Sediment yield at southwest Ethiopia's forest frontier

Abstract

AbstractDeforestation is one of the major factors affecting soil erosion in tropical regions but to what extent does the crop growth in deforested areas protect the land from erosion? We evaluated the effect of deforestation on suspended sediment yield at the scale of zero‐order catchments by contrasting five paired small forest and cropland catchments at Ethiopia's southwestern forest frontier. Suspended sediment samples were collected from nine San Dimas flumes and one V‐notch weir installed in catchments draining the natural forest and cropland, at different altitudes. The suspended sediment data were collected from June 8 to October 30, 2013 and 2014. The suspended sediment yield of both land‐use types was strongly correlated with the corresponding runoff discharge. The results show that the average seasonal suspended sediment yield from cropland (17.0 ± 7.6 Mg ha−1) is four times higher than from the paired forests (4.0 ± 1.9 Mg ha−1). High sediment yields from forests are related to livestock grazing, but forests still have an important role in the protection of the surface soil from erosion at southwest Ethiopia's forest frontier. Land management in southwestern Ethiopia's highlands will need a strong change in paradigm, in which the overall belief in the recently imported mahrasha ard plough is abandoned, oxen and other cattle decreased in number and kept in homesteads, the forests being protected from human and livestock interferences and the open farmlands turned into agroforestry. Such an approach is still possible as all required elements are available in the landscape.