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Biodiversity and Climate Change
Preparer: Patricia N. Manley, Sierra Nevada Research Center, Pacific Southwest Research Station
Newer (2012) version of this paper is available here.
Biological diversity is essential to maintaining ecosystem processes and services. Climate change poses a significant threat to biological diversity (Parmesan and Yohe 2003). Before climate change became a credible threat, biological diversity was considered at risk at regional to global scales in response to many human stressors, land use in particular. Losses of biological diversity over the past 100 years are historically unprecedented, thus climate change represents an additional source of stress on an already at-risk pillar of ecosystem sustainability. Temperature and precipitation are predicted to change, and many questions exist about the challenges that these climate changes may pose to biological diversity. Some research suggests that climate change poses an even greater threat to biological diversity than land use (Sala et al. 2000, Thomas et al. 2004). Species respond to environmental change based on their habitat needs, competitive abilities, and physiological tolerances. Although increases in richness are predicted for some areas (cool areas that are predicted to warm) (Curie 2001), overall biological diversity is expected to decline precipitously. Cumulative effects of climate change and land use are difficult to assess.
Global and regional climate models project climate warming, particularly average summer temperatures, and increased variability in precipitation amount, timing, and form (rain vs. snow). In addition, projected increases in nitrogen and carbon dioxide (CO2) will have different effects on different species. Climate change will have the greatest proportional effects on biodiversity in biomes with extreme climates. In other words, the changes expected – temperature, nitrogen, precipitation, and atmospheric CO2–are likely to have the greatest proportional effect in areas where these elements are most limiting (Sala et al. 2000). Higher latitudes and elevations are where these primary effects are expected to be most marked (Currie 2001, Root et al. 2003, Hampe and Petit 2005). Secondary effects of biotic exchange will affect areas that have lower diversity and higher isolation, such as Mediterranean and grassland ecosystems (Sala et al. 2000).
The most significant effects of climate change on biological diversity are expected to be in response to increases in summer temperatures (Currie 2001). Theoretically, ecological communities could move up in elevation and latitude (Walther et al. 2002); however, successful migrations will depend on the rate of climate change relative to essential habitat needs and key community interactions. More likely is that existing communities will become decoupled, with some species able to track favorable climate envelopes, while others will lag behind (Midgley et al. 2002). Species most at risk of climate change are those with small geographic ranges (e.g., local endemics), narrow physiological tolerances, limited dispersal abilities, stenotypic habitat associations, strong interspecific dependencies, low genetic diversity, and those that have recently experienced population declines (Midgley et al. 2002). The likely result will be the extinction of many species, reduced biological diversity, and changes in the composition of remaining communities. Temperature changes alone are expected to result in the extinction of a minimum of 18 to 24 percent of all species by 2050 (Thomas et al. 2004).
Resulting communities are expected to reflect species able to profit by altered climatic conditions, the invasibility of original communities, and the energetic limits imposed by climatic conditions (Currie 2001). Mediterranean and grassland ecosystems are expected to be particularly vulnerable to invasion because of their moderate diversity and relative ecological isolation, whereas northern temperate forests have relatively low vulnerability (Sala et al. 2000). Reductions in biological diversity in existing communities are likely to diminish the ecosystem services and resilience of those communities to environmental stressors by reducing their functional redundancy (Kremen 2005, Loreau et al. 2001, Reich et al. 2004).
Major uncertainties remain regarding the fate of biological diversity and what options exist for adaptation and mitigation (Thomas et al. 2004). Species extinctions are expected to lag behind climate changes, particularly in longer lived species. The composite effects of climate change and land use are unknown, and at worst could be multiplicative. It is also difficult to predict the competitive and adaptive abilities of species in areas with no current ecological analog. Finally, effects on the genetic diversity and adaptability of species are likely to be significant (Hampe and Petit 2005) but largely are unknown (Parmesan and Yohe 2003).
Options for Management
- Identify ecoregions and communities most at risk and develop landscape design options for maximizing the ability of species to persist and disperse and communities to retain similar compositional structures.
- Evaluate the adequacy of current management indicators (e.g., species, guilds, habitat measures) in informing ecological changes and risks to biodiversity associated with climate change, and determine how they may need to be revised to improve their performance and the management responses they may invoke.
- Evaluate ecological risks and management options along major ecological transition zones within and between ecoregions to conserve important strongholds of at-risk species and communities.
- Develop biodiversity conservation opportunity and risk maps at forest and ecoregional scales that can be used to inform management about the location, vulnerabilities, and management recommendations for ecologically significant areas expected to be sensitive to climate change. For example, identify primary corridors that would facilitate latitudinal and elevational migrations of the majority of native species.
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The following topic papers are on the Climate Change Resource Center Web site (http://www.fs.fed.us/ccrc):
"Wildlife—Mammals," Wildlife—Birds," "Aquatic Ecosystems," Water Supply and Water Quality," and "Amphibians and Reptiles."
The Grinnell Resurvey Project at the Museum of Vertebrate Zoology, University of California, Berkeley is gathering information on changes in species composition across an elevational gradient in California from the early 20th century to present: http://mvz.berkeley.edu/Grinnell/index.html
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Manley, P. 2008. Biodiversity and Climate Change. (May 20, 2008). U.S. Department of Agriculture, Forest Service, Climate Change Resource Center. http://www.fs.fed.us/ccrc/topics/biodiversity.shtml