydrologic modeling and the effect of urban forests on runoff quantity and quality!Larsen, E.W., J. Fleckenstein and E.G. McPherson!2001!Davis, CA: University of California, Davis-Department of Geology!Published Reports!Cooperative Research in Urban Hydrology!!PDF!Larsen, E.W., J. Fleckenstein and E.G. McPherson. 2001. Investigation into hydrologic modeling and the effect of urban forests on runoff quantity and quality. Davis, CA: University of California, Davis-Department of Geology. 53!!!water !
86!7/18/2002 5:11:00 PM!Rainfall interception by urban forests!Xiao, Q!1998!Davis, CA: University of California. Ph.D. Dissertation!Dissertations/Thesis!Modeling Urban Tree Rainfall Interception!cufr_86_XQ98_54.PDF!PDF!Xiao, Q. 1998. Rainfall interception by urban forests. Davis, CA: University of California. Ph.D. Dissertation. 184!!!
87!7/18/2002 5:13:00 PM!Winter rainfall interception by two mature open grown trees in Davis, CA!Xiao, Q., E.G. McPherson, S.L. Ustin, M.E. Grismer, and J.R. Simpson!2000!Hydrological Processes. 14(4)!Articles in Journals!Modeling Urban Tree Rainfall Interception!4/cufr_87.pdf!PDF!Xiao, Q., E.G. McPherson, S.L. Ustin, M.E. Grismer, and J.R. Simpson. 2000. Winter rainfall interception by two mature open grown trees in Davis, CA. Hydrological Processes. 14(4): 763-784!precipitation; throughfall; stemflow; evaporation; interception; canopy interception dynamic processes; field instrumentation; measurement system; pressure gauge; urban forests; open grown trees!A rainfall interception measuring system was developed and tested for open-grown trees. The system includes direct measurements of gross precipitation, through fall and stemflow, as well as continuous collection of micrometeorological data. The data were sampled every second and collected at 30-s time steps using pressure transducers monitoring water depth in collection containers coupled to Campbell CRlO dataloggers. The system was tested on a 9-year-old broadleaf deciduous tree (pear, Pyrus calleryana 'Bradford') and an 8-year-old broad leaf evergreen tree (cork oak, Quercus suber) representing trees having divergent canopy distributions of foliage and stems. Partitioning of gross precipitation into throughfall, stemflow and canopy interception is presented for these two mature open-grown trees during the 1996-1998 rainy seasons. Interception losses accounted for about 15% of gross precipitation for the pear tree and 27% for the oak tree. The fraction of gross precipitation reaching the ground included 8% by stemflow and 77% by throughfall for the pear tree, as compared with 15% and 58%, respectively, for the oak tree. The analysis of temporal patterns in interception indicates that it was greatest at the beginning of each rainfall event. Rainfall frequency is more significant than rainfall rate and duration in determining interception losses. Both stemflow and through fall varied with rainfall intensity and wind speed. Increasing precipitation rates and wind speed increased stemflow but reduced throughfall. Analysis of rainfall interception processes at different time-scales indicates that canopy interception varied from 100% at the beginning of the rain event to about 3% at the maximum rain intensity for the oak tree. These values reflected the canopy surface water storage changes during the rain event. The winter domain precipitation at our study site in the Central Valley of California limited our opportunities to collect interception data during non-winter seasons. This precipitation pattern makes the results more specific to the Mediterranean climate region!
88!7/19/2002 1:26:00 PM!A new approach to modeling tree rainfall interception!Xiao, Q., E.G. McPherson, S.L. Ustin and M.E. Grismer!2000!Journal of Geophysical Research 105(D23)!Articles in Journals!Modeling Urban Tree Rainfall Interception!4/cufr_88.pdf!PDF!Xiao, Q., E.G. McPherson, S.L. Ustin and M.E. Grismer. 2000. A new approach to modeling tree rainfall interception. Journal of Geophysical Research 105(D23): 29,173-29,188!!A three-dimensional physically based stochastic model was developed to describe canopy rainfall interception processes at desired spatial and temporal resolutions. Such model development is important to understand these processes because forest canopy interception may exceed 59% of annual precipitation in old growth trees. The model describes the interception process from a single leaf, to a branch segment, and then up to the individual tree level. It takes into account rainfall, meteorology, and canopy architecture factors as explicit variables. Leaf and stem surface roughness, architecture, and geometric shape control both leaf drip and stemflow. Model predictions were evaluated using actual interception data collected for two mature open grown trees, a 9-year-old broadleaf deciduous pear tree (Pyrus calleryana "Bradford" or Callery pear) and an 8-year-old broadleaf evergreen oak tree (Quercus suber or cork oak). When simulating 18 rainfall events for the oak tree and 16 rainfall events for the pear tree, the model over estimated interception loss by 4.5% and 3.0%, respectively, while stemflow was under estimated by 0.8% and 3.3%, and throughfall was under estimated by 3.7% for the oak tree and over estimated by 0.3% for the pear tree. A model sensitivity analysis indicates that canopy surface storage capacity had the greatest influence on interception, and interception losses were sensitive to leaf and stem surface area indices. Among rainfall factors, interception losses relative to gross precipitation were most sensitive to rainfall amount. Rainfall incident angle had a significant effect on total precipitation intercepting the projected surface area. Stemflow was sensitive to stem segment and leaf zenith angle distributions. Enhanced understanding of interception loss dynamics should lead to improved urban forest ecosystem management!water !
89!7/19/2002 1:28:00 PM!Water meters: one opinion - trees may suffer!McPherson, E.G!1998!TREE Davis Newsletter: Branching Out. 5!Articles in Periodicals!Miscellaneous Water Literature!!PDF!McPherson, E.G. 1998. Water meters: one opinion - trees may suffer. TREE Davis Newsletter: Branching Out. 5: 2!!!water !
90!7/19/2002 1:30:00 PM!Volunteer-based urban forest inventory and monitoring programs: results from a two-day workshop, Sacramento, 1999!Tretheway, R., M. Simon, E.G. McPherson and S. Mathis (eds)!1999!Sacramento: Sacramento Tree Foundation!Conference Proceedings!Volunteer-Based Inventory and Monitoring!5/cufr_90.pdf!PDF!Tretheway, R., M. Simon, E.G. McPherson and S. Mathis (eds). 1999. Volunteer-based urban forest inventory and monitoring programs: results from a two-day workshop, Sacramento, 1999. Sacramento: Sacramento Tree Foundation. 33!!!stewardship !
91!7/19/2002 1:33:00 PM!Monitoring urban forest health!McPherson, E.G!1993!Environmental Monitoring and Assessment. 26!Articles in Journals!Miscellaneous Tree Stewardship Literature!cufr_91_EM93_12.PDF!PDF!McPherson, E.G. 1993. Monitoring urban forest health. Environmental Monitoring and Assessment. 26: 165-174!!Renewed interest in urban forestry has resulted in significant public investment in trees during the past few years, yet comprehensive urban forest monitoring programs are uncommon. Monitoring is an integral component of a program to sustain healthy community forests and long-term flows of net benefits. Volunteer-based monitoring will promote continued public involvement and support in community forestry. To overcome constraints to monitoring in urban environments, programs must be personally relevant, socially desirable, scientifically credible, and economically feasible. A three-tiered monitoring approach is presented. Canopy cover analysis documents net gains and losses in regional urban forest cover. Simplified detection monitoring uses trained volunteers to better understand tree population dynamics, while intensive monitoring characterizes urban forest functions and stressors. Implementation of an urban forest health initiative to develop, place, and evaluate monitoring programs is advocated!have shown that landscapes with trees and vegetation produce more relaxed physiological states in humans than landscapes that lack these natural features (Schroeder, 1989). The benefits to public health of urban forests have not been translated into monetary terms, but are potentially very significant (Ulrich, 1984). Also significant are the many other intangible benefits urban forests provide such as wildlife habitat, esthetic surroundings, meaningful 167 MONITORING URBAN FOREST HEALTH connections between people and the natural environment, settings for important emotional and spiritual experiences, stronger sense of community, and the personal empowerment of residents. Although research continues to reveal the significance of urban forests, it has provided little information for managers regarding the influence of species composition, diversity, age structure, and location on the flow of these benefits. The call to 'think globally and act locally' has been heard by residents of almost every community, large and small. A concern for the long term health of our planet has led many citizens to environmental stewardship activities, including participation in local tree planting programs. Grass-roots urban forestry has been spurred on by President Bush's America the Beautiful program, the American Forest's Global ReLeaf program, and programs such as Tree City, USA sponsored by the National Arbor Day Foundation. Not since the City Beautiful movement during the early twentieth century has public interest in community tree planting been this great. Urban forest health may take on added significance to the extent that urbanites' attitudes towards forests and the environment are influenced by their interactions with urban trees. 3. What Should be the Goals of Urban Forest Monitoring? I adopt Shafer's (1991) view that before forest health can be defined, one's set of values used to measure forest health must be defined. I define a healthy urban forest as one that sustains production of goods and services over the long term. Healthy urban forests maintain a steady flow of net benefits and ideally, they are managed to be profit-maximizing. Goods and services produced by healthy urban forests could include high levels of biodiversity, increased sense of place, and cost-effective environmental control (McPherson, 1990). Although increasing species diversity of our urban forests is important to their long-term ecological stability, healthy urban forests are managed to enhance other types of diversity as well. Four other types of diversity should be considered, two are above the species level (structural and functional diversity) and two are below the species level (life-cycle and genetic diversity) (Odum, 1989). The 'clean and green' look of many horticultural landscapes can mask the cultural hisotry, ecology, and unique character of sites, neighborhoods, and communities. Urban dwellers' sense of identity and belonging can be enhanced when landscapes are managed to promote sense of place (Hull and Ulrich, 1991). Trees can be cost-effective substitutes or complements to traditional fossil fuel-based technologies used for environmental improvement. For example, shade from trees was found to be 20% more cost-effective over a 40-year period than shade from metal bus shelters at hot, unshaded bus stops in Tucson (McPherson and Biedenbender, 1991). 168 E. GREGORY MCPHERSON 3.1. MONITORING GOALS I propose two goals for urban forest monitoring. First, monitoring should increase public involvement in environmental stewardship. I believe that to monitor urban forests we will need trained and motivated volunteers. Some of the current enthusiasm for tree planting must be shifted to stewardship. We must find new ways to link the health of our community trees with the health of our planet, and to bring the science of urban ecology into the minds and hearts of urban America. More people must become involved in the continuous, experiment of monitoring their own environments. Second, monitoring should help us better define, detect, and predict urban forest health. To begin, monitoring should enhance our understanding of urban forest population dynamics by telling us whether numbers are rising or falling, and depicting changes in species composition, age structure, and biomass. These data will permit initial characterization of normal and abnormal population trends. Appropriate management prescriptions could follow. Additional monitoring information could be collected to characterize major stressors such as drought, nutrient defficiency, vandalism, soil compaction, mechanical injury, ice/wind strom, pest/disease, salt, air pollution, and soil toxicity. Monitoring and computer modeling should be integrated with the goal of creating user-friendly urban forest management systems. 3.2. CONSTRAINTS ON MONITORING URBAN FORESTS Managing and also monitoring activities for greenspace are limited by factors unique to urban environments. More than half of the urban forest typically occurs on residential land. Access to this private property is difficult and levels of management skill vary among residents. About 10 to 30% of the urban forest resource occurs on public property (e.g., along streets, parks, schools) and receives more uniform levels of care from fewer managers than does residential greenspace. Most of the remaining urban greenspace (5-20%) occurs on commercial, industrial, and institutional properties and is managed by landscape contractors. Moreover, a variety of organizations and governmental agencies can exert control over urban forest management on private and public lands. Some examples include departments of planning (landscape ordinances), transportation/public works (rights-of-way), flood control (streams and channels), air quality (pollen, dust, biogenic emissions), water resources (landscape water use), solid w~,ste (green waste and landfills), and energy utilities (power line clearance, energy savings). Therefore, a myriad of masters and their social, legal, political, bureaucratic, and economic boundaries can obstruct efforts aimed at comprehensive urban forest management and monitoring. Other potential constraints to monitoring urban forests must be recognized prior to developing realistic goals. The urban environment is heterogeneous and 'representative' monitoring sites can be hard to find. Unique sampling approaches are required. Once desirable sites are located it may be difficult to obtain access and secure monitoring equipment from vandalism and theft. Urban land uses are 169 MONITORING URBAN FOREST HEALTH constantly changing, making the concept of 'permanent plots' impractical in some areas. Changing environmental conditions in cities can be confounding, and seriously complicate interpretation of base lines. Finally, local resources will be needed to conduct urban forest monitoring. 4. What Monitoring Approaches are Likely to Work? Traditional monitoring approaches applied in exurban areas focus on detecting ecosystem change, but do not promote environmental stewardship amongst the public through direct participation in monitoring. To monitor tree health and promote stewardship, urban forest monitoring must be: • personally relevant - meaningful to participants, • socially desirable - the right thing to do for the land and people, • scientifically credible - good quality assurance and quality control, • economically feasible - volunteer-based (Salwasser, 1991). 