Quality evaluation of standing trees by a stress-wave propagation method and its application I. Seasonal changes of moisture contents of sugi standing trees and evaluation with stress-wave propagation velocity

Monthly changes of moisture content and stress-wave propagation velocity in sugi (Cryptomeria japonica D. Don) standing trees at two different forest stands were studied. The stress wave propagation velocity (V-p) was measured once a month during one pear. Two trees were felled every month and moisture content (MC) of sapwood and heartwood, density and longitudinal Young's modulus of logs by vibration method (E-fr) were measured. Daily changes of V-p were also measured at forest stand A. The MC of sugi standing trees showed wide dispersion between trees, and showed no remarkable seasonal change both in heartwood and sapwood. The results are summarized as of follows: 1) The MC of standing trees showed large dispersion. Therefore no remarkable seasonal change of MC was shown between the growth period and the dormancy period. 2) In individual trees, significant monthly changes of V-p were observed. However, there was no significant difference of mean propagation velocity between measurements three years apart. 3) There was no evident daily change of the V-p in standing trees. 4) Significant correlation between E-fr of logs and V-p or E-fr of standing trees was obtained. V-p was an effective parameter to evaluate the mechanical properties of standing trees.