Wood production in a natural stand of Acacia karroo in Zimbabwe

Trees are important components of agricultural systems in the dry tropics of Africa. The assumption that exotic species are more productive than the indigenous woodland in these situations is seldom supported by quantitative data. In this study a new technique of recognising annual growth rings from the bands of marginal parenchyma has been used to model growth in a natural population of Acacia karroo Hayne, one of the most widespread and useful trees in the savanna woodlands of southern Africa. The study showed both basal area and sectional area at ankle height to be excellent predictors of total tree volume. Stands may yield from about 1 to 4 m³ ha⁻¹ year⁻¹ dependent upon spacing and site; individual trees produced up to 1 m³ of wood in 26 years. Maximum current annual increment was reached about 12 years after the trees approached breast height, thereafter declining until they became moribund about 8 years later. The economic rotation for wood production was close to the lifespan of the tree.