Rangeland management aimed at animal production can reduce, maintain or evenrnincrease range plants diversity. Although the maintenance of biodiversity has becomernone of the goals in ecosystem management, the relationship between diversity andrnecosystem characteristics such as level of herbivory, productivity, and vegetationrnstructure are still poorly understood. The way that management actions constrain (orrnperhaps magnify) rangeland biodiversity must clearly be understood for sustaining bothrnproductivity and biodiversity in rangelands. The purpose of this study was to investigaternthe floristic diversity and productivity aspects of protected aJId/or managed rangelandsrnin the Main Ethiopian Rift (MER), semi arid agI'o ecological zone. In this paper, thernmajor issues addressed include floristic diversity, vegetation description, herbaceousrnbiomass estimation, and range condition assessment. For the study we used arncombination of ecological survey (Zurich Montpelier) method and a standard rangerncondition assessment technique (adopted for the South-Eastern Ethiopian Rangelands).rnTWINSPAN computer program is used to make vegetation classifications. We examinedrnthe relationships between herbaceous biomass production and plant diversity in fourrnnative range sites differing in range condition in the Open Grasslands (2), and WoodedrnGrasslands (2) in semi-arid AEZ of MER. The results of this study have revealed thernunique vegetation and rich plant diversity of the two rangelands. Range condition of thernfour range sites ranged from poor to good and found to be supported by herbaceousrnbiomass production and grazing indicator species. Herbaceous biomass productionrnfollows a quadratic relationship with range condition. There is some indication that thernhumpback model appears to be functional in the MER rangelands. Importantrninformation generated has pictured the need for optimizing productivity and biodiversityrnconservation and elicited information on how agricultural and biodiversity conservationrninterest should be integrated for the sustainable utilization of rangelands.rnKey Words: Vegetation Description, TWINSPAN, Range condition, Main Ethiopian RiftrnVnlley