Physical and mechanical properties of some less utilised tropical timber tree species growing in Uganda

Abstract

Variation in some physical and mechanical properties of the wood in four less utilised tree species native to Uganda was examined. One mature tree each of Antiaris toxicaria, Celtis mildbraedii, Maesopsis eminii and Alstonia boonei was selected from Budongo forest in Masindi district and felled using a chain saw. Diameter at Breast Height (DBH) and stem length for each tree were measured before and after felling. Each log was cross cut into three 150 cm long billets at 5-10% of stem length (breast height 1.3m), 45% of stem length and 75% of stem length. Billets were sawn by through and through method for basic density and strength properties determination. International Standard Organisation (ISO) 3129 (1975) and ISO 3349 (1975) standards were followed to prepare test specimens and moisture content determined in accordance with ISO 3130 procedures. Strength properties were determined using a Monsanto Tensometer wood-testing machine. Tests were based on International Standard Organisation (ISO) procedures BS 373 (1957) and ISO 3133 (1975). Testing was carried out in a laboratory under temperatures of 20 3 C and relative humidity of 65 3 % based on British Standards BS 373 (1957). Basic density and strength properties of modulus of rapture, modulus of elasticity, shear strength, cleavage strength and compressive strength varied significantly (P<0.05) in the radial and axial directions within individual tree species. The properties also decreased moderately from the butt end to the top end. Basic density and strength properties decreased moderately from the pith to the centre of the radius, then increased to the bark. The strength properties of C. mildbraedii were comparable with those of M. excelsa and Khaya anthotheca that are well known and commercially utilised species. It was concluded that some lesser-utilised species are of equivalent or superior strength properties compared to commercially valued tree species such as mahogany. Lesser-utilised species should therefore be promoted as substitutes for other commonly utilised hardwoods within the range, thereby reducing pressure on the well-known and valued timbers.