Comparative Study of Species Diversity in different Land Use Units of the Borana Lowlands, Southern Oromia, Ethiopia

Abstract

Quantitative study of species diversity across different land use units and districts is important to document status of local plant biodiversity, to evaluate impact of management and for planning future management. This study aimed at determining impacts of land use units on species diversity and spatial distribution of species in two districts of Borana zone, Oromia, Ethiopia. Stratification and systematic random sampling techniques were used for data collection. Plot size of 500 m² for woody species and subplots of 0.25 m² for herbaceous species and soil samples were used. Data was analysed using both descriptive and inferential statistics. Shannon diversity index and Simpson index were determined. Relationships between vegetation and environmental variables were analysed using Redundancy Analysis (RDA) and Canonical Correspondence Analysis (CCA). The overall mean alpha, beta and gamma diversities were 29.2, 2.5 and 102.6, respectively. Average total number of species in enclosures and open access grazing sites was 113 and 96 species, respectively. Enclosures or relatively protected land use units (<em>Kalos</em>) had more species diversity than their corresponding open access grazing lands (<em>Worras</em>). Shannon diversity index ranged from 3.11 in the grazing land for dry livestock to 3.78 in the Web grazing land for lactating cattle. Similarly, Simpson index of dominance ranged from 0.034 in the Web Worra to 0.089 in grazing land for dry livestock (<em>Foora</em>). Kalos had higher Simpson diversity index than their corresponding Worras. Soil nutrients varied across land use units. Cation Exchange Capacity (CEC) was higher in enclosed than in open access grazing land use units. The study also showed that there was significant variation in P, Ca, CEC, silt and sand across the two districts (p<0.05). RDA and CCA results revealed that altitude, OM, K and N were the most important environmental variables that significantly accounted for the spatial distribution and abundance of species. It was concluded that enclosures had contributed to increased species diversity. Promoting the area enclosure as a viable strategy for biodiversity management and rehabilitation of rangelands were recommended as a result of this study.