Some properties of commercially lesser known and lesser utilized timber species of Brachystegia bussei (Harms) and Berchemia discolor (Klotzch Hemsley) from Tanzania

Two lesser known and lesser utilized indigenous tree species in Tanzania Brachystegia bussei (Harms) and Berchemia discolor (Klotzsch Hemsley) were studied to determine wood colour, moisture content, heartwood proportion, basic density, fibre length, some strength properties and their natural durability. Four trees, two from each species were sampled. A total number of 175 clear wood specimens, 90 for B. bussei and 85 for B. discolor were obtained and tested according to standard methods. Natural durability of the two tree species was investigated by subjecting the wood blocks to degradation by a wood decay fungus, Coriolopsis polyzona for a period of four months. Samples of P. angolensis a commercially well-known timber species in Tanzania were also tested for their natural durability for comparison purposes. The wood of B. bussei was found to be light brown while that of B. discolor was dark brown. The average moisture content was 50% and 46% for B.bussei and B. discolor respectively. On average the heartwood proportion for B. bussei was found to be 20% at the top of the tree, 33% at center and 33% at the bottom of the tree. On the other hand, heartwood proportion of B. discolor, was 25% at the top of the tree, 50% at the center and 75% at the bottom of the tree. Basic densities were 694 kgm3 and 864 kgm3 for B. bussei and B. discolor respectively. Results of strength tests on clear specimens showed that, on average, the overall strength properties for B. bussei and B. discolor may be considered high. In most cases they are comparable with the well-known and commercially utilized species such as Pterocarpus angolensis, Khaya anthotheca, Afzelia species, Melicia excelsa, Newtonia buchananii and other Brachystegia species. Differences between B. bussei and B. discolor in all the strength properties except modulus of elasticity (MOE), work to maximum load (Wmax), impact bending and fibre length were statistically significant (P<0.05). For both species, there were positive correlations between basic density and strength properties. Loss in weight for B. bussei heartwood and sapwood were 3% and 2% respectively while B. discolor was 4.50% for heartwood and 5.74% for sapwood. The Loss in weight for P. angolensis heartwood and sapwood were 2.70% and 5.13% respectively. The results further showed that, both species under investigation were resistant to C. polyzona and showed no significant differences (P<0.05) when compared with P. angolesis. These two studied species show potentials for a number of end uses such as construction work, sporting goods, furniture making and many others. These species are therefore, worth substituting the species compared with and many other commonly utilized hardwoods within the range, thereby reducing pressure on the well-known and well-utilized timbers.