12 Persad et al.: Effects of Emerald Ash Borer Infestation on Tree Structure • Group III: Five ash trees that after confirmed EAB infesta- tion had dead canopies (there were no signs of life in ter- minal branches). All trees had small amounts of epicormic sprouting at the base. Based on the city forester’s records, it is estimated that initial EAB infestation may have been three to four years earlier. The ultimate fracture force, moments, and bending stresses at the point of fracture were determined by applying static loads to an approximate center of gravity (visually estimated) of selected branches. Three branches from each of five ash trees in each group were loaded until failure. Forty-five branches were thus broken in this study. Pre branch-breaking measurements that were recorded included: DBH using an arborist diameter tape and branch diameter at the branch collar using a hinged caliper (12.5 cm) (Forestry Supplies, California, U.S.). Visual estimates (based on initial measurements of first few branches) of the approximate angle of the branch attachment (branch to stem attachment angles ranged from 10 to 60 degrees upward slope) were also record- ed. Only first order branches that were directly attached to the main trunk were selected. Branches were between 3 to 10 cm in diameter and any with apparent defects were not used in the trial. Study Part 1. Static Loading of Branches A 2,925 kg, 1.27 cm, three-strand rope (New England Ropes) was tied around the base of the target tree using a clove hitch knot [Rope A] (Figure 1). A 1,000 kg hand winch or ‘come along’ (Lug All Corporation, Morgan, Pennsylvania, U.S.) [C] was con- nected to rope A using a 3,960 kg, 8 mm spliced loop (Sherrill Tree, Greensboro, North Carolina) [D] and a six-coil Prusik knot. The hook in the come along could then go through the loop made in the spliced loop. Rope A was connected to the rear mounted hitch of a stationary truck (Ford F-150) and pulled taut using the come along. Rope A formed a firm horizontal anchor line to which a 3,825 kg, 7.62 cm rigging pulley (CMI, Franklin, West Virginia, U.S.) [E] was connected, using a 3,645 kg, 1.27 cm blue streak spliced loop (Samson Ferndale, Washington, U.S.) [F]. A second rope system [Rope B] consisted of a 4,005 kg yellow endless polyester strap (Buckingham) [G] that was looped using a girth hitch around the target branch at an estimated (visually) approximate center of gravity (CGv). A Dillon 500 kg dyna- mometer (Dillon Quality Plus Inc., Kansas City, Missouri, U.S.) [H] was connected using a 5,058 kg steel rigging double locking carabiner (International Safety Components, Ltd, Bangor, Gwyn- edd, UK) [I]. At the bottom of the dynamometer, another rig- ging double locking carabiner [J] was connected to a three-strand rope (3,200 kg) with an anchor bend. The rope was then threaded through the 7.6 cm rigging pulley [E] that was attached to Rope A. Rope B was then wound around the 900 kg capacity Good Rig- ging Control System (GRCS, Greg Good, Wisconsin, U.S.) [K] and mounted on a platform connected to a standard trailer hitch on the rear of the truck. The GRCS was used to apply the static load. Upon limb breakage, an arborist climber used a hand saw to prune off the entire broken limb at the point of union with the trunk. The branch was then lowered to the ground. Six main post branch-breaking measurements that offered meaningful relationships in the study were retained for further calculations: (1) Ultimate fracture force (F) determined from the dynamom- eter at time of breakage (2) Entire length of the broken branch (LB) measured along the branch (3) Distance (L = lever arm) between the projection (vertical to a horizontal plane) of the load application point and the projection (vertical to a horizontal plane) of the fracture point along a horizontal line (Lilly and Sydnor 1995) (4) Diameter (D) of the branch as close to the fracture as pos- sible and on the branch and stem-union side. Two mea- surements on opposite orientations were taken and a mean value was computed. (5) Distance of fracture point from branch union (LFU the branch (6) LFU as a percentage of the entire branch length LB Calculation of Moments and Bending Stresses The moment (M) and maximum bending stress (σ) at failure were calculated according to Lilly and Sydnor (1995). Moments (M) were calculated using the formula: M = F•L; maximum bending stress (σ) at failure was calculated using the formula: σ = 4FL/πr3 . Radius (r) used was determined from diameter (D). The Zone of Fracture Figure 1. Schematic outline of the ropes and equipment configu- ration used for static loading branches from visually un-infested and EAB-infested green ash trees in an evaluation of the material properties of ash trees in northwest Ohio in 2009. (A) Horizontal anchor rope, (B) tension rope, (C) hand winch, (D) six-coil Prusik knot, (E) rigging pulley, (F) blue streaked splice loop, (G) polyes- ter strap, (H) dynamometer, (I and J) double locking carabiner, (K) Good Rigging Control System. ©2013 International Society of Arboriculture A region of the branch consisting of the visually identified fracture (usually within approximately 30 cm on either side of the break zone) was sawed off, photographed, and labeled. This region was considered the zone of fracture (ZF) in the study. Visual checks were made on all failed branches to ensure that no areas of decay or cankers that could potentially compromise the evaluations were present. Branch cross section discs measuring 2.54 cm thick were cut 48 hours after severing the ZF from trees using a 25.4 cm com- pound miter saw. Discs were taken as close to the fracture point as possible and towards the branch collar. Discs were weighed to ) along (%LFU LB )
January 2013
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