Climate Change and...
Effects of Climate Change
- Climate Variability
- Climate Models
Effects of Climate Change
Terrestrial Ecosystems and Habitats
Janowiak, Maria K.; Swanston, Christopher W.; Nagel, Linda M.; Webster, Christopher R.; Palik, Brian J.; Twery, Mark J.; Bradford, John B.; Parker, Linda R.; Hille, Andrea T.; Johnson, Sheela M. 2011. Silvicultural decisionmaking in an uncertain climate future: a workshop-based exploration of considerations, strategies, and approaches. Gen. Tech. Rep. NRS-81. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 14 p
Land managers across the country face the immense challenge of developing and applying appropriate management strategies as forests respond to climate change. We hosted a workshop to explore silvicultural strategies for addressing the uncertainties surrounding climate change and forest response in the northeastern and north-central United States. Outcomes of this workshop included identification of broad management strategies and approaches for creating forests that can adapt to rapidly changing conditions. Four themes were prevalent in the discussion of coping with climatic change: recognize relationships between site conditions and species vulnerability, maintain and increase diversity, increase discussion about assisted migration, and place a greater emphasis on monitoring. In this paper, we draw on the workshop to outline a process for presenting information and engaging land managers in discussion of forest management challenges in an era of climate uncertainty.
Jessica E. Halofsky, David L. Peterson, Michael J. Furniss, Linda A. Joyce, Constance I. Millar, and Ronald P. Neilson. 2011. Workshop Approach for Developing Climate Change Adaptation Strategies and Actions for Natural Resource Management Agencies in the United States. Journal of Forestry. 109 (4): 219–225 (7)
Concrete ways to adapt to climate change are needed to help land-management agencies take steps to incorporate climate change into management and take advantage of opportunities to balance the negative effects of climate change. Because the development of adaptation tools and strategies is at an early stage, it is important that ideas and strategies are disseminated quickly to advance thinking and practice. Here, we offer an example of a successful workshop, focused on National Forests in the United States, which allowed quick dissemination of ideas and strategies for climate change adaptation in resource management through an interaction between scientists and managers. We share both the process used in the workshop and the outcome of facilitated dialogue at the workshop. By presenting concrete adaptation methods and showing the value of a focused scientist–manager dialogue, we hope to motivate the US Forest Service and other natural resource agencies to emulate our approach and begin the process of adapting to climate change.
A critical component of assessing the impacts of climate change on forest ecosystems involves understanding associated changes in the biogeochemical cycling of elements. Evidence from research on northeastern North American forests shows that direct effects of climate change will evoke changes in biogeochemical cycling by altering plant physiology, forest productivity, and soil physical, chemical, and biological processes. Indirect effects, largely mediated by changes in species composition, length of growing season, and hydrology, will also be important. The case study presented here uses the quantitative biogeochemical model PnET-BGC to test assumptions about the direct and indirect effects of climate change on a northern hardwood forest ecosystem. Modeling results indicate an overall increase in net primary production due to a longer growing season, an increase in NO3– leaching due to large increases in net mineralization and nitrification, and slight declines in mineral weathering due to a reduction in soil moisture. Future research should focus on uncertainties, including the effects of (1) multiple simultaneous interactions of stressors (e.g., climate change, ozone, acidic deposition); (2) long-term atmospheric CO2 enrichment on vegetation; (3) changes in forest species composition; (4) extreme climatic events and other disturbances (e.g., ice storms, fire, invasive species); and (5) feedback mechanisms that increase or decrease change.
Blate, G.M.; Joyce, L.A.; Littell, J.S.; McNulty, S.G.; Millar, C.I.; Moser, S.C.; Neilson, R.P.; O'Halloran, K.; Peterson, D.L. 2009. Adapting to climate change in United States national forests. Unasylva 231/232, Vol. 60: p. 57-62.
Climate change is already affecting forests and other ecosystems, and additional, potentially more severe impacts are expected (IPCC, 2007; CCSP, 2008a, 2008b). As a result, forest managers are seeking practical guidance on how to adapt their current practices and, if necessary, their goals. Adaptations of forest ecosystems, which in this context refer to adjustments in management (as opposed to "natural" adaptation), ideally would reduce the negative impacts of climate change and help managers take advantage of any positive impacts.
PREFACE: The U.S. Government’s Climate Change Science Program (CCSP) is responsible for providing the best science-based knowledge possible to inform management of the risks and opportunities associated with changes in the climate and related environmental systems. To support its mission, the CCSP has commissioned 21 “synthesis and assessment products” (SAPs) to advance decisionmaking on climate change-related issues by providing current evaluations of climate change science and identifying priorities for research, observation, and decision support. This Report—SAP 4.4—focuses on federally managed lands and waters to provide a “Preliminary Review of Adaptation Options for Climate-Sensitive Ecosystems and Resources.” It is one of seven reports that support Goal 4 of the CCSP Strategic Plan to understand the sensitivity and adaptability of different natural and managed ecosystems and human systems to climate and related global changes.
The purpose of SAP 4.4 is to provide useful information on the state of knowledge regarding adaptation options for key, representative ecosystems and resources that may be sensitive to climate variability and change. As its title suggests, this report is a preliminary review, defined as “the process of collecting and reviewing available information about known or potential adaptation options.” The Intergovernmental Panel on Climate Change (IPCC) notes that there are few demonstrated examples of ecosystem-focused adaptation options (see IPCC Fourth Assessment Report, 22.214.171.124 and 4.6.2). Thus, the authors of this SAP found it necessary to examine adaptation options in the context of a desired ecosystem condition or natural resource management goal, as set forth by the resource management entity. Therefore, this report explores potential adaptation options that could be used by natural resource managers within the context of the legislative and administrative mandates of the six systems examined: National Forests, National Parks, National Wildlife Refuges, Wild and Scenic Rivers, National Estuaries, and Marine Protected Areas. Case studies throughout this report examine in greater detail some of the issues and challenges associated with implementation of adaptation options, but are not intended to be geographically comprehensive or representative of the full breadth of ecosystems that exist or adaptation options that are available.
The management systems selected for this report are meant to be representative of a variety of ecosystem types and management goals, in order to be useful to managers who work at different spatial and organizational scales. Time and resource constraints do not allow for a comprehensive coverage of all federally owned and managed lands and waters, which means that some important management systems (e.g., Bureau of Land Management lands, Department of Defense lands, tribal lands, research reserves) are not featured in this report. However, this preliminary review of existing adaptation knowledge does contain science-based adaptation strategies that are broadly applicable to not only other federal lands, but also state, local, territorial, tribal, and non-governmental holdings. Adaptive Management, a key tool recognized in this report, is an important concept within the Department of the Interior, and an Adaptive Management Technical Guide1 was released in the spring of 2007. It provides a robust analytical framework that is based on the experience, in-depth consultation, and best practices of scientists and natural resource managers. The information in this SAP combined with Interior’s Technical Guide is available for managers to consider and discuss. Additional work is needed to refine and add to this body of knowledge, including conducting detailed analyses of adaptation options on a case-by-case basis.
