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

Abstract

International audienceThe interaction between vegetation and hydrologic processes is particularly tight in water-limited environments where a positive-feedback links water redistribution and vegetation. The vegetation of these systems is commonly patterned, that is, arranged in a two phase mosaic composed of patches with high biomass cover interspersed within a low-cover or bare soil component. These patterns are strongly linked to the redistribution of runoff and resources from source areas (bare patches) to sink areas (vegetation patches) and play an important role in controlling erosion. In this paper a new modeling framework that couples landform evolution and dynamic vegetation for water-limited ecosystems is presented. The model explicitly accounts for the dynamics of runon-runoff areas that controls the evolution of vegetation and erosion/deposition patterns in water limited ecosystems. The analysis presented here focuses on the interaction between vegetation patterns, flow dynamics and sediment redistribution for areas with mild slopes where sheet flow occurs and banded vegetation patterns emerge. Model results successfully reproduce the dynamics of both migrating and stationary banded vegetation patterns (commonly known as tiger bush). Modeling results show strong feedbacks effects between vegetation patterns, runoff redistribution and geomorphic changes. The success at generating not only the observed patterns of vegetation but also patterns of runoff and erosion redistribution, which gives rise to modeled microtopography similar to that observed in several field sites, suggests that the hydrologic and erosion mechanisms represented in the model are correctly capturing the essential processes driving these ecosystems