Using Holocene paleo-fire records to estimate carbon stock vulnerabilities in Hudson Bay Lowlands peatlands

Holocene fire records from charcoal are critical to understand linkages between regional climate and fire regime and to create effective fire management plans. The Hudson Bay Lowlands (HBL) of Canada is one of the largest continuous peatland complexes in the world and is predicted to be increasingly impacted by wildfire. We present three charcoal records from a bog in the western HBL and demonstrate that median fire frequency was higher in the Middle Holocene, related to warmer regional temperatures and higher evaporative demand. Holocene fire frequencies are lower than in western Canadian peatlands, supporting that the HBL lies in the transition between continental and humid boreal fire regimes. Apparent carbon accumulation rates at the site were not significantly different between the Middle and Late Holocene, suggesting that higher fire frequency and enhanced decomposition offset the potential for higher rates of biomass production. We compile records from the boreal region and demonstrate that increasing fire frequency is significantly correlated with diminishing long-term carbon accumulation rates, despite large variation in response of peatlands to fire frequency changes. Therefore, the paleo-record supports that higher fire frequencies will likely weaken the capacity of some northern peatlands to be net carbon sinks in the future.