It must be noted that a discussion of the cost and benefits of implementing the adaptation options, either individually or collectively, was not a component of the SAP prospectus and is not included in this report. Relative to ecosystems, the IPCC noted that information is very limited on the economic and social costs and benefits of adaptation measures, especially the non-market costs and benefits of adaptation measures involving ecosystem protection, among others. Since this is a preliminary report, additional information on the costs and benefits is certainly warranted.
ABSTRACT: Climate change is expected to have significant impacts on the Great Basin by the mid-21st century. The following provides an overview of past and projected climate change for the globe and for the region.
P. M. Cox, R. A. Betts, A. Betts, C. D. Jones, S. A. Spall, I. J. Totterdell (2002). Modelling vegetation and the carbon cycle as interactive elements of the climate system. International Geophysics 83: 259-279
ABSTRACT: The climate system and the global carbon cycle are tightly coupled. Atmospheric carbon in the form of the radiatively active gases, carbon dioxide and methane, plays a significant role in the natural greenhouse effect. The continued increase in the atmospheric concentrations of these gases, due to human emissions, is predicted to lead to significant climatic change over the next 100 years. The best estimates suggest that more than half of the current anthropogenic emissions of carbon dioxide are being absorbed by the ocean and by land ecosystems (Schimel et al., 1995). In both cases the processes involved are sensitive to the climatic conditions. Temperature affects the solubility of carbon dioxide in sea water and the rate of terrestrial and oceanic biological processes. In addition, vegetation is known to respond directly to increased atmospheric CO2 through increased photosynthesis and reduced transpiration (Sellers et al., 1996a; Field et al., 1995), and may also change its structure and distribution in response to any associated climate change (Betts et al., 1997). Thus there is great potential for the biosphere to produce a feedback on the climatic change due to given human emissions.
Despite this, simulations carried out with General Circulation Models (GCMs) have generally neglected the coupling between the climate and the biosphere. Indeed, vegetation distributions have been static and atmospheric concentrations of CO2 have been prescribed based on results from simple carbon cycle models, which neglect the effects of climate change (Enting et al., 1994). This chapter describes the inclusion of vegetation and the carbon cycle as interactive elements in a GCM. The coupled climate-carbon cycle model is able to reproduce key aspects of the observations, including the global distribution of vegetation types, seasonal and zonal variations in ocean primary production, and the interannual variability in atmospheric CO2 . A transient simulation carried out with this model suggests that previously-neglected climate-carbon cycle feedbacks could significantly accelerate atmospheric CO2 rise and climate change over the twenty-first century.
D. Schimel, J. Melillo, H. Tian, A. D. McGuire, D. Kicklighter, T. Kittel, N. Rosenbloom, S. Running, P. Thornton, D. Ojima, W. Parton, R. Kelly, M. Sykes, R. Neilson, B. Rizzo (2000). Contribution of increasing CO2 and climate to carbon storage by ecosystems in the United States. Science 287 (5460): 2004-2006
ABSTRACT: The effects of increasing carbon dioxide (CO2 ) and climate on net carbon storage in terrestrial ecosystems of the conterminous United States for the period 1895-1993 were modeled with new, detailed historical climate information. For the period 1980-1993, results from an ensemble of three models agree within 25%, simulating a land carbon sink from CO2 and climate effects of 0.08 gigaton of carbon per year. The best estimates of the total sink from inventory data are about three times larger, suggesting that processes such as regrowth on abandoned agricultural land or in forests harvested before 1980 have effects as large as or larger than the direct effects of CO2 and climate. The modeled sink varies by about 100% from year to year as a result of climate variability.
ABSTRACT: This paper presents examples of environmental changes in the Canadian Rockies in the context of a 1.5°C increase in mean annual temperatures over the last 100 years. During this period increases in winter temperatures have been more than twice as large as those during spring and summer. Glacier cover has decreased by at least 25% during the 20th century and glacier fronts have receded to positions last occupied ca. 3000 years ago. These two lines of evidence suggest that the climate of the late 20th century is exceptional in the context of the last 1000 to 3000 years. Detailed studies in three closely located upper treeline sites document variable responses of vegetation to climate change that reflect species differences as well as local differences in microclimate and site conditions. Treeline has advanced upslope in response to climate warming, but site and species differences control the rate and nature of the advance. Human impacts on the environment compound the changes due to climate warming. Historic photographs indicate significant changes in the type and density of forest cover due to the absence of significant forest fires within these National Parks during the last 70–80 years. The visual impact of these changes, which partially reflects a policy of fire suppression, is far greater than the impact of changes associated with more direct tourist-related impacts. It is therefore important that monitoring programs examine vegetation changes over the entire landscape rather than focussing exclusively on supposedly climate-sensitive sites.
ABSTRACT: Key risks associated with projected climate trends for the 21st century include the prospects of future climate states with no current analog and the disappearance of some extant climates. Because climate is a primary control on species distributions and ecosystem processes, novel 21st-century climates may promote formation of novel species associations and other ecological surprises, whereas the disappearance of some extant climates increases risk of extinction for species with narrow geographic or climatic distributions and disruption of existing communities. Here we analyze multimodel ensembles for the A2 and B1 emission scenarios produced for the fourth assessment report of the Intergovernmental Panel on Climate Change, with the goal of identifying regions projected to experience (i) high magnitudes of local climate change, (ii) development of novel 21st-century climates, and/or (iii) the disappearance of extant climates. Novel climates are projected to develop primarily in the tropics and subtropics, whereas disappearing climates are concentrated in tropical montane regions and the poleward portions of continents. Under the high-end A2 scenario, 12-39% and 10-48% of the Earth's terrestrial surface may respectively experience novel and disappearing climates by 2100 AD. Corresponding projections for the low-end B1 scenario are 4-20% and 4-20%. Dispersal limitations increase the risk that species will experience the loss of extant climates or the occurrence of novel climates. There is a close correspondence between regions with globally disappearing climates and previously identified biodiversity hotspots; for these regions, standard conservation solutions (e.g., assisted migration and networked reserves) may be insufficient to preserve biodiversity.
