- 36 views
- 68 downloads
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
- Thesis
-
- Degree
- Master of Science
-
- 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.