Uncovering the Dynamic Nature of Fire Refugia Across Landscapes in Oregon's Western Cascades

Author

Alec Scott Dyer, Portland State UniversityFollow

Sponsor

Portland State University. Department of Geography

First Advisor

Andrés Holz

Term of Graduation

Spring 2024

Date of Publication

6-20-2024

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Geography

Department

Geography

Language

English

Physical Description

1 online resource (v, 83 pages)

Abstract

With increased fire activity, the presence of fire refugia is critical to support forest resiliency and mitigate large-scale vegetation conversion, however, the persistence of fire refugia within burn perimeters over time is uncertain. This study examines the dynamic nature of fire refugia by mapping the decline in forest cover over time, identifying spatiotemporal patch- and landscape-scale patterns and the biophysical drivers of delayed mortality following the 2020 Labor Day Fires occurring in Oregon’s western Cascades. After three years post-fire, delayed mortality accounted for an additional 8.5% of forest loss (total of 24,147 hectares in all five burns) compared to pre-fire forest cover and had a disproportionate impact on high immediate burn severity areas, especially in high-elevation forests, fire-sensitive conifer species, and in cool, wet topographic positions. This loss of refugia resulted in a 9% increase in the isolation of high-severity burned patches from any seed-providing refugia. Analysis of the biophysical drivers of delayed mortality highlighted that first-order fire effects on trees (i.e., fire injuries during the 2020 wildfires) were the single most important factor, outweighing the influence of climate stressors in high burn severity conditions, including the June 2021 heatwave, and of topography. Overall, these findings highlight how delayed mortality can impact the ecological functions of fire refugia pertaining to crucial wildlife habitat and seed dispersal. Considering species’ functional traits relating to fire tolerance, sensitivity, and resilience may prove useful in establishing more effective post-fire management strategies and in developing a more comprehensive framework of conifer forest resiliency under novel fire regimes.

Rights

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Comments

Partial support from the National Science Foundation (NSF Award #1832483).

Persistent Identifier

https://archives.pdx.edu/ds/psu/42323

Recommended Citation

Dyer, Alec Scott, "Uncovering the Dynamic Nature of Fire Refugia Across Landscapes in Oregon's Western Cascades" (2024). Dissertations and Theses. Paper 6655.