Relationships between vegetation composition and environmental variables in the Borana rangelands, southern Oromia, Ethiopia

Abstract

Topography, climate and soil are the three important environmental abiotic factors that affect vegetation composition in rangelands. Determination of environmental factors that are responsible for the spatial distribution and abundance of vegetation is useful in ecological restorations and grazing land use planning. This study was conducted in the Borana lowlands to quantitatively explore relationships between vegetation composition and abiotic environmental factors. A combination of stratification and systematic random sampling techniques were employed to collect vegetation and environmental data in 58 plots of 500 m² size. Redundancy Analysis (rda) and Canonical Correspondence Analysis (cca) were used to detect patterns of vegetation variation that were explained by the assessed environmental variables. cca and rda ordination diagrams revealed that the composition and distribution of both woody and herbaceous vegetation were mainly determined by altitude, soil pH, calcium, cation exchange capacity and magnesium. Density of woody plants was negatively correlated with altitude. Species richness was positively correlated with sand and altitude but negatively correlated with soil nutrients and clay content. It is concluded that the measured environmental variables significantly account for variation in the composition and distribution of the plant species composition in the Borana lowlands. Therefore, rangeland managers should incorporate environmental factors in planning and implementing restoration activities and planning grazing land use.