The role of vegetation patterns in structuring runoff and sediment fluxes in drylands

Abstract

The dynamics of vegetation-driven spatial heterogeneity (VDSH) and its function in structuring runoff and sediment fluxes have received increased attention from both geomorphological and ecological perspectives, particularly in arid regions with sparse vegetation cover. This paper reviews the recent findings in this area obtained from field evidence and numerical simulation experiments, and outlines their implications for soil erosion assessment. VDSH is often observed at two scales, individual plant clumps and stands of clumps.At the patch scale, the local outcomes of vegetated patches on soil erodibility and hydraulic soil properties are well established. They involve greater water storage capacity as well as increased organic carbon and nutrient inputs. These effects operate together with an enhanced capacity for the interception of water and windborne resources, and an increased biological activity that accelerates breakdown of plant litter and nutrient turnover rates. This suite of relationships, which often involve positive feedback mechanisms, creates vegetated patches that are increasingly different from nearby bare ground areas. By this way a mosaic builds up with bare ground and vegetated patches coupled together, respectively, as sources and sinks of water, sediments and nutrients.At the stand scale within-storm temporal variability of rainfall intensity controls reinfiltration of overland flow and its decay with slope length. At moderate rainfall intensity, this factor interacts with the spatial structure of VDSH and the mechanism of overland flow generation. Reinfiltration is greater in small-grained VDSH and topsoil saturation excess overland flow. Available information shows that VDSH structures of sources and sinks of water and sediments evolve dynamically with hillslope fluxes and tune their spatial configurations to them.Rainfall simulation experiments in large plots show that coarsening VDSH leads to significantly greater erosion rates even under heavy rainfall intensity because of the flow concentration and its velocity increase.

Influence of three plant species with different morphologies on water runoff and soil loss in a dry-warm river valley, SW China

“…Differences in soil environments, and water runoff and soil loss production capacity for bare and plant-covered surfaces increased the heterogeneity of sources and sinks of soil material and runoff water (Imeson and Prinsen, 2004;Puigdefabregas, 2005). These heterogeneous patterns are very important in controlling water runoff and soil loss (Rey, 2004), and some research (Valentin et al, 1999;Martínez Raya et al, 2006) documented the banded or stripped pattern of vegetation would reduce much more water runoff and increase productivity.…”

Causes and underlying processes of measurement variability in field erosion plots in Mediterranean conditions

“…Some authors suggested that the size of the bare patches between plants is the dominant factor determining the production of runoff at plot scale (Lavee et al, 1998), relating this fact to the connectivity of fluxes within the system (Puigdefábregas, 2005). Accordingly, the closer the bare and crusted areas from the outlet of the plot, the higher the soil loss.…”

Rainfall timing and runoff: The influence of the criterion for rain event separation

“…This makes hydrological studies difficult in these areas (Heydarpour, 1989). Runoff is a fundamental process because it leads to water redistribution, and it modulates soil water availability and plant functioning (Huxman et al, 2004;Lázaro, 2004;Sánchez and Puigdefábre-gas, 1994), especially in semiarid environments (Aguiar and Sala, 1999;Calvo-Cases et al, 2003;Porporato et al, 2002;Puigdefábregas, 2005); and is highly dependent on rainfall.…”