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McAulay, Julia

University of British Columbia

Wildfires are increasing in frequency and severity due to climate change and land management practices, presenting challenges to forest ecosystems, including in the southern interior of British Columbia (BC). This study investigates how burn severity and salvage logging affect the natural regeneration of interior Douglas-fir (Pseudotsuga menziesii var. glauca), a species of cultural, ecological, and economic importance with inconsistent regeneration success. I conducted two studies near Williams Lake, BC: one in the Interior Douglas-fir climatic zone (IDFdk3), and the other in a transitional area between the Interior Cedar-Hemlock (ICHmk3) and Sub-boreal Spruce (SBSdw1) climatic subzones. The first study focused on how burn severity (i.e., low, moderate, high) affected seedling biomass and ecophysiology using foliar nutrient analyses and stable isotope analyses of foliar, stem, and soil water content. The second study examined both burn severity (i.e., moderate, high) and salvage logging (i.e., salvaged, not salvaged) impacts on seedling traits using foliar stable isotopes. The findings from my first study (IDFdk3) indicate that when there was no salvage logging, seedlings grew larger in moderate and high severity sites compared to low severity sites and did not experience greater water stress at those sites. Light availability emerged as the primary growth-limiting factor, and differences in nutrient composition did not influence seedling growth. In my second study (ICHmk3 and SBSdw1), there was a complex interplay between salvage logging and burn severity, affecting seedling biomass, photosynthesis (via δ¹³C stable isotope analyses), and stomatal conductance (via δ18O stable isotope analyses) differently across severity levels. In moderate severity sites that were not salvage logged, lower biomass, δ¹³C, and δ¹⁸O values indicated reduced photosynthesis and stomatal conductance, likely due to reduced sunlight exposure. In high-severity sites, where sunlight was already abundant, salvage logging added stress without improving seedling growth. My study underscores the critical role of light availability in interior Douglas-fir seedling growth and highlights the complex interactions between burn severity and salvage logging on post-fire regeneration. These findings suggest that land management strategies should consider burn severity when planning salvage logging, with long-term monitoring and adaptive approaches necessary for effective post-wildfire recovery.

Text

2025-01-02

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90002

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/