Small-scale effects of annual and woody vegetation on sediment displacement under field conditions

Interactions between desert vegetation and erosive forces are prominent and are part of landscape evolution in deserts. The role of annual herbaceous plants in these processes is usually overlooked. Likewise, the interactions and relative contributions of the different erosive forces are rarely studied.We examined the effects of mound-forming shrubs and annual plants on sediment dispersal at small spatial scales in the semi-arid shrubland of the northern Negev Desert of Israel. We conducted a field experiment to test the displacement of dyed sediment by wind, runoff and rain splash in 5. ×. 5. cm areas on shrub-mounds, placed under the canopy and on mound margins, and on the biological soil crust-covered intershrub space. As experimental treatments, we used artificial rain covers and removal of annuals and their litter.We found that 1) most sediment displacement was caused by rain splash, which was effectively reduced by shrub canopy and less so by annual plant cover, and 2) runoff effects were limited to a fraction of rain events, took place only in the intershrub space, and were significantly reduced by annual plants and their litter. The combined effect of shrubs, annuals, and litter on sediment movement was significantly stronger than the effect of any single element.Accordingly, we conclude that, in addition to shrubs, herbaceous annual plants play a significant role in shrub-mound growth and maintenance, and thus also, in erosion control and vegetation pattern formation in dryland landscapes. Since herbaceous plants enhance mound formation, which in turn enhances shrub growth, our findings are further evidence of the crucial feedback interactions that are central to understanding ecosystem functioning, dynamics and pattern formation in water-limited ecosystems.