Differences between banded thickets (tiger bush) at two sites in West Africa

This paper deals with the influence of edaphic condi- tions on the spatial structure of banded thickets or tiger bush (Brousse tigree). It is based on two sites in West Africa, with similar climatic conditions but located on contrasting substrates. The spatial structure was described with standardized charac- teristics including thicket spacing, thickethiter-thicket con- trast, upslope/downslope asymmetry and species zonation throughout the vegetation band. Recruitment and senescence features of woody stands were emphasized in order to under- stand current dynamics. Data were collected ontransects oriented perpendicular to the contours and so to the thickets as well. A standardized analytical procedure was applied to data from both sites to ensure consistent and thorough delineation of thickets. The overall periodicity of thickets, the woody flora and the dominant species Corizbretunz iiiicrarztlzurn were similar at the two sites. However, thicket spacing, thickethter-thicket con- trast and upslope/downslope floristic asymmetry of the thickets were higher in the less favourable site. Also seedlings were less abundant, with a greater dependence on pre-existing thickets. Not all banded vegetation systems show sharp contrasts and are strongly asymmetric, since such characteristics are likely to be reinforced by adverse environmental conditions. As a consequence, current dynamics may be more diverse than expected. Quantified inter-site comparisons can greatly help to classify African banded vegetation systems and to discuss potential dynamic outcomes.