USDA Forest Service

Pacific Southwest Research Station


Pacific Southwest Research Station
800 Buchanan Street
Albany, CA 94710-0011

(510) 883-8830

United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Urban Ecosystems and Social Dynamics Program

Urban Ecosystems and Processes

Since 1992 we have provided our customers with reliable scientific evidence that urban forests add real value to communities. Among their many benefits, trees reduce energy costs, intercept air pollutants, store carbon, and reduce stormwater runoff.

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What's New

Trees with browns leaves in autumn line both sides of a city street with parked cars and no traffic.
The state of California's street trees

Although the number of street trees in California has increased from 5.9 million in 1988 to 9.1 million in 2014, street tree density has declined by 30% as cities added more streets than trees. The total annual benefits provided by street trees are $1 billion and $5.82 in benefits is returned for every $1 spent on tree care. Research Forester Greg McPherson and colleagues describe the structure, function and value of California's street trees.

Supporting documents

Science in Practice

Workers planting trees in the city
Million Trees Los Angeles: carbon sink or source?

Are urban Tree Planting Initiatives (TPIs) likely to be effective means for reaching local carbon dioxide reduction targets? Research forester Greg McPherson and partners determined that a large-scale TPI, Million Trees Los Angeles (now called City Plants), is achieving success in terms of survival, growth and performance.

A photo of a tree in the city
New research evaluating tree species for climate adaptation

Climate change poses challenges for California, where an already parched region is expected to get hotter and, in its southern half, significantly drier. Research forester Greg McPherson and partners are identifying the resilience of different tree species to future climate exposure and threats from pests and disease in the Central Valley.

CO2 graphic
California's climate change policies and programs

Station research and partner California ReLeaf’s advocacy efforts have resulted in $17.8 million in cap-and-trade auction revenues for California Department of Forestry and Fire Protection’s (CAL FIRE) Urban and Community Forestry Program in 2014-15, the largest one-year single-state allocation for urban forestry. Research forester Greg McPherson and partners published an article that traces the history of this effort.

Text:Carbon storage in urban trees. Background: Trees on a city street
A New Approach to Quantifying Carbon

California is at the forefront of efforts in the U.S. to develop policies that address climate change, including the first set of protocols that allow urban forestry projects to participate in the state's cap-and-trade program. In his blog for American Forests, Greg McPherson describes hurdles that make it difficult to "cash-in" by selling carbon credits. The Climate Action Reserve is streamlining their Urban Forest Protocol to make it more attractive by reducing costs and expanding the scope of projects. Read more on the American Forests' blog or visit the American Forests Carbon Offsets and Urban Forests website for more information.

Graphic of city with hot spots
Urban Tree Canopy (UTC) Assessments

A new generation of remote sensing and GIS technologies have spurred UTC assessments for urban forest planning and management. This top-down approach was applied in San Jose, CA, where the council proposes to plant 100,000 trees by 2022. The San Jose Urban Forest Inventory and Assessment found that the annual ecosystem services and property values for the current urban forest provide $239.3 million in benefits. The city contains 2.1 million potential tree planting sites and by estimating the benefits of planting 100,000 trees, it was found that the benefits would increase almost 7% to $255.8 million annually. The city is using the report as a baseline for a proposed study of climate change impacts on the urban forest. This knowledge is especially important in the San Francisco Bay area, where increasing temperatures and fluctuations in precipitation might cause salt intrusion from rising sea levels. The FS study has helped the city of San Jose see the big picture and what they need to do to prepare for the changes to come.

City trees with large buildings in the background
Growing and Governing Green Infrastructure

Urban green infrastructure, including urban forests, is an important strategy for providing public goods and increasing resiliency while reducing ecological footprints and social inequity in metropolitan areas. In a recent paper, Drs. Robert Young and Greg McPherson found that visioning, planning and management of six large-scale tree planting initiatives was largely dominated by the public sector, unlike more transdisciplinary strategies in environmental governance. Many of these initiatives have had little success becoming institutionalized. In a previous paper, they described strategies for sustaining such initiatives. Also, Dr. Young described the role of planning in advancing these initiatives, and identified best practices that can inform future efforts to expand tree planting on a metropolitan scale.

