Biodiversity of ligneous species in semi-arid to arid zones of southwestern Niger according to anthropogenic and natural factors

Floristic diversity, abundance and disappearance of woody species were investigated at four sites of southwestern Niger, two in the semi-arid, two in the arid zone. The woody vegetation was assessed on transects from villages to bush, the measured parameters being number of individuals, height, diameter and number of stems. Questionnaires were used in the field to record information provided by the population for the disappeared species. Sites in the semi-arid zone were species richer than those in the arid zone. In terms of land-use there was a significant difference among and within sites and the number of trees increased with the distance from the village to the bush. A total of 23 species had completely disappeared from the study sites, i.e. five from the semi-arid and 18 from the arid zone. Thirteen different causes of tree species loss were recorded, six of them being of anthropic and seven of natural origin. Four disappeared species were consumed as leaves, buds, flowers and fruits while others were used as firewood and timber. All disappeared species were part of the traditional pharmacopeia. The plantation of useful species is suggested to improve re-introduction.