There are many names for the resinous, fragrant heartwood produced primarily by trees in the genus Aquilaria. The commoner names include agarwood, aloeswood, eaglewood, gaharu or oudh, and it is also mentioned in the Old Testament as ‘aloe’ or ‘ahaloth’. This valuable and highly fragrant wood has been used in many ways for over two thousand years, especially as incense in Buddhist, Hindu, and Islamic traditional ceremonies, and as a significant component of traditional Ayurvedic, Tibetan and Far Eastern medicine and Middle Eastern perfumes.
The genus Aquilaria of the Thymelaeaceae (Daphne family) consists of generally fast-growing trees found in lowland tropical forests. It occurs naturally in South and Southeast Asia, from the foothills of the Himalayas (Bhutan) and northern India, through Myanmar, IndoChina (Lao PDR, Cambodia, Vietnam), Thailand, Malaysia, the Philippines and Indonesia to Papua New Guinea. Seedlings of most species establish best in shady, moist conditions, but large adult trees sometimes become emergent in the forest and can withstand full sun. Some species can be found growing on steep, rocky, exposed slopes, and in regions that experience a hot, dry season. Wherever they occur naturally, they provide an important source of livelihood for local communities who harvest the fragrant agarwood to sell.
Other genera in the family of the Thymelaeaceae known to produce agarwood include Gonystylus, Gyrinops, Aetoxylon, Enkleia, Wikstroemia and Phaleria. However, it is still unclear which species within these taxa produce agarwood and in what quantities. The taxonomy of Aquilaria is in need of review. A new species, A. rugosa L.C. Kiet & Kessler, was described in 2005 from central Vietnam and northern Thailand, and a possible new species has been reported from Lao PDR (Sourioudong Sundara, pers. com.).
How the agarwood resin is produced by the tree
It has long been known that the production of the fragrant resin is associated with wounding and associated fungal invasion, possibly assisted by insects. As a response to the fungal infection, the tree produces a resin high in volatile organic compounds that aids in suppressing or retarding the growth of the fungus. Various fungi are associated with agarwood formation although it is still not completely clear which ones make the plant generate the resin.
While the unaffected wood of the tree is light in colour the resin dramatically increases the mass and density of the affected wood, changing its colour to dark brown or black. In natural forests, only an estimated 7-10% of the trees are infected by the agarwood fungus (Ng et al., 1997). The major constituents of agarwood oil are sesquiterpenes, which are difficult to synthesize artificially, and therefore there are presently no good substitutes for high quality agarwood.
Exploitation and trade in agarwood
Today, the demand for agarwood far exceeds supply. A recent study revealed that supply rates are only 40% of the demand and a litre of agarwood oil can be sold for around $US10,000 – 14,000 on the market (Vietnam Chemical Technology Institute, 2007). Indeed agarwood is reputed to be the most expensive wood in the world and it is estimated that specialized buyers are prepared to pay as much as ten times more for this product.
There are no obvious external signs that a tree may contain agarwood and, if it does, the quantity can only be fully determined after the tree has been felled and cut open. The search for the product therefore results in indiscriminate felling of trees and degradation of habitats, causing a loss of the ecological niche for agarwood producing species and a dramatic decline in wild Aquilaria species in the last few decades.
Populations of eight Aquilaria and 15 Gonystylus species have declined to the point at which they are categorized as threatened according to the 2007 IUCN Red List (IUCN, 2007). Out of four listed species of Wikstromia two are believed to be extinct. All species of Aquilaria, Gonystylus and Gyrinops are listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) requiring CITES Parties to issue export permits or reexport certificates in international agarwood trade.
Even though it is illegal to cut and harvest agarwood-producing species in most countries of Southeast Asia, the value of agarwood is so high that wild populations continue to be under threat in all countries where the taxa occur. Tracking down and documenting trade quantities is therefore challenging, and it is virtually impossible to determine which species are being traded, as all agarwood reported in trade is generally referred to as Aquilaria spp. or A. malaccensis.
Agarwood is exported in various forms (wood chips, powder, oil and as finished products such as perfumes, incense and medicines), and the main importers are countries in the Middle and Far East – in particular the United Arab Emirates and Saudi Arabia (where agarwood is known as oudh), as well as Hong Kong, Taiwan and Japan.
Artificial agarwood induction and harvesting practices
While a large part of agarwood comes from the exploitation of wild plants, local communities, over time, have developed a number of techniques to artificially induce the generation of agarwood, although with uneven rates of success. For instance, communities in northern Vietnam cut a hole in the trunk or main branches of Aquilaria trees. If the wound is kept open by regular chipping, agarwood generation may be induced after several years and can be extracted in nominal quantities each time when chipped, as long as the tree remains alive. This method may be adapted and further developed as “tapping” of agarwood, and may be a more sustainable alternative to felling the entire tree.
