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Author ORCID Identifier

https://orcid.org/0000-0002-1793-3945

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Environmental Conservation

Year Degree Awarded

2020

Month Degree Awarded

February

First Advisor

Brian C. P. Kane

Second Advisor

H. Dennis P. Ryan III

Third Advisor

Wesley R. Autio

Fourth Advisor

Yahya Modarres-Sadeghi

Subject Categories

Forest Management

Abstract

During pruning, arborists often intend to increase a tree’s resistance to wind loading by selectively removing branches, but there are few studies examining the efficacy of these interventions, especially for large, open-grown trees. In this study, the mass and vibration properties of Senegal mahogany (Khaya senegalensis) and rain tree (Samanea saman) were measured before and after the crowns of trees were incrementally raised or reduced between 0 and 80%. In addition, the wind-induced vibration and bending moments of Senegal mahoganies were monitored before and after the same pruning treatments. For both species, total mass and leaf mass both decreased faster on reduced than raised trees. The frequency and damping ratio of trees varied with the severity of pruning for reduced, but not raised, trees. The frequency of reduced trees generally increased with pruning severity. In contrast, damping ratio of reduced trees generally decreased with the severity of pruning, except for the unique increase in damping ratio on Senegal mahoganies reduced by 10 to 20%. Post-pruning vibration properties were significantly related to the post-pruning morphometric attributes of reduced, but not raised, trees. For reduced trees, most of the examined tree and branch attributes better explained variability in post-pruning frequency than damping ratio.

At each pruning severity, Fourier energy spectra showed that raised trees continued to vibrate primarily at their fundamental mode. As the severity of pruning increased, however, reduced trees vibrated progressively less than raised trees at all analyzed frequencies. Similarly, the average 30-minute maximum bending moment associated with a given 30-minute maximum wind speed decreased more for reduced than raised trees at low pruning severities. For those seeking to decrease the likelihood of tree failure, the results suggest that arborists should reduce trees to change their vibration properties and wind loads, but trees should be reduced by small amounts to avoid the undesirable decrease in damping ratio. Although the observed changes on reduced trees contributed favorably to risk mitigation, there are many adverse biological consequences of some pruning methods, especially topping, that shorten tree parts without considering the anatomy of trees or remove an excessive amount of branches and leaves, and arborists should use good judgment when pruning trees to reduce their size without unnecessarily disturbing tree growth and development. Moreover, these mechanical properties will inevitably change as trees grow after pruning, and more work is needed to understand both the long-term biological and mechanical consequences of pruning treatments.

DOI

https://doi.org/10.7275/9rwz-5774

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