How Does Oud Form Inside the Tree? The Mechanism of Formation

The tale of oud begins in a place that many do not expect: not in a nursery where it is planted, nor in a factory where it is made, but in a wound that befalls a healthy tree so it responds to it with its aromatic weapon. For oud is not a fruit that grows, but rather a response of defense that accumulates in the wood of the tree over the course of years. In this article we trace the mechanism of formation step by step — from the first injury to the saturation of the wood and its transformation — as science understands it today, with what it holds of certainty and what it holds of questions still open. And this article is a part of the complete guide to oud.

1. From an ordinary tree to an aromatic treasure

In order to understand how oud forms, we ought to begin from a fact that may seem strange: the tree in which oud arises is in its origin an ordinary tree, its wood light in color, light in weight, almost devoid of scent. Nothing in its first appearance suggests that it will one day carry one of the most precious aromatic materials on the face of the earth.

This tree belongs mostly to two botanical genera: Aquilaria, which is the most widespread, and Gyrinops, which prevails in the eastern regions of the range of oud. And we detailed the nature of this material in the article what is oud?, and the structure of the resinated wood in the article what is agarwood?; as for here, our question is entirely different: not "what is oud?" but how does a pale wood devoid of aromatic value transform into a dark, heavy oud deep in scent.

And the concise answer that we will detail in the rest of the article is that this transformation is not a growth but a reaction. For the healthy tree that lives its life without something bad befalling it may reach its whole age without producing oud to mention. But when it is exposed to an injury that penetrates its internal tissue, it releases a chain of defensive responses that are believed to be responsible for the arising of the aromatic resin that accumulates in the wood so it grants it its color, its weight, and its scent.

In other words: oud is the story of a wound that healed in an exceptional manner. And just as some trees secrete a gum or a resin upon their injury to protect themselves, likewise the trees of Aquilaria and Gyrinops are believed to secrete — in response to the injury — an aromatic material that is the origin of oud. The difference is that this material, in these trees specifically, is characterized by an aromatic complexity and a persistence upon heating that made it a treasure sought across the centuries.

2. The trigger: the wound and the injury

The starting point in the formation of oud, according to what the studies indicate, is the injury. For the healthy, uninjured wood rarely forms an aromatic resin worth reckoning. But when the internal tissue of the tree is penetrated and exposed to factors that disturb its balance, that is regarded as the spark that is believed to release the process of formation.

And the images of the injury that researchers connect with the arising of oud are numerous, and among them:

The physical injury: the break of a large branch, or a split in the trunk by the action of a storm or a lightning strike or a natural accident, or a wound that penetrates the bark to the wood. Such a wound opens the door before the entry of other factors into the interior of the tree.

The boring of insects: some insects bore tunnels in the trunk of the tree or its branches, so they make extended internal wounds, and may carry with them microscopic organisms into the depth of the tissue. And this path is believed to be among the most common of the paths of natural injury.

The microbial and fungal infection: many researchers deem it likely that the entry of microscopic organisms — foremost among them some fungi — into the wounded wood plays a pivotal role in provoking the defensive response of the tree. However, the precise nature of this role, and which organisms are the most influential, is still a subject of research and scientific discussion, and we cannot be decisive about it here.

And the common denominator between all these images is that the wound is the point of departure. For the injury is not a side incident in the story of oud, but its first chapter. And from here came the phrase that often recurs: oud is nothing but the healing of a wound that continued for years. Nonetheless, we ought not to imagine that every wound produces oud; for the matter of why some trees become resinated and others do not, despite all of them being exposed to injuries, is a matter standing on its own with its factors that are still a subject of study.

3. The tree's defensive response: the secretion of the resin

When the tree is injured, it does not stand helpless. For according to the prevailing scientific understanding, it releases a chain of defensive responses, much of which is described as a plant chemical defense (phytochemical defense): the tissues surrounding the site of the injury begin to secrete resinous aromatic materials whose original function is believed to be the protection of the tree and the attempt to isolate the damage and resist the spread of the foreign factors in its tissue.

This dark aromatic resin is the essence of oud. For oud is nothing but the wood that was saturated with this defensive material. And for this reason it can be said that what we value in oud of a depth of scent, a weight, and a dark color is, in its origin, the trace of a silent battle that the tree waged in defense of itself.

And the resin itself is a material complex in composition, its aromatic characteristics varying with the difference of the tree, the origin, and the conditions of formation, and we devote to it an independent axis in this guide titled "what is oud resin?" in which we detail the nature of this material alone. And it suffices us here to establish its role in the mechanism of formation: the resin is what the tree secretes, and it is what accumulates, and it is what transforms the wood.

And it is important that we avoid the exaggeration in simplifying this process. For we are not speaking of a single simple reaction, but of a complex biological response that is deemed likely to include multiple chemical changes in the cells of the wood over a long time. And we deliberately avoid here naming particular compounds or specific enzymes as being responsible, because the details of this chemistry are still under study, and we do not want to grant the reader a certainty that the current knowledge does not support.

4. The saturation of the wood and its transformation

Oud does not form all at once. For after the tree begins to secrete the resin around the site of the injury, this resin takes to accumulating gradually, absorbing into the cells of the neighboring wood, and extending in the tissue over the course of years, indeed decades in many cases. And the more the time lengthens and the density of the saturation increases, the more the wood grows dark and heavy and deep in scent.

