14 of the lowest branch), and subtracting minimum from maximum; crown diameter (CD) as the average width of a crown measured at its widest point in two perpendicular directions; height to vertical center of a crown as one-half TCH plus minimum height; trunk taper calculated as –(R-r)/R (Leiser and Kemper 1973) where R trunk radius at 15 cm (6 in) above the top- most root and rradius at 1.37 m (4.52 ft) above the top-most root; projected crown frontal area calculated as 0.5× the vertical surface area of a cone (whose dimensions were: height0.667 × TCH and radius 0.5 × CD) plus 0.25 × the surface area of an ellipsoid (whose dimensions were: radius 1 0.333 × TCH and radius 20.5 × CD); and crown volume as calculated from the volume of a cone plus one half the volume of an ellipsoid. We used this to estimate the shape of the crown of Highrise live oak, which appears as a cone resting on top of half an ellipse. On 6 November 2003, 44 of these trees representing those most similar to the mean of each of these characteristics were moved from MTF to the Environmental Horticulture Teaching Unit (Gainesville, FL, USDA hardiness zone 8b); 27 of these were used in this study. Test trees averaged 8.9 cm [3.56 in; standard deviation (SD)0.14] caliper, 6.1m(20.13 ft; SD0.42) tall, and 1.9 m (6.27 ft; SD 0.87) crown diameter. Trees were irrigated regularly, including the day before testing. Experimental Design Three effects were evaluated: 1) pruning dose; 2) pruning type; and 3) wind speed. From those three effects, 60 treatment com- binations (five pruning types × four pruning doses × three wind speeds) were targeted. Trees were randomly assigned to a prun- ing type. The physical characteristics used to select the 27 trees from the nursery were used to compare trees assigned to pruning types. There were no differences in tree characteristics among pruning types with one exception. The elevation to the vertical center of the canopy was statistically (P 0.039) less [3.63 m (11.98 ft)] for trees assigned to the thinned pruning type than for those assigned to the reduced pruning type [3.91 (12.90 ft)]. Because that was the only difference among types, no further adjustments were made in the assignment of trees to pruning types. The five pruning types included 1) lion’s tailed; 2) raised; 3) reduced; 4) structural; and 5) thinned. Each tree within a type was pruned to four targeted pruning doses in the following se- quence: 1) no pruning (0% foliage removed); 2) 15% foliage removed; 3) 30% foliage removed; and 4) 45% foliage removed. Actual doses were measured after foliage was removed from the tree and these doses varied from the targeted doses as described subsequently. Within a pruning dose, each tree was subjected to a sequence of three targeted wind speeds of 6.7 m/s (15 mph), 13.4 m/s (30 mph), and 20.1 m/s (45 mph). Actual wind speeds were measured while trees were blown with gusts up to 33.5 m/s (75 mph). Trees were blown when ambient winds were less than 2.2 m/s (5 mph). Pruning doses used in the statistical analyses were not the targeted doses but were the measured percentage of total tree foliage dry weight removed. Foliage on parts of the crown re- moved by pruning was stripped from branches and dried sepa- rately from branches to calculate actual percentage foliage re- moved (pruning dose) on all pruned trees. Mean total tree foliage dry weight was measured by stripping all foliage from 13 trees after they were tested and drying to a constant weight [mean 2 kg (4.4 lb; standard error0.13)]. Measured percentage of foliage removed (i.e., actual pruning dose) on each test tree was calcu- ©2008 International Society of Arboriculture Gilman et al.: Effects of Pruning Dose and Type lated as dry weight of foliage removed during pruning ÷ mean total tree foliage dry weight (2 kg) × 100. Total removed dry mass (branches + foliage) was highly correlated with removed foliage dry mass (R2 85%); removed foliage percentage was used in the data analysis. Pruning types were blocked in time so that each block con- tained a lion’s tailed, raised, thinned, and reduced tree. One block was pruned, then the next, and so on. Trees in the fifth pruning type, structural pruning, were pruned after all other trees in the study were tested. This is described in detail subsequently. One person was chosen to prune all trees to maintain consis- tency, and trees were pruned on the day of testing. The first four lion’s tailed trees were blocked in time with other pruning types. The 15% pruning dose removed all primary and higher order branches [1.27 cm (0.51 in) diameter and smaller] at the trunk and along branches within the lowest 15% of crown height and the most interior 15% of crown radius. The 30% and 45% pruning doses were applied in a similar fashion. We dried and weighed removed foliage and found too little was removed to meet our targeted dose levels. Therefore, after testing of all blocked trees, three additional trees were lion’s tailed, but pruning dose was estimated visually in an attempt to remove targeted doses. The first three raised trees were blocked in time with other pruning types. The central leader was marked at 15%, 30%, and 45% of TCH. The 15% pruning dose was applied by removing all primary lateral branches at the trunk beginning at the base of the crown up the main leader to the 15% mark. The 30% and 45% dose levels were applied in a similar fashion. We dried and weighed removed foliage and found foliage removed at each dose exceeded targeted levels so after testing of all blocked trees, three additional trees were included to better approximate tar- geted pruning doses. Pruning dose for the additional raised trees was estimated visually in an attempt to remove the targeted doses. Pruning was carried out as before, but if removal of a large limb would have caused an excessive dose, it was treated as a second leader and raised as per the main leader. The first four reduced trees were blocked in time with other pruning types. The main leader was marked at 85%, 70%, and 55% of TCH. Pruning was accomplished by first removing the main leader at the designated mark followed by heading the exterior of the remaining crown to reestablish each crown’s original three-dimensional shape but in a smaller version. No foliage was removed from interior parts or from the lower side of a crown. We dried and weighed removed foliage and found foliage removed from three trees exceeded targeted pruning doses. Therefore, after testing of all blocked trees, three addi- tional trees were reduced by visually approximating targeted dose levels. Four trees were thinned and blocked in time with other prun- ing types. Thinning was conducted by making removal and re- duction cuts throughout the entire crown, especially at the outer half of the crown. No branches were removed from the trunk. Pruning dose was determined in the field as a visual estimate of live foliage removed. Thinning produced a uniformly dense tree without changing the crown’s dimensions. Two trees were structurally pruned. Structural pruning in- volved making primarily reduction cuts (with occasional re- moval cuts) to shorten and slow growth of stems competing with the main trunk and to develop scaffold branches. No branches were removed from the trunk. Little thought was given to crown
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