Disturbance legacies and paludification mediate the ecological impact of an intensifying wildfire regime in the Clay Belt boreal forest of eastern North America.

English Abstract:

High moisture levels and low occurrences of wildfires have contributed during recent millennia to the accumulation of thick layers of organic soil and to a succession into open black spruce (Picea mariana)-Sphagnum dominated forests in the Clay Belt boreal landscapes of eastern North America. In these forests, the anticipated increase in drought frequency with climate change could lead to a shift in forest structure and composition, and to a subsequent transfer of the stored carbon back into the atmosphere via increased fire disturbance and decomposition. Herein we conducted modeling experiments using the Canadian Fire Effects Model (CanFIRE) to investigate potential changes in forest structure and composition in response to a changing fire regime. Vegetation dynamic was governed by the fire danger and behaviour that affect tree mortality and postfire recruitment of species, and by long-term successional pathways that are driven by postfire recruitment and forest age. Results from multiple scenarios suggested that fire danger will rise significantly during the 21st century in the Clay Belt forest. The burn rate was projected to change from 4.2%/decade during 1971-2000 to 18.6%/decade during 2071-2100. Stand mortality, fire intensity and areas affected by crown fires were also projected to increase significantly. A shift in forest composition did not occur over the simulation period across most of our fire regime scenarios. Moist and cool conditions in these forests prevent high depth of burn and contribute to the ecological resistance of these forests to increasing fire danger.