Analyzing charcoal particles in lake sediments to reconstruct historical fires: Fallison Lake, Northern Wisconsin

Background/Question/Methods

Our research investigates the interaction of forest fires and historical logging with changes in vegetation composition surrounding a Northern Wisconsin lake. Charcoal and pollen data were analyzed from the top 40 cm of a sediment core from Fallison Lake, in the Northern Highlands lake district. Two AMS radiocarbon dates indicate that this represents 500 years of fire and vegetation history. Extensive logging took place in northern Wisconsin forests in the late 1800s and early 1900s, with fire suppression legislation being passed by the 1930s.

Results/Conclusions

Charcoal counts over the last 500 years indicate a decrease in charcoal accumulation about 1500 CE, well before European settlement and logging. The drop in charcoal corresponds to a decrease in white pine (Pinus strobus) and an increase in birch (Betula) pollen. It is difficult to interpret the increase in birch (a short-lived disturbance species) in response to a decrease in fire. Future research will include a longer charcoal and pollen sequence to put this change in context. A small increase in charcoal particles was observed around the turn of the 20^th century, perhaps due to slash fires associated with logging. Following this, charcoal counts remained lower, as fire surpression became effective. The increase in Ambrosia pollen takes place in two stages, increasing from 0-0.7% before 20 cm (probably mid-1800s) to 1-2% and increasing further (>3%) after 15 cm (representing the peak of logging and agriculture after ~1910 CE).