Changes in the availability and uses of wild yams according to climatic dryness and land-cover in Western Burkina Faso (West Africa): a joint ecological and ethno-botanical approach using GIS and remote-sensing

Abstract

The regional variability in the uses of wild yams is assessed according to their availability in relation with land-use and climatic conditions from the South to the North sudanian sectors in Western Burkina Faso. The study involves field studies and modelling of the geographical distribution of yams and seeks correlations between environmental and ethno-biological data. Terrain analysis consists of phyto-ecological surveys and interviews with local inhabitants. A cluster analysis of a multi-date image of data obtained by remote-sensing is used to assess land-cover. The Bayesian post-probabilities of occurrence of each species are inferred using Weight of Evidence modelling linked to a Geographical Information System. The model is implemented with land-cover units and annual Moisture Availability Index evidential-layers and is driven by species presence data. The probabilities of occurrence of each species throughout the whole area as well as within and without the protected areas and in the vicinity of the sites of enquiries are calculated. A multi-factorial analysis makes it possible to shed light on the relationships among land use, the availability of yams, the uses of yams, knowledge and local practice. Results provide statistical evidence of spatial association between the yam species and the environmental descriptors taken into account. The study also provides evidence of an important regional variability in the actual uses and knowledge of wild yams. The rather widespread use of wild yams as a food complement, in social relations and as merchandise in local trade in the North of the area studied, which is far less observed in the South, is one of the major components of this variability.