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Yellowstone National Park Report

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The paleoecologic record provides unique insights into the response of coinmunities to environmental perturbations of different duration and intensity. Climate is a primary agent of environmental change and its long-term effect on the vegetation of the Yellowstone region is revealed in a network of pollen records. Fire frequency is controlled by climate, and as climate changes so too does the importance of fire in shaping and maintaining spatia\l patterns of vegetation. The prehistoric record of Yellowstone's northern range, for example, shows the response of vegetation to an absence of major fires in the last 150 years (Whitlock et al. 1991; Engstrom et al. 1991). In longer records spanning the last 14,000 year8, periods of frequent fires are suggested • by sediments containing high percentages of fire-adapted trees and high amounts of charcoal (Bamosky et al. 1987).