Quantitative characterization of decay detection in standing trees of Korean pine based on Resistograph and ERT

In order to quantify the extent of wood decay of Korean pine (Pinus koraiensis), fifteen Korean pine standing trees were selected in Wuying National Forest Park of Heilongjiang Province of northeastern China. Resistograph and PiCUS Treetronic ERT were applied to gain the variation of micro-drilling resistance and the distribution of cross-sectional electrical resistivity, which were compared in the same direction. Mass loss rate was measured through increment wood cores. Resistance loss, defined by the extent of micro-drilling resistance's decline, was compared with mass loss rate by regression analysis. Besides, abnormal extent of electrical resistivity was defined by the averages of electrical resistivity of decay and healthy portion and regression analysis was performed to derive the relation between it and resistance loss. The decay area can be located by the resistance curve on the electrical resistivity profile and computed through supervised classification. The percent of decay area we calculated was examined by its relation with mass loss rate with the method of ordinary linear square. The results indicated that: 1) the average of resistance loss had a significant linear relation with mass loss rate and Resistograph can be used to accurately detect the decay in one dimension. 2) Significant changes on the electrical resistivity profile took place where there was a noticeable decline on the micro-drilling resistance curve. Resistance loss showed a significant exponential relationship with abnormal extent of electrical resistivity and it can also be deduced that ERT detection was more sensitive to mild wood decay, while Resistograph detection was sensitive to severe decay. 3)The location and area of wood decay can be confirmed by combining Resistograph and ERT technique and there was a high linear correlation between the percent of calculated decay area and mass loss rate.