Fire activity in northeast Ontario during the Holocene as inferred by sedimentary macrocharcoal

Abstract

Wildfire management can benefit from knowledge of past wildfire response to changing environmental conditions. We extracted a high-resolution macrocharcoal record from a small deep lake with a relatively small watershed in northeastern Ontario to examine evidence of fire activity in the area over the last 6,300 cal yBP. Peak analysis of the macrocharcoal sequence showed a relatively stable average fire return interval (FRI) of 155-183 years from the Holocene Thermal Maximum (HTM) till present. Although the FRI remained relatively stable, charcoal accumulation rates, background charcoal levels, and peak magnitude varied between periods of substantial change in vegetation delineated by pollen analysis including a period of maximum warmth from c. 6,300 to 3,600 years before present when pollen-inferred temperatures were ~2ºC warmer than present. Overall high charcoal levels coupled with high variability occurred during this warm and humid HTM Period while charcoal levels were consistently low during the cool and dry Post-HTM Period (3,600 – 1,600 cal yBP). Charcoal levels increased and became variable again during the cool and wet Modern Period (1,600 cal yBP – present) but did not reach the high concentrations observed in the HTM. The variation of charcoal levels within pollen-inferred climate zones showed that wildfire activity on the regional-to-local scale (such as fire size) changed in response to climate and vegetation despite relatively stable FRIs. In addition, charcoal morphology was quantified and compared to the climate zones and showed distinct trends in relative abundances of morphological particles in the different climate periods.