Pruning is commonly used to mitigate the risk of tree failure by selectively removing tree parts exposed to the wind, but there have been few studies examining changes in wind loads after pruning, especially for large, open- grown trees. In this study, the wind-induced vibration and bending moments of Senegal mahogany (Khaya senegalensis) were monitored before and after a series of pruning treatments: crowns were either raised or reduced at incremental severities between 0 and 20 %. Under ambient wind loads, axial trunk deformation was measured using two displacement probes installed orthogonally on each tree, and each displacement probe was calibrated using a static load test to convert the measured trunk deformation to a bending moment. During each pruning treatment, ambient wind conditions and trunk deformation were monitored simultaneously for extended periods of time. As pruning severity increased, Fourier spectra showed that raised trees continued to vibrate primarily at their fundamental mode, but reduced trees vibrated progressively less than raised trees. Similarly, the average 30-minute maximum bending moment, associated with a given 30-minute maximum wind speed, decreased more for reduced than raised trees. Consistent with existing studies of small trees, the results suggest that arborists should reduce trees to decrease wind loads and, concomitantly, the likelihood of tree failure. Still, excessive leaf loss may constrain the usefulness of increasingly severe pruning on reduced trees: average leaf area index decreased by half on trees reduced by 20 %. More work is needed to understand the long-term physiological and mechanical consequences of pruning treatments.

Illustrative figure

Figure 1: Using displacement probes mounted on the lower trunk of each tree, wind-induced deformation (m) was measured and converted to a bending moment (N\(\cdot\)m) using a calibration coefficient determined from a static load test.

Materials

Paper (preprint))

BibTeX citation

@article{BurchamAutioModarresSadeghiKane:2021,
    Author = {Daniel C. Burcham, Wesley R. Autio, Yahya Modarres-Sadeghi, and Brian Kane},
    Doi = {10.1016/j.ufug.2021.127100},
    Journal = {Urban Forestry & Urban Greening},
    Month = {3},
    Pages = {127100},
    Title = {After pruning, wind-induced bending moments and vibration decrease more on reduced than raised Senegal mahogany (Khaya senegalensis)},
    Volume = {61},
    Year = {2021}}