Potential Changes in the Distributions of Western North America Tree and Shrub Taxa under Future Climate Scenarios .
Sarah L. Shafer, Patrick J. Bartlein, and Robert S. Thompson (2001).
Ecosystems-and-nbsp; 4:200-215.

Abstract:-and-nbsp; Increases in atmospheric greenhouse gases are driving significant changes in global climate.-and-nbsp; In order to project potential vegetation response to future climate change, this study uses response surfaces to describe the relationship between bioclimatic variables and the distribution of tree and shrub taxa in western North America.-and-nbsp; The response surfaces illustrate the probability of occurrence of a taxon at particular points in climate space.-and-nbsp; Climate space was defined using three bioclimatic variables: mean temperature of the coldest month, growing degree days, and a moisture index.-and-nbsp; Species distributions were simulated under present climate, using observed data (1951-1980, 30-yr mean), and under future climate (2090-2099, 10-yr mean), using scenarios generated by three general circulation models: HADCM2, CGCM1, and CSIRO.-and-nbsp; The scenarios assume a 1% per year compound increase in greenhouse gases and changes in SO₄ aerosols based on the IPCC IS92a scenario.-and-nbsp; The results indicate that for many tree and shrub taxa potential range changes under future climate conditions could be large.-and-nbsp; Shifts in the potential ranges of species are simulated to occur not only northward but in all directions, including southward of the existing ranges of certain species.-and-nbsp; The simulated potential distributions of some species become increasingly fragmented under the future climate scenarios, while the simulated potential distributions of other species expand.-and-nbsp; The magnitudes of the simulated range changes imply significant impacts to ecosystems and shifts in patterns of species diversity in western North America.