Effect of Elevation on the Density and Species Composition of Encroacher Woody Plants in Borana Rangeland, Southern Ethiopia.

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.

Do Herbaceous Species Functional Groups Have a Uniform Pattern along an Elevation Gradient? The Case of a Semi-Arid Savanna Grasslands in Southern Ethiopia.

Knowledge of the total (overall) and individual herbaceous vegetation species relating to a distinctive site might help in the development of management strategies for a large number of threatened herbaceous species. This paper assesses the total and functional group herbaceous biomass, species richness, evenness, and diversity at four elevation classes in Borana rangelands of arid thorn bush savanna grasslands in Southern Ethiopia. At each elevation class, a grid of 20 × 20 m main plot was placed, and individual herbaceous species samples were collected randomly from five 1 m2 quadrants within the main plot. Using a single-factor analysis of variance (ANOVA), the effects of four elevation classes were considered on whole-vegetation, grasses, graminoid, and forb species diversity, evenness, richness, and biomass. A total of 49 herbaceous species were recorded. Of the total identified herbaceous species, three grass species and two graminoid species were found across all studied elevation classes, but the forb species did not overlap along the studied elevation classes. The total richness, diversity, and evenness of herbaceous species were considerable and significant along elevation classes. The grass, graminoid, and forb species richness, diversity, and evenness responded differently, and the functional group of species may be a good indicator of the community processes of grassland across elevation classes. The contribution of forb richness to the total richness was more pronounced than grass and graminoid, which indicates the shift of savanna grassland to grazing tolerant herbaceous species. The results suggest that the pooled data analysis of herbaceous vegetation community structure and biomass could obscure complicate trends of the functional group at elevation classes and for managing herbaceous species in savanna grasslands, the management models should focus on the functional group species composition, community structure, and biomass.