ARBORICULTURE ARBORICULTU URBAN FORESTRY Volume 34, Issue 4, July 2008 & CONTENTS Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) www.isa-arbor.com Michael Pavlis, Brian Kane, J. Roger Harris, and John R. Seiler The Effects of Pruning on Drag and Bending Moment of Shade Trees .............................................................207 Abstract. Arborists assume that pruning can help reduce the risk of tree failure by reducing the pressure exerted on trunks by wind (drag- induced bending moment), but there are few studies that quantify this effect. We simulated wind by driving trees in the back of a pickup truck from 0 to 24.5 m/s (0 to 55 mph) and measured drag-induced bending moment as well as tree morphometric data for Freeman maple (Acer × freemanii), swamp white oak (Quercus bicolor Willd.), and shingle oak (Quercus imbricaria Michx.). Measurements were taken before and aſter application of one of three American National Standards Institute A300 pruning types (raising, reduction pruning, thinning). Reduction of drag-induced bending moment differed by pruning type, largely in accordance with the mass of foliage and twigs removed. The effective- ness of pruning types was also species-dependent because crown architecture affected how much mass each pruning type removed. In general, per unit of mass removed, reduction pruning more effectively reduced the drag-induced bending moment than thinning or raising. Reduction pruning reduced the center of pressure height and, presumably, increased crown porosity aſter pruning. Prediction of the reduction of drag- induced bending moment was not reliable based on reduction in crown area aſter pruning. We discuss the practical applications of our findings. Key Words. Bending Moment; Drag; Pruning. Ryan Eckstein and Edward F. Gilman Evaluation of Landscape Tree Stabilization Systems .........................................................................................216 Abstract. We conducted pull tests on newly planted 7 cm (2.8 in) caliper, container-grown Quercus virginiana ‘SDLN’ PP#12015, Cathedral Oak® to sim- ulate wind loading on nine commonly used landscape tree stabilization systems. Maximum force required to rotate the root ball 20° was used to compare systems. Terra Toggle™, Brooks Tree Brace, and 2 × 2’s anchoring the root ball withstood the largest forces. Typically, trees secured by these three broke before the systems failed indicating that the systems were very effective. T-stakes, dowels, and Tree Staple™ performed no better than nonstaked controls. The three guying systems tested, ArborBrace®, Duckbill®, and rebar and ArborTie®, were statistically similar and required more force to failure than con- trols, but less than the group that withstood the largest forces. Direction of pulling had no influence on force to failure for any stabilization system tested. Key Words. Bracing; Guying; Planting; Pulling Tests; Stabilizing; Tree Staking; Wind. John Gathright, Yozo Yamada, and Miyako Morita Tree-Assisted Therapy: Therapeutic and Societal Benefits from Purpose-Specific Technical Recreational Tree-Climbing Programs ....................................................................222 Abstract. This article explains how program design can increase the therapeutic and societal benefits from programs focused on technical recre- ational tree-climbing. We compare a recreational program with a tree-assisted therapy program that includes purpose-specific therapeutic, edu- cational, and motivation elements. We find that the additional elements included in the tree-assisted therapy program were effective in enhancing the benefits from the tree-climbing activity. Key Words. Community Forests; Environmental Psychology; Mood States; Outdoor Recreation; Societal Benefits; Tree-Assisted Therapy; Tree-Climbing; Urban Forests. ©2008 | International Society of Arboriculture | ISSN:1935-5297
July 2008
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