How agarwood forms, and why most trees never make any

Most valuable raw materials in perfumery are something a plant makes on purpose. A rose makes its scent to be found. A citrus peel makes oil to defend its fruit.

Oud is different. It is what a tree makes when it is injured.

Agarwood is a resin, not a wood

The tree is Aquilaria, a genus of tall, unremarkable evergreens across South and Southeast Asia. Cut a healthy one and the timber inside is pale, light and almost odourless. It is worth very little.

Then something goes wrong for the tree. Lightning splits it, insects bore into it, a fungus enters the wound. The tree responds by flooding the damaged heartwood with a dark, dense oleoresin that suppresses the microbes attacking it.

That resin-soaked heartwood is agarwood. Its smell comes mainly from two chemical families: sesquiterpenoids, and 2-(2-phenylethyl) chromones, the second giving the warm, balsamic, long-lastingly sweet character that makes oud recognisable across a room (Shivanand et al., Molecules, 2022).

The name of that paper says the thing exactly: the fragrant molecules of a wounded tree.

Why only about 1 wild Aquilaria in 10 carries resin

Here is the number that explains everything downstream. In the wild, only about 10% of Aquilaria trees are infected and produce resin.

The other nine are healthy, and to a perfumer a healthy Aquilaria is worth almost nothing.

You cannot tell which is which from outside with any certainty. So the traditional search for agarwood was never a harvest in the agricultural sense: it was a hunt through forest for the rare tree that had been unlucky, with the diagnostic often made by cutting.

Scarcity here is not a market condition that arrived recently. It is written into the biology.

20 years to form, 50 for the best resin

Time compounds the scarcity. Natural agarwood takes about twenty years to form, and the best yields come from trees aged fifty and older. The resin accumulates slowly around the wound, year after year, in a tree that is doing nothing else remarkable in the meantime.

Cultivation has answered part of this. Plantation Aquilaria is inoculated deliberately, and induced methods can produce usable resin in as little as six months. That is why the share of plantation material differs so sharply between species: more than 99% of traded Aquilaria crassna is plantation-grown, against 57% of A. malaccensis.

Induced agarwood is real agarwood by chemistry. Whether it is the same thing by smell, and by price, is a question the trade argues about constantly.

What a wounded tree explains about the oud price

Put the three facts together and the economics stop being mysterious.

A material occurs in one tree in ten, takes twenty years to appear, improves for another thirty, and cannot be identified reliably without damaging the tree you are inspecting. Chips run from about £20 a kilo to £6,000 depending on resin content, and the oil can reach £20,000.

It also explains the poaching. When the valuable trees cannot be told apart from the worthless ones, and the valuable ones are decades old, the incentive is to cut many and sort afterwards. That is the mechanism behind the felling of protected incense trees in Hong Kong, and behind the international controls that now govern the trade.

For how those controls work in practice, and what a CITES permit does and does not prove about a shipment, the technical side of this is in what a CITES permit on agarwood proves and in why oud is so expensive.