Measuring a tree in front of a home
Newly Developed Growth Models for Common ash

Paula Peper, retired FS, partnered with Oakville, Southern Ontario, Canada Forestry Services' Claudia Alzate, John McNeil and Jalil Hashemi to develop the first growth models for common ash tree species. The results are now available in the online article Allometric equations for urban ash trees (Fraxinus spp.) in Oakville, Southern Ontario, Canada. Increased knowledge of tree growth will enable more accurate forecasts of ecosystem services, tree maintenance assessments and analyses of alternative management scenarios to determine best management practices for sustainable urban forestry.

Trees on a city street
New Tool: Release of ecoSmart Landscapes (beta)

A beta release of ecoSmart Landscapes, a free web-based tool, is available through the ecoSmart Landscapes Portal at The software program developed by ecoLayers allows users to determine building energy use, carbon sequestration, rainfall interception and the fire threat posed by their landscapes. ecoSmart Landscapes (eSL) integrates trees, shrubs, grass-covered rain gardens, engineered soils and cisterns through a Google Map user interface. Analytical models produce reports so users can visualize future carbon, water, energy, and fire impacts of landscapes at the residential parcel scale. Use Google Chrome, Firefox or IE9 to access. Read the PSW News Release for more information.

Recent Publications

cover imageWhat is the value of a tree? What environmental services do they provide and at what cost? Our new Trees Pay Us Back brochures answer these and other questions. Produced in partnership with CAL FIRE Urban and Community Forestry, these brochures present information on trees in the 16 U.S. climate zones where research was conducted for our Community Tree Guide series and i-Tree Streets. From the Southern and Northern California Coast to the Northeast, Coastal Plain, and Central Florida regions, click to view and download the PDF for your region.

New approach to quantify and map urban forest carbon. By incorporating age-related differences among census block groups that influence tree species composition and stand structure, this novel approach improves carbon estimates and increases the resolution at which carbon can be mapped across a region.

Special Issue on Water Scarcity and Urban Forest Management. The articles in this special issue of Arboriculture & Urban Forestry offer "lessons learned" from a serious drought in Australia to inform future policy, research, design and management.

Trees Give Roads a Breath of Fresh Air May was Clean Air Month and the role of roadside trees in cleaning the air and helping us feel better was described in a recent blog. A multidisciplinary group of researchers, planners and policymakers from the U.S. Environmental Protection Agency, U.S. Forest Service and other organizations found that strategically planting trees near busy roadways may significantly enhance air quality. Their findings were published recently in the Transportation Research Board magazine.

All Trees Not Equal. Greg McPherson's blog supports the California Urban Forest Council's Invest From the Ground Up campaign by providing guidelines for selecting and locating trees to maximize climate, energy and environmental benefits.

Greenhouse Gas Inventory of an Ornamental Tree Production System. This article reports the results of a study to determine the greenhouse gas (GHG) emissions from nursery production of ornamental trees for urban forestry.

Comparison of Methods for Estimating Carbon Dioxide Storage by Sacramento's Urban Forest. This chapter by Drs. Elena Aguaron and Greg McPherson in Carbon Sequestration in Urban Ecosystems determines and examines variability among CO2 estimation approaches.

CO2 in Claremont, CA for the Inland Empire Climate Region
Carbon dioxide stored by selected tree species in Claremont, CA at various intervals after planting (1 metric tonne = 2,204.6 lb).

This animation illustrates the differences among tree species as they age in terms of the amount of carbon dioxide (CO2) they store in their above and below ground wood (biomass). Use the arrow below the chart to stop the animation at any of 5 age intervals. For example, stopping at the 35 year interval allows a clear visual comparison showing tulip tree and holly oak each store 5 or more metric tonnes of CO2 between ages 35 and 55, while Callery pear, Turkish pine, and Chinese pistache store less than 1 tonne.

Animation Data: .xlsx, .pdf

Last Modified: Apr 2, 2015 02:37:41 PM