Wind erosion and dust flux in undisturbed and disturbed dryland ecosystem along the grassland-forest continuum: A conceptual framework spanning gradients of woody plants

Wind erosion and associated soil transport and dust flux are important processes, particularly in dryland ecosystems where ground coverage is inherently low due to water limitation.  Woody plant height and spacing determine spatial density of roughness elements, thereby directly affect wind erosion.  Despite the extensiveness of dryland ecosystems, until recently there have been few measurements of wind erosion rates in many dryland ecosystem types, especially over periods including both low and high wind speeds, and these few existing measurements have not been systematically placed within the context of the grassland-forest continuum.  We report wind erosion estimates for 4 new grassland and woodland sites, evaluate available estimates of wind erosion for undisturbed and disturbed sites in dryland ecosystems, and propose a new conceptual framework for wind erosion along the grassland-forest continuum.  On the basis of our findings, we propose that (1) for relatively undisturbed ecosystems, shrublands have inherently higher erosion rates—due to wake interference flow associated with the spatial concentration of woody roughness elements; and (2) for disturbed ecosystems, the potential maximum erosion rate decreases with increasing amount of woody plant coverage—due to effects of canopy height and density on air flow patterns and because the minimum amount of ground cover at a site tends to increase as woody plant coverage increases.  Consequently, potential wind erosion rates span the widest range of values in grasslands and associated systems with no woody plants (e.g. agricultural fields), an intermediate range in shrublands and a relatively small range in woodlands and forests.