Large-scale influences of climate and forest composition on spruce budworm-wildfire interaction in central Canada

The spruce budworm (SBW) and wildfire are key natural disturbance factors in central Canada’s forests. The periodic outbreaks of this insect defoliator cause extensive forest damage which constitutes an important fire hazard. To better understand how climate and forest composition affect post-outbreak fire hazards, we studied the spatiotemporal relationships between these disturbances as reflected in Ontario’s 1941-2005 GIS records for fire and SBW defoliation. Within the vast region defoliated at least once by SBW since 1941, fires tended to occur 3-9 years after an outbreak. The strength of this SBW-wildfire interaction and the start and duration of this ‘window of opportunity’ for wildfire varied systematically across Ontario. Fires occurring within the (location-dependent) ‘window of opportunity’ accounted for 53.5% of the 2,710, 000 ha burnt. SBW-wildfire interactions tended to occur in a region bounded in the south by hardwood content, in the north by host species content, and in the west by moisture. Within this region, the frequency of SBW defoliation had a discernible effect. These results can be partly explained by the interaction of two opposing processes operating on different time scales.