4.1. VOLUNTEER-BASED MONITORING I propose a three-tiered monitoring approach that is accomplished by trained volunteers and local technical experts. Limited resources will make it impossible to hire professionals for urban forest monitoring. However, volunteer cadres could be trained to provide credible information. It should be recognized that the motivation, length of commitment, and required training for a volunteer usually differ from that of a paid employee (Wilson, 1976). Volunteers are typically motivated to participate by power (influence and creativity), achievement (new knowledge and experience), and affiliation (contact with people and groups). Most volunteers length of commitment is one or two days, but some will make a long term commitment. It is important that the latter group be involved in all phases of program development. Volunteers will require special training for most urban forest monitoring tasks. Moreover, training will need to be repeated on a regular basis. Volunteer participation is usually related to volunteers' perception of the value of their task. If the task is highly valued and likely to have an impact, they will usually participate. Non-profit community forestry programs have been established in over 300 cities across the U.S. Most of these programs have educational sessions and training workshops for tree planting and tree care activities. Before granting trees for planting, some programs require that applicants agree to monitor the transplants for several years following installation. Urban forestry training and education materials are passed down to community groups through a network of state urban forest councils, state foresters, and regional Forest Service specialists. Implementing urban forest monitoring through existing volunteer-based community forestry 170 E. GREGORY MCPHERSON programs appears feasible. The joint EPA Environmental Monitoring Assessment Program (EMAP) and USDA Forest Service's Forest Health Monitoring (FHM) offer workable approaches for urban forests if simplified to account for volunteer participation. A three-tiered approach for monitoring urban tree health is proposed. 4.2. CANOPY COVER ANALYSIS Tree cover analyses usually involve interpretation of aerial photographs to provide information about the amount and distribution of tree cover throughout a community. Findings can be used to gauge the amount of influence trees have on the environment. As the first-tier in monitoring urban forest changes, periodic analysis of canopy cover can indicate whether there is a net loss or gain in greenspace over time. Policies and management can then focus on relative needs for new plantings, preservation of existing forest cover, and routine care of existing urban forest resources. Urban forest cover data also indicate the potential for new tree plantings in different areas. Analyses show the amount of area occupied by other urban surfaces that impede or facilitate planting, such as buildings, pavement, water, grass, and bare soils (Nowak, 1991). Relations between existing tree cover and planting potential among different land use types (e.g., residential, commercial, industrial) are also helpful in prioritizing future plantings (Rowntree, 1984). Canopy cover analysis usually involves dividing regions into smaller areas with permanent boundaries. Dots are randomly located on aerial photographs (scale about 1 : 4800) and classified according to land use and cover type. Cover proportions are calculated by dividing the number of dots in the category of cover type by the total number of dots in that area. Aerial photo interpretation is tedious and time consuming. It is best conducted by a limited number of trained volunteers with long term commitments to the program. Biased results can be reduced by initially checking for differences between interpretors and using only a few individuals for the task. 4.3. SIMPLIFIED DETECTION MONITORING In the FHM program, detection monitoring occurs at a national network of permanent plots to establish baselines, detect change, and trigger more in-depth evaluation if problems are discovered (Radloff et al., 1991). Data are collected on a wide variety of health indicators (e.g., soils, foliage, lichens). This approach could be simplified for urban forests by focusing on indicators of population dynamics in 'representative' locations. For example, on one or two days each year teams of trained volunteers might collect information regarding plant species, size, and condition at selected locations along streets (residential and arterial), park-type areas (e.g., parks, campuses, golf courses, schools), commercial/industrial areas (professionally maintained), residential areas (high and low density), and in plots on unmanaged lands (e.g., riparian, wooded, and wetlands). Trained homeowners could collect similar data MONITORING URBAN FOREST HEALTH 171 on all trees at their residences, thereby supplementing information for residential locations. These 'permanent plots' would be revisited annually to track long term change in urban forest structure. Data collected by the volunteers would be used to assess rates of planting, mortality, and growth by both species and locations. In some circumstances, it may be feasible to collect additional information related to symptoms and causes of tree mortality and decline. Photographs of each plot from permanent camera stations could be taken annually to visually illustrate urban forest change. Some volunteers may be interested in analyzing tree rings from sections of removed trees to explore relations between tree species, locations, climates, and growth rates. If field data collection is perceived as having little value, active participation by volunteers is unlikely. Several ways to increase the perceived value of monitoring are to: (1) provide tools that volunteers can use to easily analyze the data, assess the health of their urban forest, and estimate the benefits it provides; (2) illustrate how to use monitoring results to make better management decisions; and (3) link participation in monitoring to grants for tree planting. Awards that recognize exemplary monitoring programs could also elevate the importance of monitoring in the public's mind. 4.4. INTENSIVE MONITORING The purpose of intensive urban forest monitoring differs from detection monitoring because the focus expands to include urban forest function, as well as structure. Intensive monitoring should measure long term effects of large-scale tree plantings or ecological restoration projects on urban forest structure and function. Neighborhood-scale permanent plots could be established in relatively stable areas. Research scientists, local greenspace managers, and trained volunteers could work together to identify relevant issues, locate desirable sites, and establish protocols for intensive monitoring. In addition to tracking changes in plant populations, monitoring could assess changes in: (1) meteorological variables that influence energy use, air quality, and human comfort; (2) deposition rates of particulate and gaseous pollutants, nutrients, and metals; (3) water relations such as rainfall interception, runoff, and evapotranspiration rates; (4) root growth, soil conditions, and soil microbial activity; (5) cycling rates for nutrients, carbon, and heavy metals; (6) visual qualities that influence scenic beauty estimates; (7) abundance and diversity of selected wildlife species; and (8) the demographics, preferences, use patterns, and physiological/psychological reponses of those consuming goods and services produced by the greenspace in question. Short term intensive measurements could supplement continuous extensive measurements to capture more detailed data at appropriate time intervals. Although the role of experts will be more important in intensive monitoring than in simplified detection monitoring, significant opportunities for public involvement and education could still exist. Trained volunteers with long term commitments to the program could assist with routine measurements and data analysis, similar to 172 E. GREGORY MCPHERSON 'weather watchers' who regularly report to television news stations. Local Extension scientists and university researchers could use intensive monitoring sites as outdoor laboratories for hands-on training of students. Public participation in tracking success and failure and quantifying the flow of benefits and costs will strengthen support and involvement in community forestry programs. It will also increase the likelihood of integrating monitoring results with the management process. 5. Summary and Conclusions The small size of urban forests belie their importance unless one considers that large sums of money are dedicated to their management and that the value of environmental, social, and economic benefits they provide is substantial. Renewed interest in urban forestry has resulted in significant public investment in trees during the past few years, A long term commitment to monitoring urban forest change will help insure that this investment provides large returns to future generations, as well as continued public involvement and support in community forestry. Healthy urban forests maximize and sustain long term flows of net benefits. They are also sources of pride within communities. Urban forest monitoring should ultimately enhance the health of our community forests by increasing public involvement in their stewardship and helping managers better define, detect, and predict urban forest health. A three-tiered approach to urban forest monitoring is presented. Canopy cover analysis uses trained volunteers to determine existing canopy cover by geographic areas and land uses within the community. Net gain or loss of forest cover can be detected through periodic analysis of aerial photographs. Simplified detection monitoring assesses plant population changes in representative field locations. Several ways to make sometimes tedious monitoring tasks meaningful to volunteers are discussed. Intensive monitoring relies on experts as well as volunteers to assess the impacts of large scale planting or ecological restoration projects on urban forest structure and functions. Although survey,; are now tracking numbers of new plantings associated with America the Beautiful, and new methods and technologies for inventorying the urban forest resource are being investigated, this paper is one of the first to scrutinize the topic of urban forest monitoring. Clearly, there is need for more viewpoints, study, and refinement. If urban forest monitoring is important, how do we go about developing and implementing workable programs? I suggest that an urban forest health initiative be established with the goal of developing, placing, and evaluating the success of monitoring programs in a dozen U.S. cities by 1996. A steering committee with representatives of volunteer groups, professional urban forest managers, landscape industry organizations, and urban forest researchers should help set the agenda and direct the program. Urban forest managers, volunteers, and researchers can work in concert to determine the who, what, when, where, and hows of urban forest monitoring. An extensive network of national, regional, state, and local urban MONITORING URBAN FOREST HEALTH 173 forestry groups can be used to identify communities where the prototype program can be implemented and evaluated. Once evaluated and revised, the program can be delivered to communities throughout the U.S. The future costs of ailing urban forests may far outweigh the present costs of investing in monitoring programs aimed at checking the vital signs of this increasingly important natural resource. References Akbari, H., Davis, S., Dorsano, S., Huang, J. and Winnett, S. (Eds.): 1992, Cooling Our Communities: A Guidebook On Tree Planting and Light-Colored Surfacing. U.S. Environmental Protection Agency, Washington, D.C. Birdsey, R.A.: 1990, 'Inventory of Carbon Storage and Accumulation in U.S. Forest Ecosystems', in: H.E. Burkhart, G.M. Bonnor and J.J. Lowe (Eds.), Research in Forest Inventory, Monitoring, Growth and Yield, (Report No. FWS-3-90). School of Forestry and Wildlife Resources, Virginia Polytechnic Institute and State University, Blacksburg, VA, pp. 24-31. Dwyer, J., McPherson, G., Schroeder, H. and Rowntree, R.: 1992, 'Assessing the Benefits and Costs of the Urban Forest', J. Arbor. 18, 227-234. Hull, R.B. and Ulrich, R.S.: 1992, 'Health Benefits and Costs of Urban Trees', in: P.D. Rodbell (Ed.), Proceedings of the Fifth National Urban Forest Conference. American Forestry Association, Washington, D.C., pp. 69-72. International Society of Arboriculture (Ed.): 1991, A National Research Agenda for Urban Forestry in the 1990's. International Society of Arboriculture, Urbana, IL. MacCleery, D.W.: 1992, 'Timber Growth, Removals, Standing Timber Volume, and Timberland Area in the United States, By Ownership', Unpublished technical report. USDA, Forest Service, Washington, D.C. McPherson, E.G.: 1990, 'Creating an Ecological Landscape', in: P. Rodbell (Ed.), Proceedings of the Fourth Urban Forestry Conference. American Forestry Association, Washington, D.C., pp. 63-67. McPherson, E.G., 1991, 'Economic Modeling for Large-Scale Tree Plantings', in: E. Vine, D. Crawley and P. Centolella (Ed.), Energy Efficiency and the Environment: Forging the Link. American Council for an Energy-Efficient Economy, Washington, D.C., pp. 349-369. McPherson, E.G. and Biedenbender, S.: 1991, 'The Cost of Shade: Cost-Effectiveness of Trees Versus Bus Shelters', J. Arbor 17, 233--241. McPherson, E.G., Nowak, D.J., Sacamano, P.L., Makra, E. and Prichard, S.E.: 1992, Chicago's Evolving Urban Forest. USDA Forest Service, Northeastern Forest Experiment Station, Chicago Urban Forest Climate Project, Chicago, IL. Nowak, D.J.: 1991, 'Urban Forest Development and Structure: Analysis of Oakland, California', Ph.D. Dissertation, University of California, Berkeley, CA. Nowak, D.J.: in press, 'Atmospheric Carbon Reduction by Urban Trees', J. Environ. Manag. Odum, E.P.: 1989, 'Diversity in the Landscape: The Multilevel Approach', Georgia Landscape. Spring, 4. Radloff, D., Loomis, B., Barnard, J. and Birdsey, R.: 1991, 'Forest Health Monitoring: Taking the Pulse of America's Forests', in: Agriculture and the Environment: The 1991 Yearbook of Agriculture. U.S. Government Printing Office, Washington, D.C., pp. 4147. Rodbell, P.D. (Ed.): 1992, Proceedings of the 5th National Urban Forestry Conference, Alliances for Community Trees, American Forestry Association, Washington, D.C. Rowntree, R.A.: 1984, 'Forest Canopy Cover and Land Use in Four Eastern United States Cities', Urb. Ecol. 8, 55-67. Salwasser, H.: 1991, 'Biological Diversity and Sustaining Ecological Systems', Keynote remarks and unpublished paper from the Symposium On Biodiversity of Northwestern California, Santa Rosa, CA, 11 pp. Sampson, R.N., Moll, G.A. and Kielbaso, J.J.: 1991, Urban Forests, Carbon Storage, and Energy Conservation. American Forestry Association, Washington, D.C, Schroeder, H.W.: 1989, 'En- 174 lb- E. GREGORY MCPHERSON vironment, Behavior, and Design Research on Urban Forests', in: E.H. Zube and G.T. Moore (Eds.), Advances in Environment, Behavior, and Design. Plenum, New York, pp. 87-117. Shafer, J.D.: 1991, 'A Silviculturalist's Creed', in: Proceedings of the Symposium On Management of Forest Pests Through Silviculture, pp. 1-5. Ulrich, R.S.: 1984, 'View Through a Window May Influence Recovery from Surgery', Science 224, 420--421. Wilson, M.: 1976, The Effective Management of Volunteer Programs. Johnson Publishing, Boulder, CO!
92!7/19/2002 1:34:00 PM!Comparison of five methods for estimating leaf area index of open-grown deciduous trees!Peper, P.J. and E.G. McPherson!1998!Journal of Arboriculture. 24(2)!Articles in Journals!Evaluating Methods for Establishing Leaf Area!6/cufr_92.pdf!PDF!Peper, P.J. and E.G. McPherson. 1998. Comparison of five methods for estimating leaf area index of open-grown deciduous trees. Journal of Arboriculture. 24(2): 98-111!LAI; leaf area; hemispheric photography; allometry; ceptometer; image processing; plant canopy analyzer!We compared the accuracy of five methods used to estimate leaf area index (LAI) of eight open-grown deciduous trees, including six white mulberries (Morus alba) and two black cherries (Prunus serotina var. rufula). The methods included the use of four instruments (AccuPAR ceptometer, CI-100 Plant Canopy Analyzer, image processing with the AgVision System, LI-COR LAI-2000 Plant Canopy Analyzer) and the application of a logarithmic regression equation. The image processing method demonstrated the highest probability of accurately estimating LAI (P = 0.99). However, all methods showed bias toward returning LAI estimates that did not increase as actual LAI increased when the mulberry tree data were examined separately from the cherry data. Additional research is necessary to determine whether this bias is real or merely a function of the limited sample size!
