Arboriculture & Urban Forestry 34(4): July 2008 Table 4. Postpruning prediction of drag (D) and bending moment (BM) at 22.4 m/s from tree characteristics.z Pruning type Tree mass (kg) Raise (n 16) D P value Adjusted R2 BM P value Reduce (n 16) D Adjusted R2 P value Adjusted R2 BM P value Thin (n 16) D Adjusted R2 P value Adjusted R2 BM P value Adjusted R2 zThe best predictor (based on adjusted R2 < 0.0001 0.73 < 0.0001 0.85 < 0.0001 0.73 < 0.0001 0.81 < 0.0001 0.72 < 0.0001 0.66 yCalculated as the geometric mean of X and Y crown width. xCalculated as the geometric mean of X and Y trunk diameter at pivot point. and bending moment, but the increase was smallest for reduction pruning. Wind Velocity Differences among pruning types were consistent at all wind speeds for each species. For all species, the absolute reduction in drag and bending moment resulting from pruning as well as the reduction in drag and bending moment per unit tree mass re- moved was consistent among wind speeds (Table 3). When nor- malized by crown area removed, however, drag and bending moment increased postpruning, and the increase was greater at greater wind speeds for shingle and swamp white oaks (Table 3). Drag and Tree Characteristics To a limited degree, pruning treatment influenced the tree char- acteristics (mass, height, crown height, crown width, crown area, and trunk diameter) that best predicted post-pruning drag (Table 4). With all species pooled together, tree mass was the best predictor of postpruning drag for all pruning treatments. Trunk diameter was the second best predictor of post-pruning drag for raised and thinned trees, whereas crown width was the second best predictor of post-pruning drag for reduced trees. For all pruning methods, crown area was the worst predictor of drag. Across all pruning types, tree mass was the best predictor of post-pruning bending moment. Tree height was the second best predictor of post-pruning bending moment for raised trees, whereas crown width was the second best predictor of post- pruning bending moments for reduced trees. Crown height was the second best predictor of post-pruning bending moments for thinned trees. Crown width was the worst predictor of bending moments for raised trees, whereas crown area was the worst predictor for reduced and thinned trees. Pruning Effects on Tree Dimensions The effect of pruning on tree dimensions (mass, center of pres- sure height, crown area, crown height, and crown width) differed by pruning treatment within each species (Table 5). For Freeman maple, reduction pruning reduced tree mass, center of pressure height, and crown width more than thinning and raising, whereas raising reduced crown height more than reduction pruning and thinning. Pruning treatments reduced crown area equally well. For swamp white oak, pruning treatments reduced tree mass and crown area equally well, but reduction pruning reduced the cen- ter of pressure height more than thinning and raising. Raising and reduction pruning reduced crown height more than thinning, and reduction pruning reduced crown width more than thinning. Table 5. Mean percent change (percent )z in tree mass, center of pressure height (CPH), and crown area by treatment.y Species Freeman maple Raise (n 5) 11.7 (1.92) ax Thin (n 6) Reduce (n 6) 23.7 (3.09) b P value 0.0012 Swamp white oak Raise (n 5) 12.8 (0.17) a Thin (n 4) 0.8136 Shingle oak 11.3 (0.670) a Reduce (n 4) 13.3 (0.485) a P value Raise (n 7) 18.7 (1.45) a Thin (n 5) 0.0025 12.4 (1.38) b Reduce (n 6) 14.4 (0.206) b P value 15.0 (0.805) a −2.35 (0.273) a 20.7 (2.13) a 5.61 (3.29) b 26.8 (0.599) a 0.0038 0.6184 −10.6 (2.00) a 48.0 (0.735) a −3.29 (1.92) a 51.2 (2.70) a 7.28 (8.02) b 40.4 (3.54) a 0.0005 0.2311 −8.91 (3.17) a 57.8 (1.54) a −1.30 (0.08) a 57.8 (1.89) a 4.50 (2.52) b 46.5 (3.37) a 0.0012 0.2523 zCalculated: [prepruning value – postpruning value]/[prepruning value]. yStandard deviations (in parentheses) follow each mean. xMeans within a column followed by the same letter are not different by Tukey’s honestly significant difference at 0.05. ©2008 International Society of Arboriculture 24.2 (6.00) a 0.00 (0.00) b 12.4 (0.894) c < 0.0001 13.4 (1.67) a 0.00 (0.00) b 16.8 (3.89) a 0.0460 8.15 (0.585) a 0.00 (0.00) b 20.6 (4.93) c < 0.0001 6.61 (1.31) a 0.00 (0.00) a 21.1 (5.31) b 0.0003 Pruning method Percent tree mass Percent CPH Percent crown area Percent crown height Percent crown width −8.50 (3.38) a 28.9 (1.72) a Tree height (m) 0.0187 0.31 0.0015 0.52 0.6188 −0.05 0.4705 −0.03 0.0729 0.16 0.0052 0.40 Crown height (m) 0.0061 0.14 0.0314 0.26 0.5786 −0.05 0.0730 0.16 0.0517 0.19 0.0026 0.45 Crown width (m)y < 0.0001 0.51 0.3183 0.01 0.0001 0.63 0.0044 0.41 0.0001 0.52 0.0449 0.20 Trunk diameter (m)x < 0.0001 0.53 0.0069 0.40 0.0009 0.52 0.0051 0.40 0.0001 0.61 0.0051 0.40 −0.02 0.0906 0.14 0.8462 −0.07 0.9131 −0.07 0.9222 −0.07 0.4663 -0.03 value) is underlined and the slope () and intercept (B) for that relationship are presented in the right-most column. 97.7, −10.1 19.4, 51.0 118, −38.8 53.3, 53.6 42.3, −26.0 Crown area (m2) 0.9804 211 , B for best predictor 28.7, 36.6 7.83 (0.307) a 0.00 (0.00) b 17.5 (5.23) a 0.0126 0.00 (0.00) a 0.00 (0.00) a 21.9 (6.53) b < 0.0001
July 2008
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