Portland State University. Department of Geography
Term of Graduation
Date of Publication
Master of Science (M.S.) in Geography
1 online resource (v, 36 pages)
Climate variability impacts on Pacific Northwest forests are of great concern, especially on evergreen coniferous ecosystems which dominate a large portion of the landscape. Understanding the effect of climate variability and its potential impacts on forest regeneration is crucial, as this is a foundational process with long-lasting consequences on structure and composition of future ecosystems. The objective of this study was to uncover the possible influences of natural climate variability on conifer tree establishments on the Muddy Rivers Lahar following the 1980 eruption of Mount St. Helens, WA. We hypothesized that tree establishment increased gradually over time, tree establishments was limited by moisture availability and ENSO with temperature mediating tree establishment at higher elevations. Tree-establishment dates at the annual-scale were determined from ca. 744 individual conifer trees that were harvested along the Muddy Rivers Lahar. Tree establishment distribution by species and shade tolerance groups were clustered and plotted to graphically interpret possible spatial patterns across the Lahar. Years of high tree establishment are primarily associated with above average temperature conditions during winter, spring and summer of the year of establishment, but also prior and after the establishment year, suggesting a climatic effect on germination, cone production, and seedling survival, respectively. Our findings also suggest that temperature and tree species traits (i.e. shade tolerance) mediated climate-establishment relationships. Combined, our results suggest that under ongoing warming trends, tree establishments have not been negatively affected at the elevation and maritime conditions of the Muddy River Lahar.
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Falcon-Dvorsky, Ignacio D., "Warmer Conditions Favor Conifer Tree Establishment at the Muddy River Lahar in Mt. St. Helens, Washington" (2020). Dissertations and Theses. Paper 5595.
Available for download on Wednesday, March 31, 2021