Woody plant encroachments are major concerns across the grasslands biome, while the patterns of individual species existence at a landscape level can be limited locally and regionally. The paper assesses the species composition, community structure, and density of individual and combined encroacher woody species in terms of tree equivalent per hectare (TE ha-1) within five different height classes at four elevation levels in Borana arid thorn bush savanna grasslands in Southern Ethiopia. At each elevation class, a grid of 20 × 20 m main plot was placed, and samples were collected randomly from three 100 m2 sub-plot within the main plot. Using a single-factor analysis of variance, the effects of four elevation classes were considered on encroacher woody plant species composition, total, and individual density (TE ha-1) within height classes. A total of 22 encroacher woody plant species composition were identified. The identified woody plants are seemingly a threat to the Borana rangelands of Southern Ethiopia with various patterns of distribution and density (TE ha-1) among the different elevation levels. Of the identified species, Acacia reficiens had the highest density (1052.22 ± 265.34 TE ha-1) at elevation level II. The most important encroaching species in each elevation level was varied considerably, while the combined woody plants density (TE ha-1) within height classes across elevation levels showed minimal variations. This suggests that the management of a specific ecological site might require greater focus in terms of the functional traits of individual woody species composition, density coverage within height classes, and community structure. Hence, identifying the patterns, distribution, and density of encroaching woody species is crucial for the control of key encroacher woody species at a landscape level.
Keywords: Borana rangelands; Savannas ecosystem; Shrub encroachment; Species composition; Tree equivalent.