Long-term fire history in northern Quebec: implications for the northern limit of commercial forests

Fire frequency is expected to increase in boreal forests over the next century owing to climate change. In Quebec (Canada), the location of the northern limit of commercial forests (c. 51 degrees N) was established in 2000 taking into account mainly forest productivity and fire risk. The location of the limit is currently under debate and is being re-evaluated based on a more extensive survey of the territory. We characterized the natural variability of fire occurrence (FO) in the area surrounding the northern limit, and these results are a useful contribution to discussions on the re-evaluation of its location. Regional FO over the last 7000years was reconstructed from sedimentary charcoal records from 11 lakes located in three regions surrounding the northern limit (i.e. south, north and near the limit). Holocene simulated precipitation and temperature from a general circulation model (GCM) were used to identify the long-term interactions between climate and fire. Fire histories displayed similar trends in all three regions, with FO increasing from 7000calibrated years before present (cal. years BP) to reach a maximum at 4000-3000cal. years BP, before decreasing during the late-Holocene. This trend matches the simulated changes in climate, characterized by drier and warmer conditions between 7000 and 3500cal. years BP and cooler and moister conditions between 3500 and 0cal. years BP. Northern ecosystems displayed higher sensitivity to climate change. The natural variability of FO was narrower in the southern region compared with the limit and northern regions. An abrupt decrease in FO was recorded close to and north of the limit at 3000 cal. years BP, whereas the decrease was more gradual in the south. Synthesis and applications. We reconstructed the natural variability in fire activity over the last 7000years near the current location of the northern limit of commercial forests in Quebec. Fire occurrences were more sensitive to climate change near to and north of the limit of commercial forestry. In the context of predicted increase in fire activity, the lower resilience of northern forests advocates against a northern repositioning of the limit of commercial forests.