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Abstract

Little is known about the disturbance history of low-elevation forest and steppe vegetation in the western United States, nor about the relative importance of climate and human activity in shaping present-day plant communities. We analyzed pollen and high-resolution macroscopic charcoal records spanning the last 2100, 1000, and 550 cal years from 3 small lakes in Jackson Hole, Wyoming, to reconstruct the vegetation and fire history along a gradient from steppe to dry forest. The pollen data suggest little change in vegetation in the last 2 millennia, aside from a long-term trend toward more forest at the expense of steppe. One site showed an expansion of mesophytic taxa in the last 350 years as a result of local changes in hydrology, and another site was dry prior to AD 1000 and showed fluctuations in steppe composition thereafter. The longest record suggests that fire frequency was higher before AD 1200 than after. Comparison of 3 charcoal records for the last 550 years indicates widespread fire episodes in AD 1980–2000, 1780–1810, ca. 1550, and 1420–1430. Changes in the vegetation and fire history of the last 2000 years show a response to effectively drier conditions prior to AD 1200 and wetter conditions during the Little Ice Age. Evidence of human influences was muted at best. Native Americans apparently did not alter the vegetation and fire regimes significantly during their occupation of Jackson Hole. Euro-American activities also had minor registration in the paleoecologic record: humans may have been directly responsible for fires in the mid- and late 19th century and indirectly responsible for the recent expansion of forest at the end of the 20th century.

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