Arboriculture & Urban Forestry 35(3): May 2009 159 Figure 1. Tree stabilization systems evaluated on field-grown, balled and burlapped white ash (Fraxinus americana L. ‘Autumn Purple’). From left to right, staking, guying, and root ball anchoring. three 5 cm × 5 cm × 91 cm (2 in × 2 in × 36 in) anchors were driven 61 cm vertically into the soil 76 cm equidistant from the trunk. A strap was attached to the base of each anchor with a clove hitch backed by a half hitch and secured around the trunk and over the lowest scaffold branch with a bowline. For the root ball anchoring system, four 5 cm × 5 cm × 76 cm (2 in × 2 in × 30 in) anchors were placed snug against the root ball on four corners and driven vertically into the soil until the top of the an- chors were flush with the top of the root ball. Two 2.5 cm × 5 cm × 91 cm (1 in × 2 in × 30 in) horizontal braces were then placed on top of each pair of vertical anchors and secured across the root ball using four 5 cm (2 in) #10 wood screws. Root ball anchoring was installed prior to backfilling the planting hole. Wind Load Experiment To determine appropriate wind-simulating forces for the TSS ex- periments, wind-induced bending moments were measured for a sub-sample of six ash trees using the method of Smiley and Kane (2006). Each tree was severed from its root ball just above the flare and secured in a steel sled mounted in the rear of a pickup truck (Figure 2). A prusik cord was tied around the trunk at a height of 83.8 cm (2.75 ft) and attached to a 1.8 m (6 ft) sec- tion of 0.6 cm (0.25 in) extra-high-strength steel cable using a steel carabiner and a microascender. The horizontally-oriented cable was attached to a 2268 kg capacity Dillon ED Junior dy- namometer (Weigh-Tronix Inc., Fairmont, MN), which was then secured to the front rack of the sled. The truck was then driven on a straight, nearly level course from 0 to 24.5 m/s (0 to 55 mph). As the truck was driven, a passenger recorded the force measured by the dynamometer at 7, 11, 16, 20, and 25 m/s (15, 25, 35, 45, and 55 mph). For each tree, two runs were made in opposite di- rections to minimize the effect of directional winds and the force values were averaged for each speed interval. This procedure in- troduces a component of force due to vehicle acceleration, but Kane et al. (2008) estimated it to be less than 2% of actual drag. To calculate wind-induced bending moments, force values were multiplied by the dynamometer attachment height on the trees. Figure 2. Truck-mounted tree sled used for measuring wind- induced bending moment of white ash (Fraxinus americana L. ‘Autumn Purple’) from 0 to 24.5 m/s (0 to 55 mph). Tree Pulling Procedure Trees in the short-term experiment were pulled in June 2006, five weeks after planting, to assess TSS performance before roots had substantially grown out of the root ball. Trees in the long-term TSS experiment were pulled in December 2006, seven months after planting, to assess TSS impact on tree development and stability. Volumetric soil moisture of the backfill soil in planting holes was 29.6% (SE = 0.6) and 27.6% (SE = 0.4) when trees were pulled during the short-term and long-term experiments, respectively. The same pulling procedure was used in both ex- periments. A 12-volt winch (XD 9000i, Warn Industries, Inc., Clackamas, OR) was bolted to the bucket of a skid-steer loader ©2009 International Society of Arboriculture
May 2009
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