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

This paper deals with the influence of edaphic conditions on the spatial st ructure of banded thickets or tiger bush (brousse tigree). It is based on t wo sites in West Africa, with similar climatic conditions but located on co ntrasting substrates. The spatial structure was described with standardized characteristics including thicket spacing, thicket/inter-thicket contrast, upslope/downslope asymmetry and species zonation throughout the vegetation band. Recruitment and senescence features of woody stands were emphasized in order to understand current dynamics. Data were collected on transects o riented perpendicular to the contours and so to the thickets as well. A sta ndardized analytical procedure was applied to data from both sites to ensur e consistent and thorough delineation of thickets. The overall periodicity of thickets, the woody flora and the dominant speci es Combretum micranthum were similar at the two sites. However, thicket spa cing, thicket/inter-thicket contrast and upslope/downslope floristic asymme try 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 asy mmetric, since such characteristics are likely to be reinforced by adverse environmental conditions. As a consequence, current dynamics may be more di verse than expected. Quantified inter-site comparisons can greatly help to classify African banded vegetation systems and to discuss potential dynamic outcomes.