Fire and vegetation history of the last 2000 years in Jackson Hole, Grand Teton National Park, Wyoming

Abstract

Fire is an important natural disturbance in the western U.S., and information on how fire occurrence has varied in the past is critical to understanding modern ecosystem processes and their link to climate change. Long-term fire and vegetation histories are obtained from charcoal and pollen records preserved in lake sediments. Most charcoalbased fire-history studies have been conducted in middle- and high-elevation forest ecosystems, where glacial and other natural lakes are abundant. We have almost no information on the long-term fire history of low-elevation forest and steppe. The last 2000 years is of particular interest because it encompasses both human-induced and natural environmental change. Pollen and high-resolution macroscopic charcoal records obtained from three lakes in Jackson Hole were studied to reconstruct the vegetation and fire history over the last 2000 years in low-elevation ecosystems.

The influence of centennial-scale climate change on fire regimes was evident in the charcoal records. During the relatively dry Medieval Climate Anomaly (ca. AD 800-1300), charcoal accumulation rates decreased at a site located near the forest/steppe ecotone, which suggests that forests may have been fuel-limited and experienced fewer fires than at present. During the Little Ice Age (ca. AD 1500-1900), charcoal accumulation rates decreased at a site in lodgepole pine forest and increased at a site in sagebrush steppe, suggesting forest fuels were too wet to burn, but on the steppe combustible fine fuels increased. Euro-American settlement is also evident as a decrease in pine pollen percentages after ca. AD 1900 due to forest clearance.