M. W. Williams, P. D. Brooks, T. Seastedt (1998). Nitrogen and carbon soil dynamics in response to climate change in a high-elevation ecosystem in the Rocky Mountains, U.S.A.. Arctic and Alpine Research 30 (1): 26-30
ABSTRACT: We have implemented a long-term snow-fence experiment at the Niwot Ridge Long-Term Ecological Research (NWT) site in the Colorado Front Range of the Rocky Mountains, U.S.A., to assess the effects of climate change on alpine ecology and biogeochemical cycles. The responses of carbon (C) and nitrogen (N) dynamics in high-elevation mountains to changes in climate are investigated by manipulating the length and duration of snow cover with the 2.6 X 60 m snow fence, providing a proxy for climate change. Results from the first year of operation in 1994 showed that the period of continuous snow cover was increased by 90 d. The deeper and earlier snowpack behind the fence insulated soils from winter air temperatures, resulting in a 9 degrees C increase in annual minimum temperature at the soil surface. The extended period of snow cover resulted in subnivial microbial activity playing a major role in annual C and N cycling. The amount of C mineralized under the snow as measured by CO2 production was 22 g m-2 in 1993 and 35 g m-2 in 1994, accounting for 20 net primary above-ground production before construction of the snow fence in 1993 and 31fashion, maximum subnivial N2 O flux increased 3-fold behind the snow fence, from 75 mg N m-2 d-1 in 1993 to 250 mg N m-2 d-1 in 1994. The amount of N lost from denitrification was greater than the annual atmospheric input of N in snowfall. Surface litter decomposition studies show that there was a significant increase in the litter mass loss under deep and early snow, with no significant change under medium and little snow conditions. Changes in climate that result in differences in snow duration, depth, and extent may therefore produce large changes in the C and N soil dynamics of alpine ecosystems.
ABSTRACT: Terrestrial ecosystems influence climate by affecting how much solar energy is absorbed by the land surface and by exchanging climatically important gases with the atmosphere. Recent model analyses show widespread qualitative agreement that terrestrial ecological processes will have a net positive feedback effect on 21st-century global warming, and, therefore, cannot be ignored in climate-change projections. However, the quantitative uncertainty in the net feedback is large. The uncertainty in 21st-century carbon dioxide emissions resulting from terrestrial carbon cycle–climate feedbacks is second in magnitude only to the uncertainty in anthropogenic emissions. We estimate that this translates into an uncertainty in global warming owing to the land surface of 1.5°C by 2100. We also emphasise the need to improve our understanding of terrestrial ecological processes that influence land–atmosphere interactions at relatively long timescales (decadal–century) as well as at shorter intervals (e.g. hourly).
ABSTRACT: Evidence from woodrat middens and tree rings at Dutch John Mountain (DJM) in northeastern Utah reveal spatiotemporal patterns of pinyon pine (Pinus edulis Engelm.) colonization and expansion in the past millennium. The DJM population, a northern outpost of pinyon, was established by long-distance dispersal (~40 km). Growth of this isolate was markedly episodic and tracked multidecadal variability in precipitation. Initial colonization occurred by AD 1246, but expansion was forestalled by catastrophic drought (1250–1288), which we speculate produced extensive mortality of Utah Juniper (Juniperus osteosperma (Torr.) Little), the dominant tree at DJM for the previous ~8700 years. Pinyon then quickly replaced juniper across DJM during a few wet decades (1330–1339 and 1368–1377). Such alternating decadal-scale droughts and pluvial events play a key role in structuring plant communities at the landscape to regional level. These decadal-length precipitation anomalies tend to be regionally coherent and can synchronize physical and biological processes across large areas. Vegetation forecast models must incorporate these temporal and geographic aspects of climate variability to accurately predict the effects of future climate change.
ABSTRACT: For more than a century it has been postulated that the Holocene vegetation of western Europe has changed in significant ways. A half-century ago a lively debate revolved on whether there were one or two dry intervals causing bogs to dry out and become forested, or whether instead the climate warmed to a maximum and then cooled. Today none of these climatic schemes is accepted without reservation, because two nonclimatic factors are recognized as significant: the differential immigration rates of dominant tree types (e.g., spruce in the north and beech in the south) brought unexpected changes in forest composition, and Neolithic man cleared the forest for agriculture and thereby disrupted the natural plant associations.
In North America some of the same problems exist. In the hardwood forests of the Northeast, which are richer than but otherwise not unlike those of western Europe, the successive spread of white pine, hemlock, beech, hickory, and chestnut into oak dominated forests provides a pollen sequence that may yield no climatic message. On the other hand, on the ecotone between these hardwood forests and the conifer forests of the Great Lakes-St. Lawrence area, the southward expansion of spruce, fir, and tamarack in the late Holocene implies a climatic cooling of regional importance, although the progressive conversion of lakes to wetlands favored the expansion of wetland forms of these genera.
In the southeastern states the late-Holocene expansion of southern pines has uncertain climatic significance. About all that can be said about the distribution and ecology of the 10 or so species is that some of them favor sandy soils and are adapted to frequent fires. In coastal areas the expansion of pines was accompanied by development of great swamps like Okefenokee and the Everglades—perhaps related to the stabilization of the water table after the early Holocene rise of sea level. The vegetation replaced by the pines in Florida consisted of oak scrub with prairie-like openings, indicating dry early Holocene conditions, which in fact had also prevailed during the time of Wisconsin glaciation.
In the Midwest the vegetation history provides a clearer record of Holocene climatic change, at least along the prairie border in Minnesota. With the withdrawal of the boreal spruce forest soon after ice retreat, pine forest and hardwood forest succeeded rapidly, as in the eastern states. But prairie was not far behind. By 7000 years ago the prairie had advanced into east-central Minnesota, 75 miles east of its present limit. It then withdrew to the west, as hardwoods expanded again, followed by conifers from the north. The sequence easily fits the paleoclimatic concept of gradual warming and drying to a maximum, followed by cooling to the present day. It is supported by independent fossil evidence from lake sediments, showing that lakes were shallow or even intermittently dry during mid-Holocene time.
Here we have a paleoclimatic pattern that is consistent with the record from glaciers in the western mountains—a record that involves a late-Holocene Neoglaciation after a mid-Holocene interval of distant glacial recession. Just as the Neoglaciation is time-transgressive, according to the review of its evidence by Porter and Denton, so also is the mid-Holocene episode of maximum warmth, and they are thus both geologic climate units. The warm episode is commonly termed the Hypsithermal, which, however, was defined by Deevey and Flint as a time-stratigraphic unit that is supposed to have time-parallel rather than time-transgressive boundaries. It was defined on the basis of pollen-zone boundaries in western Europe and the northeastern United States that have a sound biogeographic but questionable paleoclimatic basis. Perhaps it should be redefined as Porter and Denton suggest, as a geologic-climate unit with recognizable time-transgressive boundaries that match the gradual geographic shifts in the general circulation of the atmosphere and the resulting location of storm tracks and weather patterns. Holocene glacial and vegetational progressions provide a good record of climatic change, if one can work out the lag effects related to the glacial economy and the geographic factors controlling tree migration. The terminology for the Holocene, where so much time control is available, should indicate the dynamic character not only of the climate but also of the geologic and biogeographic processes controlled by climate.
