Regional-scale hydrologic settings buffer black spruce regeneration in the presence of post-fire droughts

  • Author / Creator
    Lanti-Traikovski, Alexander A.
  • Climate change is increasing the frequency of droughts and wildfires, reducing tree
    recruitment, and altering post-fire species composition. In Canada’s western boreal forests, postfire recruitment, particularly of drought-intolerant coniferous species like black spruce, has
    declined in recent decades to the benefit of early-successional species like jack pine and
    trembling aspen. Groundwater supplied to forests via adjacent peatlands may help to resist such
    reductions in recruitment and compositional shifts, particularly during droughts. The degree to
    which peatlands buffer adjacent forests from drought-induced regeneration failure may therefore
    depend on topographic position and soil texture, factors that govern groundwater connectivity. I
    examined how these topoedaphic factors influence upland tree regeneration from post-fire
    drought, defined in this study as the post-fire climate moisture deficit across sampled fires. Since
    higher-positioned peatlands (bogs, poor fens) are mostly fed by precipitation, they are more
    vulnerable to drought compared to fen-like peatlands at lower topographic positions that are fed
    by groundwater. I therefore hypothesized that regenerating forest density, growth, and
    composition at lower topographic positions would be buffered from post-fire drought by water
    sources from the adjacent fen across a range of soil textures. Specifically, I predicted that tree
    density, volume, and proportions of black spruce should decline with high topographic positions,
    favoring instead jack pine and aspen following post-fire drought. I tested this prediction by
    measuring 58 post-fire upland forest stands ranging from 5 – 20-years old that experienced wet
    or dry post-fire weather. Study sites spanned local (relative to adjacent peatland) and regional
    topographic position (relative to a regional low) gradients. I used generalized linear mixed
    effects models to test interactions between these local and regional topographic positions, soil
    texture, and post-fire climate. I found significant reductions in regenerating black spruceiii
    proportions at high regional topographic positions across fine- and coarse-textured soils with
    post-fire drought. Total regeneration (stem density), tree volume (basal area), and species of jack
    pine and aspen showed no correlations with post-fire drought. This study highlights that
    hydrologically well-connected areas of Alberta’s boreal forest may act as refugia from drought
    and fire for drought-intolerant black spruce, and that more predominant upland jack pine and
    aspen species appeared to be resilient under the current fire regime. Larger scale ecohydrological
    dynamics therefore interact with forest regeneration and should be considered to identify areas
    that may resist altered post-fire trajectories.

  • Subjects / Keywords
  • Graduation date
    Spring 2024
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.