Factors influencing tree vigor and structural failure along powerline corridors in Northern California: A multi-species analysis

Author

• David Justin Dorval, Cal Poly HumboldtFollow

Graduation Date

Summer 2026

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources, option Forestry, Watershed, & Wildland Sciences

Committee Chair Name

Rosemary Sherriff

Committee Chair Affiliation

Cal Poly Humboldt Faculty or Staff

Second Committee Member Name

Lucy Kerhoulas

Second Committee Member Affiliation

Cal Poly Humboldt Faculty or Staff

Third Committee Member Name

Kerry Byrne

Third Committee Member Affiliation

Cal Poly Humboldt Faculty or Staff

Keywords

Tree failure, Tree vigor, Power lines, Northern California

Subject Categories

Natural Resources

Abstract

Tree failures (e.g., stem breakage, uprooting, or branch drop) can pose significant risks to public safety, particularly along powerline corridors for the risk of power outages and wildfire ignitions. In California, tree-related powerline failures have led to severe ecological and human costs in recent years. Despite extensive research on tree failure in urban environments and post-disturbance contexts, comparatively little empirical work has examined where powerlines intersect largely unmanaged stands. This study evaluates tree failure trends across multiple forest types in Northern California by examining how tree-level characteristics influence recent growth and failure occurrence in regionally dominant tree species. Specifically, the study investigates (1) which tree- and site-level characteristics are associated with recent tree vigor over the past 10 years and whether these relationships differ between built (adjacent to powerlines) and unbuilt (undeveloped interior forest) plots; and (2) which characteristics (defects and tree vigor) are predictive of structural tree failure. Across four counties, 49 sites were randomly sampled using a paired approach (built and unbuilt) with 1,288 trees used for analysis. Linear mixed effects models were used to analyze tree vigor (10-year growth) and binomial logistic regression was used to evaluate structural failure.

Tree size and crown structure were consistently associated with recent growth, whereas structural defect metrics (i.e., architectural, biological, or physical) were the most consistent predictors of failure probability. Tree vigor showed weak and inconsistent relationships with failure, indicating that reduced vigor alone is not a reliable indicator of structural failure likelihood. Differences in both vigor and failure probability between built and unbuilt plots were marginally significant or non-significant across species, suggesting that intrinsic tree characteristics and structural condition play a greater role in failure probability than proximity to infrastructure. These findings indicate that vegetation management in forested powerline corridors should prioritize the identification and mitigation of trees with severe structural defects, while accounting for species-specific differences in how these characteristics influence failure probability. Using an approach that weights certain tree characteristics by species can improve the effectiveness of selection criteria used to identify trees for pruning and removal, thereby reducing unnecessary treatments while maintaining infrastructure safety.

Comments

This thesis is planned for future publication.

Citation Style

Elsevier Journal of Forest Ecology and Management

Recommended Citation

Dorval, David Justin, "Factors influencing tree vigor and structural failure along powerline corridors in Northern California: A multi-species analysis" (2026). Cal Poly Humboldt theses and projects. 2598.
https://digitalcommons.humboldt.edu/etd/2598

Collaboration

1