ABSTRACT: Evidence from paleoclimatological research indicates that major climatic changes, such as the rapid increase in temperatures at the end of the Younger Dryas event ~11000 years ago, can occur over the span of a few decades. Vegetation response to climatic variation and change, is, by contrast, often assumed to occur gradually over much longer timescales. Two recent papers confirm earlier, theoretical predictions that changes in species composition of plant communities following climatic shifts can, however, occur with striking rapidity.
ABSTRACT: Sediments from Rapid Lake document glacial and vegetation history in the Temple Lake valley of the Wind River Range, Wyoming over the past 11,000 to 12,000 yr. Radiocarbon age determinations on basal detrital organic matter from Rapid Lake (11,770 ± 710 yr B.P.) and Temple Lake (11,400 ± 630 yr B.P.) bracket the age of the Temple Lake moraine, suggesting that the moraine formed in the late Pleistocene. This terminal Pleistocene readvance may be represented at lower elevations by the expansion of forest into intermontane basins 12,000 to 10,000 yr B.P. Vegetation in the Wind River Range responded to changing environmental conditions at the end of the Pleistocene. Following deglaciation, alpine tundra in the Temple Lake valley was replaced by aPinus albicaulis parkland by about 11,30014 C yr B.P.Picea andAbies , established by 10,60014 C yr B.P., grew withPinus albicaulis in a mixed conifer forest at and up to 100 m above Rapid Lake for most of the Holocene. Middle Holocene summer temperatures were about 1.5°C warmer than today. By about 540014 C yr B.P.Pinus albicaulis andAbies became less prominent at upper treeline because of decreased winter snowpack and higher maximum summer temperatures. The position of the modern treeline was established by 300014 C yr B.P. when Picea retreated downslope in response to Neoglacial cooling.
FIRST PARAGRAPH: With the prospect of global warming, it is interesting to look back at past climate change and its effects on vegetation. Although the greatest change in climate probably occurred during deglaciation, 12,500 to 11,000 years ago, significant climate changes have occurred more recently in the intermountain region of the western United States, the vast area in the West lying between the Sierra Nevadas and Cascades and the Rocky Mountains (Antevs 1938, Davis 1982, Mehringer and Wigand 1990). Climate changes during this period caused major shifts in plant distribution and composition throughout the region. However, rates of vegetation change during the past 120 years, primarily due to anthropogenic factors, have been unprecedented in the intermountain region (Miller et al. 1994).
ABSTRACT.—Plant macrofossil analyses of 16 radiocarbon-dated woodrat middens spanning the past 4000 years from the Wind River Canyon region in central Wyoming provide information concerning late Holocene development of juniper woodlands. The study sites are currently dominated byJuniperus osteosperma , withJ. scopulorum present locally. Woodlands in the region were dominated byJ. scopulorum from ca 4000 yr BP until at least 2800 yr BP.Juniperus osteosperma invaded and expanded before 2000 yr BP. This expansion fits a regional pattern ofJ. osteosperma colonization and expansion in north central Wyoming during a relatively dry period between 2800 and 1000 yr BP. At the time the Wind River Canyon region was colonized byJ. osteosperma , the species had populations 50–100 km to both the north and south. Long-distance seed dispersal was required for establishment in the study area. Genetic studies are necessary to identify source populations and regions.
ABSTRACT: The forests of the Siskiyou Mountains are among the most diverse in North America, yet the long-term relationship among climate, diversity, and natural disturbance is not well known. Pollen, plant macrofossils, and high-resolution charcoal data from Bolan Lake, Oregon, were analyzed to reconstruct a 17,000-yr-long environmental history of high-elevation forests in the region. In the late-glacial period, the presence of a subalpine parkland ofArtemisia , Poaceae,Pinus , andTsuga with infrequent fires suggests cool dry conditions. After 14,500 cal yr B.P., a closed forest ofAbies ,Pseudotsuga ,Tsuga , andAlnus rubra with more frequent fires developed which indicates more mesic conditions than before. An open woodland ofPinus ,Quercus , andCupressaceae , with higher fire activity than before, characterized the early Holocene and implies warmer and drier conditions than at present. In the late Holocene,Abies andPicea were more prevalent in the forest, suggesting a return to cool wet conditions, although fire-episode frequency remained relatively high. The modern forest ofAbies andPseudotsuga and the present-day fire regime developed ca. 2100 cal yr B.P. and indicates that conditions had become slightly drier than before. Sub-millennial-scale fluctuations in vegetation and fire activity suggest climatic variations during the Younger Dryas interval and within the early Holocene period. The timing of vegetation changes in the Bolan Lake record is similar to that of other sites in the Pacific Northwest and Klamath region, and indicates that local vegetation communities were responding to regional-scale climate changes. The record implies that climate-driven millennial- to centennial-scale vegetation and fire change should be considered when explaining the high floristic diversity observed at present in the Siskiyou Mountains.
Nowak, C.L., R. S. Nowak, R.J. Tausch, P.E. Wigand (1994). Tree and shrub dynamics in northwestern Great Basin woodland shrub steppe during the late-Pleistocene and Holocene. American Journal of Botany 81 (3): 265-277
ABSTRACT: During the last 12,000 to 30,000 years, a large proportion of the dominant trees and shrubs in modern assemblages of woodland and shrub steppe vegetation in the northwestern Great Basin have undergone relatively small changes in their geographic ranges. A woodland tree,Juniperus osteosperma , has an extensive temporal and spatial fossil record from 11 woodrat midden locales that were sampled in the northwestern Great Basin. Above 1,300 m elevation,J. osteosperma has been continuously present in that fossil record for at least the last 30,000 years. However,J osteosperma was lost at elevations below 1,300 m sometime during the last 10,000 years, during the Holocene. Although the elevational ranges of six shrub taxa show changes during the Holocene, geographic ranges of 11 other shrub taxa have been largely static. Of the woodland and shrub steppe species examined,Pinus monophylla has experienced the greatest change in its geographic range during the late-Pleistocene and Holocene.Pinus monophylla has migrated northward across the Great Basin from Pleistocene refugia in the southern portions of this region. The rate of latitudinal migration was more rapid along the eastern side of the Great Basin than on the western side. Thus, the species that comprise modern woodland and shrub steppe communities of the northwestern Great Basin appear to have two strategies to cope with climate change. First are species, as exemplified byJ. osteosperma , whose geographic ranges were relatively insensitive to climate change and are termed orthoselective species. High genetic variation within species and the formation of coenospecies likely allowed these species to cope with climatic change by genetic adaptation. Secondly, other species, as exemplified byP. monophylla , have experienced shifts in their geographic range during past climate changes and more clearly fit the migration model of species response to climate change.