93!7/19/2002 1:36:00 PM!Comparison of four foliar and woody biomass estimation methods applied to open-grown deciduous trees!Peper, P.J. and E.G. McPherson!1998!Journal of Arboriculture. 24(4)!Articles in Journals!Evaluating Methods for Establishing Leaf Area!cufr_93_PP98_36.PDF!PDF!Peper, P.J. and E.G. McPherson. 1998. Comparison of four foliar and woody biomass estimation methods applied to open-grown deciduous trees. Journal of Arboriculture. 24(4): 191-200!Allometry; carbon; subsampling; surrogate; urban forest; crown!Concern about global climate change and the effects that increasing atmospheric carbon dioxide could have on the earth has risen in recent years. Methods for accurately and efficiently quantifying carbon storage and annual carbon fluxes are needed to determine what role urban forests may have in reducing levels of atmospheric CO2. This will require the development of techniques for estimating foliar and woody biomass of individual trees. In this study, 2 sampling methods and 2 regression formulas for estimating foliar and above-ground woody biomass were tested against the actual above-ground biomass of 8 open-grown deciduous trees (2 species). There was no significant difference between one of the subsampling methods and actual foliar, woody, and total above-ground biomass. There were indications that the method's precision in estimating foliar biomass could be improved by modifying the sampling method. The second sampling method predicted foliar biomass of heavily pruned trees within 8% of actual measurements. For unpruned or lightly pruned trees, one of the regression equations showed no significant difference between estimates of foliar biomass and actual biomass!: Nancy, France, and Vancouver, BC. Univ. Maine, Col. Life Sci. and Agric., Orono, ME. Jo, H.K., and E.G. McPherson. 1995. Carbon storage and flux in urban residential greenspace. J. Env. Mgmt. 45:109-133. McPherson, E.G., and P.L. Sacamano. 1992. Energy savings with trees in Southern California. Tech. rpt. USDA For. Serv. Pac. Southwest. Res. Sta., Western Ctr for Urban For. Res. 187 pp. Nowak, D.J. 1994. Urban forest structure: The state of Chicago's urban forest, pp 83-94. In McPherson, E.G., D.J. Nowak, R.A. Rowntree (Eds.). Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. USDA For. Serv. Northeast. For. Exp. Sta. Gen Tech Rpt. NE-186. Radnor, PA. Nowak, D.J. 1996. Estimating leaf area and leaf biomass of open-grown deciduous urban trees. For. Sci. 42(4): 504-507. Peper, P.J., and E. G. McPherson. 1998. Comparison of five methods for estimating leaf area index of open-grown deciduous trees. J. Arboric. 24(2):98-111. Rowntree, R.A., and D.J. Nowak. 1991. Quantifying the role of urban forests in removing atmospheric carbon dioxide. J. Arboric. 17:269-275. Shinozaki, K., K. Yoda, K. Hozumi, and T. Kira. 1964. A quantitative analysis of plant form-the pipe model theory. I. Basic analyses. Jpn J. Eco. 14(3):97-105. Simpson, J.R., and E.G. McPherson. 1996. Estimating urban forest impacts on climate-mediated residential energy use, pp 462-465. In 12th Conference on Biometeorology and Aerobiology. American Meteorological Society. Boston, MA. Soil Conservation Service. 1977. Soil survey of Solano Country, California. USDA Soil Conserv. Sew., Davis, CA. 65 pp. Valentine, H.T., L.M. Tritton, and G.M. Furnival. 1984. Subsampling trees for biomass, volume, or mineral content. For. Sci. 30(3):673-681. Valentine, H.T., V.C. Baldwin, Jr., T.G. Gregoire, and H.E. Burkhart. 1994. Surrogates for foliar dry matter in Ioblolly pine. For. Sci. 40(3):576-585. Acknowledgments. This project would not have been possible without the assistance of Linda George, who main¬tains the Solano Urban Forest Research Site, and field tech¬nicians Uma Ramakrishnan, Richard Bagaoisan, Melissa Kaufman, Nina Luttinger, and Tin-Wah Wong. We especially thank Sylvia Mori and Harry Valentine for providing statisti¬cal and technical support that was critical to this study. Western Center for Urban Forest Research & Education Pacific Southwest Research Station USDA Forest Service c/o Department of Environmental Horticulture One Shields Avenue University of California Davis, CA 95616-8587 200 Peper and McPherson: Comparing Foliar and Woody Biomass Estimation Methods R~sum~. Deux m~thodes d'echantillonnages restreints et deux formules de r~gression ont ~te testees pour I'estimation de la biomasse foliaire, ligneuse et/ou totale de I'arbre avec huit arbres feuillus croissants en milieu ouvert. Les tests comparatifs de T n'ont montre aucune difference significative entre la m0thode d'0chantillonnage et les valeurs de biomasse foliaire, ligneuse et totale reelles. II n'y avait pas non plus de difference significative entre les estim~s gener~s & partir d'une des formules de biornasse et la biomasse totale r~elle. Cependant, un examen rapide de I'applicabilit~ des m0thodes a montr~ un potentiel pour calibrer les r~sultats des deux equations de biomasse afin de produire des estim6s pr6cis de la biomasse des arbres urbains. D'autres tests sont n~cessaires pour d~terminer I'applicabilit~ des m~thodes & un plus large ~ventail d'esp0ces et de sites de I'environnement urbain. Zusammenfassung. Yon acht freistehenden Laubb&umen wurde die aktuelle Biomasse mit Werten aus zwei Sammelmethoden und zwei Regressionsformeln zur Bestimmung von Laubmase, Holzmsse und/oder der ganzen oberirdischen Biomasse verglichen. Die gepaarten t-Tests zeigten keine signifikante Differenz zwischen der einen Sammelmethode und der aktuellen Biatt-, Holz- und oberirdischen Gesamtbiomasse. Es gab auch keine signifikante Differenz zwischen den Sch&tzungen aus einer Biomassenformel und der tats&chlichen oberirdischen Biomasse. Trotzdem zeigte eine visuelle 0berpr~fung der Anwendbarkeit dieser genannten Methoden, dal3 hier ein Potential besteht, um akurate Sch&tzungen der Biomasse yon Stadtb&umen zu erhalten. Um die Anwendbarkeit der Methoden auf eine Reihe von Baumarten und Standorten zu bestimmen, sind weitere Testreihen notwendig. Resumen. Se probaron dos m~todos de submuestreo y dos f6rmulas de regresi6n para estimaci6n foliar, biomasa maderable y/o biomasa total arriba del terreno, contra la biomasa real de 8 arboles deciduos de crecimiento abierto. Pruebas de t apareadas no mostraron diferencia significativa entre uno de los m~todos de submuestreo y el follaje real, biomasas maderable y total arriba del terreno. Tarnpoco hubo diferencia significativa entre las estimaciones generadas con una de las f6rmulas de biomasa y la biomasa total arriba del terreno. Sin embargo, una inspecci6n visual sobre la aplicabilidad de los metodos mostr6 potencial para la calibraci6n de las respuestas en ambas ecuaciones para producir estimaciones precisas de biomasas de drboles urbanos. Se necesitan pruebas adicionales para determinar ia aplicabilidad de los m~todos a un rango de especies y sitios en el ambiente urbano. Journal of Arboriculture 24(4): July 1998 201 URBAN FOREST IMPACTS ON REGIONAL COOLING AND HEATING ENERGY USE: SACRAMENTO COUNTY CASE STUDY by James R. Simpson Abstract. Urban forests impact energy use for cooling and heating as a result of their moderating influence on climate. To evaluate the regional magnitude of these impacts, a large-scale analysis framework was developed and applied to Sacramento County, California, as a case study. Heating, cooling, and peak electrical energy use changes resulting from modification of solar radiation, air temperature, and wind speed by the existing urban forest were estimated for representative residential and commercial buildings. This is combined with building age and size, canopy and tree cover, and tree density (trees/ha) for 71 county subdivisions. Annual cooling savings are approximately 157 GWh (US$18.5 million) per year--12% of total air conditioning in the county. Net effects on heating are small, with 145 TJ (US$1.3 million) saved annually. Peak energy-use reductions result in avoided costs of US$6 million. The resulting large-scale analysis incorporates a manageable level of detail not previously available. Sensitivity of results to selected input data is demonstrated. was used as a case study. The resulting estimates incorporate a level of detail in model elements previ¬ously unavailable, without being unmanageably com¬plex. Multidimensional "what-if" sensitivity analysis of the model to uncertainties in selected input values is demonstrated. This methodology, applied to existing trees, is suitable for assessment of energy benefits of current or planned urban tree planting programs. It is one part of the Sacramento Urban Forest Ecosystem Study (SUFES), whose goal is to determine relation¬ships between urban forest structure and function and the associated benefits and costs (McPherson 1998). Together with ongoing research on urban tree growth and health, and impacts on climate, hydrology, and air quality, SUFES findings will aid in development of management strategies for sustainable urban forest ecosystems and in making these concepts of greater use to arborists, managers, policy makers, and local governments. The moderating influence of climate on energy used for cooling and heating buildings (referred to subse¬quently as space-conditioning energy use) has been demonstrated primarily at the scale of individual build¬ings (Heisler 1990; Huang et al. 1990; Meier 1990/91 ; McPherson 1994; Simpson and McPherson 1996). Substantial energy savings on the scale a city can re¬sult (Akbari et al. 1990; Rosenfeld et al. 1996). For example, Akbari et al. (1990) made national estimates based on increases of 1.5 trees per unit, 15% canopy cover, and 19% urban albedo. Savings from trees were approximately 11%, based on their observation that trees and reduced urban albedo produced similar sav¬ings. Regional-scale air temperature and wind-speed reductions were responsible for 7% savings; the re¬maining 4% was due primarily to tree shade, and to a lesser degree wind-speed reduction. Energy savings, together with the other benefits of urban green space, have generally been shown to outweigh the associ¬ated costs, such as those for irrigation, disposition of green waste, and tree removal (McPherson 1995; Hildebrandt et al. 1996). The objective of this paper is to extend results from studies of tree impacts on space conditioning of single buildings (Simpson and McPherson 1995, 1996, 1998) to a regional scale. Sacramento County, California, Methods For a description of the study area and sampling units, see McPherson 1998 (pp. 175-177 of this issue). Tree impacts were estimated by summing energy use calculated for representative residential and com¬mercial buildings of different types over the total num¬ber of units of each type in the county. First, heating and cooling energy use per unit of conditioned floor area (CFA), referred to subsequently as unit energy density (UED), were determined for single-family, 2- to 4-unit, and 5+ -unit residential structureS (referred to as low, medium, and high density) as a function of age of con¬struction (vintage), or as a function of size for commer¬cial structures. Residential density and size of commercial structures are referred to collectively as "building type." Second, UED changes due to modifi¬cation of solar radiation, air temperature, and wind speed by trees were estimated and adjusted based on equipment and diversity factors. Third, energy-use data are combined with numbers of buildings and their vin¬tage/size distribution, tree cover, and tree density (.trees/ ha) for each SubRAD (Sub-Regional Assessment Dis¬trict) (McPherson and Simpson 1995) to estimate space-conditioning impacts. Benefits were assessed based on retail costs of energy to residential and commercial customers. Unless otherwise stated, all future reference 202 Simpson: Urban Forest Effects on Heating and Cooling to UEDs are to adjusted values. Details are given in the appendix to this article. Tree and building data. Data from the Sacramento Area Council of Governments' 1994 Housing Module (SACOG 1995) were used to define the population of residential units and obtain a current inventory of units by SubRAD and density. Their inventory, which was divided into pre-1980, 1980-1984, and post-1984 vin¬tages for each SubRAD, is based on 1990 census data updated with building permit completion data. As of ,January 1994, the population of residential units in Sacramento County was 441,071. Sixty-five percent (287,551) were single-family detached, 3% (15,027) mobile homes, 10% (43,608) structures with 2 to 4 units, and 22% (95,757) structures with 5 or more units. Building energy-use data based on pre-1978, 1978-1983, and post-1983 vintage definitions were applied to pre-1980, 1980-1984, and post-1984 building num¬bers, respectively. Tree density (trees/ha) for each SubRAD, numbers ,of existing trees per unit (trees on the property within .20 m [66 ft] of the structure), and land cover are based on McPherson and Simpson (1995) and McPherson (1998). Tree canopy and building cover, defined as percentage of surface area covered by buildings or vertical projection of tree crowns, were determined for each SubRAD by dividing cover area found for each land use (low and high density, residential and com¬mercial/industrial) by the total area for that land use. Energy costs. Residential electric and gas rates have a 2-tiered structure; higher (peak) rates are charged for usage over a fixed threshold in a billing period (approximately 1 month duration). Based on analyses of typical buildings, changes in residential energy use were found to occur primarily at peak rates for cooling (electricity; $0.12695/kWh) and average rates for natural gas (mean of peak, $0.711/therm and off-peak, $0.527/therm, or $0.62/therm). Average rates were used for calculation of total energy use ($0.104/ kWh and $0.62/therm). Commercial electric rates of $0.068 and $0.081 were used for large and small/ medium commercial and industrial buildings, respec¬tively (Hildebrandt, personal communication 4/24/96). Residential heating costs are based on equipment saturation data for natural gas, heat pump, and elec¬tric resistance heat (Sarkovich, personal communica¬tion 9/5/96). Annual space-heating energy use for commercial buildings was estimated from UEDs taken from EIA (1994) for climate zone 4 and conditioned floor areas supplied by the Sacramento Municipal Util¬ity District (SMUD) (Hildebrandt, personal communi¬cation 4/24/96). Commercial gas rates were $0.991 and $0.442 per therm for small/medium and large us¬ers, respectively. Based on total consumption by fuel source for EIA climate zone 4, it is estimated that 8% of commercial space heating is electric. Other small or indeterminate heating sources (e.g., fuel oil and dis¬trict heat) are treated as if gas heat is being used. After a brief summary of tree and building cover for the county, energy use and changes due to cli¬mate modifications are presented in both energy and dollar units. Effects of solar radiation, air temperature, and wind-speed reductions on cooling and heating are treated. Results are presented for the entire county, as well as by sector, vintage, and building type; im¬pacts on high- versus low-density residential building types, residential versus commercial buildings, and old versus new vintages are presented as well. Results Approximately 3.5 million (Table 1) of Sacramento County's estimated 6 million trees (McPherson 1998), or 59%, are located in residential and commercial land areas. Of these, 32% (1.1 million, 2.4 trees/unit) have shading potential (i.e., are located within 20 m [66 ft] of residential and commercial structures). Most trees (2.97 million, 84%) are located in low- and medium-density residential land areas, where they have the greatest potential to influence space-conditioning energy use. Existing tree cover averaged by land use ranged from 17% for low- and medium-density residential to 4% for large commercial land uses. Average building cover was greatest in high-density residential (37%), 26% in me¬dium- to low-density residential, and lowest in commer¬cial/industrial land areas (22%). Total space-conditioning energy use estimated for the county without trees is 1,439 GWh, 2,037 MW, and 20,277 TJ (terajoules) for annual cooling, peak cool¬ing, and annual heating, respectively (Table 2). Trees reduce these by 157 GWh (10.9%), 124 MW (6.1%), and 145 TJ (0.7%) for annual cooling, peak cooling, and annual heating, respectively. Annual energy use for the county agreed closely!
