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

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

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