Holocene Fire History Reconstruction of a Mid-Evaluation Mixed-Conifer Forest in the Eastern Cascades, Washington
Date of Degree Completion
Master of Science (MS)
Megan K. Walsh
Second Committee Member
Third Committee Member
Karl D. Lillquist
Fire histories of mid-elevation mixed-conifer forests (MEMC) are uncommon, particularly in the eastern Cascades of Washington. As a result, fire regimes and the effects of 20th century fire suppression in these forests are not well understood. In the summer of 2014 a 7.80 meter-long sediment core was extracted from Long Lake, located approximately 45 km west of Yakima, WA, which exists in a grand fir-dominated mixed-conifer forest. Fire activity for the Long Lake watershed was reconstructed using macroscopic charcoal analysis and pollen analysis was used to reconstruct vegetation change through time. Charcoal results show low fire activity in the early Holocene and the first half of the middle Holocene. After ca. 6000 calendar years before present (cal yr BP) fire activity was high until ca. 500 cal yr BP. Pollen analysis indicates a woodland environment existed at the site in the early Holocene, with the modern coniferous forest beginning to establish at ca. 6000 cal yr BP. Based on a comparison of the Long Lake record to a high- and low-elevation fire history reconstruction, fire regimes in the Long Lake watershed seem to be intermediate between high- and low-elevation regimes. Similar to a high-elevation forest, the Long Lake record exhibits a general increase in fire activity during the late Holocene and a decrease in fire activity at the onset of the Little forest in that there is frequent fire during the late Holocene, and there is a fire suppression signal beginning ca. 100 cal yr BP. Most importantly, the last ~500 years of the Long Lake fire history reconstruction shows a clear departure from the established fire regime during the previous ~5500 years. Fifty fire episodes occurred in the late Holocene, but only a single fire episode was recorded after 500 cal yr BP (at ca. AD 1850). The Long Lake fire record indicates that using fire management strategies designed for low-elevation forest may be appropriate for managing for resiliency in MEMC forests in the eastern Cascades.
Rushton, Zoe, "Holocene Fire History Reconstruction of a Mid-Evaluation Mixed-Conifer Forest in the Eastern Cascades, Washington" (2019). All Master's Theses. 1209.
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