@Adam, bhanny
you raise some points in your response which I will address by grouping them into topics so that the discussion can be academic rather than pure individual convictions.
1. Properties of wild oudh wood vs properties of cultivated oudh wood.
2. Resin formation in natural wood vs resin formation in cultivated wood.
10 years ago there wasn't much researched based literature on the topic of agarwood, however today there is a growing library, and I am glad you brought up these points because discussing them will shed more light on why these logs form the way they do and how they differ from agarwood formations in the wild.
1. Properties of wild oudh wood vs properties of cultivated oudh wood.
According to Prof. Robert A. Blanchette at the University of Minnesota whilst referencing Gibson defines the Aquilaria and Gyrinops as tropical hardwood trees in the family Thymelaeaceae, he then further elaborates that both Aquilaria and Gyrinops are not an important timber species and the wood produced is light and not decay resistant. The bark of the tree has been used in the past to make paper and twine and the wood sometimes reported to be used to make boxes or other small items. You can read further about Gibsons discussion in the following journal
Gibson, I.A.S. 1977. The role of fungi in the origin of oleoresin deposits of agaru in the wood of Aquilaria agallocha Roxb. Bano Biggyan Patrika (Journal of Forest Science) 6:16–26.
Further more Pojanagaroon, S.; Kaewrak, C states the following about the characteristics of Aquilaria species 'The healthy wood of Aquilaria trees is white, soft and without scented resins', this provides further understanding of the nature of the actual wood before infection. Once the infection is introduced the characteristics change and this is what we need to look at as well.
You can read more about this topic in the research paper write by Pojanagaroon, S.; Kaewrak, C. Mechanical methods to stimulate aloes wood formation in Aquiliria crassna Pierre ex H Lec (kritsana) trees. ISHS Acta Hort. 2006, 676, 161–166.
How is this important to us? it clarifies the property of the agarwood tree in wild. When we know that the wood produced by these trees are light compared to other hardwoods, and that it is not a timber species, then we know that it will not behave like other hardwoods when processed; chopped, milled, carved etc.
Secondly this also opens up for us another aspect of research and that is the wood cell structure. We can now look at the actual cell structure of this type of tree and how the vessels, fibres and parenchyma behave. Vessels which are the transport tubes within these trees have two types the Xylem is one and the other is phloem. The Xylem is of particular importance when looking at the inoculation process and why these hollow logs form.
For further reading please refer to the below
Wei, J.H.; Zhang, Z.; Yang, Y.; Meng, H.; Feng, J.D.; Gan, B.C. Production of agarwood in Aquilaria sinensis trees via transfusion technique. CN101755629B, 2010.
How does the wood differ in the cultivated trees? The difference is mainly due to the fact that the trees are not allowed to fully develop. When the trees are not allowed to fully develop and are inoculated in the transition period between young tree and mature tree then there are certain changes in the cell structures that have not completed and therefore the physical properties of the wood at the cell level would be different and how they handle the fungus would vary.
Agarwood trees in in transitional stages between primary growth and secondary growth suffer not having the different types of tubes being well defined. The transporters tubes and other cell structures that are related not being developed and defined has consequences on how the tree with standards attacks. In this phase the xylem (vessels and tracheids) and phloem categories are not mutually exclusive, and the main nutrient and water transport tubes are combined in the xylem category.
This is very important to note because later on when we discuss the inoculation and why the cores become hollow in the cultivated woods and not the wild woods, this is the one of the main reasons. For further readings please see
Editorial Board of Chinese Pharmacopoeia. Chinese Pharmacopoeia; Chinese Medicine Science and Technology Publishing House: Beijing, China, 2010; pp. 172–173.
Naef, R. The volatile and semi-volatile constituents of agarwood, the infected heartwood of Aquilaria species: A review. Flavour. Fragr. J. 2011, 26, 73–89.
2. Resin formation in natural wood vs resin formation in cultivated wood.
One of the major cell structure elements within the tree that the inoculation process depends on is the transport tubes within the structure. Growers aim to get the inoculation into the xylem structures as the xylem bundle of transport tubes and vessels carry the inducer all the way down the tree. Due to water transportation, the inducers are transported to the whole body of the tree, thus forming an overall wound in the tree, and as a result, agarwood is finally formed in the Aquilaria trees in a short period of time. Please view figure 1.
Due to most trees being inoculated at a young age, with sustained constant pumping of the inoculate into the xylem and the transportor tubes having not developed into their specific structures there isn’t a lot of structural support in the cell walls to hold up against the inducer assault and the core rots and crumble please view figure 3 . The xylem carries the inducers uniformly down its tubes forming fairly uniform logs within the core of the tree. Please view figure 2. You can note the clear cylindrical shape through the development of the resin.
In the wild when the fungus attacks the tree, the trees immune system traps the fungus in pockets and therefore the oudh forms in pockets. Then another attack will happen some time latter and likewise the tree will defend itself by surrounding the fungus and suffocating it with what turns to be oudh resin pockets. For columns to be possible in the wild then there needs to be fungus pouring into the tree at a rate similar to or greater than the inoculate being pumped in at a time when the tree is in its transitional phase.
Research that has been conducted on samples from the wild that demonstrate fungus attack occurs in phases and usually when the tree is older. This makes it nearly impossible that the wild trees will form agarwood in the manner that has been the topic of our discussion.
For further reading please read the article written by Robert Blanchette etal Growing Aquilaria and Production of Agarwood in Hill Agro-ecosystems.
