Wind reduction patterns around isolated biomass for wind erosion control in a desertified area of Central Sudan

The aim of this study was to assess the effectiveness of sparse vegetation, feature common in arid zone, to reduce wind force (velocity) and hence protect the surface and regions downwind from drifting sand and their consequences. Respectively 4 (with heights h of 4, 3.2, 2 and 1.66 m), 2 (with h of 3 and 2.5 m) and 3 (with h of 1.04, 0.9 and 0.8 m ) well established single biomass configurations of Leptadenia pyrotechnica trees, Prosopis juliflora trees and Panicum turgidum grass, were selected in the field. Solar powered cup anemometer wind measurements with a data logger system were taken at heights of 0.25 and 0.5 h, at distances 0.5 and 1 h, at four sides of the tree in the prevailing wind direction and perpendicular to it, and additionally at 2, 4 and 6 h windward and leeward. The protection effectiveness of the biomass was calculated as a wind reduction ratio and in terms of objects protection, which was evaluated using the dimensionless protection index (É). The study showed that windward protection provided by Leptadenia and Prosopis at level 0.25h and distance 0.5 h was similar, w ith a wind reduction ratio R0.8, while Panicum showed comparably higher R-values. Even at the 0.5 h level, Panicum showed an R of 0.65 at 0.5 h distance. Leew ard, at 0.25 h level differences were small, R increasing from 0.6/0.7 to 0.8/1 with distance, Leptadenia protecting best. At higher level (0.5 h) at distances 0.5 and 1 h Prosopis gave better protection than the other two at distances 0.5, 1 and 2 h. The research is an exam ple of simple experimental work under difficult environmental conditions in Africa. It was part of studies in which additional attention was paid to quantification aspects under such conditions as well as to the problems it helped solve in the African societies concerned as agrometeorological service

Agroforestry solutions to some African wind problems

The Traditional Techniques of Microclimate Improvement-Project was in several cases called upon to find urgently required local solutions to problems caused by wind in Africa, using trees in an agroforestry setting. In Sudan, this was related to wind-induced sand encroachment towards an irrigated area, which could be solved by a shelterbelt. Also, sand settlement by trees and grasses in the source area was researched. In Nigeria, land reclaimed from desertification by multiple shelterbelts had to be brought again into agricultural use under conditions of hot dry winds. In Kenya, mulched intercropping had to be practised under conditions of strong winds, which was made possible by applying hedges all around and intercropped trees. Reductions of strong winds were also studied in north Tanzania with a sufficient and an insufficient density of scattered trees for soil protection. Keeping shade trees appeared necessary for wind protection of coffee on the slopes of the Kilimanjaro, also in northern Tanzania