Formation of gaharu occurs in the trunk and roots of trees that have been infected by a parasitic ascomycetous mould, Phaeoacremonium parasitica, a dematiaceous (dark-walled) fungus. As a response, the tree produces a resin high in volatile organic compounds that aids in suppressing or retarding the fungal growth, a process called tylosis. While the unaffected wood of the tree is relatively light in colour, the resin dramatically increases the mass and density of the affected wood, changing its colour from a pale beige to dark brown or black. In natural forest only about 7% of the trees are infected by the fungus. A common method in artificial forestry is to inoculate all the trees with the fungus. Oud oil can be distilled from agarwood using steam, the total yield of agarwood (Oud) oil for 70 kg of wood will not exceed 20 ml (Harris, 1995).
In wild forest, gaharu is caused by natural factors such as trees struck by lightning, animal and insect attacks, forest fires, wind or storm damage and trees invaded by fungus. For instance, when ants drill holes on its trunk to build their nests, the tree will produce a fragrant, protective oil to heal these wounded areas. Unfortunately, ants’ hormone secretion prevents the tree from protecting itself. And since the defense mechanism associated with wounding keeps performing its part, the tree ultimately dies from having to continuously release oil to fix the problem. Finally, local loggers will harvest areas surrounding ants’ nests, which are now dark brown/black as they turn into the so-called gaharu.
Normally, eight years are the average amount of time for a tree to produce fine quality gaharu and for loggers to appropriately collect it. However, the rapid rise in demand has led to destructive harvesting practices in the rush to find gaharu and caused the government to forbid the extraction and trading of the natural resin. Therefore, any wild gaharu available for sale at the moment is either extremely expensive or a fake product made from non-infected Aquilaria wood impregnated with cheap oil and colored by human interventions.
Lately, efforts to turn gaharu into a plantation crop have generated very positive results and earned strong support from the authority. No dirty trick, no excessive usage of chemical fertilizers, no harmful substances application. The plantation process simply duplicates that of the nature, i.e. physically damaging the tree with the help of blades, drilling holes or fire damage. Although there are injections of fungal compound similar to ants’ hormone to keep the wounds open, they are subject to a close scrutiny to ensure appropriate content, not to mention that each and every element in the compound is carefully chosen and tested beforehand. Also, at the time when gaharu is extracted, the compound wears off already.
In terms of heath and safety, cultivated gaharu is by no means inferior compared to its wild counterpart. Hence, the quality of oil yielded is probably the sole difference between these two. Due to commercial purposes, plantation crops are harvested on a 2-year basis, and correspondingly, the quality of cultivated gaharu oil can only reach a maximum of 50%. Nevertheless, despite being of moderate quality, the resin manages to effectively fulfill functions that it was born for as well as expected by consumers.