94!7/19/2002 1:38:00 PM!Equations for predicting diameter, height, crown width, and leaf area of San Joaquin Valley street trees!Peper, P.J., E.G. McPherson and S.M. Mori!2001!Journal of Arboriculture. 27(6)!Articles in Journals!Equations for Predicting Diameter, Height, Cr!cufr_94_PP01_39.PDF!PDF!Peper, P.J., E.G. McPherson and S.M. Mori. 2001. Equations for predicting diameter, height, crown width, and leaf area of San Joaquin Valley street trees. Journal of Arboriculture. 27(6): 306-317!Urban forest; tree growth; predictive equations; size relationships; leaf area!Although the modeling of energy-use reduction, air pollution uptake, rainfall interception, and microclimate modification associated with urban trees depends on data relating diameter at breast height (dbh), crown height, crown diameter, and leaf area to tree age or dbh, scant information is available for common municipal tree species. In this study, tree height, crown width, crown height, dbh, and leaf area were measured for 12 common street tree species in the San Joaquin Valley city of Modesto, California, U .S. The randomly sampled trees were planted from 2 to 89 years ago. Using age or dbh as explanatory variables, parameters such as dbh, tree height, crown width, crown height, and leaf area responses were modeled using two equations. There was strong correlation (adjusted R 2 > 0.70) for total height, crown diameter, and leaf area with dbh. Correlations for dbh with age and crown height for several species were weaker. The equations for predicting tree sizes and leaf area are presented and applied to compare size and growth for all species 15 and 30 years after planting. Tree height, crown diameter, and dbh growth rates tended to slow during the second 15 years, but the leaf area growth rate increased for most species. Comparisons of predicted sizes for three species common to Modesto and Santa Monica trees suggest that pruning has a significant impact on tree size and leaf area, potentially more than climate and soil characteristics!
95!7/19/2002 1:40:00 PM!Characterization of the structure and species composition of urban trees using high resolution AVIRIS data!Xiao, Q., S. Ustin, E.G. McPherson and P. Peper!1999!In: Green, R.O., (ed). Summaries of the 8th JPL Airborne Earth Science workshop. Pasadena: California Institute of Technology Jet Propulsion Laboratory!Articles in Conference Proceedings!Characterizing Urban Forest Structure and Spe!cufr_95_XQ99_56.PDF!PDF!Xiao, Q., S. Ustin, E.G. McPherson and P. Peper. 1999. Characterization of the structure and species composition of urban trees using high resolution AVIRIS data. In: Green, R.O., (ed). Summaries of the 8th JPL Airborne Earth Science workshop. Pasadena: California Institute of Technology Jet Propulsion Laboratory: 451-460!!!
96!7/19/2002 1:41:00 PM!Predictive equations for dimensions and leaf area of coastal Southern California street trees!Peper, P.J., E.G. McPherson and S.M. Mori!2001!Journal of Arboriculture. 27(4)!Articles in Journals!Predictive Equations for Dimensions and Leaf!cufr_96_PP01_40.PDF!PDF!Peper, P.J., E.G. McPherson and S.M. Mori. 2001. Predictive equations for dimensions and leaf area of coastal Southern California street trees. Journal of Arboriculture. 27(4): 169-180!Urban forest; tree growth; predictive equations; dimensional relationships; leaf area!Tree height, crown height, crown width, diameter at breast height (dbh), and leaf area were measured for 16 species of commonly planted street trees in the coastal southern California city of Santa Monica, USA. The randomly sampled trees were planted from 1 to 44 years ago. Using number of years after planting or dbh as explanatory variables, mean values of dbh, tree height, crown width, and leaf area responses were modeled using two equations. There is strong correlation (adjusted R 2 > 0.70) between dbh as a function of number of years after planting, and total height, crown dian1.eter, and leaf area as a function of dbh. Correlation is weaker between measures of crown height and dbh. This is probably due to crown pruning increasing the variability among measurements for trees having the same or similar dbh. Equations for less-il1.tensively pruned species displayed adjusted R 2 greater than 0.70. Equations are presented for predicting din1.ensions and leaf area and applied to compare tree sizes and growth for all species 15 and 30 years after planting!
97!7/19/2002 1:43:00 PM!Measuring and analyzing urban tree cover!Nowak, D.J., R.A. Rowntree, E.G. McPherson, S.M. Sisinni, E. Kerkmann and J.C. Stevens!1996!Landscape and Urban Planning. 36!Articles in Journals!Miscellaneous Biometrics Literature!cufr_97_DN96_31.PDF!PDF!Nowak, D.J., R.A. Rowntree, E.G. McPherson, S.M. Sisinni, E. Kerkmann and J.C. Stevens. 1996. Measuring and analyzing urban tree cover. Landscape and Urban Planning. 36: 49-57!!!in Ecology, Vol. 9, Quantitative Plant Ecology. Univ. of California, Los Angeles. H',dverson, H.G., 1985. Urban forest cover and aggregation from high-altitude aerial photographs. In: B.A. Hutchinson and B.B. Hicks (Editors), The Forest-Atmosphere Interaction, Proc. First Environmental Measurements Conf.. 23-28 October 1983, Oak Ridge, TN. Reidel, Dordrecht, pp. 337-348. Hansen, AJ. and di Castri, F., 1992. Landscape Boundaries: Consequences for Biotic Diversity and Ecological Rows. Springer, New York. Haque. F., 1987. Urban forestry: 13 city profile. Unasylva, 155(39): 14--25. Holscher. C.E.. 1973. City forests of ,Europe. Nat. Hist., 82(9):. 52-54. Huang, YJ., Akbari, H. and Taha, H., 1990, The wind-shielding and shading effects of trees on residential heating and cooling requirements. ASHRAE Trans., 96:1403-1411. Jim, C.Y., 1989. The distribution and configuration of ttr~ cover in urban Hong Kong. GooJoumal, 18: 175-188. Kerkmann, F?, 1995. Tree Canopy Cover and Planting Opportunities in San Jose, California. Kerkmann and Associates, Rich- mond, CA. ¢ Kfichler, A.W., 1967. Vegetation Mapping. Ronald, New York. K~chler. A.W., 1969. Potential natural vegetation. U.S. Geologi- cal Survey Map, Sheet 90. U.S. GeoL Surv., Washington, DC. Laveme, R.J., 1993. Evaluation of urban forest resources in Ann Arbor, Michigan. In: American Foresu'y ~ An Evolving Tradition, Proc. 1992 Society of American Foresters (SAF) National Convention, 25-27 October 1992, Richmond, VA. SAF Publ. 92-O1, SAF, Bethesda, MD, pp. 98-102. Lindgren. B.W. and McElrath, G.W., 1969. Introduction to Probability and Statistics. Macmillan, London. Maxotz, G.A. and Coiner, J.C., 1973. Acquisition and characterization of surface material data for urban climatological studies. L Appl. Meteorol., 12: 919-923. McPherson, E.G., Nowak, DJ., Sacamano, P.L., Prichard, S.E. and Makra. E.M., 1993. Chicago's evolving urban forest: initial report of the Chicago Urban Forest Climate Project. US For. Sere. Gen. Tech. Rep. NE-169. Mocssner, K.D.. 1947. A crown density scale for photo interpreters. J. For., 45: 434--436. Mortimer, A.M., 1981. Urban forest structure in El Paso, Texas, and Ciudad Juarez, Mexico. M.A. Thesis, Syracuse University, Syracuse, NY.. Nowak, D3., 1991. Urban forest dcvt:Iopmeot and structure: analysis of Oakland, California. Ph.D. Dissertation, University of California. Berkeley. Nowak, D.J., 1993a. Remote sensing and urban forcslry. In: American Forestry ~ An Evolving Tradition. Proc. 1992 Society of American Foresters (SAF) National Convention. 25-27 October 1992, Richmond, VA. SAF Puhl. 92-01, SAF, Bethesda, MD, pp. 103-108. Nowak, DA., 1993b. Historical vegetation change in Oakland and. its implications for urban forest management. J. Arboric., 19:. 313-319. Nowak, DJ., 1994. Air pollution removal b'y Chicago's urban forest. In: E.G. McPhcrson, D.J. Nowak, and R.A. Rowntre~ (Editors), Chicago's urban forest ecosystem: results of the Chicago Urban Forest Climate Project. US For. Serv. Gem. Tech. Rep. NE-186. pp. 63-81. Richaxds, N.A., 1992. Optimum stocking of urban ffr.es. J. At- boric., 18: 64.-68. Rodgers L.C. and Harris, M.K., 1983. Remote sensing survey of pecan trees in five Texas cities. J. Arboric., 9:. 208-213. Rowntrec, R.A., 1984. Forest canopy cover and land use in four Eastern United States cities. Urban Ecol,, 8: 55-67. Rownttcc, R.A. and Nowak, DJ., 1991. Quantifying the role of urban forests in removing atmospheric carbon dioxide. J. Arboric., 17: 269-275. .... / ,. 57 °t' ' ft. D J. Nowak et al./ Landscape and Urhan Planning 36 (1996) 49-37 Sanders, R.A.. 1984. ISle determinants of urban forast structure. Urban Ecol., 8: 13-27. 5chcaffcr, R.I.,., MendenhaIl, W. and Oft, L.. 1986. Elementary Sui'vey Sampling, Duxbury, Boston, MA. Talarchek, G.M. and Henderson. M.. 1985. The New Orleans Urban Forest: Suructere and Management. Xavier University " of Louisiana, New Orleans. Turner, M.G. and Ga~:lner, R.H., 1991. Quantitative Methods in [..andscape Ecology. Springer, New York. • U.S. Deparzmen. of Energy, 1994. Voluntary Reporting of Green-hou~ Oa.~s under Section 1605(b) of the Energy Policy Act of 1992: General Guidelines. U.S. Department of.Energy, Waxhington, DC. ? ?!
98!7/19/2002 1:46:00 PM!Describing urban forest cover: an evaluation of airborne videography!Sacamano, P.L., E.G. McPherson, J. Myhre, M. Stankovich, R.C. Weih!1995!Journal of Forestry. 93!Articles in Journals!Miscellaneous Biometrics Literature!cufr_98_PS95_74.PDF!PDF!Sacamano, P.L., E.G. McPherson, J. Myhre, M. Stankovich, R.C. Weih. 1995. Describing urban forest cover: an evaluation of airborne videography. Journal of Forestry. 93: 43-48!!In 1990 the USDA Forest Service initiated the Chicago Urban Forest Climate Project (CUFCP) to better understand the effects of urban vegetation on the urban environment (McPherson et al. 1993, 1994). Through the CUFCP, new methods for investigating and quantifying the effect of trees on the urban ecosystem have been developed and examined (McPherson et al.1994). As part of this effort, scientists have worked cooperatively with the Village of Oak Park; NASA's affiliate Space Remote Sensing Center (SRSC); and the Forest Service Forest Pest Management, Methods Application Group (FPM/MAG) to demonstrate the utility of two airborne videography systems compared to traditional aerial photography for interpreting urban land cover. Comparisons are made among the different types of imagery in terms of accuracy. Cost of imagery and implications for integration with geographic information systems (GIS) are also considered. The results are intended to identify the more useful and economical means for accurately describing urban forest cover!
99!7/19/2002 1:47:00 PM!Strategies to prevent damage to sidewalks by tree roots!Barker, P.A. and P.J. Peper!1995!Arboricultural Journal. 19!Articles in Journals!Controlling Rooting Depth of Transplanted Tre!cufr_99_PB95_3.PDF!PDF!Barker, P.A. and P.J. Peper. 1995. Strategies to prevent damage to sidewalks by tree roots. Arboricultural Journal. 19: 295-309!!Several types of root barriers tested in field experiments in northern California inhibited development of shallow tree roots. The need for an improved barrier design to prevent development of potentially harmful circling roots inside a barrier was indicated. The performances of various currently marketed root barriers with internal vertical ribs were compared to augment product descriptions by their manufacturers!
100!7/19/2002 1:48:00 PM!Street trees and urban infrastructure: getting at the root of the problem!Peper, P.J. and E.G. McPherson!1997!Arborist News. 6(2)!Articles in Journals!Controlling Rooting Depth of Transplanted Tre!cufr_100_PP97_37.PDF!PDF!Peper, P.J. and E.G. McPherson. 1997. Street trees and urban infrastructure: getting at the root of the problem. Arborist News. 6(2): 34-35!!!
