Sexual and vegetative recruitment of trembling aspen following a high-severity boreal wildfire

Abstract Background High-severity fire is rare in trembling aspen-dominated forests of the boreal region. The post-fire recruitment strategy of aspen, by either vegetative suckering or sexually (i.e., by seed), has considerable implications for subsequent forest structure, genetic diversity, and ecological resilience to shifting climatic and disturbance regimes. In this study, we take advantage of the unique opportunity provided by the Chuckegg Creek Wildfire Fire (310,000 ha) in northern Alberta, Canada, which burned at high severity through aspen stands before and after spring green-up, to document how phenology, fire severity, and stand characteristics affect recruitment one year following the fire. Results We found sites were dominated either by high-density patches of seedlings or a fairly uniform density of suckers, with few sites occupied by both. Sites dominated by seedlings burned predominantly after green-up. Using boosted regression trees, we found that surface fire severity best predicted both aspen seedling and sucker density at sites. Seedlings were favoured at sites that burned at high surface severity and after spring green-up, whereas suckering density was highest at sites that burned at moderate-high surface severity before green-up. Conclusion Our research highlights the influence of surface fire severity and phenology on aspen recruitment. High fire severity, particularly after aspen green-up, reduced suckering while promoting seedling recruitment. Aspen seedlings filled the recruitment gap caused by this lowered, suckering response, providing an alternate route for aspen forest adaptive capacity after high-severity surface fire.