FUTURE CLIMATE IN THE YELLOWSTONE-NATIONAL-PARK REGION AND ITS POTENTIAL IMPACT ON VEGETATION

Biotic responses to future changes in global climate are difficult to project for a particular region because the responses involve processe s that operate at many spatial scales. This difficulty is exacerbated in mountainous regions, where future vegetation changes are often port rayed as simple upward displacements of vegetation zones in response t o warming. We examine the scope of future responses that may occur in a mountainous area by illustrating the potential distributions of sele cted tree taxa in the region of Yellowstone National Park. The output of a coarse-resolution climate model that incorporated a doubling of c arbon dioxide concentration in the atmosphere was interpolated onto a 5-minute grid of topographically adjusted climate data. The output was also used as input into statistical relationships between the occurre nce of individual taxa and climate. The simulated vegetation changes i nclude a combination of elevational and directional range adjustments. The range of high-elevation species decreases, and some species becom e regionally extirpated. The new communities have no analogue in the p resent-day vegetation because they mix low-elevation montane species c urrently in the region with extralocal species from the northern and c entral Rocky Mountains and Pacific Northwest. The projected climate ch anges within the Yellowstone region and the individualism displayed by species in their potential range adjustments are equal or greater tha n the changes seen in the paleoecologic record during previous warming intervals. Although the results support conservation strategies that include habitat connectivity, the magnitude of the changes may exceed the ability of species to adjust their ranges. The predicted patterns call into question the adequacy of current management objectives to co pe with the scope of future changes.