101!7/19/2002 1:49:00 PM!Synopsis of tree root response to circling root barriers!McPherson, E.G. and J. Lichter!1998!Western Arborist. 25!Articles in Journals!Controlling Rooting Depth of Transplanted Tre!cufr_101_EM98_67.PDF!PDF!McPherson, E.G. and J. Lichter. 1998. Synopsis of tree root response to circling root barriers. Western Arborist. 25: 40-41!!!indicate that barriers can effectively deflect roots downward, but the extent to which this retards their movement upward and subsequent infrastructure damage is unclear. The purpose of this study was to quantity the effects of four circling barrier products on root growth and distribution. Root numbers, diameter, and depth below ~ound were measured for Raywood ash (Fraxinus oxycarpa 'Raywood') and Lombardy poplar (Populus nigra "Itatica') three years after the trees were planted with and without circling root barriers. The primary effect of the barriers was to reduce the number of tree roots compared to control trees with no barriers. Theoretically, fewer roots should mean less damage to sidewalks and curbs. However, one large root in the wrong place can wreak more damage than many small roots. Thus, fewer roots do not necessarily mean less infrastructure damage, Root diameter and depth also can contribute to damage. The study found little difference in root diameters and depths for trees with and without barriers. Generally, roots of all treatments and the controls became smaller in diameter and shallower in depth from 30 to 150 cm away from the outside of barriers. Also, differences in root response among the barrier types minor. was relatively An important finding of this study is that subsurface soil cultivation resulted in significantly deeper roots compared to roots from trees in uncultivated soil. Cultivation resulted in lower soil bulk densities, presumably accounting for a greater number of surface roots in the uncultivated plots. This study indicates that after roots grow under barriers their distribution is largely controlled by plant genetics and the soil environment. Deep cultivation of soil may reduce damage caused by shallow roots, especially in otherwise compacted soils. Selecting tree species with slower, smaller growing root systems may delay conflicts between roots and paving. The authors conclude by noting that further work is needed to link sidewalk damage with root system size, distribution, and rate of development. Long term studies of root barrier effects on tree health and structural stability are needed as well. Greg McPherson Project Leader/Research Forester USDA Forest Service, Western Center for Urban Forest Research and Education Davis, CA continued on next page... 41 For now, the results of this and a few other studies coupled With our experience will John Lichter, M.S. have to suffice. After utilizing root barri- Tree Associates ers for twenty years,'Condon concludes Winters, CA News You Can Use... The international Board held its winter meeting at the Stakis Birmingham Metropole Hotel. 1998 Conference The Annual Conference will be held at the National Exhibition Cenier (NEC) in Birmingham. The NEC is directly adjacent to the Stakis Metropole Hotel. Both are directly accessible (10 minutes shuttle ride) to the Birmingham International airport and train station. All are some distance from downtown Birmingham (15 minutes train ride). Practitioner's Perspective The results of this study indicate that under similar conditions, the use of root bar-tiers only sigmificantly affects one of three factors (the number of roots) which influence the likelihood of root damage to infrastructure. This information underscores the need for a multi-faceted approach to reducing hardscape damage from tree roots. Dan Condon, City Ar-borist of Santa Barbara says his department is using a combination of approaches including root barriers (at planting and following root priming), tree replacement, appropriate species selection, larger planting areas and innovative sidewalk design: C0ndon pointed Out that the results of this study suggest that Your International Representative Reports. . . Western.Arborist that "root barriers buy time." We'll see. ~: deeper soil cultivation prior to planting: may help to reduce the likelihood of root damage by encouraging deeper roots (the study also revealed significantly greater growth rates from culttivation). Although the final program is still beingdeveloped, I was impressed with the overall quality of the educational program. I'd like to encourage your attendance at this meeting. It looks to be a great one. Certification John Hendticksen and Derek Vannice reported on the activities of the Certification program including completion of surveys of both Certified Arborists and consumers by Communication. Research Associates. Both groups responded very favorably to Certification. While this raaY be possible on certain sites, Condon was quick to point out that for street treea, the results of cultivation (lower soil bulk densities) are contrary to the needs Of the engineers and contrac-toes building the sidewalk who desire high soil densities under hardscape to avoid soil settling. European Office The Society has established an office in Europe, headquarters in England. Russell Ball, former Executive Director of the National Tree Officers Association, has assumed the position of European Senior Executive. New Chapters The Board Approved Sweden, the Czech Republic and Spain as the 34th, 35th and 36th chapter of the ISA. Similar to the researchers, both Condon and Chris Boza, Urban Forester, City of Chico have: observed that roots grow toward the soil surface after being deflected by root barriers. Therefore, the possibility ofhards.cape damage from these roots exists. However, as Boza points out, trees planted with root barriers have deeper buttress roots which reduces the likelihood of damage from these larger roots. Nominations The Board approved the following candidates for the position of International vice- president: John Hendricksen ~- Norm Easey If you have any questions, comments or concerns about the ISA, please feel free to contact me: HortSeience, Inc. PO Box 754 Pleasanton, CA 94566. 510-484-0211 hortsci 1 @ix.neteorn.com Respectfully submitted, As the authors point out, arborists would benefit from further research in this area. • James R. Clark ......... ............ " ..... International Representative. :~ :=": "~ ~!
102!7/19/2002 1:50:00 PM!Comparison of root barriers installed at two depths for reduction of White Mulberry roots in the soil surface!Peper, P.J!1998!In: Watson, G.W. and D. Neely, (eds). The landscape below ground II: proceedings of an international workshop on tree root development in urban soils; 1998; San Francisco. Champaign, IL: International Society of Arboriculture!Articles in Conference Proceedings!Miscellaneous Biometrics Literature!6/cufr_102.pdf!PDF!Peper, P.J. 1998. Comparison of root barriers installed at two depths for reduction of White Mulberry roots in the soil surface. In: Watson, G.W. and D. Neely, (eds). The landscape below ground II: proceedings of an international workshop on tree root development in urban soils; 1998; San Francisco. Champaign, IL: International Society of Arboriculture: 82-93!!!
103!7/19/2002 1:52:00 PM!Root barrier and extension effects on Chinese Hackberry!Peper, P.J. and S. Mori!1999!Journal of Arboriculture. 25(1)!Articles in Journals!Controlling Rooting Depth of Transplanted Tre!6/cufr_103.pdf!PDF!Peper, P.J. and S. Mori. 1999. Root barrier and extension effects on Chinese Hackberry. Journal of Arboriculture. 25(1): 1-8!!!
104!7/19/2002 1:54:00 PM!Costs of street tree damage to infrastructure!McPherson, E.G. and P.J. Peper!1996!Arboricultural Journal. 20!Articles in Journals!Costs Associated with Damage to Infrastructur!cufr_104_EM96_21.PDF!PDF!McPherson, E.G. and P.J. Peper. 1996. Costs of street tree damage to infrastructure. Arboricultural Journal. 20: 143-160!!Street trees are an important component of the 'green infrastructure' in cities but damage caused by roots to sidewalks, kerbs and gutters and sewers is a multimillion dollar problem. To determine the magnitude of this problem, municipal foresters were surveyed in 15 cities. Total annual concrete and sewer repair costs attributed to tree damage averaged $4.28 per street tree and ranged from $0.18 to $13.65 per tree. On average, repair costs are equivalent to 25 per cent of annual tree maintenance expenditures; sidewalk repair costs are the single largest expense in all cities, averaging $3.01 per tree. Annual curb, gutter and sewer repair costs averaged $1.14 and $1.66 per tree respectively and damage is highly variable among cities tending to be most severe in older city areas with deteriorating infrastructure and large trees. Mitigation measures applied by tree managers are discussed!
105!7/19/2002 1:54:00 PM!Infrastructure repair costs associated with street trees in 15 cities!McPherson, E.G. and P.J. Peper!1996!In: Watson, G.W. and D. Neely (eds). Trees and building sites. Savoy, IL: International Society of Arboriculture!Articles in Conference Proceedings!Costs Associated with Damage to Infrastructur!cufr_105_EM96_22.PDF!PDF!McPherson, E.G. and P.J. Peper. 1996. Infrastructure repair costs associated with street trees in 15 cities. In: Watson, G.W. and D. Neely (eds). Trees and building sites. Savoy, IL: International Society of Arboriculture: 49-63!!Street trees are an important component of the "green infrastructure" in cities but damage caused by roots to sidewalks, curbs and gutters, and sewers is a multimillion-dollar problem. To determine the magnitude of this problem, municipal foresters were surveyed in 15 cities. Total annual concrete and sewer repair costs attributed to tree damage averaged $4.28 per street tree and ranged fro $0.18 to $13.65 per tree. On average, repair costs are equivalent to 25% o the annual tree program expenditures. Sidewalk repair costs are the single largest expense in all cities, averaging $3.01 per tree. Annual curb and gutter and sewer repair costs averaged $1.14 and $1.66 per tree, respectively. Damage is highly variable among cities and tends to be most severe in older areas of cities with deteriorating infrastructure and large trees. Mitigation measures applied by tree managers are discussed!
107!7/19/2002 2:03:00 PM!Expenditures associated with conflicts between street tree root growth and hardscape in California!McPherson, E.G!2000!Journal of Arboriculture. 26(6)!Articles in Journals!Street Tree-Sidewalk Conflicts in California!cufr_107_EM00_11.PDF!PDF!McPherson, E.G. 2000. Expenditures associated with conflicts between street tree root growth and hardscape in California. Journal of Arboriculture. 26(6): 289-297!Root growth, sidewalk damage, tree-sidewalk interaction, urban forestry!A survey of 18 California cities indicated that approximately $70.7 million (se $11.1 million) was spent annually statewide due to conflicts between street tree root gro:wth and sidewalks, curbs and gutters, and street pavement. The largest single expenditure was for sidewalk repair ($23 million, se $9.5 million), followed by curb and gutter repair ($11.8 million, se $2.6 million), and trip and fall payments and legal staff time ($10.1 million, se $2.2 million). Property owners paid 39% and 17% of tree-related sidewalk and curb and gutter repair costs, respectively. Substantial funds were invested to remove and replace trees in conflict with hardscape ($6.8 million, se $3.6 million), and for inspection and repair administration programs ($5.9 million, se $1.3 million). Root pruning ($2.5 million, se $2.0 million) and root barriers ($676,854, se $175,655) were the most important mitigation and prevention measures. Restricted planting space and the type of tree species selected were reported as the most important factors responsible for hardscape damage!
109!7/19/2002 2:09:00 PM!Costs due to conflicts between street tree root growth and hardscape!McPherson, E.G. and P.J. Peper!2000!In: Costello, L., E.G. McPherson, D.W. Burger and L. Dodge, (eds). Proceedings of the symposium on strategies to reduce infrastructure damage by tree roots. Cohasset, CA: Western Chapter, International Society of Arboriculture!Articles in Conference Proceedings!Street Tree-Sidewalk Conflicts in California!cufr_109_EM00_81.PDF!PDF!McPherson, E.G. and P.J. Peper. 2000. Costs due to conflicts between street tree root growth and hardscape. In: Costello, L., E.G. McPherson, D.W. Burger and L. Dodge, (eds). Proceedings of the symposium on strategies to reduce infrastructure damage by tree roots. Cohasset, CA: Western Chapter, International Society of Arboriculture: 15-18!!!
110!7/19/2002 2:12:00 PM!Reducing tree root damage to sidewalks in California communities: a collaborative study!McPherson, E.G., L.R. Costello, E. Perry, and P.J. Peper!2000!In: Dodge, L., (ed). Report of the Elvenia J. Slosson Fund for Ornamental Horticulture; 1998-1999. Davis: UC Davis Division of Agriculture and Natural Resources!Articles in Conference Proceedings!Street Tree-Sidewalk Conflicts in California!cufr_99.pdf!PDF!McPherson, E.G., L.R. Costello, E. Perry, and P.J. Peper. 2000. Reducing tree root damage to sidewalks in California communities: a collaborative study. In: Dodge, L., (ed). Report of the Elvenia J. Slosson Fund for Ornamental Horticulture; 1998-1999. Davis: UC Davis Division of Agriculture and Natural Resources: 8-12. . 5!!!
111!7/19/2002 2:14:00 PM!Tree root intrusion in sewer systems: review of extent and costs!Randrup, T.B., E.G. McPherson and L.R. Costello!2001!Journal of Infrastructure Systems. 7(1)!Articles in Journals!Compendium of Practices to Reduce Infrastruct!cufr_111_TR01_41.PDF!PDF!Randrup, T.B., E.G. McPherson and L.R. Costello. 2001. Tree root intrusion in sewer systems: review of extent and costs. Journal of Infrastructure Systems. 7(1): 26-31!!Interference between trees and sewer systems is likely to occur in old systems and in cracked pipes. Factors that contribute to damage include old pipes with joints, shallow pipes, small-dimension pipes, and fast-growing tree species. Because roots are reported to cause >50% of all sewer blockages, costs associated with root removal from sewers is substantial. In smaller-dimension pipes, root removal every year or every other year is common. Major resources are put into replacement and renewal of existing pipes, which is sometimes accelerated because of root intrusion. Collapse repair costs are greater than new construction, but costs associated with root removal may be one-sixth the cost of pipe replacement/renewal due to roots. Major breaks and stoppages seem to occur more frequently in older systems than in new. Therefore, it seems worthwhile to carry out preventative maintenance of the older parts of the sewer system!!
