Reconstructing Holocene Fire and Landscape History Using Charcoal and Lake Sediments in Big Belt Mountains, Montana

Abstract

A 4215-year-old sediment record from a shallow kettle lake in the Big Belt Mountains of Central Montana was analyzed for charcoal to develop a preliminary fire history for this area. Two sediment cores, each approximately 155cm long, were retrieved and described. One was analyzed for charcoal content and radiocarbon dated. A simple age-depth model was constructed using the radiocarbon dates from two wood fragments (at 14cm and 143cm depth) to provide a preliminary age constraint to the fire history. Three distinct fire regimes are indicated in the charcoal record. The first was a period of low fire intensity and frequency that persisted from approximately 4215-3700 cal yr BP. The second fire regime occurred from ~3700-2700 cal BP and is characterized by higher fire intensity and frequency. This period was at first dominated by grass charcoal, but later peaks are dominated by wood charcoal. Charcoal abundance in this period is 100-200 times higher than in the preceding period. After ~2700 cal yr BP, charcoal abundance returns to lower levels indicating lower fire frequency. This corresponds to other regional paleoclimate records that show conditions becoming cooler and wetter at about 3000 cal yr BP (Whitlock et al 2012, Travis 2015).