Taxonomy and Nomenclature
Species Name: Aquilaria malaccensis Lamk
Family Name: Thymelaeaceae
Synonym: Aquilaria agallocha
English: agarwood, aloewood, eaglewood, malayan eaglewood tree.
French: Bois d’aigle de Malacca.
Indonesian: alim, halim, kareh, gaharu, garu, ketimusan.
Spanish: madera de Agar.
Thai: kritsanaa, mai hom.
Habitat It is found in primary and secondary forest, mainly in lowland and on hillsides at 200 – 750 m altitude, Koeppen climate type A – B with temperatures of 14 – 32 °C and annual rainfall of 2.000 – 4.000 mm. It grows on sandy clay soil.
Distribution Bangladesh, Bhutan, India, Indonesia, Iran (Islamic Republic of), Malaysia, Myanmar, Philippines, Singapore, Thailand.
Habit Tree, up to 20 – 40 m tall and 60 cm in diameter.
Bark Young bark is light brown with fine hairs, older bark is smooth and whitish in color.
Wood without resin is white, light and soft, while wood with resin is hard, dark and heavy.
Leaves alternate, elliptic or lanceolate, 3-3.5 cm wide and 6-8 cm long with 12-16 pairs of veins.
Flowers hermaphroditic, up to 5 mm long, fragrant and yellowish green or white.
Inflorescence a terminal or axillary umbel.
Fruit Green, egg-shaped capsule, leathery exocarp with fine hairs, 4 cm long and 2.5 cm wide. There are two seeds per fruit. Mature fruits are blackish brown.
Seed Ovoid, blackish brown and densely covered with red-brown hair. There are about 1500 seeds per kg. Seeds are recalcitrant. Viability drops when the seeds are dried to a moisture content between 35% and 20% mc, with rapid loss in viability occurring below 20% mc and total loss at 7-11% mc. The seed cannot be stored for long and it is recommended to sow shortly after harvest. Storing in open sacks in a dry room may prolong viability.Most seeds germinate within three weeks.
The fact that not all trees wounded or inoculated develop the aromatic resin may indicate a significant degree of phenotypic variation with regard to disease resistance in natural populations (Alexander 1992). Experimental results show that different genotypes of woody plants differ in their behavior as host when attacked by fungi or insects. Moreover, different genotypes of the same fungal or insect species may be successful to different degrees as parasites with different genotypes of the host (Hattemer and Melchior 1993).
It could be that several varieties exist within the relevant Aquilaria species and that certain strains or varieties are more sensitive or responsive than others to fungal attack (Rao and Dayal 1992). Over the long term, fungal parasites, which usually have a restricted host range, do worse in mixed stands than in solid or single-species stands (Bakshi 1954). Accordingly, the clustering habit of Aquilaria may have maintained the species or, more likely, a provenance´s unique gaharu-producing capabilities. As noted by Parker (1992), any limitation on pollen dispersal may constrain the potential benefits of sexual reproduction vis-a-vis reducing the pathogen impact.
Thus, a clustering habit may work against the tree but to the advantage of pathogens. Alternatively, it could be that the prodigious output of resin by some trees, especially found in the same cluster, may be an evolutionary response to a particularly virulent local pest. Information on the extent of pathogen diversity and the effect of host species diversity on pathogen populations is poor. As is increasingly recognized, host-parasite relationships are complex and constantly evolving (Hines and Marx 2001).
Research on the impact of plant-host genetic diversification on genetic diversity of plant pathogenic microorganisms, especially fungi, is scarce and generally focused on agricultural crops (Fritz and Simms 1992, Groth and Christ 1992, Hattemer and Melchior 1993).
In some wild host pathogen systems, extinction and recolonization events occur with noticeable frequency (Burdon and Silk 1997). Patch distribution of a natural host population tends to result in fungal populations that show large amplitudes in size, relatively local and frequent extinctions, and asynchrony in the dynamics of neighboring genes (Burdon and Silk 1997). Thus, the etiology of gaharu formation may be the result of a long and constantly changing relationship between several biological elements.
Viable and non-viable seeds can be separated before sowing by flotation. Empty or dead seed float while full and viable seeds sink in water. A light sowing media is preferred e.g. prepared by mixing soil, organic compost and paddy husk 1:1:1. Seeds are sown on top of the seedbed, then pressed lightly into the medium and covered with a layer of 1-2 cm fine compost. Nursery beds, and later transplant beds, should be kept under shade. Most seeds germinate within three weeks and fresh seed should have about 70-80% germination. When the seedlings have three leaves they are transplanted into polybags. Before planting out, the shade should be gradually reduced.
Vegetative propagation is relatively easy. Mass propagation can be done by rooting of cuttings after treatment with rooting hormones. Other types of vegetative propagation are marcotting (air-layering), occultation and tissue culture.
