The role of surface water redistribution in an area of patterned vegetation in a semi-arid environment, south-west Niger

Abstract

The surface hydrology of a semi-arid area of patterned vegetation in southwest Niger is described. In this region alternating bands of vegetation and bare ground aligned along the contours of a gently sloping terrain give rise to a phenomenon known as 'brousse tigrée' (tiger bush). At the selected study site the vegetation bands are 10-30 m wide, separated by 50-100-m-wide bands of bare ground. Five species of shrub dominate, Guiera senegalensis, Combretum micranthum, C. nigricans, Acacia ataxacantha and A. macrostachya. Herbaceous vegetation is generally limited to the upslope edges of vegetation bands. A comprehensive field programme was undertaken to investigate the hydrology. Topographic, vegetation and surface feature surveys were carried out in conjunction with the measurement of rainfall, surface and subsurface hydraulic conductivity, particle size and soil moisture content. Four types of vegetation class are recognised, each tending to occupy a constant position relative to the others and to the regional slope. In a downslope direction the classes are: bare ground, grassy open bush, closed bush, bare open bush, bare ground etc. The nature of the ground surface is closely linked to the vegetation class. Over the bare, bare open and grassy open classes various types of surface crust are present with each type of crust tending to occupy a constant position on the regional slope relative to the vegetation class and other crust types. Below closed bush crusts are generally absent. The typical downslope sequence from the downslope boundary of a vegetation band is: structural (sieving) crust → erosion crust → (gravel crust) → sedimentation crust → microphytic sedimentation crust → no crust → sieving crust, etc. It is also shown that these crust types are dynamic and evolve from one to the other as hydrological conditions change. Hydraulic conductivities of surface crusts are low, typically falling within the range 10 −6-10 −7 m s −1. The presence of large expanses of crust over bare regions tends to generate runoff , which moves

Self-Organization of Vegetation in Arid Ecosystems

“…1a), and gap patterns with bare spots in the vegetation with a diameter of 5-20 m ( fig. 1b; Bromley et al 1997;Aguiar and Sala 1999;Ludwig et al 1999b;Valentin et al 1999;Couteron and Lejeune 2001). On slopes steeper than 0.2% in arid regions, typical regular-banded vegetation patterns with a band width in the range of a few tens of meters are observed (Klausmeier 1999;Leprun 1999;Valentin et al 1999;d'Herbes et al 2001).…”

“…Vegetation patterning is generally linked to the mechanism by which plants increase surface-water infiltration into the soil, in combination with low annual rainfall conditions (Bromley et al 1997;Klausmeier 1999;Leprun 1999;Ludwig et al 1999a;HilleRisLambers et al 2001). During rain showers, some rainwater will infiltrate into the soil, while the remainder will run off as surface water to other areas.…”

Representation of landscape variability and lateral redistribution processes for large-scale hydrological modelling in semi-arid areas

“…Extending to the scale of hillslopes or small catchments, additional variability of landscape characteristics influences the runoff redistribution. Characteristic sequences of surface types in terms of vegetation cover, soils and surface crusts with variable infiltration characteristics were shown for hillslope transects in semi-arid Africa by Perrolf and Sandström (1995), Bromley et al (1997) and D'Herbès and or for semi-arid Spain (Nicolau et al, 1996). Bergkamp (1998) distinguished in a hierarchical way five spatial scale levels by characteristic discontinuities in the geomorphological and soil properties, ranging from the terracette level, via various hillslope scales to the catchment scale.…”

“…This patchiness influences, on the one hand, total evapotranspiration rates of the land surface by the interaction of energy and momentum fluxes from bare and vegetated patches (Boulet et al, 1999). On the other hand, the patchiness gives rise to redistribution of runoff and associated sediments and nutrients, with bare soil surfaces tending to act as source areas of surface runoff and vegetated patches as sink areas, receiving runon from bare soil surfaces for re-infiltration (Puigdefabregas and Sanchez, 1996;Bromley et al, 1997;Reid et al, 1999;Valentin and d'Herbès, 1999;Cammeraat, 2002). Extending to the scale of hillslopes or small catchments, additional variability of landscape characteristics influences the runoff redistribution.…”

Vegetation dynamics during different abandoned year spans in the land of the Loess Plateau of China

“…Meanwhile, though a positive effect of land abandonment on vegetation diversity has been found by several studies (Dana and Mota 2006;Donath et al 2007), a negative affect was also found by some (Rickert et al 2012;Jacquemyn et al 2011). In terms of vegetation patterns, much research focuses on a two-phase mosaic structure of high-and low-vegetation cover patches, which commonly presents itself in semi-arid ecosystems (Pellerin et al 2009;Puigdefabregas 2005;Bromley et al 1997;Cerda 1997;Wilcox et al 2003). Mechanisms of patch formation and dynamics have also been conducted (Mayor et al 2008;Liu et al 2013;Aguiar and Sala 1999;Bautista et al 2007).…”