Nondestructive Evaluation of Standing Trees With a Stress Wave Method

The primary objective of this study was to investigate the usefulness of a stress wave technique for evaluating wood strength and stiffness of young-growth western hemlock and Sitka spruce in standing trees. A secondary objective was to determine if the effects of silvicultural practices on wood quality can be identified using this technique. Stress wave measurements were conducted on 168 young-growth western hemlock and Sitka spruce trees. After in situ measurements, a 0.61-m-long bole section in the test span was taken from 56 felled trees to obtain small, clear wood specimens. Stress wave and static bending tests were then performed on these specimens to determine strength and stiffness. Results of this study indicate that in situ stress wave measurements could provide relatively accurate and reliable information that would enable nondestructive evaluation of wood properties in standing trees. The mean values of stress wave speed and dynamic modulus of elasticity for trees agreed with those determined from small, clear wood specimens. Statistical regression analyses revealed good correlations between stress wave properties of trees and static bending properties of small, clear wood specimens obtained from the trees. Regression models showed statistical significance at the 0.01 confidence level. Results of this study also demonstrate that the effect of silvicultural practices on wood properties can be identified with the stress wave properties of trees. This indicates that this nondestructive stress wave technique can be used to track property changes in trees and help determine how forests could be managed to meet desired wood and fiber qualities