ABSTRACT: Vegetation records spanning the past 21 kyr in western North America display spatial patterns of change that reflect the influence of variations in the large-scale controls of climate1 . Among these controls are millennial-scale variations in the seasonal cycle of insolation and the size of the ice sheet, which affect regional climates directly through changes in temperature and net radiation, and indirectly by shifting atmospheric circulation. Longer vegetation records provide an opportunity to examine the regional response to different combinations of these large-scale controls, and whether non-climatic controls are important. But most of the longer North American records2, 3 are of insufficient quality to allow a robust test, and the long European records4-9 are in regions where the vegetation response to climate is often difficult to separate from the response to ecological and anthropogenic controls. Here we present a 125-kyr record of vegetation and climate change for the forest/steppe border of the eastern Cascade Range, northwest America. Pollen data disclose alternations of forest and steppe that are consistent with variations in summer insolation and global ice-volume, and vegetational transitions correlate well with the marine isotope-stage boundaries. The close relationship between vegetation and climate beyond the Last Glacial Maximum provides evidence that climate variations are the primary cause of regional vegetation change on millennial timescales, and that non-climatic controls are secondary.
ABSTRACT: Plant macrofossils extracted from fossil woodrat (Neotoma spp.) middens at a single locale in the northwestern Great Basin were used to examine vegetation dynamics during the last 30 000 yr. Although the modern assemblage of xeric species at the study site is a recent occurrence, a large proportion of the modern plant taxa near the study locale were also found 12 000 - 30 000 yr BP. The persistence of extant species through time was likely facilitated by within-species genetic diversity and the formation of coenospecies. The diverse topographic and microhabitat features in the northwestern Great Basin also allowed different species to coexist during glacial periods. Changes in species composition occurred during two time intervals: 20 000 - 30 000 and 10 000 - 12 000 yr BP. Vegetation changes during 20 000 - 30 000 yr BP were cyclic; community composition oscillated between two groups of taxa. Vegetation changes between 10 000 - 12 000 yr BP occurred during the Pleistocene-Holocene transition and were largely directional from the Pleistocene assemblages through two transition assemblages to a Holocene assemblage. These changes in species composition generally reflect changes in climate. The presence of relatively mesic species during 10 000 - 30 000 yr BP is consistent with the regional late-Pleistocene climate, and the gradual loss of relatively mesic species during the Holocene parallels the change to a more xeric climate. Contrasted with other areas of North America and Europe, the magnitude of vegetation changes at our study area were relatively small. Furthermore, the persistence of many species through time at this site in the northwestern Great Basin also differs from results at other study sites in North America and Europe. These differences are probably related to land form characteristics and genetic diversity within species.
ABSTRACT: The 14 papers collected herein treat diverse aspects of the aquatic history of the Great Basin of the western United States and collectively attempt to summarize and integrate portions of the vast body of new information on this subject that has been acquired since the last such compilation was published in 1948. In the first section, four papers (Lowenstein, Negrini, Reheis et al., Sack) focus on the physical aspects of the Great Basin paleolake histories, whereas a fifth paper (Oviatt) summarizes the contributions to the study of Bonneville Basin lacustrine history made by two early giants of the field, Grove Karl Gilbert and Ernst Antevs. In the second section, four papers synthesize perspectives on Great Basin aquatic history provide by diatoms and ostracods (Bradbury and Forester), fishes (Smith et al.), aquatic insects (Polhemus and Polhemus), and aquatic snails (Hershler and Sada), whereas a fifth (Sada and Vinyard) summarizes the conservation status of the diverse aquatic biota that is endemic to the region. In the final section, three papers integrate terrestrial biotic evidence pertaining to Great Basin aquatic history derived from pollen from cores (Davis), floristics (Wigand and Rhode), and the mammal record (Grayson), whereas a fourth (Madsen) examines the relationship between Great Basin lakes and human inhabitants of the region. Although diverse in scope and topic, the papers in this volume are nonetheless linked by an appreciation that integration of geological, biological, and anthropological evidence is a necessary and fundamental key to a mature understanding of Great Basin aquatic systems history.
ABSTRACT: A biogeographic model, MAPSS (Mapped Atmosphere-Plant-Soil System), predicts changes in vegetation leaf area index (LAI), site water balance and runoff, as well as changes in biome boundaries. Potential scenarios of global and regional equilibrium changes in LAI and terrestrial water balance under 2 x CO2 climate from five different general circulation models (GCMs) are presented. Regional patterns of vegetation change and annual runoff are surprisingly consistent among the five GCM scenarios, given the general lack of consistency in predicted changes in regional precipitation patterns. Two factors contribute to the consistency among the GCMs of the regional ecological impacts of climatic change: (1) regional, temperature-induced increases in potential evapotranspiration (PET) tend to more than offset regional increases in precipitation; and (2) the interplay between the general circulation and the continental margins and mountain ranges produces a fairly stable pattern of regionally specific sensitivity to climatic change. Two areas exhibiting among the greatest sensitivity to drought-induced forest decline are eastern North America and eastern Europe to western Russia. Regional runoff patterns exhibit much greater spatial variation in the sign of the response than do the LAI changes, even though they are deterministically linked in the model. Uncertainties with respect to PET or vegetation water use efficiency calculations can alter the simulated sign of regional responses, but the relative responses of adjacent regions appear to be largely a function of the background climate, rather than the vagaries of the GCMs, and are intrinsic to the landscape. Thus, spatial uncertainty maps can be drawn even under the current generation of GCMs.