112!7/19/2002 2:16:00 PM!Space wars: can trees win the battle with infrastructure?!McPherson, E.G., L.R. Costello and D.W. Burger!2001!Arborist News. 10(3)!Articles in Journals!Street Tree-Sidewalk Conflicts in California!cufr_112_EM01_73.PDF!PDF!McPherson, E.G., L.R. Costello and D.W. Burger. 2001. Space wars: can trees win the battle with infrastructure?. Arborist News. 10(3): 21-24!!A symposium was held March 31 through April 1, 2000, at the University of California, Davis, to explore strategies to reduce conflicts between tree roots and infrastructure. Fifty participants shared current research findings, identified research and development needs, and developed the basis for a multidisciplinary approach to solve the problem. This article describes highlights of the symposium and future directions of an emerging research and education program. All references cited below are from the symposium proceedings, Strategies to Reduce Infrastructure Damage by Tree Roots indicate that they direct roots downward and buy time before roots return to more favorable conditions near the surface. Effectivene,~s depends on correct installation, soil conditiOns, and tree rooting patterns (Gilman). Linear root barriers (12 inch) are placed in trenches parallel to the sidewalk where roots are cut. Several inches of backfill between the barrier and walk p:rovide room for root expansion (Dunn). In Modesto, after sidewalks are removed, the concrete is r epoured to a depth of 12 inches adjacent to the cut tree roots. This concrete root barrier delays subsequent damage (Gilstrap). Structural soils developed at Cornell (Bassuk and Grabosky) are being evaluated in California cities such as Palo Alto, Davis, and Santa Monica (Warriner). They provide the structural stability required for compacted base material under pavement, and at the same time have sufficient pore space for root growth. With compaction, the angular aggregate (g to 1~ inch) locks into place and creates voids with water, oxygen, and soil for root nutrition. The clay loam soil stays attached to the stone with a binder. Heroic efforts are made to save mature trees from the: chain saw when roots cause hardscape damage. Retaining large anchor roots is necessary if root cutting threatens tree stability In Sunnyvale, concrete is poured over roots sandwiched between two 10-gauge steel plates (Dunn). The bolted plates force the root to expand laterally instead of vertically, thereby reducing upward pressure on the sidewalk. In other cases, foam and sand backers are used between the root and concrete to absorb upward pressure from radial expansion of the roots. Sidewalks gradually ramped or elevated on piers also are used to preserve large roots (Seegebrech0. Alternate paving strategies are yet another means of reducing costs associated with tree root growth and sidewalk repair. Interlocking or unit pavers are more flexible than concrete and less costly to repair. Asphalt and decomposed granite are acceptable substitutes for concrete in certain situations (Mason). Modifications such as these must meet Americans with Disabilities " Act standards for accessibility Many cities narrow or meander sidewalks around the trunks of large trees after the trees have outgrown their space. Sometimes sidewalks are designed and installed to provide additional space for each street tree (Figure 4). In some cases, curbs Figure 4. This walk in Redwood City was initially designed to accommodate anticipated tree root growth (from Mann). are moved out into the street when it is the only tree preservation alternative (Mann). Other root and soil management strategies include • creating gavel-filled trenches that lead roots under walks (Urban)    waterjetting to increase soil moisture at depth and thus promote deep rooting (Gil~trap)    using chemical treatments such as allelopathic chemicals androot toxins    injecting gel or other materials between the sub-base and concrete to reduce oxygen for root growth (Gamstetter)    modifying the temperature at the interface to repel roots    using glass block or optical fibers in concrete to increase light at the interface and thus repel roots. In Redwood City, where City Council policy frowns on planting small "toy trees," parkways as narrow as 2 feet are being retrofitted with large-statured shade trees (Figure 5). Trees are planted at the edge of the sidewalk using half of a grate ($250). This design provides adequate space for the tree to grow and commits the city to widening the sidewall< as the trunk expands (Mann). Other cities are experimenting with different materials and engineering practices. Alternatives include flexible paving, compressible subgrades, and reinforced concrete (Urban). A new tool for detecting tree roots below pavement is ground-penetrating radar (impulse radar). Tree roots produce a distinctive signature that can be used to determine depth and size prior to excavation (Seegebrecht). Planning and design strategies have potential to eliminate tree root-hardscape conflicts when they are incorporated into the development process up front. Unfortunately, trees are regarded as "flexible" design components and inserted in the space not occupied by utilities or paving at the end of the process (Sealana). The life expectancy of most sidewalks is 20 to 30 years, while street trees can live 40 to 60 years or longer (Gamstetter). There is need to study the cost effectiveness of designing hardscape to match the life cycles of trees. Good details and specifications are essential to tree survival and health in restricted growing space. Deep planting, along with pea-gravel mulch is one strategy to reduce shallow rooting (Figure6). Figure 5. Ia, ge-statured trees planted in a narrow parkway in Redwood oty "borrow" space from the sidewalk (from Mann). 22 www.isa-arbor.com ARBOtlIST'PIEW5 Space Wars (continued) increased awareness and coordination among city departments. Now money is budgeted up front for tree relocation when improvement projects threaten street trees. Arborists review site plans and are con-suited before tree roots are removed, and tree protection zones are defined and enforced (Warriner). Figure 6. Planting trees below grade has reduced root- hardscape conflicts in San Jose (from Beaudoin). Specifications should cover everything from root pruning to sub-base preparation for sidewalk construction on a variety of soil types (Beaudoin). Several cities have achieved better sidewalk and tree management by combining staff into a single department. Santa Monica's Community Forest Management Plan 55V P5 The symposium was a first step to developing solutions by involving researchers and practitioners. The symposium spawned its own Web site (telework.ucdavis.edu/treeroots) and a structural soils Listserv (contact Nina Bassuk to subscribe, nlb2@comell.edu). Priorities were identified for    new research and development    communication and outreach    field testing and follow-up research    policy, economics, and education With assistance from symposium pamci-pants and others, Larry Costello, Katherine Jones, and Greg McPherson are developing the Compendium of Pracftces to Reduce Infrastructure Damage by Tree Roots. Due to be published m 2002, the compendium will document the application and effectiveness of state-of-the-art strategies. Funding for the compendium is from the Forest Service's Center for Urban Forest Research. Future funding for research on this problem may be spurred by results from the ISA Research Trust's current efforts to develop a new agenda for urban forest research (Watson). The need to manage risk associated with tree-related trip-and-fall hazards makes finding solutions to tree root-hardscape conflicts a priority Because space for trees in cities continues to diminish, there is an urgent need for science-based solutions. "Smart Growth" policies encourage more compact development, while an increasing number of underground utilities vie for limited space. Too often, developers, planners, and engineers fail to integrate trees into infrastructure design up front. In existing WHAT TREE ROOTS THINK WHEN THEY SEE BIOBARRIER. T rees and shrubs provide shade, beauty and oxygen, but their roots can cause an incredible amount of damage. Biobarrier sends roots in a new direction.., away from your sidewalk, building or landscaped area. Easily installed Biobarrier Root Control System is a durable geotextile fabric with permanently attached nodules containing trifluralin. The trifluralin is gradually released from the nodules to create an invisible "no trespassing" zone beside the structure you want protected. Rated by the US EPA as less toxic* than table salt, trifluralin works by preventing root tip cell division, which is how roots grow. When root tips reach the zone of trifluralin, they are rerouted to grow in another direction. Porous and flexible. Biobarrier blocks only roots, so water, air and nutrients flow through it, allowing healthier soil conditions for the tree. And because it is a flexible fabric, you choose exactly how much you need and where to place it to fit the contours of your specific site. Works invisibly. Biobarrier is installed completely underground. Unlike hard barriers, it doesn't need to protrude above the soil in order to work. This ensures the area around your tree is more attractive and less of a tripping hazard and liability. Guaranteed and maintenance-free for 15 years. Biobarrier is the only root barrier on the market that is guaranteed for 15 years. That means you'll have a decade-and-a-half of no maintenance worries, no labor costs, no hardscape or landscape damage, and no complaints. Biobarrier lets you direct roots so they can continue to grow and nourish the tree without damaging your investment. With Biobarrier, you can have your tree and your sidewalk too. Bio barrief Biobarrier detours roots from your sidewalk, building or landscape. 1-800-382-8467    615-847-7000    Fax 615-847-7068 . www.reemay.corn    Emaik biobarder@reemay.com *Based on acute oral LD-50 Biobarrier is of Reemay, Inc. Circle 202 on Reader Service Card JUNE 2001 23 24 mycorrhizaROOTS" Soluble Powder FOR ALL TREES AND SHRUBS Pt (Pisolithus) Rhlzopogon amylopogon Rhizopogon villosuli Rhizopogon fulvigelba Rhizopogon luteolus Laccaria lacatta Laccaria bicolor Scleroderma cepa Scleroderma citrinum / Space Wars (continued) development, there is public pressure to retain existing trees that have created trip-and-fall hazards, but very little is known about the relative effectiveness of mitigation strategies. Given the large amount of money spent on root-hardscape conflicts, a broad-spectrum research and education program will produce savings for municipalities that will more than pay for itself. There is hope for thriving trees if we work together to defeat the "Space Wars" problem. E. Gregory McPherson is a research forester.and project leader at the Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, Davis, California. Laurence Costello is a environmental horticulture advisor at the University of California Cooperative Extension, San Bruno, California. David Burger is a professor in the department of environmental horticulture, University of California, Davis. Glomus mosseae Glomus intraradJces GIomus clarum Glomus monosporus Glornus deserticola GIomus brasilianum Glomus aggregatum Gigaspora margarita Net Wt   16 ozs   (455 g) Expiration Date: rg0~l~. 3120 Weatherford Road- Independence. MO   64055 NO '"   Splinters NOT   ..Delamination.   ..Warping EVER] "GUARANTEED" DICA Marketing Co. Carroll, IA 51401 800-610-DICA (3422) FAX 712-792-1106 Circle 203 on Reader Service Card Circle 204 on Reader Service Card <input type="hidden" name="ProductText" value=" By E. Gregory McPherson, Laurence R. Costello, and David W. Burger The data are in: Trees are losing the battle for space along city streets. Confined to ever-smaller cutouts and planting strips, it's no wonder that roots carve out their space at the expense of sidewalks, curbs, and driveways. Conflicts between tree roots and infrastructure create trip-and-fall hazards for pedestrians, and conflicts can cause large, stately trees--those that provide the greatest bene-fits---to be removed only because their roots have repeatedly heaved sidewalks (Figure 1). When this happens, trees lose and cities lose (Figure 2). liil.([ i lV li.li.iili liIl] l=l li;ll'-l/i.i Approximately $71 million is spent annually by cities in California due to conflicts between tree roots and hard-scape. One-third of this amount is spent on sidewalk repair and, surprisingly, $2.26 is spent on legal remedies for every $1 spent on mitigation (root barriers, root cutting, etc.). Managers reported that restricted planting space and poor tree species selection were the most frequently occurring causes of conflicts (McPherson and Peper). Field assessments in Modesto, California, found that soil characteristics and tree size alone were not good predictors of sidewalk damage. Rootstock variation among different species of ash (Fraxinus spp.) appeared to be important, but mor£ detailed investigation is needed. Results from Modesto's uniform, sandy loams may not apply where softs differ (Costello, Perrg, and Kelley). Root depth and growth pattern are inheritable traits. Research with three A symposium was held March 31 through April 1, 2000, at the University of California, Davis, to explore strategies to reduce conflicts between tree roots and infrastructure. Fifty participants shared current research findings, identified research and development needs, and developed the basis for a multidisciplinary approach to solve the problem. This article describes highlights of the symposium and future directions of an emerging research and education program. All references cited below are from the symposium proceedings, Stratefftes to Reduce Infrastructure Damage by Tree Roots (Costdlo et al. 2000), available for $12.50 from ISA's Western Chapter. To order, call (530) 892-1118 or go to www.wcisa.neL All proceeds go to the ISA Research Trust. Figure 1. Trees that win the battle for space often pay with their lives later. Figure 2. This excavated ginkgo (Ginkgo biloba) tree root system illustrates that healthy trees need a substantial amount of underground space (from Duma). species (Shamel ash [Fro.)dnus uhdei], pistache [Pistac/a chinensis], and zelkova [Zelkova serrata]) uses the latest technologies to identify and propagate deep-rooted individuals. Roots are tenderly excavated with a supersonic air spade, marked and photographed at several angles, scanned, and imported into a three-dimensional modeling program that aids visualization of roofing patterns (Figure 3). Individuals with vertical roots have been vegetatively propa- gated for field trials (Burger). A survey of tree root expenditures associated with Danish municipal sewers found that roots are not perceived as a major problem. Annual tree-related expenditures were only 1.2 percent of total sewer system costs, and roots were only in sewers laid before 1980. As older sewer systems are renovated, the problem will decrease further (Randmp). In England, the impacts of trenching on tree roots have been severe. To counter the problem, new specifications call for the use of hand-digging or trenchless technology, re ekgntion of roots greater than 1 inch in diameter, and careful backfilling around roots (Jackson, Smith, and Roberts). Relatively little is known about the physiology of root impedance. The pressure exerted by roots axially and radially is substantial (Feldman). For instance, a 15-inch segment of root 1 inch in diameter exerts 175 psi, and this force can lift a sidewalk slab 10 feet long and 4 feet wide (Dunn). ..iVliIlilVl. l(..; Root barriers are commonly used at time of planting and as a retrofit measure to obstruct mot growth folowing root cutting. JUNE 2001 www.isa-arbor.com 21 Space ~Zars (continued) Figure 3. Three-dimensional model of an excavated root system (from Burger). Studies indicate that they direct roots downward and buy time before roots return to more favorable conditions near the surface. Effectivene,~s depends on correct installation, soil conditiOns, and tree rooting patterns (Gilman). Linear root barriers (12 inch) are placed in trenches parallel to the sidewalk where roots are cut. Several inches of backfill between the barrier and walk p:rovide room for root expansion (Dunn). In Modesto, after sidewalks are removed, the concrete is r epoured to a depth of 12 inches adjacent to the cut tree roots. This concrete root barrier delays subsequent damage (Gilstrap). Structural soils developed at Cornell (Bassuk and Grabosky) are being evaluated in California cities such as Palo Alto, Davis, and Santa Monica (Warriner). They provide the structural stability required for compacted base material under pavement, and at the same time have sufficient pore space for root growth. With compaction, the angular aggregate (g to 1~ inch) locks into place and creates voids with water, oxygen, and soil for root nutrition. The clay loam soil stays attached to the stone with a binder. Heroic efforts are made to save mature trees from the: chain saw when roots cause hardscape damage. Retaining large anchor roots is necessary if root cutting threatens tree stability In Sunnyvale, concrete is poured over roots sandwiched between two 10-gauge steel plates (Dunn). The bolted plates force the root to expand laterally instead of vertically, thereby reducing upward pressure on the sidewalk. In other cases, foam and sand backers