A RECONSTRUCTION OF FOREST FIRES FROM JENNY LAKE, GRAND TETON NATIONAL PARK, WYOMING

Forest fire activity is closely linked with changes in climate; therefore, the interaction between climate and fire activity needs to be understood on longer timescales. Here, we present a 14,400 year-long sediment-charcoal record from Jenny Lake in Grand Teton National Park, WY. We counted the abundance of charcoal from two size fractions, 125-250 μm and >250 μm, at 2 to 4 cm intervals across the core and use radiocarbon analysis on terrestrial macrofossils to establish age control and to calculate charcoal accumulation rates. We compared these results with pollen records from Hendrick Pond, located only 11 km from Jenny Lake in Jackson Hole, to determine how Holocene climate variability and vegetation dynamics affect fire regimes.

We find that there was sparse fire activity during the late-glacial and early Holocene, when sub-alpine and alpine herb and shrub taxa such as Picea and Artemisia were present. An increase in biomass burning at 9,500 cal yr BP coincides with establishment of conifers (Juniperus) and birch trees (Betula) between 10,500 and 9,500 cal yr BP. Further establishment of Pinus Contorta and Pseudotsuga occurred between 9,000 and 7,000 cal yr BP. Afterward, fire activity slowed briefly until the middle Holocene, which shows periods of Intense burning ~ 4500 cal yr BP. Picea and Abies became more dominant towards the present, while the fire tolerant Pseudotsuga became less prevalent in the modern forest. Following this peak, fire activity gradually decreased with the establishment of the modern forest. Together, this study provides an insight into the relationship between vegetation, climate, and fire activity in alpine regions of the western US.