Acacia mangium Willd. - A Fast Growing Tree for Tropical Plantation

Anatomical, physical and mechanical properties of A. mangium wood

The sapwood of A. mangium is white and sharply defined from the darker brown heartwood. The wood has fine texture and straight or interlocked grain. The average values for fiber length, diameter, lumen diameter and wall thickness are 934, 25, 18 and 3.3 μm for 4-year-old samples and 1017, 20, 12 and 4.3 μm for 8-year-old samples respectively. The fibre length increases from pith to bark and decreases with stem height. The vessel percentage decreases with increasing tree height. The wood is diffuse-porous with mostly solitary vessels. The rays are uniseriate. The average percentage of fibres, vessels and rays are 85, 7-11 and 5-6 respectively. The average fibre length is reported to be 1.0-1.2 mm (1,000-1,200 μm).

A. mangium has a comparatively low proportion of parenchymatous cells, a relatively high proportion of prosen-chymatous cells and a low proportion of vessels, indicating satisfactory strength properties. It is short fibred (870 μm), characterized with small fibre diameter (18.9 μm) and small wall thickness (2.7 μm). Wu et al. (1988) studied the anatomical structure of A. mangium wood. They observed libriform fibres with inclusions, small longitudinal parenchyma with calcium crystals and vessels with silica crystals. Although the mean value of specific gravity of trees in natural stands is 0.56-0.60, plantation grown lumber is found to have a low range of specific gravity (0.40-0.45) (Mergen et al. 1983). Peh and Khoo (1984) also reported a low density for A. mangium wood (380-480 kg/m³). Scharai-Rad Kambey (1989), from Indonesia, reported about the properties and possible uses of the wood of mangium, and the wood density of 501 kg/m³.

Ong (1985) reported the shrinkage, density, strength and hardness of wood from 12-year-old trees. There were considerable variations between and within trees. Scharai-Rad and Budiarso (1988) classified this as a species of medium strength properties. According to them its bending strength is 83.5 N/mm², crushing strength is 37.0 N/mm² and modulus of elasticity (MOE) is 10.6 kN/mm². The wood is reported to be moderately strong with an average bending strength value of 65 N/mm² in green condition (Sattar et al. 1993). An investigation of the variation of wood density, fibre length and shrinkage within and between trees as well as between 3 provenances of 8-year-old A. mangium in Sabah by Sining (1989) showed that basic density ranged from 430 to 500 kg/m³. The variations of wood properties among provenances and among trees were less significant than within trees. Basic density and fibre length increased from pith to bark, shrinkage increased as basic density increased from pith to bark. However, among parameters, the shrinkage decreased as the basic density increased. Wu and Wang (1988) compared the wood properties of A. mangium with A. auriculiformis. They found that its shrinkage and variation were generally less, and strength properties were greater in A. auriculiformis.

Utilization of wood

A. mangium wood makes attractive furniture and cabinets, molding, door and window components (Mergen et al. 1983). The wood is also suitable for light structural works, agricultural implements, boxes and crates (Awang and Taylor 1993).

A. mangium is generally regarded as non-durable timber (Razali and Mohd 1993). It is quite amenable to preservative treatment (Mergen et al. 1983). The treated wood may not give good performance in ground contact. It has a relatively narrow sapwood band and is not a suitable species to be used for exterior and outdoor purposes. The wood seasons fairly rapidly without serious defects. Warping, end splitting and surface checking are negligible. The timber kiln-dries well and fairly rapidly, without serious defects when suitable kiln schedules are used (Awang and Taylor 1993).

It has high incidence of knots, which causes good-quality sawn timber to be unobtainable in significant quantities. Knots can be eliminated through proper pruning regimes. The presence of flutes and incidence of rots and termite attack all detract from both quality and quantity of sawn timber (Razali and Mohd 1993).

Peh et al. (1982) and Peh and Khoo (1984) reported the suitability of A .mangium for pulping with high yields, quality of kraft, NSSC pulps and produced paper with good optical, physical and surface properties (Logan 1987). A. mangium has the highest pulp yield and required the least cooking chemicals when compared with other species like Eucalyptus deglupta and Gmelina arborea (Becker 1987). So, it is currently being grown with the primary use for pulp and paper in Sumatra, Sabah and Vietnam.

A. mangium timber is reported to be easily peeled and the green veneers of tight, smooth and acceptable quality were obtained (Chai 1989). The timber is also suitable for the production of decorative veneers.

Wood of A. mangium has been successfully utilized for the manufacture of particle boards (Mergen et al. 1983). It is reported to be suitable for many re-constituted wood products, such as being medium density fibre board (MDF) (Tomimura et al. 1987). The calorific value of the timber is also relatively high, 4,800-4,900 k cal per kg, so the wood can make good biofuel, reasonably good quality charcoal, charcoal briquettes and activated carbon (Awang and Taylor 1993). Trans-sectional view of wood is finely shown in Fig. 7.

^{Fig. 7. A. mangium tree with heart rot.}