Decreasing frequency of forest fires in the southern boreal zone of Québec and its relation to global warming since the end of the 'Little Ice Age'

Although an increasing frequency of forest fires has been suggested as a consequence of global warming, there are no empirical data that have shown a climatically driven change in fire frequency since the warming that has followed the end of the 'Little Ice Age'. We present here evidence from fire and tree-ring chronologies that the post-'Little Ice Age' climate change has profoundly decreased the frequency of fires in the northwestern Québec boreal forest. A 300-year fire history (AD 1688-1988) from the Lake Duparquet area (48°28' N, 79°17' W) shows an important decrease, starting 100 years ago, in the number and the extent of fires. This decrease in fire frequency is also associated with a long- term increase in the mean ring width of northern white cedar (Thuja occidentalis L.) in the same area. Agreement between the standardized tree-ring chronology and fire years, together with a negative correlation with a drought index reconstructed for the AD 1913-1987 period, shows that the decrease in fire frequency may be related to a reduced frequency of drought periods since the end of the 'Little Ice Age'. The contradictory results between predicted and observed effects of warming on fire frequency call into question our present capability to generalize the effect of increasing CO₂ levels on fire frequency.