Graduation Date

Summer 2017

Document Type

Dissertation/Thesis

Program

Master of Science degree with a major in Natural Resources, option Forestry, Watershed, & Wildland Sciences

Committee Chair Name

Rosemary Sherriff

Committee Chair Email

sherriff@humboldt.edu

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Phillip van Mantgem

Second Committee Member Email

pvanmantgem@usgs.gov

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Jeffrey Kane

Third Committee Member Email

Jeffrey.Kane@humboldt.edu

Third Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Environmental Science and Management

Abstract

Climate change is predicted to increase the frequency, duration, and severity of drought events across many bioregions. Forest managers have two active management techniques to promote resistance and resilience to drought: prescribed fire and mechanical thinning. Generally applied to reduce fuels and fire hazard, treated areas may also reduce competition for resources that may improve tree-growth during drought and reduce mortality. The recent severe and prolonged drought in California allowed me to investigate the effects of climate stress and fuel treatments on tree growth responses in a dry mixed-conifer forest ecosystem.

To assess tree-growth responses to fuel treatments during severe drought I collected and analyzed tree core samples from 300 ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) trees in the mixed-conifer forests of Whiskeytown National Recreation Area in northern California. Tree-ring data was used to investigate factors that influenced tree-growth during the study period (2008-2015). Growth was positively associated with crown ratio and negatively associated with local competition and climate water deficit (1-yr lag). Douglas-fir generally had higher annual growth than ponderosa pine, though factors affecting growth were the same for both species. Overall, trees in thinning treatments had higher drought resistance compared to untreated stands. Drought resistance was significantly higher in treated stands compared to untreated stands during both years of extreme drought (2014-2015) for ponderosa pine but only one year (2014) for Douglas-fir. This information can help land managers decide on forest management practices that may enhance forest resistance to future drought events.

Citation Style

APA

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