Abstract

Information on the effect of Mabira Forest Reserve degradation on water, soil and nutrient losses is scanty. This study was carried out to quantify runoff, soil and nutrient losses in six restoring forest regimes namely: 0 to 3, 10 to 20, 20 to 30, 30 to 40, 40 to 50, and >55 years of last disturbance. In each, a plot measuring 150 by 50 m was demarcated. Within this plot, three sub-plots each of 20 × 2 m and located 50 m apart were established for runoff, soil and nutrient losses measurement for period of two rain seasons. A runoff trap pre-calibrated to collect 1% of runoff was installed on each sub-plot. In addition, the forest regimes were characterized for some physio-chemical properties. Overall, annual runoff and soil loss across the forest regimes were low ranging between 20 to 160 m³ha^-1 and 10 to 380 kg ha^-1, respectively. Runoff and soil loss followed a parabolic trend along the forest age with the minimum in the 20 to 30 years forest regime. Annual nitrogen, phosphorus and potassium losses significantly varied from 0.11 to 4.26, 0.01 to 0.18 and 0.08 to 6.63 kg ha^-1 respectively across the forest regimes. Bulk density was highest in the 30 to 40 year regime.

Key words: Soil erosion, bulk density, forest degradation.