Document Type

Thesis

Date of Degree Completion

Winter 2021

Degree Name

Master of Science (MS)

Department

Cultural and Environmental Resource Management

Committee Chair

Megan Walsh

Second Committee Member

Michael Pease

Third Committee Member

Susan Kaspari

Abstract

The recent rise in severe wildfires in the Pacific Northwest (PNW) has created a heightened sense of urgency and reignited public interest in wildfire risk. In order to put this rise into a broader spatial and temporal context, a more in-depth look at fire histories from frequently burned areas in the eastern Cascades is needed. The first major objective of this study was to determine if CharAnalysis, a statistical program developed to reconstruct fire history from macroscopic charcoal-based records, is appropriate for use with charcoal records from the eastern Cascades of Washington. The second major objective was to develop a regional synthesis of post-glacial fire activity for the eastern Cascades using the seven existing charcoal-based records by developing a regional biomass burning curve, which was then compared to the existing PNW synthesis. Broad-scale trends in biomass burning in the eastern Cascades during the Holocene were then contextualized using existing records of past climatic variability, vegetation shifts, and human activity.

Results from the first objective determined that CharAnalysis is either an inappropriate, moderately appropriate, or appropriate tool for use with charcoal records from the eastern Cascades depending on the site’s vegetation and fire regime. Results from completing the second objective indicate that biomass burning in the eastern Cascades rose throughout the post-glacial period, likely due to climate shifts, the establishment of modern forests (particularly after ca. 7,000 cal yr BP), and increased human use of fire in the late Holocene. This increase continued until ca. 500 cal yr BP, when fire activity drastically declined, first from cooler climatic conditions, and then due to indigenous population decline and land-use changes that occurred as a result of Euro-American settlement (ca. 100 cal yr BP). Similar trends in Holocene fire activity were observed between the eastern Cascades and the PNW biomass burning curves, but with greater levels of burning in the eastern Cascades in the middle to late Holocene. By completing this analysis, much needed data points from multiple sites on the eastern side of the Cascades now contribute to our understanding of past and future drivers of fire activity in the PNW.

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