Agarwood is not simply the wood of a particular tree. Its distinctive fragrance develops through a natural process in which certain trees produce aromatic resin in response to injury and stress.
Agarwood begins inside a living Aquilaria tree. The tree itself is not agarwood; the fragrant material develops within the wood as the tree responds to certain forms of stress or injury.
When parts of the tree are damaged or exposed to stress, the tree can begin a natural defensive response. This is one of the conditions associated with the development of aromatic resin.
As the tree responds, aromatic resin develops and accumulates within affected areas of the wood. The resin is what gives agarwood much of its distinctive color, weight, and fragrance.
The aroma can vary greatly depending on the tree, the resin, and how the material develops.