Agriculture, Ecosystems and Environment 105 (2005) 267–271 Biodiversity of ligneous species in semi-arid to arid zones of southwestern Niger according to anthropogenic and natural factors Larwanou Mahamane a,∗ , Saadou Mahamane b a Département de Gestion des Ressources Naturelles (DGRN), Institut National de Recherches Agronomiques du Niger (INRAN), BP 429 Niamey, Niger b Département de Biologie végétale, Université Abdou Moumouni de Niamey, BP 10662 Niamey, Niger Received 13 December 2002; received in revised form 1 March 2004; accepted 5 March 2004 Abstract 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. © 2004 Elsevier B.V. All rights reserved. Keywords: Diversity; Disappeared species; Semi-arid zone; Arid zone; Niger 1. Introduction In the Sahelian countries and particularly in Niger, the woody species occupy a significant place in the dy- namics of the ecosystems and in the socio-economic life of the human population (Saadou, 1990; Gerard et al., 1997). The current Sahelian landscape is a result of natural and cultural factors, the biolog- ical diversity of woody species being linked to physio-geographical and climatic alterations. An es- ∗ Corresponding author. Tel.: +227-973442; fax.: +227-722252. E-mail addresses: larwanou@caramail.com, m.larwanou@coraf.org (L. Mahamane). timated 2.124 plant species occur in Niger including 1.461 species of angiosperms (Saadou, 1998) while the flora of the southwestern part of the country is poorly known. The degradation of the terrestrial ecosystems be- came apparent during the drought years 1973 and 1984 as a loss of woody and herbaceous perennial species, along the valleys and on the plains (Grouzis, 1988). The natural regeneration of the woody species is threatened by the scarcity of rain, their abnormal distribution in time and space, along a south–north gradient in particular (Ozer and Erpicum, 1995). Like many Sahelian countries, Niger shows signs of a reduction in the biological diversity of tree 0167-8809/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2004.03.004