are used between the root and concrete to absorb upward pressure from radial expansion of the roots. Sidewalks gradually ramped or elevated on piers also are used to preserve large roots (Seegebrech0. Alternate paving strategies are yet another means of reducing costs associated with tree root growth and sidewalk repair. Interlocking or unit pavers are more flexible than concrete and less costly to repair. Asphalt and decomposed granite are acceptable substitutes for concrete in certain situations (Mason). Modifications such as these must meet Americans with Disabilities " Act standards for accessibility Many cities narrow or meander sidewalks around the trunks of large trees after the trees have outgrown their space. Sometimes sidewalks are designed and installed to provide additional space for each street tree (Figure 4). In some cases, curbs Figure 4. This walk in Redwood City was initially designed to accommodate anticipated tree root growth (from Mann). are moved out into the street when it is the only tree preservation alternative (Mann). Other root and soil management strategies include    creating gavel-filled trenches that lead roots under walks (Urban)    waterjetting to increase soil moisture at depth and thus promote deep rooting (Gil~trap)    using chemical treatments such as allelopathic chemicals androot toxins    injecting gel or other materials between the sub-base and concrete to reduce oxygen for root growth (Gamstetter)    modifying the temperature at the interface to repel roots    using glass block or optical fibers in concrete to increase light at the interface and thus repel roots. In Redwood City, where City Council policy frowns on planting small "toy trees," parkways as narrow as 2 feet are being retrofitted with large-statured shade trees (Figure 5). Trees are planted at the edge of the sidewalk using half of a grate ($250). This design provides adequate space for the tree to grow and commits the city to widening the sidewall< as the trunk expands (Mann). Other cities are experimenting with different materials and engineering practices. Alternatives include flexible paving, compressible subgrades, and reinforced concrete (Urban). A new tool for detecting tree roots below pavement is ground-penetrating radar (impulse radar). Tree roots produce a distinctive signature that can be used to determine depth and size prior to excavation (Seegebrecht). Planning and design strategies have potential to eliminate tree root-hardscape conflicts when they are incorporated into the development process up front. Unfortunately, trees are regarded as "flexible" design components and inserted in the space not occupied by utilities or paving at the end of the process (Sealana). The life expectancy of most sidewalks is 20 to 30 years, while street trees can live 40 to 60 years or longer (Gamstetter). There is need to study the cost effectiveness of designing hardscape to match the life cycles of trees. Good details and specifications are essential to tree survival and health in restricted growing space. Deep planting, along with pea-gravel mulch is one strategy to reduce shallow rooting (Figure6). Figure 5. Ia, ge-statured trees planted in a narrow parkway in Redwood oty "borrow" space from the sidewalk (from Mann). 22 www.isa-arbor.com ARBOtlIST'PIEW5 Space Wars (continued) increased awareness and coordination among city departments. Now money is budgeted up front for tree relocation when improvement projects threaten street trees. Arborists review site plans and are con-suited before tree roots are removed, and tree protection zones are defined and enforced (Warriner). Figure 6. Planting trees below grade has reduced root- hardscape conflicts in San Jose (from Beaudoin). Specifications should cover everything from root pruning to sub-base preparation for sidewalk construction on a variety of soil types (Beaudoin). Several cities have achieved better sidewalk and tree management by combining staff into a single department. Santa Monica's Community Forest Management Plan 55V P5 The symposium was a first step to developing solutions by involving researchers and practitioners. The symposium spawned its own Web site (telework.ucdavis.edu/treeroots) and a structural soils Listserv (contact Nina Bassuk to subscribe, nlb2@comell.edu). Priorities were identified for    new research and development    communication and outreach    field testing and follow-up research    policy, economics, and education With assistance from symposium pamci-pants and others, Larry Costello, Katherine Jones, and Greg McPherson are developing the Compendium of Pracftces to Reduce Infrastructure Damage by Tree Roots. Due to be published m 2002, the compendium will document the application and effectiveness of state-of-the-art strategies. Funding for the compendium is from the Forest Service's Center for Urban Forest Research. Future funding for research on this problem may be spurred by results from the ISA Research Trust's current efforts to develop a new agenda for urban forest research (Watson). The need to manage risk associated with tree-related trip-and-fall hazards makes finding solutions to tree root-hardscape conflicts a priority Because space for trees in cities continues to diminish, there is an urgent need for science-based solutions. "Smart Growth" policies encourage more compact development, while an increasing number of underground utilities vie for limited space. Too often, developers, planners, and engineers fail to integrate trees into infrastructure design up front. In existing WHAT TREE ROOTS THINK WHEN THEY SEE BIOBARRIER. T rees and shrubs provide shade, beauty and oxygen, but their roots can cause an incredible amount of damage. Biobarrier sends roots in a new direction.., away from your sidewalk, building or landscaped area. Easily installed Biobarrier Root Control System is a durable geotextile fabric with permanently attached nodules containing trifluralin. The trifluralin is gradually released from the nodules to create an invisible "no trespassing" zone beside the structure you want protected. Rated by the US EPA as less toxic* than table salt, trifluralin works by preventing root tip cell division, which is how roots grow. When root tips reach the zone of trifluralin, they are rerouted to grow in another direction. Porous and flexible. Biobarrier blocks only roots, so water, air and nutrients flow through it, allowing healthier soil conditions for the tree. And because it is a flexible fabric, you choose exactly how much you need and where to place it to fit the contours of your specific site. Works invisibly. Biobarrier is installed completely underground. Unlike hard barriers, it doesn't need to protrude above the soil in order to work. This ensures the area around your tree is more attractive and less of a tripping hazard and liability. Guaranteed and maintenance-free for 15 years. Biobarrier is the only root barrier on the market that is guaranteed for 15 years. That means you'll have a decade-and-a-half of no maintenance worries, no labor costs, no hardscape or landscape damage, and no complaints. Biobarrier lets you direct roots so they can continue to grow and nourish the tree without damaging your investment. With Biobarrier, you can have your tree and your sidewalk too. Bio barrief Biobarrier detours roots from your sidewalk, building or landscape. 1-800-382-8467    615-847-7000    Fax 615-847-7068 . www.reemay.corn    Emaik biobarder@reemay.com *Based on acute oral LD-50 Biobarrier is of Reemay, Inc. Circle 202 on Reader Service Card JUNE 2001 23 24 mycorrhizaROOTS" Soluble Powder FOR ALL TREES AND SHRUBS Pt (Pisolithus) Rhlzopogon amylopogon Rhizopogon villosuli Rhizopogon fulvigelba Rhizopogon luteolus Laccaria lacatta Laccaria bicolor Scleroderma cepa Scleroderma citrinum / Space Wars (continued) development, there is public pressure to retain existing trees that have created trip-and-fall hazards, but very little is known about the relative effectiveness of mitigation strategies. Given the large amount of money spent on root-hardscape conflicts, a broad-spectrum research and education program will produce savings for municipalities that will more than pay for itself. There is hope for thriving trees if we work together to defeat the "Space Wars" problem. E. Gregory McPherson is a research forester.and project leader at the Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, Davis, California. Laurence Costello is a environmental horticulture advisor at the University of California Cooperative Extension, San Bruno, California. David Burger is a professor in the department of environmental horticulture, University of California, Davis. Glomus mosseae Glomus intraradJces GIomus clarum Glomus monosporus Glornus deserticola GIomus brasilianum Glomus aggregatum Gigaspora margarita Net Wt   16 ozs   (455 g) Expiration Date: rg0~l~. 3120 Weatherford Road- Independence. MO   64055 NO '"   Splinters NOT   ..Delamination.   ..Warping EVER] "GUARANTEED" DICA Marketing Co. Carroll, IA 51401 800-610-DICA (3422) FAX 712-792-1106 Circle 203 on Reader Service Card Circle 204 on Reader Service Card ">!
114!7/19/2002 2:25:00 PM!Managed development of tree roots II: ultra-deep rootball and root barrier effects on Southwestern Black Cherry!Barker, P.A!1995!Journal of Arboriculture. 21(5)!Articles in Journals!Controlling Rooting Depth of Transplanted Tre!cufr_114_PB95_2.PDF!PDF!Barker, P.A. 1995. Managed development of tree roots II: ultra-deep rootball and root barrier effects on Southwestern Black Cherry. Journal of Arboriculture. 21(5): 251-259!Arboriculture, root barrier, root development, root growth, root weight, sidewalk damage, trunk diameter, urban forestry!Three-year-old seedlings of southwestern black cherry (Prunus serotina subsp. virens var. virens) with rootballs 35 and 70 cm deep were field planted in northern California in April 1986 to compare the effects on root development of rootballs of two depths and a root barrier, which was a polyethylene casing around the rootballs of half of the trees of each treatment. Three growing seasons later, the roots were excavated to a depth of 32 cm in an area within a radius of 1m from the tree trunks and dry weights of the exposed roots of each tree determined. There was no significant difference in root dry weights between the two rootball types. The casing, on the other hand, significantly reduced root dry weights for each rootball type!
115!7/19/2002 2:27:00 PM!Managed development of tree roots I: ultra-deep rootball and root barrier effects on European Hackberry!Barker, P.A!1995!Journal of Arboriculture. 21(4)!Articles in Journals!Controlling Rooting Depth of Transplanted Tre!7/cufr_115.pdf!PDF!Barker, P.A. 1995. Managed development of tree roots I: ultra-deep rootball and root barrier effects on European Hackberry. Journal of Arboriculture. 21(4): 202-208!australis, root barrier, root growth, root weight, sidewalk damage, trunk diameter, urban forestry!Four-year-old seedlings of European hackberry (Celtis australis) with rootballs 35 cm (14 in.) and 70 cm (28 in.) deep, were field planted in nor1hem California in April 1986 to compare root development as affected by rootball depth and a casing that fit snugly around the rootball to function as a root barrier. Three growing seasons later, the roots of each tree were excavated to a 32-cm depth in an area within approximately 1 m radius from the trunk and the dry weights of these roots determined. Root weight was significantly different between the two root barrier treatments but not between the two rootball depths!of the root systems of deciduous trees. Black Rock Forest Bul. No. 15, Harvard Black Rock Forest, Harvard University, Cambridge, Massachusetts. 8. Wilson, Marshall. 1988   Beauty of trees costs homeowners. The Dispatch, Gilroy, California, November 18, page 1. 9. Wong, T.W., J.E.G. Good, and M.P. Denne. 1988. Treeroot damage to pavements and kerbs in the city of Manchester. Arboricultural Journal 12:17-34   Zusammenfassung. Vom S0dl. Z(Jrgelbaum (Celtis aus-tralis) wurden Jungpflanzen mit 35 cm und 70 om tiefen Wurzelballen im Norden Californiens ausgepflantzt, um das Wurzelwachstum in Bezug auf 1. Wurzelballentiefe und 2. auf eine Wurzelsperre, die genau um den Wurzelballen passt, zu vergleichen. Nach drei Wachstumsperioden wurden die Wurzeln in einem Abstand von lm zum Stamm bis zu einer Tiefe von 0.32m ausgegraben und die Trockengewichte bestimmt. Das Wurzelgewicht war deutlich unterschiedlich zwischen den beiden Wurzelbegrenzungsbehandlungen, abet nicht zwischen den zwei Wurelballentiefen!
125!7/25/2002 1:53:00 PM!Fire hazard assessment of South Lake Tahoe!de Jong, L!2003!Fire Management Today!Articles in Journals!Alternative Prescriptions for Firewise Reside!cufr_125.pdf!PDF!de Jong, L. 2003. Fire hazard assessment of South Lake Tahoe. Fire Management Today. 63(2)!!!
126!7/25/2002 1:55:00 PM!Improving Fire Hazard Assessment at the Urban-Wildland Interface: Case Study in South Lake Tahoe, CA!de Jong, L!2002!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!Published Reports!Alternative Prescriptions for Firewise Reside!8/fire_1.pdf!PDF!de Jong, L. 2002. Improving Fire Hazard Assessment at the Urban-Wildland Interface: Case Study in South Lake Tahoe, CA. Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research. 11!urban-wildlife interface, fire hazard assessment, fire safety law!A fire hazard assessment was conducted on private, developed lots in South Lake Tahoe, a high fire hazard urban-wildland interface community in Northern California. Fire hazard was assessed in terms of the minimum standards set forth in the National Fire Protection Association's (NFPA) Standard 299 and homeowner practices such as compliance with the fire safety law PRC 4291, construction materials of the home, and irrigation. In addition, the influence on small parcel fire hazard by neighbors was assessed!
127!7/25/2002 1:56:00 PM!Urban forestry at the urban-wildland interface!de Jong, L. and G. McPherson!2003!In Review!!Alternative Prescriptions for Firewise Reside!!None!de Jong, L. and G. McPherson. 2003. Urban forestry at the urban-wildland interface. In Review!!!
128!7/25/2002 2:09:00 PM!A practical approach to assessing structure, function, and value of street tree populations in small communities!Maco, S.E. and E.G. McPherson!2003!Journal of Arboriculture 29(2): March 2003!!A Practical Approach to Benefit Cost Analysis!cufr_128.pdf!PDF!Maco, S.E. and E.G. McPherson. 2003. A practical approach to assessing structure, function, and value of street tree populations in small communities. Journal of Arboriculture!Urban forest valuation; urban forest managment; street tree inventory!This study demonstrates an approach to quantify the structure, benefits, and costs of street tree populations in resource-limited communities without tree inventories. Using the city of Davis, California, U.S., as a model, existing data on the benefits and costs of municipal trees were applied to the results of a sample inventory of the city's pulic and private street trees. Results indicate that Davis maintained nearly 24,000 public street trees that provided benefits, with a benefit-cost ratio of 3.8:1. The city can improve long-term stability of this resource by managing maintenance, new plantings, and stand rejuvenation of a city zone basis!
129!7/25/2002 2:09:00 PM!Assessing canopy cover over streets and sidewalks in street tree populations!Maco, S.E. and E.G. McPherson!2002!Journal of Arboriculture 28(6): November 2002!!Miscellaneous Publications!cufr_129.pdf!PDF!Maco, S.E. and E.G. McPherson. 2002. Assessing canopy cover over streets and sidewalks in street tree populations. Journal of Arboriculture: 270-276. . 28(6)!!!
130!7/25/2002 2:43:00 PM!Parking lot shade tree inspection and monitoring guide!McPherson, E.G!1999!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!Published Reports!Sacramento Parking Lot Tree Shade Ordinance!!None!McPherson, E.G. 1999. Parking lot shade tree inspection and monitoring guide. Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research: 1. . 17!!!
132!7/25/2002 3:56:00 PM!A benefit-cost analysis of ten street tree species in Modesto, California, U.S.A!McPherson, E.G!2003!Journal of Arboriculture 29(1): January 2003!Articles in Journals!Quantifying Benefits and Costs of Modesto's U!!PDF!McPherson, E.G. 2003. A benefit-cost analysis of ten street tree species in Modesto, California, U.S.A. Journal of Arboriculture!Urban forest valuation; economic analysis; tree selection; benefit-cost analysis!Tree work records for ten species were analyzed to estimate average annual management costs by dbh class for six activity areas. Average annual benefits were calculated by dbh class for each species with computer modeling. Average annual net benefits per tree were greatest for London plane (Platanus acerifolia) ($178.57), hackberry (Celtis sinensis) ($148.42), and Modesto ash (Fraxinus velutina 'Modesto') ($126.16) and least for pear (Pyrus calleryana cvs.) ($33.65), pistache (Pistacia chinensis) ($64.98), and camphor (Cinnamomum camphora) ($71.36). Benefit-cost ratios (BCRs) were greatest for plane (24.3:1), ginkgo (7.4:1), and camphor (7.3:1). Species with the lowest BCRs were sweetgum (liquidambar styraciflua) (2.4:1), pear (2.6:1), and pistache (3.3:1). Aging of sweetgum and Modesto ash will result in reduced net benefits because BCRs decreased once trees reached the 46 cm dbh class. Uses of benefit-cost data to increase future net benefits are discussed!
