248 Johnstone et al.: Quantifying Wood Decay in Sydney Bluegum (Eucalyptus saligna) [N = 30, P (whole tree) = 0.2100, P (basic density) = 0.3332, r2 = 0.1373]. Tests such as the variance inflation factor (VIR) on whole tree wood density and basic density revealed very little multicolliniarity for these independent variables in the multiple regression analysis (VIR < 2 in all cases). There was no linear or logarithmic statistical relationship between the Picus system data and the percentage of wood moisture content even when all the smaller trees were excluded (Linear, N = 30, P = 0.4149, r2 = 0.0239; Logarithmic, N = 30, P = 0.4072, r2 Results for the Resi System The relationship between the Resi system and whole tree wood density was statistically significant (P < 0.05) using linear analy- = 0.0247). ses (N = 36, P = 0.0030, r2 = 0.2307). Logarithmic statistical re- lationships between whole tree wood density and the Resi system were more significant than the linear relationships (Logarithmic, (N = 36, P = 0.0027, r2 = 0.2835; = 0.2354, Figure 6a). The linear and loga- rithmic statistical relationship between whole tree wood density and the Resi system was more significant when the trees less than or equal to 200 mm in diameter at 0.3 m in height were exclud- ed from the analysis (Linear, N = 30, P = 0.0025, r2 Logarithmic, N = 30, P = 0.0015, r2 = 0.3061) (Figure 6b). There was a linear and logarithmic relationship between the Resi system data and the basic wood density of the trees measured at 1.5 m (Linear, N = 36, P = 0.0431, r2 = 0.1150; Logarithmic, N = 36, P = 0.0378, r2 = 0.1208), but not when the smaller trees = were excluded from analysis (Linear, N = 30, P = 0.3503, r2 0.0312; Logarithmic, N = 30, P = 0.3388, r2 = 0.0327). There was no linear or logarithmic statistical relationship between the Resi system data and the percentage of wood moisture content even when all the smaller trees were excluded (Linear, N = 30, P = 0.5682, r2 = 0.0118; Logarithmic, N = 30, P = 0.5286, r2 = 0.0143). Multiple regression analysis was performed comparing the Resi system as a dependent variable and whole tree wood density and basic density as independent variables, to remove basic density as a factor influencing the relationship between whole tree wood density and the Resi system. There was a significant statistical re- lationship between whole tree wood density and the Resi system data [N = 36, P (whole tree) = 0.0203, P (basic density) = 0.3613, r2 larger trees were analyzed [N = 30, P (whole tree) = 0.0045, P (basic density) = 0.8200, r2 = 0.2502], which became even more significant when only the = 0.2849]. Tests such as the variance inflation factor (VIR) on whole tree wood density and basic den- sity revealed very little multicolliniarity for these independent variables in the multiple regression analysis (VIR < 2 in all cases). Results for the Visual Method The relationship between the visual method and whole tree wood density was not statistically significant (P < 0.05) in linear and logarithmic analysis (Linear, N = 36, P = 0.5150, r2 = 0.0126; Logarithmic, N = 36, P = 0.5530, r2 = 0.0104) (Figure 7a). Even when only the larger trees were included, there was no signifi- cant statistical relationship between the visual method and whole tree in either linear or logarithmic analysis (Linear, N = 30, P = 0.5759, r2 = 0.0113; Logarithmic, N = 30, P = 0.6286, r2 = 0.0085) (Figure 7b). Tree #26 (13.53%) and tree #21 (8.07%) were not deemed outlying data points for statistical analyses in the visual method of decay estimation, as the decay in this cross- section was clearly visible and easy to verify as correct, as were all cross-sections used to estimate decay using the visual method. There was no linear or logarithmic statistical relation- ship between the visual method data and the percentage of wood moisture content even when all the smaller trees were excluded (Linear, N = 30, P = 0.6555, r2 = 0.0072; Logarith- mic, N = 30, P = 0.6703, r2 = 0.0066). Also there was no rela- Figure 6. (a) The percentage of decay using the Resi system versus whole tree wood density in kg/m3 . Includes all 36 Eucalyp- = 0.2354. (b) The percentage of decay using the Resi system versus the whole tree wood density in kg/m3. These data exclude the smaller trees #17, #19, #24, #25, #31, and #34; therefore, 30 Eucalyptus saligna trees are included in this data set. Trend line = logarithmic regression, P = 0.0015, r2 = 0.3061. ©2010 International Society of Arboriculture tus saligna trees. Trend line = logarithmic regression, P = 0.0027, r2 tionship between the visual method data and the basic wood density of the trees measured at 1.5 m, even when the smaller trees were excluded from analysis (Linear, N = 30, P = 0.2364, r2 = 0.0497; Logarithmic, N = 30, P = 0.2416, r2 Multiple = 0.0486). regression analysis was performed compar- ing the visual method as a dependent variable and whole tree wood density and basic density as independent vari-
November 2010
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