Date of Award

Fall 2026

Abstract

Beech leaf disease (BLD) is an emerging forest disease affecting American beech (Fagus grandifolia), yet its effects on tree growth remain incompletely quantified. This study used dendrochronological methods to evaluate patterns of growth decline associated with BLD across multiple sites in the northeastern United States. Basal area increment (BAI) and relative BAI (relBAI) were used to quantify growth, with relBAI standardizing beech growth to co-occurring non-beech species to account for site-level environmental variation. Mixed-effects models were used to assess growth decline as a function of time since county-level BLD detection, disease severity, and hierarchical variation among trees and sites. The final lag-0 model treated the county-level detection year as an ambiguous onset year and excluded it from the modeled post-detection response period. Growth decline increased progressively in the years following county-level BLD detection, indicating a sustained, multi-year reduction in growth rather than an abrupt, single-year response. Models including the single-year BLD severity score did not improve model performance relative to the model excluding BLD severity, indicating that this field-measured severity metric did not explain additional variation in growth decline beyond time since detection and BBD severity. Beech bark disease (BBD) severity also had no detectable effect on growth decline and did not modify the rate of decline through time. Substantial variability was observed among trees and sites, highlighting heterogeneity in growth responses across the study system. These results support interpreting BLD-associated growth decline as a progressive, time-dependent process and emphasize the importance of longer-term monitoring for assessing disease impacts on forest health.

Document Type

Master's Thesis

First Advisor

Jeff Garnas

Second Advisor

Cameron McIntire

Third Advisor

Michael Simmons

Department or Program

Natural Resources and Environmental Studies

Degree Name

Master of Science

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