Abstract
This study, based on a high initial-density plantation of Acacia salicina trees, which was later thinned to facilitate high individual-tree growth suitable for saw-timber production, investigates the effect of thinning on some wood quality parameters. Trees were planted in 1998, at a density of 6400 trees ha(-1) (with spacing of 1.25 x 1.25 m). Annual mechanical thinning, started after two years in half of the population, was continued till 2003. From 2004 to 2010, the densities of 400 and 3200 trees ha-1 were maintained for the thinned and unthinned stands, respectively. In 2010, five trees selected randomly from each of the two stands were felled and disk samples obtained to determine wood specific gravity, fiber length, shrinkage behavior, sapwood-heartwood ratio, and growth-ring width. Tree thinning increased the width of annual growth rings by 155-185 % in comparison with growth rings in unthinned population. At a given height level, production of sapwood and heartwood was 4-5 times and 4-6 times higher in thinned population than in unthinned population. Fibre length showed no significant change, but the impact of thinning on fibre length varied with position across the radius of the wood disc. However, thinning caused specific gravity of wood to decline form 0.523 in unthinned population to 0.503 in thinned population (3.8 % reduction). Tangential shrinkage of wood in thinned trees exhibited a clear variation pattern along the radius, with the highest mean value (8.24 %) recorded near the periphery of the wood disc and the lowest (7.28 %) near the centre (pith region).