Publications

Naudts, J.,  De Geyndt, K.,  Nyssen, J.,  Deckers, J.,  Mitiku, H.,  Moeyersons, J. & Poesen, J. 2004. ‘The trap efficiency for sediment and carbon in exclosures on steep slopes. A case study from the Tembien Highlands, Tigray, Ethiopia’. Coll . internat. ‘Land Use, Erosion and Carbon Sequestration’, Montpellier 2004. Book of abstracts, 23. Bulletin du Réseau Erosion , 615-662.

Résumé de colloque

Abstract In an attempt to reverse land degradation, exclosures have been set up in many places across the highlands of Tigray, northern Ethiopia, to control soi1 erosion and to improve biomass productivity. Local farmers are entitled -under certain conditions- to use some ofthe resources found in the closed lands (by cutting grass, taking wood, etc.). In this way exclosures constitute a valuable alternative for the local communities, notwithstanding the high land pressure in this part of the Ethiopian Highlands. Land management and consequences for soi1 erosion and sediment accumulation were studied during a fïeld survey near the village of Hechi, in the Tembien highlands (northern Ethiopia). Land-use changes over the last 40 y were analysed and different soi1 profiles were described, both in a flat topographical position and on a steep slope (slope gradient of 0.4 - 0.6 m m-l). The research included soi1 profiles under overgrazed rangeland, cropland, recently closed area (15 years) and under dense natural vegetation, which has been protected as a result of its very strict religious status. In the 202 ha large study area, the area covered by forests strongly decreased, from 10 to 4 % between 1963 and 1994. As a consequence of the exclosure policy, which started during the 1980s it increased again to 6 % in 2000. Physical and chemical analysis of the soi1 profiles show that deforestation on steep slopes and cultivation of the cropland of the flat areas had caused much soi1 10s~. In a dense, natural forest on the steep slope, some 1.4 m of sediment was found to be accumulated in the soi1 profile. In a more recent exclosure, 40 cm of sediment has accumulated since the closure of the area (15 years ago). This sediment has an average organic carbon content of 4.1 % of the soi1 weight. In the flat area there was more erosion and less soi1 development in the cropland than in a comparable setting in a protected churchyard. The ‘exclosure’ land management practice brings soi1 erosion in degraded areas to a standstill. Besides improved infiltration, less runoff, improved biomass and biodiversity, this technique brings about the accumulation of large amounts of carbon-rich colluvial material, even on steep slopes, and allows thus for a relatively fast regeneration of soi1 productivity in these areas