Vitex doniana sweet: A potential lesser-known and lesser utilized agro-forestry timber species in Kilosa District, Morogoro Tanzania

Abstract

Tanzania is classified as among the 15 poorest nations in the world, with an estimated per capita income of less than US$ 190. Over 80 % of the country’s population of about 46 million lives in rural areas. Living in such a poor country, the people have few feasible alternatives to exploiting the forest resources resulting in high deforestation rate estimated at 2 % annually. Nevertheless, many timber species are still not known to users, resulting into over-exploitation of few well-known timber species. The timber stakeholders need alternatives and the national economies need better ways to derive value from the remaining forests in order to maintain their many useful but under-valued functions. One option is to optimize the production and utilization of lesser-known and lesser-utilized indigenous timber species which are potential for agro-forestry. One of such species is Vitex doniana Sweet which belongs to the family Lamiaceae. It is a deciduous tree with medium-growth rate and is widespread in tropical Africa. V. doniana is being threatened by habitat loss. This paper attempts to analyze some potentials of V. doniana as an agroforestry tree. The studied properties were: i) Physical – Tree dimension, form and quality, wood colour, texture, workability and basic density ii) Strength - Static bending, compression, shear and cleavage and iii) Anatomical - growth rings, vessels arrangement, density and size, gum deposits, parenchyma and ray tissue. The average physical properties are as follows: The sapwood is white while the heartwood is pale greyish-brown and basic density is 650 kg m-3. The strength properties are: Modulus of elasticity (11,100 N mm-2), Modulus of rapture (98.14 N mm-2), Work to maximum load before failure (0.131 mm N mm-3) and Total Work (0.239 mm N mm-3). The impact bending strength was 1.02 m, Hardness (4,580 N), Compression parallel to the grain (52.5 N mm-2), Shear parallel to the grain (15.6 N mm-2) and Cleavage (9.0 N mm-1). This species depicts well-marked growth rings and therefore ring-porous, meaning a course textured timber. The average strength properties are closely comparable to those of Tectona grandis (Teak). Also, Vitex doniana has other multiple benefits: bears edible fruits, suitable as ornamental tree and windbreak, shade and its leaves are useful as vegetable and as well as for soil improvement.