Paper No. 11
Presentation Time: 4:00 PM
A 13,000 YR FIRE HISTORY AT SWIFTCURRENT LAKE, GLACIER NATIONAL PARK, MONTANA, USA
MACGREGOR, Kelly, Geology, Macalester College, 1600 Grand Avenue, St. Paul, MN 55105, KUTVIRT, Jacqueline, Geology, Macalester College, St. Paul, MN 55105, MYRBO, Amy, LacCore/CSDCO, Department of Earth Sciences, University of Minnesota, 500 Pillsbury Dr. SE, Minneapolis, MN 55455, RIIHIMAKI, Catherine A., Biology Department, Drew University, 36 Madison Ave, Madison, NJ 07940, BRADY, Kristina, LacCore, University of Minnesota, 500 Pillsbury Dr SE, Minneapolis, MN 55455 and LOCATELLI, Emma Rose, Geology and Geophysics, Yale University, Kline Geology Laboratory, 210 Whitney Ave, New Haven, CT 06511, macgregor@macalester.edu
Variability in fire activity, a proxy for aridity and paleoecological change, is important to quantify in the northern Rocky Mountains (NRM) because the region is sensitive to climate change. Fire activity in the Western US has been linked to vegetation dynamics (e.g., available biomass, adaptive fire regimes), seasonality (e.g., precipitation and temperature extremes) and regional climate changes. Using a high-resolution charcoal stratigraphy from a sediment core, we reconstruct a ~13,000 yr long fire history from Swiftcurrent Lake, located on the eastern side of the Continental Divide in the high elevation (1490 m), subalpine landscape of Glacier National Park, Montana. Our record shows distinct temporal patterns in fire activity and highlights how localized climate changes are in the topographically complex NRM.
We analyzed the record using CharAnalysis. Preliminary results show very low fire activity from the beginning of the record at ~13,000 yr BP to 7630 yr BP (Mazama ash unit). Fire activity increased between 7630 yr BP and ~3600 yr BP. At 3600 yr BP, fire activity increased and stayed high until ~2100 yr BP. Fire frequency decreased between 2100 yr BP and the present with particularly low levels between ~650 yr BP and ~300 yr BP. In the last 150 yrs, background levels of fire activity increased, with a charcoal peak associated with the historic Heavens Peak Fire of 1936 AD.
Mean fire return interval, a strong indicator of vegetative regimes, was long (~800 years) during late Pleistocene and early to mid-Holocene, and shortened to ~100 years at around 3600 yr BP. This shift is consistent with increased climatic variability and seasonality observed at similar NRM western sites. Pollen analysis is currently being conducted in order to confirm vegetation changes indicated by the shift in fire regime from late Pleistocene-early Holocene to the middle Holocene at Swiftcurrent Lake.
