A set of rainfall simulator experiments was carried out in a logged forest in Tasmania, Australia, to quantify the impact of logging and fire on runoff and soil loss. A large, portable rainfall simulator was developed for the experiments to help overcome problems associated with spatially varying hydraulic and erosion properties of the soil. Simulated rainfall events with intensities of approximately 35, 75, and 150 mm h-1 were applied to four 300 m2 plots with different levels of surface disturbance: severely burnt, logged and burnt with high mechanical disturbance, logged with low mechanical disturbance, and undisturbed. The experiments indicated that the amount of runoff and soil loss from the plots depended on the type and degree of disturbance to the natural biotic crust developed on this soil. Erodibility per unit runoff was greatest on the severely burnt plot; but runoff on the mechanically disturbed site was so great that it produced the highest total sediment yield on an event basis. Runoff production was similar on the three plots where the natural biotic crust was largely intact and was low relative to the plot with high mechanical disturbance. Total sediment yield was typically higher on logged plots than on unlogged plots. ¿ 1999 American Geophysical Union