The forestry industry is still one of the most important industries in Sabah, despite the rapid shrinkage of forested areas. Logs for timber are produced mainly from natural forests and partly from plantation forests in Southeast Asia. In the case of Sabah, for example, logs produced from natural forests and plantation forests totaled 2,588,417 m3 and 250,018 m3, respectively, in 2001. Of logs from natural forests, species of Dipterocarpaceae are the most important element, making up 65.8% of the total volume. However, these valuable resources are now precipitously declining as a result of overexploitation of the natural forests, and there is an urgent need to consider the sustainable supply and effective utilization of timber. It is thus very important to increase the share of timber from plantation forests to prevent the degradation of natural forests. Acacia mangium is the commonest plantation tree species in Southeast Asia. In Sabah, out of a total 130,655 ha of forest plantation, 106,581 ha are planted with fast-growing species, of which A. mangium account for about 72%. However, 94.6% of logs of A. mangium produced in 2002 were exported to other countries without any processing in Sabah. The purpose of this study was to investigate the basic wood properties of A. mangium to enable more effective use of its timber.
For the investigation of basic wood properties such as wood density and length of wood fiber, 13 year old Acacia mangium Willd. trees in the plantation of Segaliud Lokan of the Forest Research Centre of Sabah (FRC) were investigated. In 2003, eleven trees of several sizes (height: 21.8 –33.7 m, DBH: 14.3 – 42.8 cm) were cut, and sample disks were collected every 2 m, starting at breast height. After drying in an air-conditioned room, a disk at each position was cut into strips 3 cm wide, containing pith, using a bandsaw. The strips were divided into small blocks every 3 cm (1 cm at the strip taken at DBH) from the pith using a hatchet. The air-dried densities of each block were measured using a floating method. Small pieces of wood were taken from the blocks every 3 cm (1 cm at the strip taken at DBH) from the pith, and macerated using Franklin’s method (6% acetic acid, 6% hydrogen peroxide, 60 ˚C x 48 hrs). The length of the wood fibers was measured under a light microscope equipped with a measurement system (VM-60N Video Micrometer, Olympus)
Fig. 1 shows the radial variation in wood density and the length of wood fibers at breast height in the trunks. The wood density and the length of wood fibers increased from the pith to the bark, and showed almost constant values in the outer part from 9 cm distance from the pith. Fig. 2 shows longitudinal variation in the wood density and length of wood fiber. There was no significant difference in the pattern of radial variation of the wood density and the fiber length among the disks taken from different height positions on the trunk.
These results indicate that the wood outer part from 9 cm from the pith has uniform properties in A. mangium planted in Sabah. This means that trees with a higher growth rate produce more wood with uniform properties than trees with a lower growth rate. Our results are of potential use as fundamental data for the industry to utilize A. mangium timber more effectively, and for policymakers to select sites for plantations of A. mangium.
Fig. 1. Radial variation of (A) wood density and (B) length of wood fiber at breast height of trunks of A. mangium.
Fig. 2. Positional change in the radial variations of (A) wood density, and of (B) length of wood fiber with height of trunk of A. mangium.
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