Graduation Date

Spring 2018

Document Type

Thesis

Program

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

Committee Chair Name

Dr. Rosemary Sherriff

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Phil van Mantgem

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Jeffrey Kane

Third Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Forestry

Abstract

With the growing impacts of climate change worldwide and great uncertainty about forests’ vulnerability to a changing climate in the Pacific Northwest, knowledge of coast redwood forest response is crucial. Many of the studies investigating forest response to drought focus on inland forest types rather than coastal forests. This study examined tree growth and drought response in coastal forests at restoration thinning sites, evaluating responses to local climate, tree-level competition, and site-level factors. Tree cores were extracted from previously harvested stands at three restoration sites in Redwood National Park, California, from both thinned and unthinned stands. Douglas-fir (Pseudotsuga menziesii) and coast redwood (Sequoia sempervirens) trees > 20 cm diameter at breast height were sampled (n = 274), spanning six different thinning prescriptions with varying years of thinning treatments (1978, 1995, and 2007). Generalized linear mixed effects models were used to evaluate the influence of local climate, competition, site, stand age, time since thinning, and species on tree growth and drought response. Competition was found to be negatively associated with tree growth for both tree species (p < 0.0001), and tree-level competition had a stronger influence on growth than climatic factors at all three sites. For both species combined, mean minimum temperatures had a small negative effect (p = 0.0073) on growth, whereas mean annual precipitation had a positive effect on growth (p < 0.0001). The site closest to the coast and with the most recent thinning treatment harbored the fastest growing trees (µ = 2312 mm2 annually). Local competition had a strong negative effect on drought resistance during the recent drought (2012 to 2015) (p < 0.0001), and drought resistance did not appear to vary by treatment, site, or species. These results strongly suggest that restoration thinning treatments have the added potential of increasing tree growth and resistance to drought under current stand and climate conditions and possibly under future climate stress.

Citation Style

APA

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