133!8/5/2002 12:52:00 PM!Strategy to Reduce Infrastructure Damage by Tree Roots: A Symposium for Researchers and Practitioners!Costello, L.R., E.G. McPherson, D.W. Burger, E.J. Perry and D. Kelly!2002. [in press]!Urban Ecosystems!Articles in Journals!Compendium of Practices to Reduce Infrastruct!cufr_113.pdf!PDF!Costello, L.R., E.G. McPherson, D.W. Burger, E.J. Perry and D. Kelly. 2002. [in press] Strategy to Reduce Infrastructure Damage by Tree Roots: A Symposium for Researchers and Practitioners Urban Ecosystems!!!
136!8/5/2002 2:44:00 PM!Benefits and costs of Modesto's municipal urban forest!McPherson, E.G., J.R. Simpson, P.J. Peper and Q. Xiao!1999!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!Published Reports!Quantifying Benefits and Costs of Modesto's U!cufr_136_EM99_29.PDF!PDF!McPherson, E.G., J.R. Simpson, P.J. Peper and Q. Xiao. 1999. Benefits and costs of Modesto's municipal urban forest. Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research. 42!!!
137!8/5/2002 2:48:00 PM!City of Sacramento parking lot tree shading design and maintenance guidelines!City of Sacramento Planning Department!2002!Sacramento, CA: City of Sacramento Planning Department!Published Reports!Sacramento Parking Lot Tree Shade Ordinance!http://www.cityofsacramento.org/planning/longrange/shading_guide.pdf  View Document!Website Address!City of Sacramento Planning Department. 2002. City of Sacramento parking lot tree shading design and maintenance guidelines. Sacramento, CA: City of Sacramento Planning Department!!!
138!8/5/2002 2:52:00 PM!Sacramento urban forest ecosystem study plans!McPherson, E.G., J.R. Simpson, P.J. Peper, R.A. Rowntree, K.I. Scott and A.S. Hertz!1995!Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research!Published Reports!Sacramento Urban Forest Ecosystem Study!cufr_138_EM97_63.PDF!PDF!McPherson, E.G., J.R. Simpson, P.J. Peper, R.A. Rowntree, K.I. Scott and A.S. Hertz. 1995. Sacramento urban forest ecosystem study plans. Davis, CA: USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research. 54!!!costs !
139!8/5/2002 2:53:00 PM!Actualizing microclimate and air quality benefits with parking lot tree shade ordinances!McPherson, E.G., J.R. Simpson and K.I. Scott!2001!Wetter und Leben. 4(98)!Articles in Journals!Impacts of Shade Trees in Parking Lots in Dav!11/cufr_69.pdf!PDF!McPherson, E.G., J.R. Simpson and K.I. Scott. 2001. Actualizing microclimate and air quality benefits with parking lot tree shade ordinances. Wetter und Leben. 4(98): 353-369!!!
141!8/5/2002 3:02:00 PM!A new rainfall interception measuring system!Xiao, Q., E.G. McPherson, S.L. Ustin, M.E. Grismer and J.R. Simpson!!Presented at American Geophysical Union (AGU) meeting, Fall 1997!PowerPoint Presentations!Modeling Urban Tree Rainfall Interception!4/cufr_141.pdf!PDF!Xiao, Q., E.G. McPherson, S.L. Ustin, M.E. Grismer and J.R. Simpson. A new rainfall interception measuring system. Presented at American Geophysical Union (AGU) meeting, Fall 1997!!!
144!8/20/2002 3:51:00 PM!She saved my life!Peper, P.J!1994!Women in Natural Resources. 15(3)!Articles in Journals!Miscellaneous Publications!cufr_144_PP94_34.PDF!PDF!Peper, P.J. 1994. She saved my life. Women in Natural Resources. 15(3): 10-13!!!
145!9/2/2002 7:57:00 PM!Mapping successional boreal forests in interior central Alaska!Ustin, S.L. and Q.F. Xiao!2001!International Journal of Remote Sensing 22(9)!Articles in Journals!Miscellaneous Biometrics Literature!6/cufr_145.pdf!PDF!Ustin, S.L. and Q.F. Xiao. 2001. Mapping successional boreal forests in interior central Alaska. International Journal of Remote Sensing 22(9): 1779-1797!!!
149!10/31/2002 6:58:00 PM!Save dollars with shade!Geiger, J.R!2001!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 4p. Research summary!Research Summaries!Energy Effects of Urban Forests in California!3/cufr_149.pdf!PDF!Geiger, J.R. 2001. Save dollars with shade. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 4p. Research summary!shade, energy, planting, radiant energy, dollars, savings!Imagine a solution to rising energy prices as simple as planting trees. We've all grown up with trees, climbed in them, and probably even planted a few. But how many of us know that they significantly contribute to cooling our homes, businesses and communities?!
150!10/31/2002 7:01:00 PM!Where's the fire?!Geiger, J.R!2002!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 4p. Research summary!Research Summaries!Alternative Prescriptions for Firewise Reside!8/cufr_150.pdf!PDF!Geiger, J.R. 2002. Where's the fire?. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 4p. Research summary!fire, lots, compliance, risk, landscape maintenance, clear vegetation, flammable, fire -resistant roofing!The small lots found in South Lake Tahoe and the lack of compliance with California's fire safety laws mean a significant fire risk to the whole community, despite the fact that the city has fire-fighting resources available. While making your own property firewise is the first step, becoming fire safe is not always something you can do alone. It requires the active participation of all homeowners and businesses in the community!
151!10/31/2002 7:08:00 PM!Where are all the cool parking lots?!Geiger, J.R!2002!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 4p. Research summary!Research Summaries!Effects of Tree Cover on Parking Lot Microcli!3/cufr_151.pdf!PDF!Geiger, J.R. 2002. Where are all the cool parking lots?. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 4p. Research summary!parking lots, cool, shade, planning, growing trees, space, ordinances, lot, pavement, cities!Parking lots occupy about 10% of the land in many of our cities, and since the 1970's energy crisis there has been an increasing interest in parking lot shade ordinances. We chose Sacramento, CA as the test case to investigate how well one!
152!10/31/2002 7:15:00 PM!Working for the West!Geiger, J.R!March, 2001!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 6p. Research update!Newsletters!Center Newsletters!newsletters/UF1.pdf!PDF!Geiger, J.R. March, 2001. Working for the West. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 6p. Research update!research, benefits, yard tree, savings, management!Dear Colleague, Some of you have seen us before, but may not recognize our new look. For those who don't know us, we hope this Update will introduce our work and show how it can benefit you. We are the Center for Urban Forest Research, founded in 1992 in Davis, CA. We recently changed our name. You may remember us as the Western Center for Urban Forest Research and Education. Our research is dedicated to uncovering the mysteries of the urban forest functions to help you with management decisions. Our job is to conduct research that describes the structure of urban forests and quantifies their benefits and costs. We hope tht communities can use this information to improve the planting and care of their urban forests, and convince community leaders to support urban forest efforts with increased investments. You should also know that the work at our Center does not stop once a report is published. Much remains to be done - partnering with people like you to ensure that research results are useful. We believe that our research in only as good as the changes it inspires. Therefore, we are here to work with you to ensure that positive changes occur and that all of us derive the maximum benefits from our urban forests!
153!10/31/2002 7:18:00 PM!New research findings: Green Plants or Power Plants? A case for planting more trees!Geiger, J.R!October, 2001!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 6p. Research update!Newsletters!Center Newsletters!newsletters/UF2.pdf!PDF!Geiger, J.R. October, 2001. New research findings: Green Plants or Power Plants? A case for planting more trees. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 6p. Research update!shade, crisis, energy, conservation, planting!The response to the recent energy crisis in California by most utilities and the state has been to focus on immediate solutions to peak load demand, such as power plants, and discontinue investments in shade tree programs, a somewhat surprising move. Dr. Greg McPherson and Dr. Jim Simpson, Center for Urban Forest Research, conducted the new energy research. They understand the dilemma facing utilities and the state, and agree that more new trees will not affect the peak load demand in the near future. "It will take about 5-15 years for trees to fully contribute to the energy conservation process. However, if we don't continue investing in energy conserving trees, they will not be available in 15 years when the demand for energy will be even greater," says Dr. McPherson!
154!10/31/2002 7:20:00 PM!Where are all the "Cool" Parking Lots!Geiger, J.R!January, 2002!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 6p. Research update!Newsletters!Center Newsletters!newsletters/UF3.pdf!PDF!Geiger, J.R. January, 2002. Where are all the. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 6p. Research update!pollution, vehicles, shade, parking lot, ordinances, landscape!When the U.S. Environmental Protection Agency (EPA) needed data on how well shade reduces pollution from parked cars, they went to parking lot shading studies of the Center for Urban Forest Research. The EPA was looking for ways to cut pollution from vehicles in the Chicago, IL ozone-nonattainment area where parkied vehicles contribute approximately 5.2 tons of volatile organic compounds (VOC) per million vehicles per day. Because no studies were found for locations in the midwest, calculations from studies in California had to be adapted for conditions in Chicago where the average ozone-season temperature is approximately 82 degree rather than the study temperature of 104 degree. In addition, Chicago receives less direct sunlight, so the shading effect is less. By extrapolating from the pilot studies in Davis and Sacramento CA, the potential reduction in VOC was estimated to be 0.645 to 1.132 lbs per 1000 vehicles parked per day in parking lots with a 25% and 50% canopy of shade, respectively!
155!10/31/2002 7:20:00 PM!Is all your rain going down the drain?!Geiger, J.R!July, 2002!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 6p. Research update!Newsletters!Center Newsletters!newsletters/UF4.pdf!PDF!Geiger, J.R. July, 2002. Is all your rain going down the drain?. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 6p. Research update!rain, runoff, stormwater, waterways, drainage!Have you ever gone outside after a rainstorm and looked around thinking..!
156!11/1/2002 7:03:00 AM!UWI Landscaping Assisted by Fire Models!de Jong, L.A!2002!Fire.gov Better fire fighting through research!Articles in Periodicals!Alternative Prescriptions for Firewise Reside!http://www.fire.gov/newsletter/summer2002/page_two.htm#uwi  View Document!Website Address!Alternative Prescriptions for Firewise Residential Landscapes!UWI Landscaping Assisted by Fire Models. Summer 2002. Fire.gov Better fire fighting through research, National Institute of Standards and Technology (NIST)!Fire, models, landscaping, assisted!Scientists and engineers in the Fir Research Division of the National Institute of Standards and Technology (NIST) are developing mathematical/computational fire models to predict the spread of fires through both wildland fuels and structures. Such landscapes, where wildland fuels (trees, shrubs and grasses) and houses and/or other man made structures coexist are known as the urban-wildland interface (UWI). As people have built in more remote areas, UWI fires have become much more common, dangerous and expensive!
157!11/1/2002 7:06:00 AM!EcoSmart - A precision landscape evaluation & design tool!Geiger, J.R!2002!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 1p. Computer model summary!Research Summaries!EcoSMART - EnergyWise!ecoSmarthandout.pdf!PDF!Geiger, J.R. 2002. EcoSmart - A precision landscape evaluation & design tool. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 1p. Computer model summary!trees, remove trees, grow trees, move trees, rainfall, runoff, landscape!ecoSmart is a Web-based software program designed to evaluate the economic trade-offs between different landscape practices on residential parcels. The program estimates the impacts of strategic tree placement, rainfall management, and fire prevention practices. Users work in a computer-simulation environment to test various landscape and hydrologic alternatives to arrive at environmentally and economically sound solutions!
159!12/11/2002 9:40:00 AM!Trees in our city!Kleinman, M., Geiger, J.R!2002!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; ppt.,13!PowerPoint Presentations!Miscellaneous Publications!powerpoint/cufr_159.swf!PowerPoint!Kleinman, M., Geiger, J.R. 2002. Trees in our city. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; ppt.,13!!!
161!12/11/2002 9:49:00 AM!Planting the Seeds of Success - Marketing the community forest!Geiger, J.R., M. Johnson, M. Kleinman, and H. Voege!2002!Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 34p. Community handbook!Miscellaneous!Miscellaneous Publications!1/cufr_161.pdf!PDF!Geiger, J.R., M. Johnson, M. Kleinman, and H. Voege. 2002. Planting the Seeds of Success - Marketing the community forest. Davis, CA: Center for Urban Forest Research, Pacific Southwest Research Station, USDA Forest Service; 34p. Community handbook!community forests, funding, benefits!This handbook is a research product created by the Center for Urban Forest Research in collaboration with the California Urban Forest Council, Croker/Flanagan Marketing, Inc. and Hal Voege Consulting. The purpose of the research was to identify barriers and obstacles that prevent the effective delivery of urban forestry technology and information, allowing us - as supporters of community forests - to better communicate our messages and take urban forestry to the next level. The results of our Center's research, along with Everett Rogers' pioneering work on the art of persuasion covered in chapter 2, guided the development of this handbook and the companion PowerPoint presentation. Two related products are available: 1. A PowerPoint presentation which summarizes the research -!
162!12/11/2002 4:48:00 PM!A benefit-cost analysis of ten street tree species in Modesto, California, U.S!McPherson, E.G!2003!Journal of Arboriculture 29(1): January 2003!Articles in Journals!Miscellaneous Benefit-Cost Literature!cufr_162.pdf!PDF!McPherson, E.G. January 2003. A benefit-cost analysis of ten street tree species in Modesto, California, U.S.. Journal of Arboriculture: 1-8!!!
163!1/6/2003 9:42:00 PM!Cooling California Naturally!McPherson, E.G!2002!The Trust For Public Land