Regional-scale hydrologic settings buffer black spruce regeneration in the presence of post-fire droughts

Increasingly severe wildfires and droughts are reducing black spruce recruitment and favouring early successional species like jack pine and trembling aspen in Canada’s western boreal forests. Adjacent peatlands may mitigate these changes, depending on topographic position and soil texture, which influence groundwater connectivity. We examined tree regeneration in 58 post-fire upland forest stands (5–20 years old) across various local (adjacent peatland) and regional (relative to a regional low) topographic positions, under different post-fire drought conditions (i.e., post-fire climate moisture deficit). We hypothesized that regenerating forests at lower topographic positions, supported by primarily groundwater-fed (largely rich fen) peatlands, would be relatively buffered against post-fire drought as primarily precipitation-fed (bog and poor fen) peatlands at higher positions are more drought-sensitive. Regenerating black spruce proportions were negatively correlated with post-fire drought at regional high topographic positions, across soil textures. Post-fire stem density, tree volume, and proportions of jack pine and aspen were not correlated with post-fire drought. This study highlights that areas of Alberta’s boreal forest with large-scale hydrological connectivity may act as drought refugia for post-fire black spruce, while jack pine, and aspen are likely to remain resilient across a range of physical settings.