Impact of forest structure simplification on bird species richness in the Harena forest of the Bale Mountains National Park (BMNP), South Eastern Ethiopia

Human simplification of habitat in the Harenna forest mainly happens by permanently removing woody vegetation. We evaluated the impact of such simplification of habitat on bird species richness. Birds were counted using the point count method at points that were laid out along transect lines, and from their presence/absence, species richness was worked out. By establishing 50m by 50m quadrats at bird counting stations, we counted the number of basal remnants of cut trees and we measured vegetation structure variables such as % grass, % other herbs, % shrubs, % bush and % canopy (tree cover). Tree, bush and shrub covers did have significant positive correlation with bird species richness. As the magnitude of tree cutting increased species richness of birds declined significantly. Similarly with bird species richness, structural variables such as tree, bush and shrub covers did have significant negative correlation with the tree cutting variable. Due to this, we carried out Principal Component Analysis and the first component that was influenced mainly by tree cover and tree cutting variables significantly explained 84.7 % of the variation in bird species richness in a stepwise multiple regression analysis. Bush and shrub cover did also have significant positive contributions towards the explanatory value of the first component, thus, their positive contribution in explaining bird species richness is noteworthy. Results showed habitat simplification through tree cutting has significant negative impact on bird species richness.