D. D. Breshears, N. S. Cobb, P. M. Rich, K. P. Price, C.D. Allen, R. G. Balice, W.H. Romme, J. H. Kastens, M. L. Floyd, J. Belnap, J.J. Anderson, O. B. Myers, C. W. Meyer (2005). Regional vegetation die-off in response to global-change-type drought. Proceedings of the National Academy of Sciences 102 (42): 15144-15148
ABSTRACT: Future drought is projected to occur under warmer temperature conditions as climate change progresses, referred to here as global-change-type drought, yet quantitative assessments of the triggers and potential extent of drought-induced vegetation die-off remain pivotal uncertainties in assessing climate-change impacts. Of particular concern is regional-scale mortality of overstory trees, which rapidly alters ecosystem type, associated ecosystem properties, and land surface conditions for decades. Here, we quantify regional-scale vegetation die-off across southwestern North American woodlands in 2002-2003 in response to drought and associated bark beetle infestations. At an intensively studied site within the region, we quantified that after 15 months of depleted soil water content, >90% of the dominant, overstory tree species (Pinus edulis, a piñon) died. The die-off was reflected in changes in a remotely sensed index of vegetation greenness (Normalized Difference Vegetation Index), not only at the intensively studied site but also across the region, extending over 12,000 km2 or more; aerial and field surveys confirmed the general extent of the die-off. Notably, the recent drought was warmer than the previous subcontinental drought of the 1950s. The limited, available observations suggest that die-off from the recent drought was more extensive than that from the previous drought, extending into wetter sites within the tree species' distribution. Our results quantify a trigger leading to rapid, drought-induced die-off of overstory woody plants at subcontinental scale and highlight the potential for such die-off to be more severe and extensive for future global-change-type drought under warmer conditions.
INTRODUCTION: Global change is often perceived as human-induced modifications in climate. Indeed, human activities have undeniably altered the atmosphere, and probably the climate as well (Watson et al. 1998). At the same time, most of the world's forests have also been extensively modified by human use of the land (Houghton 1994). Thus, climate and land use are two prongs of human-induced global change. The effect of these forces on forests is mediated by the organisms within forests. Consideration of climate, land use, and biological diversity is key to understanding forest response to global change.
Biological diversity refers to the variety of life at organizational levels from genotypes through biomes (Franklin 1993). The responses of ecological systems to global change reflect the organisms that are within them. While ecologists have sometimes not seen the forest for the trees, so to speak, it is also true that forests cannot be understood without knowledge of the trees and other component species. It is the responses of individual organisms that begin the cascade of ecological processes that are manifest as changes in system properties, some of which feed back to influence climate and land use (Figure 1). Beyond its role in ecosystems, biodiversity is invaluable to humans for foods, medicines, genetic information, recreation, and spiritual renewal (Pimentel et al. 1997). Thus, global changes that affect the distribution and abundance of organisms will affect future human well-being and land use, as well as, possibly, the climate.
This article serves as a primer on forest biodiversity as a key component of global change. We first synthesize current knowledge of interactions among climate, land use, and biodiversity. We then summarize the results of new analyses on the potential effects of human-induced climate change on forest biodiversity. Our models project how possible future climates may modify the distributions of environments required by various species, communities, and biomes. Current knowledge, models, and funding did not allow these analyses to examine the population processes (e.g., dispersal, regeneration) that would mediate the responses of organisms to environmental change. It was also not possible to model the important effects of land use, natural disturbance, and other factors on the response of biodiversity to climate change. Despite these limitations, the analyses discussed herein are among the most comprehensive projections of climate change effects on forest biodiversity yet conducted. We conclude with discussions of limitations, research needs, and strategies for coping with potential future global change.
ABSTRACT: An integrated program of ecosystem modeling and field studies in the mountains of the Pacific Northwest (U.S.A.) has quantified many of the ecological processes affected by climatic variability. Paleoecological and contemporary ecological data in forest ecosystems provided model parameterization and validation at broad spatial and temporal scales for tree growth, tree regeneration and treeline movement. For subalpine tree species, winter precipitation has a strong negative correlation with growth; this relationship is stronger at higher elevations and west-side sites (which have more precipitation). Temperature affects tree growth at some locations with respect to length of growing season (spring) and severity of drought at drier sites (summer). Furthermore, variable but predictable climate-growth relationships across elevation gradients suggest that tree species respond differently to climate at different locations, making a uniform response of these species to future climatic change unlikely. Multi-decadal variability in climate also affects ecosystem processes. Mountain hemlock growth at high-elevation sites is negatively correlated with winter snow depth and positively correlated with the winter Pacific Decadal Oscillation (PDO) index. At low elevations, the reverse is true. Glacier mass balance and fire severity are also linked to PDO. Rapid establishment of trees in subalpine ecosystems during this century is increasing forest cover and reducing meadow cover at many subalpine locations in the western U.S.A. and precipitation (snow depth) is a critical variable regulating conifer expansion. Lastly, modeling potential future ecosystem conditions suggests that increased climatic variability will result in increasing forest fire size and frequency, and reduced net primary productivity in drier, east-side forest ecosystems. As additional empirical data and modeling output become available, we will improve our ability to predict the effects of climatic change across a broad range of climates and mountain ecosystems in the northwestern U.S.A.
Pataki, D.E., D.S. Ellsworth, R.D. Evans, M. Gonzalez-Meler, J. King, S.W. Leavitt, G. Lin, R. Matamala, E. Pendall, R. Siegwolf, C. VanKessel, J.R. Ehleringer (2003). Tracing changes in ecosystem function under elevated carbon dioxide conditions. BioScience 53 (9): 805-818
ABSTRACT: Responses of ecosystems to elevated levels of atmospheric carbon dioxide (CO2 ) remain a critical uncertainty in global change research. Two key unknown factors are the fate of carbon newly incorporated by photosynthesis into various pools within the ecosystem and the extent to which elevated CO2 is transferred to and sequestered in pools with long turnover times. The CO2 used for enrichment in many experiments incorporates a dual isotopic tracer, in the sense that ratios of both the stable carbon-13 (13 C) and the radioactive carbon-14 (14 C) isotopes with respect to carbon-12 are different from the corresponding ratios in atmospheric CO2 . Here we review techniques for using13 C and14 C abundances to follow the fate of newly fixed carbon and to further our understanding of the turnover times of ecosystem carbon pools. We also discuss the application of nitrogen, oxygen, and hydrogen isotope analyses for tracing changes in the linkages between carbon, nitrogen, and water cycles under conditions of elevated CO2 .
ABSTRACT: This study, as many other current investigations in palaeoecology is focused on the long-term dynamics of vegetation and the extent to which they are controlled by climate change. Climate and classes of climate change are defined and reviewed, and examples cited of vegetation response. The concepts of vegetation, plant community and equilibrium are examined, with particular emphasis on theories on short term dynamics developed by ecologists working with temperate and boreal forests. Vegetation response to climate change can be modified by anthropogenic factors, topographic diversity and soils, life-cycle characteristics and hysteresis.
