Wind Erosion Reduction by Scattered Woody Vegetation in Farmers' Fields in Northern Burkina Faso

Abstract

Wind erosion is an important soil degradation process on agricultural fields in the Sahel and is strongly affected by scattered woody vegetation. This paper analyses the effect of scattered vegetation on sediment transport in agricultural fields in northern Burkina Faso. A model was developed to simulate the changes in wind speed and sediment transport around shrubs and trees. The model was applied by using field measurements on wind speed, wind direction, and sediment transport, obtained from two farmers' fields during the rainy season of 2003. Vegetation characteristics and the density of vegetation elements differed per field. The model was used for scenario studies to test the effect of height, number, element type and spatial arrangement of vegetation elements on aeolian sediment transport. The local effects of vegetation elements on wind speed and sediment transport are small compared with the effects caused by the changes in the aerodynamic roughness length and changing wind speed at a larger scale. With relatively small changes in the characteristics of scattered woody vegetation, sediment transport can change considerably. An optimal arrangement of vegetation elements in an area in itself does not exist; it is an interrelation between the number of vegetation elements, the silhouette area and the type of vegetation elements present. This interrelation makes the use of scattered vegetation as a wind erosion control strategy attractive, as it fits in a variety of farming systems and can easily be adapted to specific needs of farmers. Therefore, scattered woody vegetation can be used to reduce sediment transport.