Wildfire risk inferred from tree rings in the Central Laurentians of boreal Quebec, Canada

Recent fire years 2002 and 2005 have been, in the context of the past 40 years, exceptional in Quebec, with area burned totalling over 1.8 million hectares. Without prolonged fire statistics and meteorological records, it remains difficult to place these events in the contexts of climate change and variability. How frequently does this type of year occur? In this study, chronologies of radial increment measurements of Pinus spp., considered reliable back to at least 1821, were calibrated to develop an index of past moisture in ground surface fuels in the Baie-Comeau area of the Central Laurentians ecoregion, Quebec (namely the Canadian Drought Code (CDC)). Over 37% of the variance in CDC observations (period 1901-2000) was recovered by the tree-ring estimates. These estimates in turn correlated well (R2=0.39) with annual area burned (AAB) by large forest fires (size >200 ha; 1959-1999) in the Central Laurentians ecoregion. The smoothed reconstruction showed the prevalence of periods of drier conditions than average from the 1840s to the 1920s, followed by an episode of moister conditions from the 1930s to the 1960s. The minimum occurrence rate of years of extreme wildfire risk in the Baie-Comeau area was estimated in the 1940s at 0.04 yr−1, while the maximum was estimated in the 1910s at 0.21 yr−1. Occurrence rate at the turn of the 21st century (0.21 yr−1) was closely similar to that recorded during the 1890-1910s (within the uncertainty bands). These long-term variations matched temporal variations in a previously published time-since-fire distribution. The combined information from these ecological sources of data provides meaningful insights for future management of wildfire risk in the Baie-Comeau area, notably to increasing adaptation capacity in response to climate change.