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

Forest fire activity is closely linked with climate change; therefore, the interaction between climate and fire activity needs to be understood on longer timescales. Here, we present a 13,900 year- long sediment-charcoal record from Jenny Lake in Grand Teton National Park (GTNP), Wyoming. We counted the abundance of charcoal across the core and use radiocarbon analysis on terrestrial macrofossils to establish age control. We identified charcoal peaks and calculated charcoal accumulation rates using the CharAnalysis code to infer the timing of local fire events at centennial to millennial timescales. To investigate how Holocene climate variability and vegetation dynamics affected fire regimes around Jenny Lake, we compared our results with a pollen record from Hedrick Pond and a lake-level reconstruction from Lake of the Woods in northwest Wyoming.

We find that there was low charcoal accumulation and sparse fire activity prior to 11,500 cal yr BP when alpine and sub-alpine herb and shrub taxa such as Picea and Artemisia occupied the Jenny Lake catchment. An increase in fire activity that began at 11,000 cal yr BP was accompanied by establishment of fire tolerant conifers Pinus Contorta and Pseudotsuga. Charcoal deposition decreased between 8,500 to 7,000 cal yr BP and later increased and attained the highest levels by 4,000 cal yr BP. Fire activity gradually decreased after 4,000 cal yr BP as the modern forest of Picea, Abies, and Pinus was established. Interestingly, periods of enhanced charcoal deposition coincide with relatively high lake-levels and wetter conditions on millennial time scales. Therefore, we hypothesize that millennial variations in fire activity over the Holocene were controlled in part by terrestrial biomass abundance and fuel availability limitations. Together, this study provides insights into the relationship between vegetation, climate, and fire activity in an alpine region of the western US.