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).