ABSTRACT: Selected findings from the Long Term Ecological Research (LTER) program are described in the field of biosphere–atmosphere interactions. The Palmer, Antarctic, site contributes evidence to the debate on the ecological effects of increased ultraviolet-B radiation; the ecological response to a warming trend over the past half-century has been clearly documented there. The North Temperate Lakes site in Wisconsin was the principal LTER site for an international study to document a 100-year trend of change in freeze and thaw dates of boreal lakes. A multidisciplinary approach to soil warming studies benefited from observations over decades and demonstrated the importance of initial conditions. The LTER Network permits investigation of atmosphere–ecosystem interactions over a long period encompassing storm events and quasi-periodic climate variability. LTER studies show that ecosystem dynamics often cannot be decoupled from atmospheric processes. Atmospheric processes are an integral component of the ecosystem and vice versa. Finally, we provide an example of how regionalization studies, often grounded in atmospheric data, add a spatial context to LTER sites and identify controls on ecological processes across broader environmental gradients.
INTRODUCTION: Among the many demands placed upon it, biogeography is now required to be a predictive science. An appreciation of the degree of global climatic warming over the past century has led to speculation concerning possible impacts on species, communities, ecosystems and overall global biodiversity. Ecologists, physiologists and biogeographers have made efforts to develop models that can be projected into predicted future scenarios (e.g., Peterson et al., 2002). Palaeobiogeography, in particular, has been called upon to provide a key to the future. ‘Back to the future’ has become a working methodology. But with global warming now quite well advanced, we are in a position to observe its actual biogeographic outcomes (see Walther et al., 2002) and compare these with the record of the past.
ABSTRACT: Accurate prediction of the ecological impacts of climatic change is a pressing challenge to the science of ecology. The current state of the art for broad-scale estimates of change in biomes and ecotones between biomes is limited to equilibrium estimates of ecological change under some future equilibrium climate. Uncertainties in these estimates abound, ranging from uncertainties in future climate scenarios to uncertainties in our ecological models and finally to uncertainties in modelling the feedbacks between the climate and the biosphere. Ecologists and policymakers need to go beyond equilibrium estimates of biosphere change to transient responses of the biosphere as the climate changes. Ecotones between biomes have been suggested as sensitive areas of change that could be effectively modelled and monitored for future change. Ecotones are also important in influencing local and regional biodiversity patterns and ecological flows. The ecological processes that could affect change at ecotones and within biomes are discussed; they include internal ecosystem processes, such as competition, and external abiotic processes, most notably drought and related disturbances. Drought followed by infestations and fire appears to be the most likely process that could mediate ecological change under a rapidly changing climate. The impacts would be apparent all across biomes, not just at ecotones. However, specific predictions about the dynamics of ecotones can be made qualitatively, based on a theory of patch scaling and diversity in relation to abiotic stressors. Under current conditions, the size of homogeneous patches is expected to be small at ecotones, but to enlarge with distance from the ecotone. Directional climatic change should promote a coalescence of patches on one side of the ecotone and increased fragmentation on the other side. Ecotones should begin to blur as viewed from a satellite only to re-form at some later date in a new location. This view is in contrast to the notion that ecotones would retain sharp distinction and simply move across the landscape. These changes are presented as hypotheses based on theory and should be testable in a mechanistic modeling framework that is only now being developed.
PREFACE: The impetus for the workshop that resulted in this book was the deliberations in many national and international forums about the research areas to be addressed in a decade-long international programme to study global environmental change. At the request of the Executive Committee of ICSU's Scientific Committee on Problems of the Environment (SCOPE), the US National Committee for SCOPE of the US National Research Council (NRC) began discussions to organize an international workshop intended to identify the contributions to the upcoming International Geosphere-Biosphere Programme: A Study of Global Change (IGBP) that could be made by biological and physical scientists working together. Discussions with a number of scientists led to the consensus that a useful focus for the workshop would be on an issue of extreme concern in conducting the interdisciplinary research required to understand the processes controlling the global environment-how to overcome the disparities in spatial and temporal scales used in different scientific disciplines. The transfer of information between these disciplines is severely constrained by disparities in scale. Thus, a workshop to identify the research needed to deal meaningfully with these scaling problems and with the spatial and temporal variability in biospheric and geospheric processes was organized.
To carry out the organization of the workshop and the identification of participants, an international Steering Committee was formed under the chairmanship of R. G. Woodmansee with T. Rosswall and P. G. Risser serving as co-chairmen. This committee included representatives of SCOPE, ICSU's International Association for Ecology (INTECOL), and members of the US National Committee for SCOPE and its parent body, the Environmental Studies Board of the US NRC. A mix of ecologists, other biological scientists, atmospheric scientists, geomorphologists, and marine scientists from 17 countries were invited to participate.
At the workshop, participants met in a plenary session and in working groups to explore the research needs for understanding interactions between the atmospheric, aquatic, and terrestrial components of the biosphere at different scales. A report authored by P. G. Risser (Risser, 1986) describes the research priorities identified for dealing with the scaling problems and for possible inclusion in the research agenda for a programme on global change. Papers presented at the workshop are published herein.
The workshop was organized with the intention that it be one of several planning efforts toward the elucidation of research priorities for an International Geosphere-Biosphere Programme. We look forward to further discussion and refinement of the topics outlined in Risser (1986) and this volume, as well as other research approaches, in other international forums.
The Steering Committee and the workshop participants wish to acknowledge with gratitude the financial support for the workshop from the US National Aeronautics and Space Administration, the US National Science Foundation, the US Department of Energy, ICSU, and SCOPE. Ruth DeFries, of the US NRC, was especially helpful in all aspects of the workshop, and her invaluable assistance was appreciated by all the participants. Joële Dallancon of SCOPE provided excellent logistical support during the workshop.
We also wish to acknowledge the previous efforts of our colleagues in setting forth the broad perspectives and challenges of the International Geosphere-Biosphere Programme: A Study of Global Change. These efforts stimulated and assisted the deliberations of the workshop. We also thank the many reviewers of papers contained in this volume.
ABSTRACT: There is now ample evidence that these recent climatic changes have affected a broad range of organisms with diverse geographical distributions. We assess these observations using a process-oriented approach and present an integrated synopsis across the major taxonomic groups, covering most of the biomes on Earth. We focus on the consequences of thirty years of warming at the end of the twentieth century, and review the responses in (1) the phenology and physiology of organisms, (2) the range and distribution of species, (3) the composition of and interactions within communities, and (4) the structure and dynamics of ecosystems, highlighting common and contrasting features amongst the taxa and systems considered.
