Hydrologic and aeolian controls on vegetation patterns in arid landscapes

Hydrological and aeolian processes redistribute sediments and nutrients within arid landscapes with important implications on the composition and structure of vegetation. Despite the relevance of wind and water erosion to the dynamics of arid and semiarid ecosystems, the interactions between these two processes remain poorly understood. Until recently, the common understanding of sediment redistribution and transport processes in desert shrublands was based on the notion that runoff originating within bare soil interspaces converges towards the “vegetated islands”, thereby leading to the deposition and accumulation of nutrient-rich sediments beneath the canopy. In this paper we present the results on intensive set of infiltration experiments from the Chihuahuan Desert, showing that in this system the infiltration capacity under the shrub canopy is smaller than that at the outer edges of the vegetated patches or in the surrounding bare soil. Hence, runoff is more likely to occur from the middle of shrub dominated areas to the bare edges. This effect may be further enhanced by natural and pyrogenic soil water repellency. These experimental results rule out the hypothesis that runoff contributes to the accumulation of nutrients under shrubs and contribute to formation of fertility islands. It is also argued that the observed differences in soil infiltration capacity are induced and maintained by the interaction of aeolian processes with the shrub canopies: canopies trap a significant fraction of nutrient rich clay particles advected by wind thereby contributing to the formation of fertile islands and to the existence of lower soil infiltration capacity in the middle of shrub-dominated soil patches.