Another technique takes the wounding a step further by plugging the wound with a piece of wood or pottery shard. This prevents the wound from closing and therefore would seem to be a more reliable method for inducing agarwood production.
A method of coppicing by indigenous Penan people is reported from Borneo (Donovan and Puri, 2004). Although harvest quantities are small, the trees develop a dense coppice and provide continuous yield. The periodic coppicing wounds the trees and promotes further formation of agarwood.
Another, more recent way of producing agarwood, is to grow trees in plantations. A drill is usually employed to make holes in the trunks and main branches of mature trees which are then inoculated with agarwood powder. Generally, agarwood is harvested when the trees are between five and ten years old. Agarwood plantations exist in a number of countries, including Bangladesh, Bhutan, India, Indonesia, Laos, Malaysia, Myanmar, Papua New Guinea, Thailand and Vietnam.
Towards conservation and sustainable management of agarwood
The high value of agarwood and the potentially lucrative nature of mass production has restricted the free exchange of information regarding sustainable production methodologies. There has therefore been little opportunity to capitalize on lessons learnt in this area. On the other hand, farmers and investors have been hesitant to invest in cultivation because of the 5-10 year wait for returns, and perhaps because of fear that agarwood produced in plantations may be of lower grade, and therefore unprofitable. In this respect, concerns are raised that cultivation may not necessarily reduce the demand and may well increase wild harvesting. Furthermore, there is the concern that increased production may flood the market and cause price deflation.
As a result, many questions remain regarding successful conservation and sustainable management of agarwood. Knowledge gaps about the biology and ecology of agarwood-producing species need to be filled and traditional, management practices should be integrated with the latest scientific research findings. In addition, it will be essential to devise mechanisms to allow benefits to return to local communities that have made available their knowledge of management practices for agarwood production.
Botanic gardens worldwide are increasingly being recognized as having a vital role in plant conservation. They function as “Noah’s Arks”, holding rare and endangered plants in protective custody until such time as they can be reintroduced into suitable wild habitat. As such, they are well-placed to play a central role in the conservation of threatened Aquilaria and other agarwood-producing species.
In collaboration with local botanic gardens and related partners in Southeast Asia, BGCI has been working on finding solutions to the challenges of agarwood conservation. A joint project with the Research Institute of Science (RIS) in Vientiane, Lao PDR, has enabled a national survey and the design of a database of wild populations of Aquilaria, including GIS data and vouchers, as well as the successful production of nursery stock for plantations of six Aquilaria species. A public exhibition on environmental resources including a display of agarwood and the inoculation process for plantation trees has been instrumental in raising awareness of the conservation status of agarwood and the need for sustainable management of this valuable natural resource.
For many years, the RIS has been encouraging rural farmers to plant Aquilaria in plantations, and as a result, there are now approximately 1,000 hectares of plantation established in Bori Khamxay Province, Lao PDR. RIS has also isolated three species of the resin-inducing fungi from wild agarwood producing trees. Using an electric drill to make small holes in plantation trees, wooden pegs infected with the fungus are hammered into the opening. Tree trunks containing agarwood are foreseen to be harvested after five years.
Capitalising on these experiences, BGCI is pursuing efforts to secure and conserve remaining wild populations of Aquilaria and other threatened agarwood- producing taxa. The plan of action, initially developed for Lao PDR, Cambodia and Vietnam includes:
• Strengthening institutional cooperation and coordination, by bringing together various stakeholders including local collectors, processors, traders, government and conservation agencies, botanic gardens and businesses;
• Capacity building and training for integrated agarwood conservation, by assisting in the development of in-country training capacity (of resource owners, users and conservation practitioners) focussing on surveying remaining wild populations, integrated ex- and in situ species recovery programmes and silviculture; and
• Practical conservation in demonstration projects, aiming to enhance i) conservation of remaining wild populations of agarwoodproducing tree species (e.g. in community managed protected areas); ii) ex situ propagation of critically endangered species in village nurseries, local botanic gardens, etc. and, iii) subsequent reintroduction into the wild.
With the implementation of this action plan it is hoped to provide a complementary approach to harvesting wild trees and to relieve pressure on the remaining highly threatened natural populations of Aquilaria and other agarwood-generating species, while supporting those local communities whose livelihoods depend on this precious natural resource.