Limber pine (Pinus flexilis), a species of the montane and subalpine regions of western Canada and the United States, is endangered in Alberta. Limber pine is thought to be dependent on fire, due to its relationship with a bird, the Clark’s nutcracker (Nucifraga columbiana), which may preferentially cache seeds in open areas. High-severity fire is thus thought to open new areas for colonization. Few studies, however, have examined regeneration of limber pine after fire, especially at the northernmost limits of its range. In this study, we examine limber pine regeneration within two Alberta burns and determine whether seedling presence and abundance are most influenced by seed dispersal or germination potential of an area. We surveyed high-severity portions of each burn for seedlings in plots where limber pine had been dominant and plots in limber pine habitat that had not contained dominant limber pine, all at sites within dispersal distance of limber pine stands. We compared results to baseline regeneration occurring within unburned limber pine stands acting as a seed source. Finally, we used AIC-based model selection to test whether soil, vegetation, seed distribution, or climate variables best explain seedling presence and abundance.
Results/Conclusions
We found only six post-fire limber pine seedlings within the burns, as compared to 124 similarly aged seedlings found in unburned plots. Seedlings within the burns were all found in plots within 200 m of an unburned limber pine stand. Model selection indicates that seed dispersal is the most likely process influencing the lack of seedling presence in the burn. By necessity, the abundance analysis was performed on the unburned dataset; model selection here showed that when seed distance is small, soil variables become important in driving abundance, although seed dispersal variables remain important. Overall, these results suggest that limber pine regeneration is not dependent on high-severity fire at the northern limits of its range. Seed dispersal by Clark’s nutcrackers may be limited to short distances, despite studies showing far-ranging caching behaviors of nutcrackers for other pine species. We speculate this may be due to limber pine’s typically open forest structure in Alberta, which allows nutcrackers to cache in open areas without the need to travel outside the stand. Further studies investigating the caching behavior of nutcrackers in Alberta’s limber pine stands could clarify whether this is indeed the cause of low regeneration in these burned areas.