Comparison of some physical, mechanical and anatomical properties of smallholder plantation teak (Tectona grandis Linn. f.) from dry and wet localities of Ghana

Abstract

Smallholder plantation teak (Tectona grandis Linn. F.) plays an important role in the socio-economic development of tropical countries. Published research on site differences with respect to anatomical, physical and mechanical properties of smallholder teak in Ghana is limited. This study compared and evaluated some physical, mechanical and anatomical properties of smallholder plantation teak trees grown in dry and wet localities of Ghana. Ages and diameters for the randomly selected trees were in the range 10–20 years and 16–47 cm dbh, respectively. Wood samples were prepared from three stem heights and three radial positions and were tested for air-dry density, bending strength (MoR), modulus of elasticity (MoE), maximum compression strength parallel to grain, shear strength and hardness, using BS standards. Heartwood proportion was evaluated on the basis of stem height and tree age. Site conditions, tree age, stem and radial positions were all important factors that influenced the wood traits investigated. Comparatively, the wet site had disproportionately low mean heartwood proportion but higher values in air-dry density, MoE, MoR, hardness and shear strength. Overall, the teak wood studied suffered a relatively low bending strength that limits its use to light construction. The smaller vessel diameter of teakwood from the dry site has implications for utilization; first, small vessel diameter presents resistance to sap conduction resulting in slower growth with higher heartwood proportion; second, in terms of finishing, it gives the wood smooth surfaces upon planing and polishing, and therefore contributing to its aesthetic value; third, during drying, dimensional stability of the wood may be assured with smaller vessels. The differences in wood traits observed between the two sites emphasize proper site selection for improved wood quality. Since the age of the teak trees accounted for significant variations of all the wood traits investigated, to ensure optimum economic returns, small teak plantation holders may have to delay the harvesting of teak trees for a few years.