Suitability of Acacia crassicarpa A. Cunn. Ex Benth., A. Leptocarpa A. Cunn. Ex Benth., A. Julifera Benth., Brachystegia boehmii Taub. and B. Spiciformis Benth. For Wood Energy Production in Tabora, Tanzania

Abstract

This study investigated the calorific values of five tree species, three of which are exotic and grown in agroforestry systems and the other two are naturally growing and indigenous in Tabora, Tanzania. Whereas the exotics are Acacia crassicarpa, Acacia leptocarpa and Acacia julifera, the indigenous species are Brachystegia boehmii and Brachystegia spiciformis. Wood fuel, primarily in the form of charcoal and firewood, is a critical energy source in developing countries, particularly for heating and tobacco curing. Understanding the calorific values of these species is essential for optimizing their use as sustainable bioenergy sources, especially in regions where biomass remains a dominant energy resource. The study was conducted at the Tanzania Agricultural Research Institute (TARI) Tumbi Centre, utilizing wood samples collected from trees at various heights and positions within the stem. Calorific values were determined using a bomb calorimeter and statistical analyses, including ANOVA and regression, were employed to compare species and assess correlations between sample positions and energy content. Results revealed that the mean calorific values of the exotic Acacia species (Acacia crassicarpa: 17.11 kJ/g, Acacia leptocarpa: 16.67 kJ/g, and Acacia julifera: 17.45 kJ/g) were not significantly different from each other but showed significant differences compared to the indigenous Brachystegia spiciformis (20.18 kJ/g). Brachystegia boehmii exhibited a calorific value of 16.66 kJ/g, similar to the Acacia species. Notably, Acacia julifera demonstrated favourable calorific properties, making it a promising tree species for further cultivation in agroforestry systems aimed at sustainable energy production. This study contributes to the growing body of knowledge on the thermal properties of agroforestry tree species, providing critical data for sustainable forestry management and energy planning. The findings underscore the importance of integrating both exotic and indigenous species into agroforestry systems to enhance energy security, support local economies, and promote environmental conservation. Recommendations are made for the adoption of Acacia julifera in community woodlots and plantations, alongside continued research into the thermal properties of other species to inform sustainable resource management practices in Tanzania and similar regions.