Status and population structures of three anthelmintic tree species along climatic gradient in Benin and the implications for conservation
Smallholder farmers make intensive use of anthelmintic plant species in the traditional treatment of animal parasitic infections. As a result, populations of these plant species are exposed to increased disturbances such as plant harvesting, threatening their stability. Information on population structure of threatened plant species is important not only for understanding their ecological status but also for conservation and restoration purposes. Using floristic and structural data from 61 plots of 0.09 ha each, we assessed the population structures of the three anthelmintic species (Bridelia ferruginea, Mitragyna inermis, and Combretum glutinosum) along the climatic gradient (Guinean, Sudano–Guinean and Sudanian climatic zones) in Benin. Structural characteristics (tree density, basal area, mean diameter, tree height), and species-specific diameter and height distribution were assessed. Results showed that B. ferruginea was found in all three climatic zones, but more prominent in the Sudano–Guinean zone with a scarcity index of less than one per cent. Mitragyna inermis and C. glutinosum were only observed in the Guinean zone and Sudanian zone, respectively. Bridelia ferruginea population structures, especially density and basal area, varied significantly among climatic zones. Diameter- and height-class distributions for the three species exhibited a bell shape with a tendency to right skewness, indicating a predominance of younger trees. These results suggest that the three species are not currently threatened in Benin; however, it would be necessary to prevent overexploitation to guarantee future sustainability.
Keywords: Bridelia ferruginea, Combretum glutinosum, Mitragyna inermis, population structure, scarcity index, West Africa