FIRE AND VEGETATION VARIATIONS OF THE LAST 4000 YEARS IN NORTHWESTERN MONTANA

Foy Lake, in northwestern Montana, provides a record of annual-to-decadal-scale landscape change for the last 3800 years. Sedimentary charcoal and pollen analyses were used to document fire and vegetation changes of the last 140 years and compare them with those of the late Holocene. The 1910 fires burned over two million acres in Idaho and Montana and charcoal from these extralocal fires was present at Foy Lake. No fire events occurred in the watershed during the last 100 years. The pollen record indicates an increase in shrubs and grasses from 1895 to 1960 as a result of vegetation changes associated with timber harvesting and livestock grazing. During the last three decades, the effects of fire suppression and a shift towards open forest are also observed in the pollen and charcoal record. In comparison, the long-term record at Foy Lake shows variability that likely reflects variations in vegetation and fire regime due to climate change. Fire activity (inferred from the frequency of charcoal peaks) was initially low from 3800 to 2200 cal yr BP, and increased from 7 episodes at 2200 cal yr BP to 14 episodes/1000 years at 800 cal yr BP. Fire episodes reached a maximum at ca. 500 cal yr BP and then decreased to present levels. The level of charcoal for the 1910 fires is not anomalous when compared with charcoal peaks (fire episodes) from the prehistoric record. The pollen record suggests an open forested landscape prior to 2200 cal yr BP. Between 2200 cal yr BP and 800 cal yr BP the forest was closed and after 800 cal yr BP the vegetation began to resemble the modern parkland. The parkland is similar to the vegetation that existed prior to the arrival of Euro-Americans about 150 years ago.