THE USE OF RAINFALL SIMULATION TESTS TO ASSESS THE INFLUENCE OF VEGETATION DENSITY ON SOIL LOSS ON DEGRADED RANGELANDS IN THE BARINGO DISTRICT, KENYA

The relationship between cover density and soil loss under simulated rainstorms of 30 and 60-minute duration and 33 mm h(-1) intensity was investigated. Soil loss varied from 0-7.3 g m(-2) for cover of 55-95% and reached maximum values of over 80.0 g m(-2) (30-minute storms) and 140.0 g m(-2) (60-minute storms) for cover of 25% or less. A critical threshold occurred at 55% cover below which erosion rates rapidly increased to over 15.0 g m(-2) (30-minute storms) and 30.0 g m(-2) (60-minute storms) during single rainstorm events. Storm duration and frequency were important determinants of erosion over more prolonged time periods. Total calculated soil loss for an 18-year period under 55% cover for frequent 30-minute storms (frequency: 3-4 times a year) was 6 times that for infrequent 60-minute storms (5-year return period).