Arboriculture & Urban Forestry 32(6): November 2006 261 the cross-sectional face of each section was measured. The extent of decay was determined by probing with a sharp knife for a boundary between the weakened decayed wood and stronger normal wood. The average of two perpendicular measurements was used as the diameter of decay. The volume for each 50 cm (20 in) long section was cal- culated using the formula for a frustum of a right circular cone (Equation 1). When decay was present on both ends, the frustum formula was used to calculate the volume of decay. If decay was only present on one end of the section, the right circular formula for cone (Equation 2) was used to estimate decay volumes. Equation 1: Volume of the frustum of a right circular cone Volume = r2 + rR + R2h 3 where: r smaller radii R larger radii, and h length of section Equation 2: Volume of a right circular cone Volume = r2h 3 where: r radius h section length/2 Data were analyzed using analysis of variance (ANOVA), and a least significant difference (LSD) procedure for un- equal sample size was used to determine differences between the means for the beginning distance of external and internal decay. Stepwise regression analysis was used to determine linear relationships in the data using the following variables: diameter at the tip (distal), diameter at trunk (proximal), di- ameter of decay at the tip, diameter decay at trunk, length of external decay, length of internal decay, first-order interac- tions, and the square of first-order variables. ANOVA, re- gression analyses, and calculations of 95% prediction inter- vals were run using the SAS System version 8.2 (SAS 1999), and LSD were calculated by hand to adjust for unequal sample size. During the stepwise procedure, significance lev- els for variable selection were set at 15% to allow for varia- tion as variables were added or removed. Significance levels for all final models were set at 5% (0.05). Percentage of volume loss was calculated then transformed using the square root before statistical analysis. Predicted values for regression models are presented in which the length of external decay along the leader was allowed to vary and the remaining vari- ables were fixed with their corresponding mean value. RESULTS Internal decay columns began at the heading cut in 46% of the leaders within 1 to 50 cm (0.4 to 20 in) from the heading cut in 33% of the leaders more than 50 cm (20 in) from the heading cut in 10% of the leaders, whereas 10% of the leaders had no decay (Table 1A). External decay began in the first 50 cm (20 in) section in 59% of the leaders, from 51 to 100 cm (20.4 to 40 in) in 7% of the leaders, greater than 100 cm (40 in) in 13% of the leaders, and no decay was present in 20% of the leaders (Table 1B). A highly significant difference (P < 0.001) was found be- tween the total length of internal decay (142.7 cm [57.1 in] and standard error [SE]11.2, 56.2 in, and SE4.4) and external decay (50.6 cm [20.2 in] and SE7.7, 19.9 in and SE 3.0). No significant relationships were found between the distance at which internal decay began from the heading cut in the leaders and either the diameter of the leader at the heading cut (P0.316) or the total length of internal decay (P0.301). A highly significant relationship was found for the total length of internal decay in the leader and four mea- surements: the length of external decay, beginning and end- ing leader diameter, and leader length (R20.45, P < 0.001) (Regression 1). Figure 1 depicts a set of predicted values and 95% prediction interval for the length of internal decay using regression 1, where X2 14 cm (5.6 in), X3 22 cm (8.8 in), and X4 251 cm (100.4 in). A highly significant relationship was found between the volume of decay in the leaders and three variables: the length of external decay, beginning and ending diameter of the leader (R2 0.90, P < 0.001) (Regression 2). A set of pre- dicted values and 95% prediction interval for volume of de- cay using Regression 2 are shown in Figure 2, whereX214 cm (5.6 in) and X3 22 cm (8.8 in). Table 1. Percentage of parent stems (leaders) in each distance class (cm) in which (A) internal and (B) external decay began from the heading cut in silver maple leaders converted from roundover to V-trims during electrical line clearance operations. A. Internal decay Distance (cm) 0 1 to 50 >50 No decay Distance (cm) 0 to 50 51 to 100 >100 No decay No. of leaders 32 23 7 7 B. External decay No. of leaders 41 5 9 14 Percentage with decay 59.4 7.2 13.0 20.3 ©2006 International Society of Arboriculture Percentage with decay 46.4 33.3 10.1 10.1
November 2006
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