Graduation Date
Spring 2026
Document Type
Thesis
Program
Master of Science degree with a major in Natural Resources, option Forestry, Watershed, & Wildland Sciences
Committee Chair Name
Dr. Lucy Kerhoulas
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
Dr. Rosemary Sherriff
Second Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Third Committee Member Name
Dr. Hannah Prather
Third Committee Member Affiliation
Community Member or Outside Professional
Fourth Committee Member Name
Dr. Stephen Sillett
Fourth Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Keywords
Bryophytes, Conifer encroachment, Epiphytes, Lichens, Quercus garryana
Subject Categories
Botany
Abstract
Oregon white oak (Quercus garryana, QUGA) is an ecologically and culturally important broadleaf tree species native to northern California and the Pacific Northwest. Fire suppression and subsequent encroachment by Douglas-fir (Pseudotsuga menziesii, PSME) and other conifers have made QUGA woodlands among the most threatened habitat types in the region. This study examines the influence of conifer encroachment on QUGA crown structure and nonvascular epiphyte (NVE) communities using ground- and crown-based sampling techniques.
Twenty-four trees were sampled across four sites in northern California along a gradient of conifer encroachment that was quantified as PSME basal area (BA). A total of 78 NVE species were identified, including 62 macrolichens (48 chlorolichens and 14 cyanolichens) and 16 bryophytes (13 mosses and 3 liverworts). Of these, 20 species were restricted to open conditions, 10 to encroached conditions, and 48 occurred in both conditions. Linear models indicated that crown asymmetry increased significantly with increasing PSME BA, whereas crown projection area, live crown ratio, and crown volume decreased. NVE species richness declined with increasing PSME BA, with most losses occurring in oak crowns rather than trunks. PERMANOVA revealed significant shifts in NVE community composition in both crowns and trunks driven by PSME BA. Beta mixed-effects models indicated that functional-group response to increasing PSME BA was strongest in crowns where bryophyte proportional dominance increased significantly, especially in lower crowns. Species-level beta regressions identified several shade-intolerant NVE taxa exhibiting robust declines in both crowns and trunks with increasing PSME BA. These results demonstrate that conifer encroachment alters both oak crown structure and epiphyte communities with pronounced impacts on crown-associated species.
Citation Style
APA
Recommended Citation
Copper, Courtney Jonell, "Effects of conifer encroachment on Oregon white oak crown structure and nonvascular epiphyte communities" (2026). Cal Poly Humboldt theses and projects. 2568.
https://digitalcommons.humboldt.edu/etd/2568