Fire disturbances are increasing under global climate change and ecological transformations of forests are occurring. Specifically, shifts from productive closed-canopy feather moss forests to low-productivity open-canopy lichen (Cladonia spp.) woodlands have been observed in boreal forests of eastern Canada. It has been hypothesized that high severity of fires would be the cause of this change, but this is difficult to validate a posteriori on mature forest stands. Because charcoal properties are affected by fire severity, we have put forward the hypothesis that the amount and physicochemical properties of charcoal (C, N, H, O, ash, surface area) would be different and indicative of a greater fire severity for open-canopy forests compared to closed canopy ones. Our hypothesis was partly validated in that the amount of charcoal found on the ground of closed-canopy forests was greater than that of open-canopy forests. However, the physicochemical properties were not different, albeit a greater variability of charcoal properties for open canopy stands. These results do not allow us to fully validate or reject our hypothesis on the role of fire severity in the shift between open and closed canopy stands. However, they suggest that the variability in fire conditions as well as the amounts of charcoal produced are different between the two ecosystem types. Furthermore, considering the role that biochar may play in improving soil conditions and promoting vegetation restoration, our results suggest that charcoal may play a role in maintaining these two stable alternative ecosystem states.

Local-scale fire regimes are controlled by climate, fuel availability, and topography. Research on long-term (i.e., Holocene timescales) fire activity in the Northwest Territories has focused on local fire dynamics, with fewer studies examining regional patterns. To investigate the impacts of climate variability on wildfire activity during the Holocene, 13 macroscopic charcoal and 3 pollen records, as well as insolation values, reconstructed temperatures, and precipitation data were analyzed to understand the interactions of climate, regional fire regimes and vegetation during the Holocene in the North Slave Region, Northwest Territories, Canada. Following deglaciation, wildfire activity across the region was low, due to lack of fuels, relatively low temperatures, and dry conditions. By ∼8200 cal yrs. BP, wildfire activity increased across the region as Picea expanded on the landscape increasing fuel availability and summer temperatures increased and peaked during the Holocene Thermal Maximum. Wildfire activity continued to increase throughout the mid-Holocene until cooler and wetter conditions developed with the onset of Neoglacial cooling around 4200 cal yrs. BP. With the onset of cooler and wetter conditions, wildfires declined regionally across the North Slave Region. The decline in wildfire activity following Neoglacial cooling can be attributed to a general decline in temperatures and changes in vegetations types and density. During the 20th century, wildfire activity increased in response to warming temperatures. With further increases in global mean temperature, it is expected that wildfire activity in the North Slave Region will increase during the 21st century.