A study of the ecology of Acacia metllifera, A. seyal and Balanites aegyptiaca in relation to land-clearing.
Two different vegetation communities, Acacia mellifera bushland and associated grassland in a drier, more northerly zone, and A. seyall Balanites aegyptiaca tall grass woodland in the wetter southerly zone, are present on the Sudan clay plains to be cleared for irrigated agriculture before the impending completion of the Roseires dam. Different problems arise in the clearing of the three species; fire tolerance, depth and type of rooting, suitability for ring-barking, (the deeply fluted trunk of B. aegyptiaca may make it difficult to ring-bark), chemical poisoning, mechanical raking, uprooting and chain-felling. Timed raking trials in different densities provided data on times of operation. A crown density scale developed from aerial photographs enabled the density of the vegetation to be assessed and made it possible to estimate the total tractor hours needed for clearing. A second trial in woodland showed that it would cost three times as much to clear land by raking chain-felled timber into rows for burning, than to clear by burning felled timber in situ. With data from these trials a second density scale was designed for estimating the total tractor hours required in each phase of clearing in the woodland of the project area. The fewer the seasons available for land clearing in the woodland community, the less can fire and other processes of decay help in reducing costs. F.s.-D.B.