Abstract

The study was conducted to assess the influences of edaphic and topographic variables on plant diversity on the slopes of Gra-kahsu forest area. Collection of vegetation data was made using systematic sampling methods, laying 19 transects and 62 quadrats, each with 20 m × 20 m for trees and 5 m × 5 m for shrubs. In each quadrat, heights (1.5 m), diameters (2.5cm) and numbers of woody species, level of grazing intensity, level of human disturbance and topographic variables were recorded. Analysis of one way using R-software was used to analyze the mean of plant diversity across the edaphic and topographic variables. The highest species richness and diversity appeared in the upper altitude gradients and the variation was significant (p<0.05). The nil and slightly grazed sites had significantly higher woody plant species diversity, density and basal area compared to the heavy grazed sites (p<0.001). Grazing pressure and human disturbance had an effect on the density and number of woody species as well as on the vegetation structure. This research concluded that, changes in woody plant vegetation, density and regeneration status are caused by interactions edaphic and topographic variables and these interactions determine the ecological of plant diversity.

Key words: Altitudinal pattern, disturbance, plant species diversity, slope.