FIRE AND ECOLOGICAL IMPACTS OF ISLAND LAKE, WYOMING: A MULTI-PROXY APPROACH

Multi-proxy reconstructions are imperative to understanding landscape-lake interactions and ecological response to climate. This study combines analysis of dendrochronology, macroscopic charcoal, and fossil diatom assemblages to reconstruct fire response in an alpine lake over the Holocene. Within Shoshone National Forest, four forest plots of different elevation and forest type were selected with the purpose of examining historic fire frequency, seasonality, extent, effects of fire on stand establishment, and relationship of fire events to climatic conditions. Diatom assemblage and charcoal accumulation rate (CHAR) were analyzed for a sediment core from Island Lake, Wyoming. The overlapping records were compared to assess lake response to fire events and climate.

Fire history of the Beartooth Mountains identified infrequent broader scale fires with isolated stand mortality and post-fire cohort establishment. Small, low severity fires were found more frequently in the lower elevation mixed-conifer forests. Two wildfires of higher severity were able to traverse an elevation and forest type gradient. Two fire event years (1900 and 1747) are manifested in the lake record as increased charcoal accumulation and changes in the diatom assemblages in response to inferred increases in the convective mixing depth, decreases in water clarity, and decreases in productivity. The bottom of the Island Lake core (7400-6150 YBP) is dominated by benthic and tychoplanktic species along with Lindavia rossii, indicating moderate mixing depth, highly transparent, and oligotrophic conditions. This is followed by a 1000-year transition period dominated by tychoplankton, indicating warmer conditions with earlier ice off and potentially lower lake level. The majority of the record (6000 to 0 YBP), which is dominated by Aulacoseira, indicates a deep lake with strong mixing. The system recently underwent a dramatic shift to dominance by Pseudostaurosira brevistriata and Staurosirella pinnata, indicative of modern warming.