Stress wave propagating velocity in Larix olgensis standing trees under a freezing condition.

In order to make practical non-destructive evaluation on the health of standing trees or to detect the inner defects in logs after tree felling during the winter period,the stress wave velocities propagating in Larix olgensis standing trees under a freezing condition,and the effects of light and moisture content on stress wave velocities were investigated under low temperature(below 0℃).The original survey data were from 30 healthy standing trees with straight trunks by using FAKOPP Microsecond Timer.The survey results showed that the longitudinal stress wave velocities of the sunny and shade sides were 4 238.7 and 4 210.6 m/s respectively,and the radial stress wave velocity was 1 834.5 m/s.Meanwhile,the paired t-test was employed to analyze the effects of light on moisture content and longitudinal stress wave velocities.Then,a linear regression model was used to relate moisture content,longitudinal stress wave velocities,and radial stress wave velocities.Results showed that: 1) the effects of light on moisture content of standing trees and longitudinal velocities of stress wave propagating in standing trees were significant,and the average moisture content in standing trees in shade was 1.6% lower than that of sunny side while the longitudinal stress wave velocity in standing trees in the shade was 28.1 m/s higher than that of the side exposed to the sun;2) the moisture content was negatively related to longitudinal stress wave velocities with a correlation coefficient of 0.90 and 0.91 for shade and suny sides,respectively.The longitudinal stress wave velocities measured in the shade and sunny sides decreased by 25.1 and 22.9 m/s respectively with a 1% increase in moisture content of standing trees.