The influence of vegetation pattern on the productivity, diversity and stability of vegetation: The case of 'brousse tigree' in the Sahel

Sample sites of 'brousse tigree' and related vegetation types are described for Mall and Niger. Species composition and physical structure of the herb aceous layer as well as woody plant population were recorded at all sites t ogether with data on soils and natural resource management. Herbage yield w as measured whereas foliage yield and wood mass were calculated using allom etry equation calibrated for each species. 'Brousse tigree' is characterize d by the regularly alternating bare-soil stripes with dense linear thickets arranged perpendicularly to the slope. There was no clear superiority in t otal plant production of 'brousse tigree' when compared to neighbouring sit e with diffuse vegetation. However, the pattern of 'brousse tigree' tended to favour woody plant yield to the detriment of herbage yield. The number o f herbaceous species recorded per site (22-26) was slightly above Sahelian vegetation average despite low number of species per l-mz quadrat (6-9), ba re soil excluded. This species richness reflects the diversity in edaphic n iches resulting from the redistribution and local concentration of water re sources and shade. The high spatial heterogeneity and species richness of t he herbaceous layer in 'brousse tigree' did not attenuate the interannual v ariation in herbage yield despite low yields. Except for the herb layer, li ttle evidence was found of grazing influence on the vegetation structure an d yield a few hundred metres away from livestock concentration points. On t he other hand, the clearing of thickets for cropping led to severe soil ero sion which threaten the resilience of 'brousse tigree'. These observations and the well-defined climatic, soil and topographic situations under which the 'brousse tigree' occurs invalidate the hypothesis of an anthropic origi n of that vegetation pattern. (C) Elsevier, Paris.