Résumé
Biodiversity can be analyzed at multiple scales: gene, variety, population, species and ecosystem. There are strong interactions between diversity with each of these levels. By scaling up from farm to regional scale, this study analyzes the diversities of agroecosystems, the evolution of cultivated species and cropping systems. According to the scale of analysis, the place of different crops changes. At the regional level sorghum is an important crop. But on farms, the cropping system evolution is characterized by diversity and the increasing place of millet in the regions which traditionally cultivated mainly sorghum and maize. Maize development is not the unique reason of sorghum depletion as the increase of millet also contributes to securing farmers income. Whether the decline of sorghum and the progress of millet will affect cultivar diversity positively or not will depend on the choices made by the farmers.