FIRE FREQUENCY DURING THE LAST MILLENNIUM IN THE GRINNELL GLACIER AND SWIFTCURRENT VALLEY DRAINAGE BASINS, GLACIER NATIONAL PARK, MONTANA

The relationships between fire, climate and vegetation under changing climatic conditions are important to understand, in part because fire frequency in the western United States has significantly increased in the past three decades. We examined the top two meters of a sediment core taken from Swiftcurrent Lake, eastern Glacier National Park, Montana, with the goal of using variability in charcoal flux as a proxy for fire history in the Grinnell Glacier and Swiftcurrent Valley drainage basins. Previous work suggests that an increase in fire-frequency occurred in the western United States over the last few centuries, and because this core site has a higher sedimentation rate compared to previous work in Swiftcurrent Lake, the fire record should be more finely resolved. A preliminary age model suggests that the core represents the last ~1700 years of sedimentation, with an average sedimentation rate of 1.2 mm/yr. Charcoal accumulation rates (CHAR) range from 0 to 72 grains cm-2 yr-1. The 1700-year fire record shows a higher number of fire events than previously found in a nearby, upvalley core. The fire return interval of the northern Swiftcurrent subbasin is roughly 46 years between fires, whereas the southern subbasin had an average return interval of 363 years between fires. The lower charcoal accumulation rates in the southern sub-basin could be due to two large upstream lakes (Lake Josephine and Lower Grinnell Lake) that serve as sediment sinks in the watershed, or the larger basin accumulation area in the southern subbasin. This shorter, more detailed record provides a new evaluation of the fire record of the Swiftcurrent Lake drainage basin and provides insights into fire return intervals in Glacier National Park.