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Fire and whitebark pine recovery strategies: drivers of post-fire natural regeneration

Whitebark pine (Pinus albicaulis Engelmann), a tree species of high-elevation forests in western North America, is listed as an endangered species in Canada. Conservation agencies have used prescribed burns as a recovery strategy to create open habitats free of competition and increase regeneration opportunities. However, questions remain with respect to the success of prescribed burns for the restoration of whitebark pine and the best practices of this technique, as well as the role wildfire plays in whitebark pine communities at the northern limits of its range. Understanding what drives whitebark pine post-fire regeneration is important for guiding future burn prescriptions and managing wildfires to implement Alberta’s provincial recovery plan effectively at a landscape scale. Luiz Drummond, former M.Sc student co-supervised by the University of Alberta’s Mike Flannigan and King’s University’s Vern Peters, assessed the effects of fire on whitebark pine regeneration on recent prescribed burns and wildfires across the federal and provincial mountain parks in western Alberta. The research aimed to better understand how site, stand and plot level factors influence seedling occurrence and density in post-fire environments.

The results showed that whitebark pine post-fire regeneration is a complex process linked to a variety of biological processes at multiple spatial scales. Regeneration occurrence increased in the first 18 years after the fire, mainly at stands with larger whitebark pine basal areas. On the other hand, seedling density had unclear patterns over time, showing that differences in seedbeds and understory conditions at smaller scales probably drive regeneration abundance. This creates a challenge in predicting regeneration abundance because of the multitude of factors that can influence post-fire conditions, such as fire severity, burning season, post-fire weather, and pre-forest composition.

The colonization of some burned stands with no mature whitebark pine trees pre-fire may suggest that fire creates new habitats for regeneration, while the lower post-fire and advanced seedling densities in the burned areas indicate that fire can have negative effects, at least in the short term. Proximal seed sources were important for regeneration occurrence, but increasing tree mortality caused by white pine blister rust and mountain pine beetle affects regeneration potential. Long-term post-fire occupancy surveys and artificial planting will likely be necessary to complement the lack of natural regeneration in burned areas and achieve restoration goals, particularly at stands experiencing high tree mortality caused by blister rust and mountain pine beetle.

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