"Ordinary biodiversity" in western Burkina Faso (West Africa) : what vegetation do the state forests conserve ?

The role of state forests in the conservation of the savannah environment of western Burkina Faso (West Africa) was assessed by considering the customary and fundamental biological components of plant diversity. The focus is on the "ordinary biodiversity" which constitutes the current environment of human populations and which generates their resources. Overall floristic composition, alpha, beta, gamma diversities and species accumulation curves of landscape units were compared inside and outside protected areas. Common species were identified according to their frequencies in landscape units and their local abundance. The occurrences of functional (life form, dispersion, etc.) and human-valued (current uses, potential threats, etc.) traits were compared. Current land uses outside protected areas have an unequal effect on the various components of plant diversity. Species richnesses and specific structures were all the more altered for woody species as agricultural pressure is high; conversely, they were maintained for herbaceous communities for which the proportion of wide-ranging species increased. The preservation of useful plant species on cultivated lands was obvious for woody species with edible fruits but less tangible for timber and service wood. It was deficient for species that furnish other non-wood products (e.g. leaves used as food or fodder), the conservation of which may be jeopardized where anthropic pressure is high. Given current land uses and dynamics, maintaining conservation areas in land use planning is crucial in order to preserve ordinary biodiversity