Historical land use pattern affects the chemistry of forest soils in the Ethiopian highlands

In the Ethiopian highlands, deforestation and land cover changes have been going on for millennia. The impact of land use changes on the chemistry of Ethiopian forest soils is, however, not well understood. We conducted a study in the Menagesha forest, where a historical land use change has been reconstructed based on Soil delta(13)C values, to determine whether the chemistry of forest soils could be related to site history. Soils from the elevational gradient were analyzed for different soil chemical properties and results were compared with concentrations of C and N. Organic C (%) was elevated in the mineral soils of mid-altitude positions, which corresponds to the least disturbed conditions since afforestation >550 years ago. There was a strong correlation between total cation exchange capacity (CECt) and organic C and between exchangeable and total Ca. The exchangeable Ca accounted for more than 70% of the total Ca in the deeper mineral soils. Estimation of total amounts of mineral elements suggests that Ca and S are accumulated in the surface soil, while the other elements are depleted. Total N and KCl extractable inorganic N were positively correlated in the litter and top mineral soils; their concentrations were higher at the mid-attitudes. The mid-altitude soils with several hundred years of undisturbed forest cover tended to have higher concentrations of organic matter, available and total N and total and exchangeable Ca than the high- and low-elevation forests, which have been disturbed more frequently. The forest soils subjected to disturbances thus tended to have lower CEC and nutrient retention capacity. The study indicates that the variation in the chemistry of forest soils along the altitudinal gradient in the Menagesha forest is related to the historical patterns of land use changes, and not to lithologically related variations. It is also suggested that the presence of forest in this otherwise open landscape leads to accumulation of base cations in the soil, especially Ca, due to deposition from the atmosphere. (C) 2003 Elsevier B.V. All rights reserved.