Graduation Date
Spring 2025
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. Kerry Byrne
Third Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Fourth Committee Member Name
Dr. Alan Tepley
Fourth Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Keywords
Northern California, Powerlines, Tree failure, Fuels
Abstract
Rural powerlines are critical for delivering electricity to communities far from urban areas but present a significant hazard when located in forested regions. During strong wind events, tree failure (i.e., broken branches, snapped stems, and windthrow) can bring combustible material in contact with high-voltage lines, causing electrical outages or setting fire to vegetation below the powerline. Additionally, elevated forest fuel loading can increase wildfire rate of spread and intensity, potentially increasing negative ecosystem impacts and decreasing containment capacity during powerline- ignited wildfires. The risks associated with rural electrical infrastructure, tree failure, and elevated fuel loading emphasize the need for improved risk assessment to prevent outages and powerline-ignited wildfires. In this study, I compared forest and microclimate conditions between the powerline corridor forest edge and the adjacent interior forest, and evaluated the site-level conditions driving levels of tree damage and dead and down fuels across diverse study sites in Northern California. I evaluated tree damage (i.e., structural damage, biotic damage, and beetle presence) and fuels (i.e., litter and duff depths, fine woody fuel loads, and abundance of coarse woody debris) at 59 sites (118 paired plots) within four dominant vegetation types: redwood (Sequoia sempervirens), Douglas-fir (Pseudotsuga menziesii), yellow pines (Pinus ponderosa, P. jeffreyi), and iii deciduous oaks (Quercus kelloggii, Q. garryana, Q. douglasii). Sampling included visual assessments of tree health and damage and line-point intercept transects to quantify forest structure and dead and down fuels. Generalized linear models (GLMs) were used to compare forest conditions between plot types: powerline corridors (Built) and the forested environment (Unbuilt). GLMs were also used to investigate trends in tree damage and fuels with site-level variables. I found that there were a few differences in forest conditions between Built and Unbuilt environments (e.g., greater variation in canopy closure in redwood and Douglas-fir Built plots, more extreme microclimate variables in Built plots for all vegetation types) but were similar for other conditions. Tree damage varied significantly with several site-level variables, including climatic water deficit, overstory species diversity, stand basal area, and plot type, with distinct relationships emerging among vegetation types. Further, deciduous oak plots had comparatively more structural and biotic damage and redwood plots had comparatively less beetle presence. Dead and down fuel levels varied by climatic water deficit, plot type, and vegetation type. Litter and duff depths were driven by climatic water deficit and woody fuel levels were driven primarily by plot type. Utility company vegetation management planning can use these results to inform further investigations into local drivers of tree damage and fuels. Management should continue, however, to be informed by species-level trends in tree damage and locally-relevant trends in fuels.
Recommended Citation
Ziegler, Zoe J., "Patterns of tree damage and fuels around powerlines in Northern California" (2025). Cal Poly Humboldt theses and projects. 2293.
https://digitalcommons.humboldt.edu/etd/2293
Collaboration
1