Past or present land degradation? Soil erosion histories and past human land use in the Pare Mountains, NE Tanzania.

Anthropogenic land degradation and severe soil erosion are widespread in East Africa and many efforts are made to reduce soil erosion and maintain ecosystem functions. In the Pare Mountains, NE Tanzania bare peaks and secondary bushland have been reported by the first European travellers at the end of the 19th century and were interpreted as the consequences of deforestation and land degradation. Despite the well known abundance of iron smelting sites in the Pare Mountains archaeological evidence for the onset and the intensity of agriculture and iron smelting is still lacking. Meanwhile, historians have postulated a phase of agriculture intensification and an economic boom during the heydays of the 19th century caravan trade. The severely eroded soils of the Pare Mountains and footslopes and the observation of the first European travellers give rise to the question as to whether the severely eroded soils observed in the Pare Mountains today are the result of modern land use and management, or if they are the consequence of the agricultural boom stimulated by the caravan trade, or if the lack of forest has been part of the Pare landscape for a much longer time; perhaps caused by the initial occupation and maintained by ongoing iron smelting.

Colluvial slope deposits of three upland catchments were investigated and allow together with evidence from swamp cores the reconstruction of soil erosion phases and regional landscape change in the Pare Mountains during the last two millennia. The investigation of colluvial slope deposits is a way of studying the consequences of human land use and local landscape change and allows the reconstruction of soil erosion and land degradation histories. Results: Distinct soil erosion commences in North Pare during the middle of the first millennium AD and is likely to be related to the onset of agricultural land use, iron smelting and the associated woodland clearances in this part of Eastern Africa. Accelerated soil erosion is recorded in the upper metres of the colluvial deposits, where abundant sandlense occurrence indicates a
change in the erosion and deposition regime, possibly due to changes in the land use. The last erosion phase is characterized by re-deposited subsoil material. This is evidence of the onset of widespread subsoil erosion on the slopes leading to the exposure of saprolith and widespread land degradation.