This study assesses effects of environmental factors on: (1) the floristic composition and diversity of plant species, and (2) plant communities in selected Prosopis juliflora (Prosopis) invaded districts of the Southern Afar Region, Ethiopia. Four sites from two districts Afar Region were selected for vegetation survey. Then, 64 sample quadrats were placed in the wood lands using preferential sampling design. Quadrats of 1 m2, 100 m2 and 400 m2 were used for recording herbaceous/seedling, sapling and tree species, respectively, with symptoms of different human disturbance effects. One hundred and sixty species belonging to 38 families were recorded in the wood land. Three plant community types namely Prosopis juliflora- Acacia tortilis, Cadaba rotundifolia - Acacia mellifera, and Acacia senegal - Aerva javanica (P < 0.05) were identified. The overall floristic diversity (H´=3.85); species richness (N=153), and a Shannon evenness (E´= 0.78) were recorded in the wood lands of the Afar Region. Environmental factors such as altitude (F= 1.36; P = 0.01), Prosopis invasions (F = 10.27; P = 0.01), grazing intensity (F = 1.45; P = 0.08), disturbance intensity (F = 1.26; P = 0.08), and slope (F = 1.95; P = 0.03) had affected the vegetation patterns in the South Afar range lands and these imply that current management practices are not satisfactory to sustain the wood lands. Unless improved management interventions are made, the sustainability of vegetation services will be at stake.

Keywords: Afar, Diversity, Grazing lands, Pastoralists, Prosopis juliflora patch