Longevity of prescribed fire effectiveness in mixed-evergreen forests of the Klamath Mountains

Author

Kaily M. FineranFollow

Graduation Date

Spring 2024

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources, option Forestry, Watershed, & Wildland Sciences

Committee Chair Name

Jeffrey M Kane

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Frank K Lake

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Rosemary L Sherriff

Third Committee Member Affiliation

HSU Faculty or Staff

Keywords

Northern California, Klamath Mountains, Prescribed fire, Fuels, Mixed-evergreen, Hardwoods, Oak-woodlands, Forestry, Fire, GLMM

Subject Categories

Forestry

Abstract

Prescribed fire is a common management tool used across the western United States to create wildfire-resilient ecosystems and communities. The Klamath Mountains of northern California, USA has experienced numerous, large wildfires in recent years. This is due in part to a combination of highly flammable fuels, uncharacteristic weather events, and high fuel accumulations as a result of fire exclusion and forest management practices. Within the last decade, local land management organizations and the Karuk Tribe have begun re-introducing prescribed fire in low elevation, mixed evergreen forests. While the long-term effects of fuel treatments are not well-known, these efforts provided a unique opportunity to assess the effectiveness and longevity of prescribed fire treatments in a forest type that has been understudied in the context of fuels management. Using a space-for-time substitution, or chronosequence approach, we surveyed a total of 178 plots across a time-since-treatment continuum from one to ten years post-fire and included unburned control plots for comparison. A generalized linear mixed-effects approach was used to analyze: 1) short-term changes in fuel loading and composition, 2) long-term trends and relationships between fuel components and other factors, and 3) the longevity of treatment effectiveness in reducing fuel loading. In this study, fuels were defined as comprising both dead surface and live woody components.

Fine fuels exhibited notable short-term reductions, ranging from 34% for litter and 74% for fine woody fuels, and returning to pre-fire conditions within 5-8 years. Duff loading declined by 77% within 1-2 years post-fire, with treatments lasting as long as 16 years before returning to pre-fire conditions. Coarse woody fuels showed no statistically significant changes, likely due to their low presence and limited consumption during prescribed burns. Douglas-fir basal area was positively associated with 1-hour and duff fuel loading, with denser canopy cover and lower bole char height also contributing to higher duff loads. Our findings strongly support the notion that the longevity of treatments is slightly shorter in mixed-evergreen ecosystems compared to other studied coniferous forests across the western United States, likely due to differences in stand composition and site productivity. We recommend that mixed-evergreen forests undergo prescribed burning at least every seven years to maintain effectiveness of treatments. Additionally, selectively removing shade-tolerant species like Douglas-fir can enhance treatment effectiveness, while thinning hardwood resprouts may not be necessary for over a decade post-fire. Findings from this study can help inform management decisions to better allocate limited time and resources in addressing fuels reduction and forest restoration in the Klamath Mountains.

Citation Style

APA

Recommended Citation

Fineran, Kaily M., "Longevity of prescribed fire effectiveness in mixed-evergreen forests of the Klamath Mountains" (2024). Cal Poly Humboldt theses and projects. 739.
https://digitalcommons.humboldt.edu/etd/739