Arboriculture & Urban Forestry 36(6): November 2010 80%) in the analysis if 25–30 samples were used (Lenth 2006). In order to allow for inaccuracies in data collec- tion, 36 Eucalyptus saligna trees were used in this study. A comparison was made between three methods of decay esti- mation and the estimation of whole tree wood density and also the wood moisture content and basic wood density at 1.5 m. Simple linear and logarithmic regression analysis was calculated using the software package SAS (Statistical Analysis System) version 9.1. Multiple regression analysis comparing the three methods of decay estimation (as dependent variables) and the whole tree wood density and basic wood density (as independent variables) was performed to assess the statistical relationship between the decay estimations and whole tree wood density independent- ly of each trees’ basic wood density. Whole tree wood density and basic wood density were tested for multicolliniarity in or- der to validate the results from the multiple regression analysis. The Picus system method for one tree (tree #24) was not con- sistent with the other trees as this tree’s Picus image was not a uni- form color. Tree #24 therefore became a statistical outlier in any analysis with the Picus system and was therefore removed from any analysis with the Picus system. Tree #24 was also a “small- er” tree (less than or equal to 200 mm in diameter at 0.3 m in height), so the analysis of larger trees only also excluded tree #24. RESULTS The Resi system showed a statistical correlation with the volume of wood decay in the Eucalyptus saligna trees as measured by the whole tree wood density and the Picus system and the visual method did not show a correlation. Basic wood density at 1.5 m did not show a statistical correlation with the Picus system or the visual method, but there was a statistical correlation between basic wood density at 1.5 m and the Resi system. There was also a sig- nificant linear and logarithmic relationship between basic wood density and whole tree wood density (Linear, N = 36, P = 0.0064, r2 = 0.1988; Logarithmic, N = 36, P = 0.0058, r2 = 0.2030). The results also suggest that the percentage wood moisture content and at 1.5 m does not affect the Picus system, the Resi system, or the visual method of decay estimation in Eucalyptus saligna trees. Results for the Picus System The relationship between the picus system and whole tree wood density was not statistically significant (P < 0.05) us- ing linear analysis (N = 35, P = 0.1199, r2 rithmic analysis (N = 35, P = 0.1259, r2 Figure 5. (a) The percentage of decay using the Picus system versus the whole tree wood density in kg/m3 = 0.0717), or loga- = 0.0695) (Figure 5a). All the trees that were larger than 200 mm in diameter at 0.3 m in height were analyzed separately because, as previously dis- cussed, the Picus system for smaller trees was slightly different because the smaller diameter trees could only accept six Picus acoustic sensors. However there was still no statistically signifi- cant linear or logarithmic relationship between whole tree wood density and the Picus system (Linear, N = 30, P = 0.0787, r2 = 0.1056) (Figure 5b). = 0.1063; Logarithmic, N = 30, P = 0.0798, r2 There was no linear or logarithmic relationship between the Picus system data and the basic wood density of the trees mea- sured at 1.5 m, even when the smaller trees were removed (Lin- ear, N = 30, P = 0.1180, r2 = 0.0846; Logarithmic, N = 30, P = 0.1142, r2 = 0.0867). However, whole tree wood density and = 0.1988; N = 36, basic density showed a very significant linear and logarithmic relationship (Linear, N = 36, P = 0.0064, r2 , excluding tree #24. Tree #24 is an outlying data point in the Picus system data set; therefore, 35 Eucalyptus saligna trees are included in this data set. (b) The percentage of decay using the Picus system versus the whole tree wood density in kg/m3 . These data exclude trees less than or equal to 200 mm in diameter at 0.3 m in height, that is trees #17, #19, #24, #25, #31, and #34. Therefore 30 Eucalyptus saligna trees are included in this data set. Logarithmic, N = 36, P = 0.0058, r2 = 0.2030). Multiple regres- sion analysis was performed comparing the Picus system as a dependent variable and whole tree wood density and basic den- sity as independent variables. There was no statistical relation- ship between whole tree wood density and the Picus system data, even when the interaction between the whole tree wood density and basic wood density was removed via multiple re- gression analysis [N = 35, P (whole tree) = 0.3712, P (basic density) = 0.2185, r2 = 0.1153]. When only larger trees were analyzed there was still no statistically significant relationship ©2010 International Society of Arboriculture 247
November 2010
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