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

• Author / Creator

  Dawe, Denyse A.

• Limber pine (Pinus flexilis), an ecologically important species of the montane and subalpine regions of western Canada and the United States, is endangered in Alberta. Limber pine is thought to regenerate following fire, due to its relationship with a bird, the Clark’s nutcracker (Nucifraga columbiana), which has long been celebrated for preferentially caching pine seeds in open areas. High-severity fire is thus thought to open new areas for colonization, and prescribed fire has been proposed as a recovery tool to stimulate natural limber pine regeneration. Few studies, however, have examined regeneration of limber pine after fire, especially at the northernmost limits of its range. In this study, I examined natural limber pine regeneration within two Alberta burns to determine if limber pine recruitment is occurring following fire, describe how ecological processes influence seedling occurrence and abundance, and define how fire affects the availability of substrates important to limber pine regeneration. I accomplished this by establishing plots within stands where, prior to fire, limber pine had been dominant and plots in limber pine habitat that had not contained dominant limber pine. This was done to test whether fire provided limber pine an opportunity to colonize new habitat, or if recruitment simply occurred in areas in which limber pine had already held a pre-disturbance presence. I also established plots within unburned limber pine stands acting as a seed source to provide a regeneration baseline as a point of comparison. Limber pine regeneration was tallied in each plot and biophysical characteristics of the plot measured.I 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 within 250 m of an unburned limber pine stand. To illuminate the cause of such low regeneration numbers within the burn, I used a likelihood-based approach to compare hypotheses of ecological processes influencing recruitment. These hypotheses, including seed dispersal, substrate availability, microclimate, and competing vegetation, were modelled against seedling occurrence and abundance in plots. Akaike information criterion (AIC) values and weights provided strongest support for insufficient seed dispersal as the cause of low seedling occurrence within the burn. Due to the low number of seedlings in the burn, the abundance analysis was performed on only the unburned dataset; model selection here showed that when seed distance is small, strong support is found for substrate variables in driving abundance, though seed dispersal variables remain important. Finally, the availability of substrates found to be important to limber pine seedling abundance in the unburned plots was compared by stand type. Similar availability of desirable substrates within the burn as in the unburned plots suggests that safe sites for limber pine regeneration occur within the burn, indicating that these areas may simply not be receiving seed from Clark’s nutcracker distribution. Seed dispersal by Clark’s nutcrackers may be limited to short distances in the areas studied, despite studies showing far-ranging caching behaviors of nutcrackers for other pine species. Overall, these results indicate that fire may not stimulate limber pine regeneration in some contexts, questioning the proposition of using prescribed burning in Alberta as a recovery tool, unless burning is supplemented by plantings of limber pine seedlings.

• Subjects / Keywords

  • fire ecology
  • Pinus flexilis
  • conservation
  • limber pine
  • endangered species
  • forest regeneration

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-shgn-k818

• License

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