Mound development as an interaction of individual plants with soil, water erosion and sedimentation processes on slopes

Abstract

In the Mediterranean region, semi-natural shrubland communities (named`matorral') often present a discontinuous cover, where isolated perennial plants alternate with bare inter-plant areas. In such ecosystems, the patchy distribution of the vegetation is usually associated with microtopographic sequences of mounds that develop under isolated plants and break the overall slope continuity.In this study, the influence of three representative species of the Mediterranean matorral (Rosmarinus officinalis, Stipa tenacissima and Anthyllis cytisoides) on slope microtopography is determined and the processes that take part in the development of microtopographic structures beneath the plant canopy are identified. The influence of slope gradient, plant species and plant parameters on the shape and height of microtopographic structures is also studied.The shape of the microtopographic structures is described by using a two-dimensional microprofilemeter and mound height is determined by measuring in the field a`mound height index' defined as the distance from the top to the bottom of the mound.The results obtained show that plant species play a major role in the shape and height of the microtopographic structures. Whereas terrace-type structures generally develop under Anthyllis shrubs, microtopographic forms associated with Rosmarinus and Stipa plants vary with slope gradient. The almost symmetric mound-type structures that develop under these two species on gentle slopes change into terrace-type structures as slope gradient increases. Moreover, statistically significant differences exist between the three species with regard to mound height. Mean values of mound height are 19Á4, 14Á6 and 4Á3 cm under the canopy of Stipa, Rosmarinus and Anthyllis respectively. Plant parameters, essentially roughness, and slope gradient have a significant influence on mound height index.Four main processes were identified as affecting mound development in the studied field site: sedimentation, differential interrill erosion, differential splash erosion and bioturbation. Plant species interact in different ways with these processes according to their morphologies. Since Stipa and Rosmarinus plants are more efficient than Anthyllis shrubs in controlling water erosion, in retaining sediments and in modifying soil properties under their respective canopies, they give rise to higher microtopographic structures that facilitate water and nutrient storage by plants on slopes.

The fate of seeds in the soil: a review of the influence of overland flow on seed removal and its consequences for the vegetation of arid and semiarid patchy ecosystems

“…As regards banded patterns, the dynamics of spotted vegetation might be more complex, as the former usually act as closed hydrological systems and the latter highly depends on the connectivity of bare areas (Saco et al, 2007). Recent studies demonstrate that it is not only the extent to which vegetation patches prevail on a slope (Parsons et al, 1996;Wainwright et al, 2000;Bochet et al, 2000;Puigdefábregas, 2005) but also the connectivity of bare areas that influences hydrological processes such as runoff and sediment transport (Bautista et al, 2007;Puttock et al, 2013). Connectivity has the advantage, as regards vegetation structure, to provide an explanatory link between abiotic and biotic components to determine the hydrological and ecological function of the system (Turnbull et al, 2008(Turnbull et al, , 2010.…”

“…These water-limited landscapes frequently show a clear spatial pattern of vegetated patches interspersed within a bare soil matrix (Aguiar and Sala, 1999) which gives rise to a mosaic-like structure of sources and sinks of resources, the bare and vegetated patches, respectively, with very different soil properties and variable interconnection (e.g. Schlesinger et al, 1990;Ludwig and Tongway, 1995;Bochet et al, 1999Bochet et al, , 2000Puigdefábregas, 2005). Vegetated patches have often been com- Temporal evolution of the total number of papers on seed fate and dispersal in drylands published between 1974 and 2013, along with the evolution of the relative number of papers focusing on secondary seed dispersal.…”

Eco-geomorphology of banded vegetation patterns in arid and semi-arid regions

“…Another common pattern is banded vegetation, also known as "tiger bush" in Africa and "mogotes" in Mexico, in which the dense biomass patches form bands, stripes or arcs (Aguiar and Sala, 1999;Ludwig et al, 1999;d'Herbes et al, 2001). Banded vegetation is usually aligned along contour lines and is effective in limiting hillslope erosion (Bochet et al, 2000). The bands favor soil conservation by acting as natural bench structures in which a gently sloping runoff zone leads downslope onto an interception zone .…”

“…He found that infiltration rates are highest close to tree stems and decline rapidly with increasing distance. In many studies in arid areas, vegetation has been observed to be located in elevated mounds of a few centimeters height (Dunkerley, 2000, and references therein; Dunkerley, 1997;Bochet et al, 2000;Eldridge and Rosentreter, 2004). Greater infiltration rates in these elevated mounds (due to the presence of roots, soil fauna, etc) would therefore induce an increase in the apparent infiltration rates, as flow depth increases and inundates these higher areas within the groves.…”

Benefits of plant strips for sustainable mountain agriculture

“…The intercepted rainfall, diverted to leaf drip or stemflow, reached the soil surface with lower kinetic energy than the non-intercepted rainfall. The plant morphology seemed to be an important factor in intercepting rainfall and therefore in reducing soil loss and runoff (Bochet et al, 2000;Isselin-Nondedeu and Bédécarrats, 2007). That is, thyme knitted to the soil surface, forming a carpet of fine leaves and stems that restrained runoff and therefore soil sediments .…”