HOLOCENE FIRE HISTORY AND GEOMORPHIC RESPONSE IN EASTERN GLACIER NATIONAL PARK, MONTANA, USA

Recent work suggests fires have a significant impact on hillslope processes post-fire, but few millennial-scale records of fire history have also examined concurrent geomorphic signature of fires in lake cores, particularly in alpine landscapes. A ~13,000 year long lake core from Swiftcurrent Lake, eastern Glacier National Park, Montana shows that fire frequency was <1 fire/ka during the late Pleistocene, with an increase at the end of the Younger Dryas coincident with an increase in xeric (arid-loving) pollen ratios. Fire frequency increased over the Holocene, coincident with a rise in arboreal taxa. Fire return intervals are at their highest (6-9 fires/ka) between 3.5 and 1.5 ka, coincident with increased grain size and terrestrial carbon inputs into the lake, reflecting enhanced hillslope activity. Peaks in fire return interval coincide with the peak and termination of glacial events and often an increase in xeric taxa, suggesting glacial periods in the area are broadly coincident with dry conditions. After a decrease during the Medieval Climactic Anomaly, fire frequency has increased in the past ~900 years, and is currently near Holocene peak values of ~9 fires/1000 years.