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

摘要

The interaction between vegetation and hydrologic processes is particularlytight in water-limited environments where a positive-feedback links soilmoisture and vegetation. The vegetation of these systems is commonlypatterned, that is, arranged in a two phase mosaic composed of patches withhigh biomass cover interspersed within a low-cover or bare soil component.These patterns are strongly linked to the redistribution of runoff andresources from source areas (bare patches) to sink areas (vegetationpatches) and play an important role in controlling erosion.In this paper, the dynamics of these systems is investigated using a newmodeling framework that couples landform and vegetation evolution,explicitly accounting for the dynamics of runon-runoff areas. The objectiveof this study is to analyze water-limited systems on hillslopes with mildslopes, in which overland flow occurs predominantly in only one directionand vegetation displays a banded pattern. Our simulations reproduce bandsthat can be either stationary or upstream migrating depending on themagnitude of the runoff-induced seed dispersal. We also found thatstationary banded systems redistribute sediment so that a steppedmicrotopography is developed. The modelling results are the first toincorporate the effects of runoff redistribution and variable infiltrationrates on the development of both the vegetation patterns andmicrotopography. The microtopography for stationary bands is characterizedby bare soil on the lower gradient areas and vegetation on steeper gradientsareas. For the case of migrating vegetation bands the model generateshillslope profiles with planar topography. The success at generating notonly the observed patterns of vegetation, but also patterns of runoff andsediment redistribution suggests that the hydrologic and erosion mechanismsrepresented in the model are correctly capturing some of the key processesdriving these ecosystems.