Trees dynamics (1955-2012) and their uses in the Senegal's Ferlo region: insights from a historical vegetation database, local knowledge and field inventories

Sahelian ecosystems are undergoing increasing anthropogenic and climatic pressures with long-lasting consequences for woody vegetation. As trees play a vital role for the local population, the main challenge is to ensure that they will endure. This study characterizes the woody vegetation, its uses and its long-term dynamics (1955-2012) in Senegal's sandy Ferlo region, in an anthropized zone near two boreholes. In 2012, inventories were made of 30 plots and surveys on vegetation dynamics and uses of tree species were conducted among herders from 30 camps. A historical vegetation database provided further information about the species diversity of the woody vegetation since 1955, and all potential uses of the species were listed through a review of the literature. We then attempted to convert these data in terms of the dynamics of provisioning services, by calculating use indices for the species and service indices for the ecosystem. With 3% tree cover in 2012, made up of 12 different tree species, the tree stands were dominated by two Sahelian species, Balanites aegyptiaca and Boscia senegalensis. The ratio between saplings and adults was up to 70.5%, which seemed to indicate a good balance among trees in the stands, but 95% of the saplings belonged to the species Balanites aegyptiaca, Boscia senegalensis and Acacia tortilis. Regarding the use value of woody species, the most commonly used were B. aegyptiaca and B. senegalensis, but also the rare A. senegal, Adansonia digitata and Ziziphus mauritiana. The data showed a decline in species diversity and numbers of saplings from 1955 to 2012 with a shift towards Sahelian species, while the uses and services trends suggest a decline in provisioning services. This could indicate an increase in the vulnerability of these ecosystems.