First Advisor

Andrés Holz

Term of Graduation

Winter 2020

Date of Publication

3-31-2020

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Geography

Department

Geography

Language

English

Physical Description

1 online resource (v, 36 pages)

Abstract

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.

Rights

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

Persistent Identifier

https://archives.pdx.edu/ds/psu/34298

Available for download on Wednesday, March 31, 2021

Included in

Geography Commons

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