UBC Theses and Dissertations
National regeneration potential of Douglas-fir following wildfire and clearcut harvesting Barker, Jason Scot
The McLure fire of August, 2003, affected over 26,000 hectares in the interior of British Columbia. The study objective was to determine the impact of wildfire and clearcutting severity on Douglas-fir regeneration potential in the Interior Douglas-fir biogeoclimatic zone. The study design consisted of five treatments that compared a range of disturbance severities: high severity burn, low severity burn, clearcut, screefed clearcut, and undisturbed forest. At each of four replicate sites per treatment, 1000 seeds were sown in late spring of 2004. Natural regeneration potential was assessed by measuring seedling performance and mycorrhizal diversity over a three-year period. Overall, the treatments with the greatest disturbance severity had the greatest natural regeneration potential due to increased resource availability. Seedling survival was considerably higher in the burn and clearcut treatments than the undisturbed forest. Seedlings in the high severity burn had significantly greater shoot height, biomass, and foliar N and P content than those in the clearcut treatments. Seedlings regenerating in the burn treatments had the lowest ectomycorrhizal colonization in the first growing season but all seedlings in all treatments were colonized by the start of the second growing season. Increased disturbance severity, either by wildfire or clearcutting, led to a uniform ectomycorrhizal community dominated by Wilcoxina sp. In contrast, the undisturbed forest was dominated by a more diverse ectomycorrhizal community. The simplification of the ectomycorrhizal community did not negatively affect seedling growth or survival. The highest biomass accumulation and foliar nitrogen content occurred in the high severity burn and were associated with the lowest levels of mycorrhizal colonization and diversity. This supports the hypothesis that plants reduce their carbon investment in mycorrhizal fungi when growing under favorable conditions. Overall, the results indicate that, given a seed source, the natural regeneration potential of Douglas-fir is high after both wildfire and clearcut harvesting.
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