Effects of the rate of decay on ultrasonic wave transmission time in squirrel-damaged Luanta fir tree

Various degrees of wood decay in Luanta fir standing trees （Cunninghamia Konishii) damaged by squirrels were assessed. The propagation time of ultrasonic wave was measured using Pundit ultrasonic meter. Biological internal quality of standing trees could be evaluated by measuring the ultrasonic traversing time on the radial axis （in the 180 and 90° direction) of tree trunks. The ratio of traversing time in the 90° direction to radial （180°) direction tended to decrease with increased decay degree. However, the percentage of increase in transmission time tended to increase with increased decay degree. Results were compared with transmission times of healthy trees in the radial direction, and the ratio of transmission times in the different orientations as predictors of decay degree. The indicators verified that the internal decay of tree could be detected using ultrasonic measurement of the radial direction. Therefore, simultaneous measurement of the transmission time of ultrasonic wave by multiple transducers arranged around the stem in different orientations, the presence and size in the tree could be determined.