Date of Award:

5-2023

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

Larissa L. Yocom

Committee

Larissa L. Yocom

Committee

R. Justin DeRose

Committee

Paul C. Rogers

Abstract

In western North America, quaking aspen (Populus tremuloides Michx.) forests have long been described as low flammability, “fireproof” forest types that are less likely to burn or burn less intensely than coniferous forests. While this assumption has been based on limited scientific research and is largely anecdotal, there is growing interest in the western U.S. to promote aspen near human developments to reduce fire risk. I investigated the available evidence for aspen forests reducing fire occurrence, behavior, and severity, and assessed possible factors that affect flammability in aspen forests to better understand when and where aspen burn, and when they do not. In the first study (Chapter 2), I conducted an extensive literature review and a survey of professionals with expertise in aspen-fire encounters to examine our current understanding of how aspen influences fire. In the second study (Chapter 3), I investigated fuel characteristics in in 80 aspen stands in Utah, U.S. that spanned gradients of tree species composition from aspen to conifer dominance and stand development stage from early to late development. I found evidence for aspen forests reducing fire occurrence, behavior, and severity under certain conditions, and results from our field campaign indicated that pure, late development aspen forests were particularly associated with lower flammability conditions. However, I also found that the aspen-fire relationship was complex; factors such as the percentage of aspen vs. conifer trees in the overstory, type and load of surface fuels, weather, and season play important roles in determining how flammable an aspen forest is. While my research supports the claim that aspen forests promote lower flammability conditions under most conditions, aspen forests are certainly not “fireproof,” and uncertainty remains regarding the future of fire in aspen under a warming and drying climate.

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