Reliability of Sonic Tomography Technology as Detector of Gaharu in Aquilaria microcarpa Baill

Abstract

Gaharu or agarwood is known as valuable products of non timber forest products (NTFP’s). Due to its economic value, the product has been subjected to over exploitation practice in Indonesia's natural forests. Therefore, some gaharu producing trees have been classified as endangered species and included into Appendix II of CITES (convention on international trade for endangered species). Traditional harvesting practice of gaharu has been insisted to fell the trees without any reliable techniques in predicting the presence of gaharu. A study was conducted to evaluate the reliability of sonic tomography technology (Picus® Sonic Tomography) in detecting the presence of gaharu within A. microcarpa trees. Thirty five of A. microcarpa with ≥ 15 cm diameter at an experimental forest area in Carita, Banten Province were selected as sample trees. Four to six transducers of Picus® Sonic Tomography were mounted circularly on the stem of sample trees at 20 cm, 130 cm, and 200 cm height from the ground (as measuring points). The transducers were connected to the software system which could record any sonic wave velocities data of each sample trees, then converted those data to be color gradation images. The result showed that sonic wave velocities within sample trees were ranged from 400 to 900 m.s-1 with average value of 700 m.s-1. There was no significant difference of sonic wave velocity among measuring points. It was also found that sample trees with high sonic velocity tend to reveal dark color of tomography image (dark brown), meanwhile the lower value of sonic velocity denoted light color (green-violet-blue). In addition as such, gaharu containing sample trees tend to reveal light color image (sonic wave velocity around 750 m.s-1), low moisture content and high density. These findings were then proven by visual observation on the felled sample tree. In concluding, sonic tomography technology shows sufficient reliability to detect the presence of gaharu in the tree.