Graduation Date
Summer 2019
Document Type
Thesis
Program
Master of Science degree with a major in Natural Resources, option Forestry, Watershed, & Wildland Sciences
Committee Chair Name
Jeffrey Kane
Committee Chair Affiliation
HSU Faculty or Staff
Second Committee Member Name
Eric Knapp
Second Committee Member Affiliation
Community Member or Outside Professional
Third Committee Member Name
Harold Zald
Third Committee Member Affiliation
HSU Faculty or Staff
Keywords
Forestry, Bark beetles, Drought, Resistance, Variable density thinning
Subject Categories
Forestry
Abstract
Long-term trends of tree mortality have increased over the last several decades, coinciding with above-average temperatures, high climatic water deficits, and bark beetle outbreaks. With the anticipation that drought and bark beetles may increase with climate change, uncertainty exists over the appropriate treatments that could ensure the future sustainability of forest resources and the ecosystem services that forests provide. Conventional thinning treatments are used to reduce stand density, with the assumption that reductions in competition can alleviate drought stress and enable trees to resist bark beetle attack. Alternative thinning treatments may also reduce stand density, but have a greater focus on increasing spatial heterogeneity. Variable density thinning is a management method intended to mimic the spatial heterogeneity that was present in mixed-conifer forests prior to logging and fire exclusion. Although the added benefits of increasing spatial heterogeneity include biodiversity, wildlife, recreation, and restoration, information is lacking on the effects that these treatments have on tree resistance to disturbances.
Since 2012, the Sierra Nevada experienced widespread tree mortality coinciding with severe drought conditions and bark beetle outbreak. This provided a unique opportunity to explore the mechanisms driving bark beetle-associated mortality following variable density thinning treatments in the central Sierra Nevada. Using dendrochronological methods, we modeled the relationship between drought resistance and bark beetle-associated mortality to evaluate if reductions in competition enhance tree resistance to bark beetles. We also determined if structural elements within variable density thinning treatments influenced the level and spatial pattern of bark beetle-associated mortality. By exploring these relationships, our findings could provide a greater understanding on the underlying mechanisms that drive mortality to disturbances and also provide information to help develop prescriptions for enhancing resistance to drought and bark beetles.
Citation Style
Forest Ecology & Management
Recommended Citation
Bernal, Alexis, "Mechanisms and spatial patterns of bark beetle-associated mortality following variable density thinning treatments in a sierra mixed-conifer forest" (2019). Cal Poly Humboldt theses and projects. 318.
https://digitalcommons.humboldt.edu/etd/318