Vegetation Patches and Runoff–erosion as Interacting Ecohydrological Processes in Semiarid Landscapes

Abstract

Ecological and hydrological processes can interact strongly in landscapes, yet these processes are often studied separately. One particularly important interaction between these processes in patchy semiarid lands is how vegetation patches serve to obstruct runoff and then how this retained water increases patch growth that, in turn, provides feedbacks to the system. Such ecohydrological interactions have been mostly demonstrated for semiarid landscapes with distinctly banded vegetation patterns. In this paper, we use data from our studies and from the literature to evaluate how strongly four ecohydrological interactions apply across other patchy semiarid vegetations, and how these interactions are affected by disturbances. We specifically address four questions concerning ecohydrological interactions: (1) if vegetation patches obstruct runoff flows during rainfall events, how much more soil water is stored in these patches compared to open interpatch areas; (2) if inputs of water are higher in patches, how much stronger is the pulse of plant growth compared to interpatches; (3) if more soil water in patches promotes greater biological activity by organisms such as earthworms that create macropores, how much does this improve soil infiltrability; and (4) if vegetation patches are damaged on a hillslope, how much does this increase runoff and erosion and decrease biomass production? We used the trigger–transfer–reserve–pulse framework developed for Australian semiarid woodlands to put these four questions into a landscape context. For a variety of patchy semiarid vegetation types in Australia, Europe, and North America, we found that patches significantly stored more soil water, produced more growth and had better infiltrability than interpatches, and that runoff and erosion can markedly increase on disturbed hillslopes. However, these differences varied greatly and appeared to depend on factors such as the intensity and amount of input events (rainstorms) and type of topography, soils, and vegetation. Experimental and modeling studies are needed to better quantify how these factors specifically affect ecohydrological interactions. Our current findings do support the conclusion that vegetation patches and runoff–erosion processes do strongly interact in many semiarid landscapes across the globe, not just banded landscapes.

Woody plant encroachment into grasslands leads to accelerated erosion of previously stable organic carbon from dryland soils

“…Thus, results support previous research finding that woody encroachment in drylands can result in a major change in ecosystem structure [Bai et al, 2009;Bird et al, 2002;Havstad et al, 2006;Schlesinger et al, 1990], characterized by an increased heterogeneity of vegetation and SOC distribution [Puttock et al, 2013]. Reduction in vegetation cover following woody encroachment decreases vegetative protection of the soil [Ludwig et al, 2005] and increases connectivity [Mayor et al, 2008;Wainwright et al, 2011], leading to accentuated water erosion fluxes [Parsons et al, 1996;Wilcox et al, 2003a]. Greater variation in SOC contents at the woody sites (Table 2) supports the theory that the alteration of hydrological functions associated with woody encroachment results in the occurrence of positive feedback mechanisms [Peters and Herrick, 2001] reinforcing the heterogeneous woody landscape structure into islands of fertility [Schlesinger et al, 1990].…”

Biogeomorphology of a Mojave Desert landscape — Configurations and feedbacks of abiotic and biotic land surfaces during landform evolution

“…Much of this research has addressed the effects of vegetation on fluvial and eolian processes (Wainwright, 2009). Many studies have shown how individuals or stands of shrubs promote run-on, infiltration, and sediment trapping (e.g., Rostagno, 1989;Dunkerly and Brown, 1995;Neave and Abrahams, 2001;Hupy, 2004, and see review by Ludwig et al, 2005). Likewise, bioturbation by small and mediumsized mammals influences hydrological and eolian processes through burrowing activity, creating heterogeneous landscape structure.…”

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

“…One particularly important interaction between these processes in patchy semiarid lands is how vegetation patches serve to control water erosion and then how this retained water runoff and soil material increase vegetation growth that, in turn, provides feedbacks to the system (Ludwig et al, 2005). These interactions could also lead to microtopography change that could further affect water runoff and soil loss processes (Bergkamp, 1998).…”