Theme:  Ecological Sustainability: Engineering Change

Session: Improving predictability of circumboreal forest fire activity and its ecological and socio-economic impacts through multi-proxy data comparisons and monitoring

Title: Wildfire size impacts long-term vegetation trajectories in boreal forests

Cécile C. Remy, Martin Lavoie, Martin P. Girardin, Christelle Hély, Yves Bergeron, Pierre Grondin, France Oris, Hugo Asselin & Adam A. Ali

In the global change context, understanding the role of climate and wildfires on the boreal forest composition is crucial to predict vegetation trajectories. We investigated the incidence of fire regime on multi-millennia vegetation trajectories in two coniferous boreal forest regions currently displaying different compositions (i.e. black spruce forests in western and white spruce – balsam fir forests in eastern region of Quebec-Labrador, Canada). We hypothesized that this difference results from dissimilar fire regimes during the Holocene, likely modulated by the climate and the relief. We performed charcoal and pollen analyses on nine lacustrine cores to reconstruct fire (frequency and size) and vegetation histories during the last 8,000 years.

Between 7000 and 2000 cal. years BP, high fire frequency in both regions, as compared to Early and Late Holocene periods likely, was likely promoted by dry and warm climatic conditions. Western landscapes submitted to larger fires than those in the eastern region were mainly composed by species adapted to fire: Picea mariana, Pinus banksiana and Alnus viridis ssp. crispa. Conversely, in the eastern landscapes, Picea sp., Abies balsamea and Betula sp., poorly fire-adapted, predominated. Then, between 2200 and 1500 cal. years BP, fires became larger in the eastern region allowing Pinus banksiana and Alnus viridis ssp. crispa, to develop in the landscape. In the coniferous boreal forests of eastern North America, the long-term vegetation trajectories were more influenced by the fire size than the fire frequency. The impact of current climate change on the rate of eclosion of large fire episodes must be the most important point to be considered in future investigations in order to supply accurate models to predict the vegetation dynamics. This effort is essential to choose appropriated forest management policies and strategies in order to attenuate the negative ecological and socio-economic consequences of increased boreal wildfire activities.