Moisture content effect on sound wave velocity and acoustic tomograms in agarwood trees (Aquilaria malaccensis Lamk.)

Gaharu or agarwood or oudh is a fragrant and highly valuable nontimber forest product obtained from several species of trees that produce it in response to wounding or fungal attack. The aims of the study were to evaluate the sound wave velocity change from green to dry conditions in agarwood and tomographic images associated with changes in the moisture content. A total of 10 trees were selected for this study; five trees were artificially inoculated and the other five were left untreated. After in situ measurement of standing trees stem using nondestructive testing (PiCUS sonic tomography), air-dried disk samples from the trees were assessed. The results showed that sonic velocity values increase from 12% to 22% as moisture content decreases from a green condition (live tree) to an air-dried condition (disk sample). Nevertheless, solid and damage areas revealed only slight differences on the tomograms. This research combines traditional visual assessment with tomography to better detect the presence of agarwood in trees.