The influence of soil properties on the formation of unstable vegetation patterns on hillsides of semiarid catchments

On hillsides of semiarid catchments regular bands of vegetation have been observed to form under low rainfall conditions. Many authors have observed the existence of a slope gradient threshold below which no banded patterns were observed; this increases with the mean annual rainfall. A simple model for soil moisture balance and vegetation growth, explicitly accounting for basic soil physics, is demonstrated and discussed. The influence of relevant soil characteristics on vegetation patterns and their patchiness is addressed by linear stability analysis. The results confirm the experimental evidence of a threshold slope gradient depending on the mean annual net water supply, and demonstrate the influence of the soil properties (saturated conductivity and capillary rise) on the stability condition and on the threshold slope. Nevertheless, the concluding remark concerns the oversimplified models for vegetation patterns, such as the one discussed here, that require properly defined effective soil parameters in order to become predictive tools.