And this accumulation does not distribute equally. For the resin concentrates around the sites of the injury and diminishes the more we move away from them, and for this reason oud often comes in the form of veins and dark spots interspersing a lighter wood, not as a mass homogeneous in color. And a single tree may carry a small, dark, resinated part surrounded by a large quantity of light wood that the resin did not reach.

And the clearest sensory trace of this saturation is the density. For the light wood is light, floating on water, whereas the piece that was saturated with resin a high saturation grows heavier until the highest of it in density may sink in water instead of floating. And this phenomenon is the origin of the naming "sinking oud" and a traditional standard of the richness of the resin, and we detailed its tale and its relationship to the density of the resin in the article sinking oud.

The density, then, is not a random attribute, but a material record of the amount of resin that accumulated in the wood over the years. And the more we understand that oud is the yield of time and saturation, the more we realize why it varies from one piece to another a great variance in the weight, the color, and the scent, even within a single tree. This natural variance is what the idea of grading oud into grades that reflect the richness of the resin in it rests upon.

5. The natural against the induced

From what preceded it becomes clear that the injury is an essential condition in the formation of oud. And here an essential difference emerges between two paths for the occurrence of this injury: a natural path in the wild, and an induced path in the farms.

In the wild, the injury happens incidentally and without human intervention: a storm breaks a branch, or an insect bores a tunnel, or an infection enters from an old wound. Then the matter is left to time and nature. And this path is slow and of unguaranteed result, for many trees may be injured and considerable oud forms only in a few of them.

In the farms, the cultivators resort to making the injury deliberately — by making wounds in the trunk or introducing materials intended to provoke the defensive response of the tree — in the hope of accelerating the formation of the resin and making it more predictable. And these methods vary and their results vary, and they are still a subject of continuous development and experimentation.

And this transformation from reliance on wild oud to cultivating it and inducing it changed the oud industry a deep change over the recent decades, and it has dimensions related to the abundance, the sustainability, and the quality of the product. And we addressed this story in its detail in the article from wild oud to the farms. As for here, it suffices us to establish the principle: whether the injury is natural or induced, the essential mechanism is one — a wound that provokes a defense that secretes a resin that accumulates in the wood.

And it is fair to say that the quality of oud is not determined by its path alone. For wild oud may reach high grades of the richness of the resin by virtue of the length of the time in which it accumulated, but cultivated oud may in its turn reach a considerable quality if it is well cared for and given enough time. For the truest judgment remains upon the piece itself with its density and its scent, not upon a theoretical classification of its source.

6. What we do not yet know

It is of scientific honesty that we pause here a frank pause. For despite the broad lines of the formation of oud — an injury, then a defensive response, then an accumulation of resin — being accepted on a wide scale, many of the precise details are still a subject of research and discussion, and we do not wish to present them to the reader as if they were a closed certainty.

For the precise trigger of the formation, and the extent of what the fungi specifically contribute against what the physical injury or the other microbial factors contribute, are matters that researchers still study and differ in their details. Likewise the reason why one tree produces abundant resin while its injured neighbor remains an ordinary wood has not yet been settled in a decisive manner. And these are not gaps we hide, but real limits of the current knowledge that we mention as they are.

And for this reason we deliberately use in this article phrases such as "it is believed" and "the studies indicate" and "it is deemed likely," and we avoid being decisive about a single final cause, or naming particular fungal species as being responsible with certainty, or mentioning precise ratios and figures for the durations of formation. For oud forms over the course of "years and decades" — and this is the truest that can be said without embellishment.

And this approach in reservation is not a weakness, but it is an extension of a principle we adhere to at Oud Treasure: we do not describe what we have not burned. For just as we do not describe the scent of an oud we have not tested ourselves, we do not present a science that has not been settled as if it were conclusive. And the reader who understands the limits of what we know is more capable of judgment than the one who is flooded with a false certainty.

7. Why this matters to the buyer

The talk of the mechanism of formation may seem theoretical, far from the concern of the buyer, and the truth is the exact opposite of that. For understanding how oud forms is the key to understanding three practical facts that you touch in the market every day: its scarcity, the variance of its prices, and the difference of its quality. And we detail these dimensions in the complete guide to oud.

The scarcity: as long as oud requires an injury, then a defensive response, then an accumulation over the course of long years, it is natural for the supply to be scant from the source. Not every tree is injured, and not every injury produces abundant resin. These accumulated conditions are the origin of the scarcity of oud, and the scarcity is the origin of its value.

The variance of the prices and the quality: because the saturation with the resin varies from one piece to another, oud varies a wide variance in the density and the scent, and hence in the price. For the price of oud is not a single number, but a range extending from daily grades within the reach of many to rare high-density pieces. And this variance is what the five-grade ladder by which we classify oud reflects.

And because the quality springs originally from the richness of the resin formed, examining oud and classifying it with honesty is a necessity, not a luxury. And we clarify how we examine oud and classify it on the quality-control page. For the buyer who understands that the value is in the accumulated resin, not in the mere color of the wood, becomes more capable of distinguishing the rich oud from others, and further from being imposed upon by appearances.

Read also

For a wider deepening, begin from the complete guide to oud which gathers the axes of the subject in one place, and from the article what is agarwood? to understand the structure of the resinated wood. And we are working on devoting independent articles to interconnected axes such as: why do some trees produce oud and not others?, then what is oud resin?, and "how long does the formation of oud take?" — we add their links here successively whenever they are completed.