160 Alvey et al.: Efficacy of Conventional Tree Stabilization Systems season shoot elongation was also measured on four randomly selected first-order branches. Three soil cores [10 cm wide × 15 cm deep (4 in × 6 in)] were extracted from the backfill soil equidistant around the root ball of each tree. Roots were hand- sorted from the cores, digitally scanned, and analyzed with WinRHIZO PRO digital image analysis software (Regent In- struments, Inc., Quebec, Canada). Roots were then oven dried and weighed. After pulling the root balls of long-term trees from the ground, a count was taken of broken roots ≥ 2 mm diam- eter that were visibly extending from the backfill soil opposite the applied load. In cases where a large root with many small- er rootlets had broken, the individual rootlets were counted. Figure 3. Configuration of pulling equipment and dynamometer used to evaluate tree stabilization systems (staking shown) on field-grown, balled and burlapped white ash (Fraxinus americana L. ‘Autumn Purple’). (Bobcat® S185, Bobcat Co., Gwinner, ND), which was posi- tioned 4.6 m (15 ft) from the tree and elevated to 1.8 m aboveg- round. The winch cable was passed through a pulley attached to the tree 1.8 m aboveground and connected to the dynamometer, which was secured to the winch-mounting bracket (Figure 3). Before pulling the trees, trunk orientation was measured both parallel to and normal to the direction of the applied force at 76 cm above the ground with an angle gauge (Johnson 700 Magnetic Angle Locator, Johnson Level & Tool Mfg. Co., Me- quon, WI). All trees were pulled parallel to the planting row in a single direction; Eckstein and Gilman (2008) found no signifi- cant difference in TSS strength when pulled in multiple direc- tions. Staked and guyed trees were oriented with two stakes/ anchors near the winch and one stake/anchor on the opposite side of the tree such that the pull was in line with the oppos- ing stake/anchor. Root ball anchored trees were oriented with the horizontal cross braces perpendicular to the plane of pull. Once the pulling apparatus was installed on the tree, the winch was used to steadily increase cable tension until the target force [690 N*m – the maximum bending moment recorded during the 25 m/s (55 mph) wind load experiment] was observed on the dy- namometer. At that point, the winch was released, the cable was removed from the tree, and trunk orientation was measured. In the short-term experiment, trees were pulled a second time with in- creasing force until either the tree or TSS failed; maximum force was then recorded. In the long-term TSS experiment, TSS com- ponents were removed prior to pulling. To avoid soil disturbance, stakes and guy anchors were not removed from the ground; only straps and guylines were removed. The horizontal cross braces were removed from the root ball anchored trees. Four succes- sive pulling loads were then applied to each tree to generate pro- gressively greater bending moments (690, 1651, 3305, and 4832 N*m). Between each successive pull, the winch was released and trunk orientation was measured. After the final pull, the root ball was winched from the ground to permit root evaluation. Tree Growth Measurements Before pulling the long-term trees, tree height, trunk orienta- tion, trunk caliper, and trunk taper were remeasured. Current ©2009 International Society of Arboriculture Data Analysis In the short-term experiment, one-way analysis of variance (ANOVA) was used to analyze the fixed effects of TSS treat- ments on tree stability and component failure force. In the long-term experiment, one-way ANOVA was used to ana- lyze the fixed effect of TSS treatments on tree stability and growth. When the treatment main effect was significant for a dependent variable, multiple comparisons were made be- tween treatment groups using Tukey’s HSD test (a = 0.05). RESULTS Short-Term TSS Experiment Under ambient site conditions [maximum recorded wind gust of 12 m/s (27 mph)], no TSS affected tree stability during the five weeks after planting (Table 2). Average change in trunk ori- entation was ≤ 2° across treatment groups. The greatest change observed in a single tree (a root ball anchored tree) was 10°, which was barely perceptible without a measuring device. When the trees were winched, there were no differences in tree sta- bility among the TSS types, all of which marginally improved stability relative to controls (Table 2). The mean change in trunk orientation was much greater in controls; however, high variance obscured statistical differences from stabilized trees. Guyed trees endured significantly greater force before fail- ure than both staked and root ball anchored trees, for which force was statistically similar (Table 2). For two-thirds of guyed trees, the initial component failure was the single anchor op- posite the direction of the applied load. Similarly, in all staked trees the initial component failure was the opposite side stake. In the majority of cases, guy anchors and stakes broke at or near the soil line. Root ball anchoring systems typically failed when the horizontal cross brace on the opposite side of the pull direction separated from one or both vertical soil anchors. Long-Term TSS Experiment No TSS affected tree height growth, shoot elongation, root diame- ter, root length, or root mass seven months after planting (Table 3). Staked trees increased in trunk caliper significantly less than guyed or root ball anchored trees, but similar to control trees. The taper of staked trees decreased during the growing season, which was mar- ginally different from guyed trees, for which trunk taper increased. Under ambient site conditions [maximum recorded wind gust of 17 m/s (38 mph)], trees with and without TSS did not differ in their stability during the seven months after planting (Table
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