The Penan noted that several species, especially palms, were often found near gaharu-producing trees. There has been a lot of interest in the extent to which discrete species association, or consociations, are correlated with site factors in the tropical forest (Wyatt-Smith 1995). Species associations on alluvial valley floors, as distinct from those on hillsides and ridges, have been detected in numerical analysis of small plots in Malaya, Brunei, and Sabah (Whitmore 1985).
Data collected in Brunei revealed that species associations were correlated with complex soil factors not clearly defined (Brunig 1970). Although Ashton (1967) found species diversity correlated with total soil phosphorus, especially at low concentrations, plant-available phosphorus is difficult to correlate with total phosphorus. Baillie (1972) found topography, which also reflects soil conditions, most closely associated with floristic composition. Most research has shown, however, that consociations result from the influence of several factors, not just soil conditions (Whitmore 1985). Thus, it may be the synergistic effect of the confluence of environmental factors that determines species composition in the gaharu habitat.
Good quality gaharu does not occur in all species of the genus Aquilaria, nor in all trees of the subset of species capable of producing the highly desirable aromatic wood. It is estimated that, under natural conditions, only one out of ten trees (of the appropriate species) contain the valuable resin (Gianno 1990, Foppes 2000, personal communication).
As early as the 18th century, it was recognized that the perfumed wood known as gaharu was the result of a pathological condition (Loureiro 1790 as cited in Ding Hou 1960). Much of the early research on Aquilaria focused on identifying the specific fungi that might stimulate resin production. Attempts at inoculation began in the 1930s (Beniwal 1989).
The discovery of several species of fungi in association with gaharu and the unpredictability of response to inoculation with the various fungal species have been disappointing. Given that the level of response has been highly variable, as the desired morphological changes in the phloem take place in some but not all trees, inoculation trials can be judged only a limited success. Most scientists agree that it is unlikely that a single, specific fungal cause will be associated with the formation of the resin, as more than 20 varieties or genetic strains of fungus have been identified in the presence of resin (Gibson 1977, Jalaluddin 1977, Rahman and Khisa 1984, Rao and Dayal 1992, Tamuli et al. 2000, Tabata et al. 2003).
The formation of abnormal tissue and anomalous flow of resin (resinosis) that is apparent in infected material is a common response brought about by physiological factors, i.e., wounding or the attack of insects or pathogens, such as fungi (Bakshi 1954, Kramer and Kozlowski 1979, Heath 1989, Rao and Dayal 1992).
Fungal spores can be dispersed by wind, water, or insects from reservoirs in the soil or diseased tissues in the same or neighboring trees (Jalaluddin 1977, Ivory and Speight 1993). Resin formation and dispersal is the tree´s attempt to inhibit the growth and spread of the pathogen. In the case of Aquilaria, one research report concluded that the range of fungal colonists decreased as the oleoresin content increased (Rahman and Basaki 1980). Wounds suffered when a branch is broken or an insect invades provide entry for a variety of parasites and pathogens. Pioneer microorganisms that infect such wounds are usually bacteria and non-decay fungi for example, Ascomycetes, Phycomycetes and Fungi imperfecti that are able to use the food materials in the chemically altered cells (Shigo 1969).
Ultimately, it is usually not one but a succession and combination of organisms and processes that leads to what is observed as the infection or decay (Shigo 1967). Research is unclear whether variation in secondary metabolites in tropical plants is genetically or environmentally based. Geographical (interpopulation) variation in secondary chemistry has been shown for several rain forest plants (Waterman and McKey 1989) There is no indication in the literature that the extent of infection is related to the type or degree of injury assumed to be the necessary prerequisite of an infection and resin formation.
The wood is hard and light with rough texture, white or brownish yellow. Main use is the agarwood, a highly appreciated and priced fragrant wood caused by accumulation of scented resin. Production of agarwood may be influenced both by genetic and environmental factors but the general understanding is that the fragrant oleoresin that permeates the heartwood of some trees is produced as a response to wounding and/or fungal infection. Agarwood contains more than 12 chemical components that can be extracted. They have a wide use in medicine (general pain reducer, dental pain, kidney and rheumatism medicine), as venom repellent, in perfume and as incense raw material. Wood without or with low content of resin can be used for boxes, interior or veneer. The inner fi brous bark has occasionally been used locally as raw material for clothing and ropes.
Resin producing trees are endangered throughout their known habitat all across Southeast Asia. The main driving force, which initiated this project, was the recognition of unsustainable Aquilaria harvesting in natural forests that resulted in the near extinction of this tree genus in Viet Nam and elsewhere. Aquilaria crassna is now listed as a protected species in Viet Nam, and Aquilaria malaccensis is a CITES red data book listed tree. Trade and harvesting restrictions will be virtually impossible to achieve if no alternative is developed to forest-based harvesting. In addition, both in the short and long-term, a natural resource base needs to be maintained to supply present and future Aquilaria plantations with genetic source material, in order to prevent plant decease, maintain diversity and possibly improve resin production.
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Learning from Traditional Knowledge of Non-timber Forest Products: Penan Benalui and the Autecology of Aquilaria in Indonesian Borneo