Graduation Year

2024

Graduation Month

May

Document Type

Thesis

Degree Name

Bachelor of Science

School or Department

Forestry and Conservation

Major

Environmental Science and Sustainability

Faculty Mentor Department

Forestry and Conservation, College of

Faculty Mentor

Philip Higuera

Keywords

climate change, wildfire, conifer seedlings, tree rings, Larix occidentalis, growth-climate relationships

Subject Categories

Environmental Sciences

Abstract

Montane and mixed-conifer forests in the northwestern United States are burning at rates greater than any time in recent decades, due to the combined impacts of global warming and historical and contemporary land use and land management. Western larch (Larix occidentalis) is a tree of high regional significance, exhibiting a variety of traits that make it resistant and resilient to fire. Because seedlings are more sensitive to environmental stressors than adults, the impacts of climate change are expected to be detectable first in juvenile trees. Recent research shows that the natural regeneration of western larch after wildfires has not been significantly impacted by recent climate change (Vieira, 2023), although the prolonged vitality of these seedlings is of question.

To understand how seedlings naturally regenerating after wildfire respond to interannual variations in climate, I studied the influence of seasonal measures of moisture and energy inputs on the annual radial growth of western larch juveniles. The study calls on 1587 destructively sampled western larch seedlings that were regenerating in post-fire ecosystems across the geographic range of the species in the US (i.e., Montana, Idaho, Washington, and Oregon). From 53 sites sampled within 30 wildfires that burned between 2000 and 2015, dendrochronological techniques were used to determine the establishment year of each seedling. Image analysis was used to then measure annual growth rings for each seedling.

I analyzed the data with a variety of statistical techniques. Using a simple correlation analysis, I assess the correlation between multiple measures of seasonal climate and radial growth of seedlings at both the site and individual tree levels. Findings reveal complex relationships between climate and radial growth, with variability in both the magnitude and direction of correlations within and among sites. I then modeled growth-climate relationships using a continuous mixed effects linear regression model to infer how annual growth varies based on different climatic factors, site-specific factors, and fire-related factors (e.g., fire severity). Results suggest that growth-climate relationships are complex. However, competition for resources was the dominant factor limiting the annual radial growth of post-fire western larch juveniles, and growth was not significantly inhibited by variations in interannual climate.

Honors College Research Project

Yes

GLI Capstone Project

no

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