ii Gary Johnson, Chad Giblin, Ryan Murphy, Eric North, and Aaron Rendahl Boulevard Tree Failures During Wind Loading Events ....................................................................... 259 Abstract. Wind loading events vary in their intensity and degree of damage inflicted on urban infrastructure, both green and gray. Damage to urban trees can begin with wind speeds as low as 25 miles per hour, especially when those trees harbor defects that predispose them to structural failures. The tree damage triangle integrates the three main factors that influence tree failures during wind loading events, namely the site characteristics, the (wind) load- ing event and any defects of the trees in question. The degree of damage that trees experience is generally a function of these factors overlapping each other. For instance, when the potential damage from wind loading events is exacerbated by poor tree architecture and compromised site conditions, the likelihood of significant damage is realized. Two studies on the damage to urban trees and the predictability of damage are reviewed; one study is a long- term gathering of wind loading events and accompanying damage to trees while the other is a case study of one storm in one city on one day. Both stud- ies revealed critical pre-existing conditions that left trees vulnerable to whole tree losses: large trees in limited boulevard widths and severed roots as a result of sidewalk repair. Keywords. Construction Damage; Tree Architecture; Wind Loading Events. Jason W. Miesbauer, Andrew K. Koeser, Gary Kling, Gitta Hasing, and Marvin Lo Impact of Planting Depth on ‘Patmore’ Growth, Stability, and Root System Morphology............................................................................................................ 270 Abstract. Trees are often deeply planted as a result of nursery and landscape practices. While past research has investigated the impact of deep planting on tree growth and survival, its impact on whole-tree stability is not well documented. Green ash (Fraxinus pennsylvanica ‘Patmore’) trees were planted at three different depths in research plots and established for nine years. In assessing aboveground growth, planting depth had no effect on stem diame- ter growth (measured as dbh) (P = 0.421; n = 32) or tree height (P = 0.501; n = 32). Static pull tests were conducted to evaluate the consequences of deep planting on tree stability. Using structure from motion (SfM) photogrammetry-derived computer models to assess root architecture, we found the most significant factors affecting tree stability were: 1) root volumes in the top 10 cm of the soil in a 90° wedge on the side opposite of the pull direc- tion; 2) root volumes 40.1 to 50 cm deep in a 90° wedge on the side opposite of the pull direction; and 3) root volumes deeper than 60.1 cm deep in a 90° wedge on the side opposite of the pull direction (final model: P < 0.001; n = 30; adjusted R2 = 0.852). The importance of structural root morphology throughout the soil profile and implications for urban root-soil relations on tree stability are discussed. Keywords. Bending Moment; Photogrammetry; Root Architecture; Tree Biomechanics; Tree Physiology; Tree Planting. Andreas Detter, Philip J. E. van Wassenaer, and Steffen Rust Stability Recovery in London Plane Trees Eight Years After Primary Anchorage Failure ............ 279 Abstract. As the intensity and frequency of strong storms increase, the potential for damage to urban trees also increases. So far, the risk of ultimate failure for partially uprooted trees and how they may recover their stability is not well understood. This study sets out to explore if and to what extent trees can regain anchoring strength after their root systems have been overloaded. In 2010, ten London Plane (Platanus × acerifolia) trees were sub- jected to destructive winching tests. Two trees were pulled to the ground while eight were loaded until primary anchorage failure occurred and were left standing with inclined stems. In 2013, two trees had failed and six were re-tested nondestructively. By 2018, another tree had failed, and we tested the remaining five again. Rotational stiffness was derived for all trials and served as a nondestructive proxy for anchoring strength (R² = 0.91). After eight years, one tree had regained its original strength, while four had reached between 71 and 82% of their initial rotational stiffness. However, three trees failed during the observation period. The results indicate that partially uprooted trees may re-establish stability over time, but some will not and may fail. In our small data set, it was not possible to identify visual criteria that could provide a reliable indication of tree stability recovery, but our data sup- port the assumption that nondestructive pulling tests can be successfully employed to determine good vigorous candidates for retention after partial uprooting. Keywords. Partial Uprooting; Pulling Test Method; Restabilization; Storm Damage; Tree Biomechanics. Jason Grabosky Observation of Wind-Loading Influences in Nonconcentric Radial Root Growth in Two Maple Species ............................................................................................................................ 289 Abstract. In 2010 and 2016, Acer saccharinum and Acer rubrum roots were harvested and processed into transverse serial sections to observe cross- sectional radial growth patterning in response to wind. Trees on the edge of a plantation and from interior positions were selected, and windward/ leeward roots were targeted for a comparative assessment. While some observations were suggestive of a response to wind exposure, they were not definitive. Particularly in the windward versus leeward comparison within either edge or interior ground in terms of root size or radial growth pattern, there were no differences observed. In general, the loss of observed upward radial growth bias very closely coincided with the ending of the Zone of Rapid Taper in the architecture of the root plate. Keywords. Edge Effect; Wind Exposure; Zone of Rapid Taper. ©2019 International Society of Arboriculture F r axinus pennsylvanica
November 2019
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