Estimation of decay or hollow-area ratios in stems of Japanese black pines by lateral impact vibration method

Abstract

The decay or hollow-area ratios in the stems of 240 living Japanese black pines in Jozan park of Matsue City were estimated by the lateral impact vibration method (LIV). The diagnosis index is a product (D Fr) of the diameter D of a tree stem and the resonance frequency Fr after lateral impact. First the following two tasks were performed: (1) 30 healthy Japanese black pines were cut down to obtain the average and range of D Fr of healthy trees, and (2) hollow disks made artificially were used to study the relationship between hollow-area ratios and the decreasing ratios of D Fr. All the trees in the park at 1 m height were tested by LIV, and the decay or hollow-area ratios (Riv) were calculated on the basis of the abovementioned two tasks. Riv in 17% and 3% of the total trees were estimated to be in the range of 1∼30 and 30∼59% respectively. To evaluate the accuracy of LIV, the decay or hollow-area ratios (Rrg and Ram) were estimated by a drilling resistance method and measured by cutting investigation. Riv had highly positive correlations to both Rrg (r=0.88, p<0.001) and Ram (r=0.80, p<0.001). This result reveals LIV is effective in estimating the decayed or hollow-area ratio inside a stem of Japanese black pine.