Jennifer Baltzer Associate Professor and Canada Research Chair in Forests and Global Change, Wilfrid Laurier University, Waterloo, ON
Title: Ecological state changes following fire in North American boreal forests
Host: Vaughan Hurry
Outline for the talk: Wildfire is essential to the maintenance of boreal forest ecosystems. However, climate warming is driving the intensification of wildfire disturbance, with increased frequency, extent, severity and duration of the fire season. These changes are expected to alter the structure, composition and function of northern forests. Previous studies of severe fire events have demonstrated changes in patterns of tree species dominance as a consequence of fire-driven changes in seedbed conditions and seed availability, indicating the potential for state changes in boreal forests in response to warming-induced changes in the wildfire regime. Predicted warmer and drier growing season conditions will likely also influence tree seedling survival following disturbance thereby altering regeneration dynamics. Such changes have the potential to affect a wide range of ecosystem functions of boreal forests including but not limited to productivity and associated land surface – atmosphere exchange, understory community composition and wildlife habitat quality.
To understand drivers of post-fire regeneration, we compiled datasets from over 1600 sites spanning the circumboreal, all of which contain comparable measurements of pre- and post-fire tree species composition and stem densities, fire severity, seed bed characteristics and key environmental metrics such as site moisture conditions; post-fire climate variables were generated from gridded datasets for all studies. We evaluated a common conceptual framework based on the results of previous studies of post-fire regeneration dynamics to determine common drivers of post-fire regeneration across sites. While the most common post-fire trajectory was self-replacement, state changes from the pre-fire dominant taxa were also very common but varied biogeographically. Seed bed conditions were consistently an important predictor of post-fire trajectory based on random forest analyses. Results will be discussed in the context of predicted changes in climate and wildfire disturbance and the implications of this for boreal forest composition and function.