ABSTRACT: Meteorologists and climatologists have produced significant new data on the fluid dynamics of the atmosphere, thus allowing biologists to examine more closely the cause-effect relation between the large-scale structure of the atmosphere and the dominant patterns of global biogeography. The inability to characterize the high-frequency variability of the weather has constrained such efforts. A method that allows year-to-year patterns of weather variability to be characterized in the contexts of global warming and cooling trends is applied in a combined analysis of long-term monthly weather records and data from an ecological monitoring project in southern New Mexico. The analysis suggests a cause-effect hypothesis of recent desertification in the North American Southwest. The links between the atmosphere and the biosphere are based on the fundamentally different responses to specific weather regimes of semidesert grasses with a C4 photosynthetic pathway and desert shrubs with a C3 photosynthetic pathway. The hypothesis appears to be of sufficient generality to explain the complex, but well-documented, floristic changes that have occurred in the same region since the last glacial maximum.
ABSTRACT: Causal attribution of recent biological trends to climate change is complicated because non-climatic influences dominate local, short-term biological changes. Any underlying signal from climate change is likely to be revealed by analyses that seek systematic trends across diverse species and geographic regions; however, debates within the Intergovernmental Panel on Climate Change (IPCC) reveal several definitions of a 'systematic trend'. Here, we explore these differences, apply diverse analyses to more than 1,700 species, and show that recent biological trends match climate change predictions. Global meta-analyses documented significant range shifts averaging 6.1 km per decade towards the poles (or metres per decade upward), and significant mean advancement of spring events by 2.3 days per decade. We define a diagnostic fingerprint of temporal and spatial 'sign-switching' responses uniquely predicted by twentieth century climate trends. Among appropriate long-term/large-scale/multi-species data sets, this diagnostic fingerprint was found for 279 species. This suite of analyses generates 'very high confidence' (as laid down by the IPCC) that climate change is already affecting living systems.
ABSTRACT: There is an increasing consensus that global climate change occurs and that potential changes in climate are likely to have important regional consequences for biota and ecosystems. Ecological restoration, including (re)afforestation and rehabilitation of degraded land, is included in the array of potential human responses to climate change. However, the implications of climate change for the broader practice of ecological restoration must be considered. In particular, the usefulness of historical ecosystem conditions as targets and references must be set against the likelihood that restoring these historic ecosystems is unlikely to be easy, or even possible, in the changed biophysical conditions of the future. We suggest that more consideration and debate needs to be directed at the implications of climate change for restoration practice.
Baron, J. S., Julius, S. H., West, J. M., Joyce, L. A., Blate, G. M., Peterson, C. H., Palmer, M. A., Keller, B. D., Kareiva, P., Scott, J. M., Griffith, B. (2008). Some guidelines for helping natural resources adapt to climate change. IHDP update 2: 46-52
DESCRIPTION; The changes occurring in mountain regions are an epitome of climate change. The dramatic shrinkage of major glaciers over the past century - and especially in the last 30 years - is one of several iconic images that have come to symbolize climate change.
ABSTRACT: Much research focuses on how the terrestrial biosphere influences climate through changes in surface albedo (reflectivity), stomatal conductance and leaf area index (LAI). By using a fully-coupled GCM (HadCM3LC), our research objective was to induce an increase in the growth of global vegetation to isolate the effect of increased LAI on atmospheric exchange of heat and moisture. Our Control simulation had a mean global net primary production (NPP) of 56.3 Gt Cyr−1 which is half that of our scenario value of 115.1 GtCyr−1 . LAI and latent energy (QE ) were simulated to increase globally, except in areas around Antarctica. A highly productive biosphere promotes mid-latitude mean surface cooling of ~2.5°C in the summer, and surface warming of ~1.0°C in the winter. The former response is primarily the result of reduced Bowen ratio (i.e. increased production of QE ) in combination with small increases in planetary albedo. Response in winter temperature is likely due to decreased planetary albedo that in turn permits a greater amount of solar radiation to reach the Earth’s surface. Energy balance calculations show that between 75° and 90°N latitude, an additional 2.4 Wm−2 of surface heat must be advected into the region to maintain energy balance, and ultimately causes high northern latitudes to warm by up to 3°C. We postulate that large increases in QE promoted by increased growth of terrestrial vegetation could contribute to greater surface-to-atmosphere exchange and convection. Our high growth simulation shows that convective rainfall substantially increases across three latitudinal bands relative to Control; in the tropics, across the monsoonal belt, and in mid-latitude temperate regions. Our theoretical research has implications for applied climatology; in the modeling of past “hot-house” climates, in explaining the greening of northern latitudes in modern-day times, and for predicting future changes in surface temperature with continued increases in atmospheric CO2 .
Deustch, C. A., Tewksbury, J. J., Huey, R. B., Sheldon, K. S., Ghalambor, C. K., Haak, D. C., Martin, P. R. (2008). Impacts of climate warming on terrestrial ectotherms across latitude. Proceedings of the National Academy of Sciences 105 (18): 6668-6672
ABSTRACT: The impact of anthropogenic climate change on terrestrial organisms is often predicted to increase with latitude, in parallel with the rate of warming. Yet the biological impact of rising temperatures also depends on the physiological sensitivity of organisms to temperature change. We integrate empirical fitness curves describing the thermal tolerance of terrestrial insects from around the world with the projected geographic distribution of climate change for the next century to estimate the direct impact of warming on insect fitness across latitude. The results show that warming in the tropics, although relatively small in magnitude, is likely to have the most deleterious consequences because tropical insects are relatively sensitive to temperature change and are currently living very close to their optimal temperature. In contrast, species at higher latitudes have broader thermal tolerance and are living in climates that are currently cooler than their physiological optima, so that warming may even enhance their fitness. Available thermal tolerance data for several vertebrate taxa exhibit similar patterns, suggesting that these results are general for terrestrial ectotherms. Our analyses imply that, in the absence of ameliorating factors such as migration and adaptation, the greatest extinction risks from global warming may be in the tropics, where biological diversity is also greatest.
ABSTRACT: Accumulating evidence points to an anthropogenic ‘fingerprint’ on the global climate change that has occurred in the last century. Climate change has, and will continue to have, profound effects on the structure and function of terrestrial ecosystems. As such, there is a critical need to continue to develop a sound scientific basis for national and international policies regulating carbon sequestration and greenhouse gas emissions. This paper reflects on the nature of current global change experiments, and provides recommendations for a unified multidisciplinary approach to future research in this dynamic field. These recommendations include: (1) better integration between experiments and models, and amongst experimental, monitoring, and space-for-time studies; (2) stable and increased support for long-term studies and multi-factor experiments; (3) explicit inclusion of biodiversity, disturbance, and extreme events in experiments and models; (4) consideration of timing vs intensity of global change factors in experiments and models; (5) evaluation of potential thresholds or ecosystem ‘tipping points’; and (6) increased support for model–model and model–experiment comparisons. These recommendations, which reflect discussions within the TERACC international network of global change scientists, will facilitate the unraveling of the complex direct and indirect effects of global climate change on terrestrial ecosystems and their components.