Graduation Date
Summer 2022
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. Lucy Kerhoulas
Second Committee Member Affiliation
HSU Faculty or Staff
Third Committee Member Name
Dr. Andrew Stubblefield
Third Committee Member Affiliation
HSU Faculty or Staff
Fourth Committee Member Name
Dr. Phillip van Mantgem
Fourth Committee Member Affiliation
Community Member or Outside Professional
Keywords
Klamath ecoregion, Shasta fir, Brewer spruce, Western white pine, Sugar pine, Sitka spruce, Western hemlock
Subject Categories
Forestry
Abstract
Frequent and intense drought events are rapidly altering stand dynamics in western North American forests. Climate, competition, and site characteristics can affect the growth responses of individual trees to drought stress. The ecological and geographical diversity of northern California provides a unique opportunity to measure these responses across species, habitat types, and levels of competitive pressure. This study used dendrochronological techniques and linear mixed-effects models to assess growth responses to drought in four montane and two coastal conifer species across 54 study sites (nine sites per species and 540 trees total) in northern California. Growth was evaluated from 2002-2018 and the drought period was from 2013-2015. There were significant differences among species and environments (coastal or montane) in growth, drought resistance and resilience, and annual latewood proportion. Growth in montane species was generally positively correlated with moisture availability (Palmer Drought Severity Index) and negatively correlated with competitive pressure. The four montane species maintained relatively stable drought resistance, resilience, and latewood proportion across the study period. In contrast, growth in the two coastal species was influenced more by tree size and crown ratio than moisture availability or competition. As the 2013-2015 drought proceeded, coastal species showed marked reductions in drought resistance and resilience and increases in latewood proportion. The six focal species endured this drought in northern California with reasonably high resistance and resilience. However, the lower resistance observed in coastal species suggests that they may be at risk for increased stress and mortality in the event of more severe, prolonged, and/or frequent droughts.
Citation Style
APA
Recommended Citation
Roletti, Gabriel J., "Drought responses across diverse conifer species, habitats, and competitive gradients in Northern California" (2022). Cal Poly Humboldt theses and projects. 586.
https://digitalcommons.humboldt.edu/etd/586