Year of Award
2023
Document Type
Thesis
Degree Type
Master of Science (MS)
Degree Name
Systems Ecology
Department or School/College
Department of Ecosystem and Conservation Sciences
Committee Chair
Dr. Philip E. Higuera
Committee Co-chair
Dr. Kimberely T. Davis
Commitee Members
Dr. Solomon Z. Dobrowski, Dr. Andrew J. Larson
Keywords
climate change, wildfire, conifer seedlings, dendrochronology, Larix occidentalis, post-fire recruitment
Publisher
University of Montana
Subject Categories
Other Forestry and Forest Sciences
Abstract
Fire plays a critical role in forests of the western United States (US), but as wildfire and climate deviate from historical patterns, increasing fire activity may significantly alter forest ecosystems. To understand the impacts of changing climate and wildfire activity on conifer forests, we studied the impact of wildfire and annual post-fire climate on western larch (Larix occidentalis) regeneration. We destructively sampled 1651 seedlings from 57 sites within 32 fires that burned at moderate or high severity from 2000-2015 in the northwestern US. Using dendrochronological methods, we estimated germination years of seedlings to calculate annual recruitment rates. We used boosted regression trees to.03 model the annual probability of recruitment as a function of wildfire-related factors including distance-to-seed-source, satellite-derived fire severity, and time-since-fire, and using annual post-fire climate variables reflecting temperature and water availability. The majority of recruitment occurred within five years after fire, and at sites with northerly aspects that were within 25 m of mature pre-fire western larch. Wildfire-related factors had the highest relative influence on post-fire recruitment (87%), whereas post-fire climate had less influence (13%). Annual recruitment probability increased with growing season actual evapotranspiration, to a maximum c. 275 mm, and then decreased. Annual recruitment probability decreased as growing season climatic water deficit increased. These patterns are consistent with shade-intolerant traits and the temperature and moisture requirements of western larch. Our results suggest that climate warming has had variable, yet net-neutral, impacts on the climate suitability for post-fire western larch regeneration across its range – with suitability increasing modestly at ‘cooler and wetter’ sites and decreasing modestly at ‘warmer and drier’ sites. Overall, there is and has been broad climate suitability for post-fire regeneration across the distribution of western larch in the US. The strong influence of wildfire-related factors on post-fire regeneration highlights the important impact that management decisions can have in promoting western larch. For instance, facilitating prescribed or managed wildfire with moderate- to high-severity patches will generate conditions most suitable for natural regeneration, as long as a seed source remains nearby. Additionally, our findings support monitoring for natural regeneration or directing outcomes by planting within the first five years after fire, consistent with current management practices.
Recommended Citation
Vieira, Spencer T., "IMPACTS OF CLIMATE AND WILDFIRE ON WESTERN LARCH REGENERATION" (2023). Graduate Student Theses, Dissertations, & Professional Papers. 12238.
https://scholarworks.umt.edu/etd/12238
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© Copyright 2023 Spencer T. Vieira