Arboriculture & Urban Forestry 40(4): July 2014 cially pines (Smiley et.al. 2000; Mickovski and Ennos 2002; Dupuy et al. 2005a). Larger diameter, mature dicot trees oſten do not have oblique roots or tap roots due to species genetics, root decay, or soil depth limitation; thus, larger trees may be more susceptible to damage from lateral root cutting than the smaller trees (personal observa- tion). Trees with tap or horizontal root system types may be affected differently by root cutting. Buttress roots are roots near the base of the tree that support the tree and equalize mechanical stress (Lilly 2011). When these roots are significantly decayed or pruned, tree stability is reduced (Smiley 2008). The purpose of this study was to evaluate the effects of buttress root pruning on tree stability and to compare different methods of assessing root loss. This type of individual root cutting was intended to simulate root loss from pruning or decay. MATERIALS AND METHODS Ten plantation-grown, 39-year-old Acer rubrum (red maple) trees with a mean diameter measured at 1.37 m (DBH) of 30 cm (S.E. = 0.2) were se- lected for testing between August 23 and 26, 2010, at the Davey Research Farm in Shalersville, Ohio, U.S. (N41.235, W81.168, elevation 378 m). Trees were spaced at 3 m within rows and 4.5 m between rows. The soil type at the site was a Ravenna silt loam with a 2%–6% slope. This soil type is some- what poorly drained and has a water table at 15 to 45 cm (Soil Survey of Portage County, Ohio 1978) Prior to conducting tests, the base of each tree was partially excavated using a supersonic air tool (Air-Spade™, GuardAir Corporation, Chicopee, Massachusetts, U.S. or Air Knife™, Allison Park, Pennsylvania, U.S.) to expose the buttress roots. Tree stability testing was conducted using the methodology described in Smiley (2008). Two roof- ing nails (5 cm) were driven into the trunk xylem 15 and 75 cm above grade. The nail at 75 cm was installed directly above the nail driven at 15 cm. A digital level (Smart Level, MD Building Products, Oklahoma City, Oklahoma, U.S.) was strapped to the trunk of the tree to ensure contact with the two nails. The level was adjusted at the beginning of the pull test to read 90 degrees (+0.05 degree). A dynamometer (Dillon ED-200+, Fairmont, Minnesota, U.S.) was attached to the trunk of the 231 subject tree, using a webbing sling. A wire rope (11.5 mm in diameter) or cable was attached to the trunk at a height of 3 m and was run directly to a hand operated mechanical winch that was anchored to the base of another tree. The 3 m attachment height was chosen so as to provide significant bending moment at the base of the trunk while minimizing trunk bending. Trees were pulled so that the trunk achieved an angle of one degree from vertical. Force was released after each pull; this was repeated three times. The peak dynamometer reading was recorded for each pull. The average of the three peak readings was recorded and used for analysis. Angle of the pull line was measured for each tree. This procedure was defined as a “pull test.” After an initial pre-root pruning pull test, trees were subjected to “individual root cuts.” These pruning cuts were made by vertically cutting the root in two planes close to the trunk using a chain saw or gas-powered masonry circular saw (Figure 1). A section of the root approximately 2 cm wide was removed to ensure that there was no connec- tion between the trunk and root and to allow sub- sequent root size measurements. The cross section was preserved and later measured on the side clos- est to the trunk for height, width, and surface area. Figure 1. Root pruning procedure showing two severed buttress roots with sections removed and the third root in the process of being pruned. ©2014 International Society of Arboriculture
July 2014
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