Graduation Date
Spring 2026
Document Type
Thesis
Program
Master of Science degree with a major in Biology
Committee Chair Name
Erik Jules
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
Melissa DeSiervo
Second Committee Member Affiliation
Community Member or Outside Professional
Third Committee Member Name
Lucy Kerhoulas
Third Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Fourth Committee Member Name
Matthew Reilly
Fourth Committee Member Affiliation
Community Member or Outside Professional
Keywords
Range shift, Fire exclusion, Climate change, Klamath Mountains, Climate refugia, Legacy plots, Abundance, Shade tolerance
Subject Categories
Botany
Abstract
The effects of climate change have and will continue to impact plant communities, including by potentially shifting species’ ranges towards topographically sheltered, cooler locations or higher elevations. In 2024, I resampled 140 vegetation plots established in 1969 in the Klamath Mountains of Northern California to assess range shifts of 46 understory species over a 55-year period. During this time, the elevational distribution of all species has increased significantly by an average of 26.9 m, but this increase was slower than necessary to track historic temperature niches given regional warming (215-311 m). Despite this overall increase, only four species exhibited significant or marginally significant changes in elevational range when assessed individually. There has also been a larger upward shift at the lower edge of most species’ ranges (x̅ = 54.4 m, versus 27.6 m at the mid-range and 9.1 m at the upper edge), suggesting that the change in distribution is mostly attributable to losses at the trailing edge. My study demonstrated that 54% of understory species decreased in frequency between surveys, while 39% increased and 7% had no change, and shade-intolerant species showed the largest proportional decline. The slower than expected movement of understory plants in response to warming may be due to either the region’s lack of disturbance (wildfire) that would allow for uphill recruitment or other limiting factors at leading edges. My study is among the first to assess how understory plant distributions are shifting given climate change and fire exclusion at high elevations in the Klamath Mountains.
Citation Style
APA
Recommended Citation
Jackson, Emily Jean, "Assessing a half-century of change in understory plant range and frequency in the Klamath Mountains of California" (2026). Cal Poly Humboldt theses and projects. 2584.
https://digitalcommons.humboldt.edu/etd/2584