Post-fire regeneration of endangered limber pine (Pinus flexilis) at the northern extent of its range

Limber pine (Anus flexilis), an understudied tree species important to montane and subalpine ecosystems, is listed as endangered in Alberta. Dispersal of seeds to newly disturbed, open areas by Clark's nutcracker (Nucifraga columbiana) is expected to facilitate post-disturbance establishment of limber pine. Prescribed burning has thus been proposed as a tool to stimulate natural regeneration, but no studies have yet surveyed limber pine's regenerative response to disturbance at the northernmost extent of its range. We examined post-fire regeneration in one prescribed burn and one wildfire at the northern edge of limber pine's distribution and compared this to a regeneration baseline of plots in nearby unburned limber pine acting as seed sources to the bums. Using a likelihood-based approach, we then compared hypotheses of ecological processes influencing seedling occurrence and abundance. Overall, we found only six post-fire limber pine seedlings within the burns, as compared to one hundred twenty-four similarly aged seedlings found in unburned plots. Akaike information criterion (AIC) identified distance to a seed source and absence of canopy cover as hurdles for seedling establishment in the burn. Analysis of seedling abundance was performed on only the unburned dataset due to low regeneration in the burned areas surveyed; model selection here showed that when distance to a seed source is small, substrate variables, including less prevalent bare mineral soil, more rocky cover, and finer soil textures, take on an important role in driving abundance. Substrates important for limber pine abundance in unburned stands were found with similar frequency in the burns, indicating limber pine colonization post-disturbance was not substrate limited but instead constrained by other factors. Our findings suggest that extensive prescribed burns and stand-replacing wildfire events at the northern extent of limber pine's range may have limited seedling regeneration in the immediate post-fire period. Conservation efforts may be well-served by focusing on fire mitigation efforts, such as thinning and other fuel treatments, in areas surrounding established limber pine stands. Finally, post-disturbance stands could benefit from supplementary seedling plantings to achieve recovery plan restoration goals for this endangered species.