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-g rowth western hemlock and Sitka spruce in standing trees. A secondary objec tive was to determine if the effects of silvicultural practices on wood qua lity 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 take n from 56 felled trees to obtain small, clear wood specimens. Stress wave a nd 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 informati on that would enable nondestructive evaluation of wood properties in standi ng trees. The mean values of stress wave speed and dynamic modulus of elast icity for trees agreed with those determined from small, clear wood specime ns, Statistical regression analyses revealed good correlations between stre ss wave properties of trees and static bending properties of small, clear w ood specimens obtained from the trees. Regression models showed statistical significance at the 0.01 confidence level. Results of this study also demo nstrate that the effect of silvicultural practices on wood properties can b e identified with the stress wave properties of trees. This indicates that this nondestructive stress wave technique can be used to track property cha nges in trees and help determine how forests could be managed to meet desir ed wood and fiber qualities.