Biodiversity in US Forests under Global Climate Change

There is increasing evidence that humans are altering the climate of the Earth (Watson and others 1997; Kerr 2000). Among the challenges to scientists concerned with climate change are predicting the consequences of global climate change and evaluating strategies for mitigating the negative effects of these changes. To date, biodiversity has not been well integrated into global change studies. Biodiversity refers to the “species, genetic and ecosystem diversity in an area” (Swingland 2000). We believe that biodiversity is highly relevant to both understanding global change and valuing its consequences. The diversity of organisms on the Earth provide a plethora of goods and services to humans, including foods, medicines, ecological services, and spiritual well-being (Pimental and others 1997). Biodiversity also influences how ecological systems respond to climate change. The responses of individual organisms to climate begins the cascade of ecological processes that are manifest as changes across landscapes, biomes, and the globe. The dynamics initiated by organisms often provide feedbacks to the atmosphere and oceans and further modify climate. Thus, the consideration of biodiversity is important for understanding ecological response to global change, predicting future responses, valuing these changes for humans, and designing strategies to mitigate negative effects. The following four papers project the potential responses of species, communities, and biomes to the changes in climate predicted under an anthropogenic doubling of atmospheric carbon dioxide (CO2) by general circulation models (GCM). They focus on the forest vegetation in the conterminous United States as reflected by changes in the distribution of biomes, community types, and tree species. Species richness of trees and terrestrial vertebrates is also analyzed. The studies were done within the context of the Forest Sector of the National Assessment of Climate Change and Variability (http://www.nacc.usgcrp.gov). Predictions about climate change vary among the several GCM that have been developed. Climate scenarios from both the older equilibrium and newer transient GCM simulations (McNulty and Aber 2001) were used to drive the biodiversity analyses reported in these papers. We put greater confidence in biodiversity outcomes that were in agreement under several climate scenarios. Disagreement among biodiversity predictions was taken as an indication of uncertainty either in the predictions of the climate or biodiversity models. Thus, the authors report major findings where most of the models agree but also point out certain areas of disagreement. The suite of papers uses three approaches to project climate change effects on forest diversity. The opening paper by Bachelet and others (2001) uses the biogeography models MAPSS and MC1 to project the potential distributions of plant biome types under climate change. These models determine leaf area based on climate, available soil water, and atmospheric CO2. Biomes are determined by rules that consider climatic thresholds and leaf area of trees, shrubs, and grasses. Wildfire is simulated internally by these models. Potential distributions of individual tree species are simulated by Iverson and Prassad (2001) and Shafer and others (2001) using statistical models. Current relationReceived: 12 May 2000; Accepted: 5 January 2001 *Corresponding author; e-mail: hansen@montana.edu Ecosystems (2001) 4: 161–163 DOI: 10.1007/s10021–001–0001-8 ECOSYSTEMS