Sediment deposition and pedogenesis in exclosures in the Tigray highlands, Ethiopia

In the Tigray highlands of Northern Ethiopia, the establishment of exclosures (i.e., areas closed for gazing and agriculture) has become an important measure to combat land degradation and restore vegetative cover. Exclosures are commonly found on steep slopes and downslope from a sediment source area. In this study their sediment trapping capacity and controlling factors were investigated. Total sediment depth turned out to be related to vegetation cover, sediment source area and in some cases slope gradient. Thickness of recent, short-term (< 20 years) sediment deposits was strongly related to distance from the top edge of the closed area, slope gradient, vegetation cover and characteristics of the sediment source area. Mean sediment deposition rates ranged between 26 and 123 Mg ha(-1) yr(-1). Under influence of vegetation and sediment deposition dark soils rich in organic matter (Phaeozems) develop. In view of their high sediment trapping capacity, exclosures are highly valued as efficient soil conservation measures in the Tigray highlands. (c) 2005 Elsevier B.V. All rights reserved.