Some physical and strength properties of immature Pinus patula trees harvested in Iringa and Njombe regions, Tanzania

Abstract

A study was conducted to determine physical and strength properties of immature Pinus patula grown in Iringa and Njombe regions of Tanzania. Sample trees aged 5 to 15 years were collected from farmers’ woodlots. The trees were categorized into 5 age classes: 5 - 7, 8 - 10, 11 - 12, 13 - 14 and 15 years. Four trees from each age class were selected and marked for felling. Diameter at breast height and stem length for each tree were measured before and after felling respectively. Three disks and planks each measuring 5 cm thick and 120 cm long respectively were cut at 1.3 m, 50% and 75% of total tree height from each sample tree for determination of wood basic density and strength properties using standard procedures. Analysis of variance was used to compare means of wood basic density and strength properties of pine wood between age classes. Results showed that P. patula wood at 5-15 years had relatively lower basic density, modulus of rupture (MOR), modulus of elasticity (MOE) and compression strength than 25 year old wood. Basic density varied significantly (p<0.05) between tree ages and increased with increase of tree age. Strength properties increased with increase in tree ages with exception of MOE and MOR in Njombe region. It was concluded that wood basic density and strength properties of P. patula at 5 - 15 years had inferior properties compared to P. patula at 25 years. It was therefore recommended that farmers should not harvest their trees for structural use purposes at the age of 15 years and below but may be for other uses like pulp and paper making. A similar study is needed for trees aged 16 to 24 years to determine the age at which farmers can start harvesting trees for structural use. However, the harvesting time should not based on physical and strength properties of wood alone but other factors such as current and mean annual increment and economic aspects.