The ecological impact of bush encroachment on the yield of grasses in Borana rangeland ecosystem

The ecological impact of woody encroachment and the responses of herbage yield to encroachment were assessed at three locations in Borana rangeland at the end of the growing season. The study was carried out in two communal grazing areas (Medhecho and Dubluk) and one Government ranch (Dida-Tuyura) in bush and/or shrub encroached and non-encroached sites. In each area. three altitude ranges were distinguished and in each altitude range one transect, covering both encroached and nonencroached rangeland, was selected. The assessment was based on the yield and botanical composition of the herbaceous layer. The grasses Cenchnis ciliaris, Chyysopogon aucheri and Panicum coloratum were common or dominant in both encroached and non-encroached sites. Pennisetum mezianum and Pennise-tum stramineum were typically found in encroached vegetation. The relative yield increased with non-encroached sites and varied at different altitude ranges from about 106% to about 150%, thus increases ranged from 75% in Medhecho to 350% in Dubluk as determined from the lower values of the ranges. The encroached vegetation had a significantly lower score for herbage yield than the non-encroached vegetation for most of the sites, although the differences were small. Differences based on altitude range were also significant for Eragrostis papposa and Pennisetum stramineum. while the three areas showed a significant difference for the mean yield of Aristida adscensionis, Cenchrus ciliaris and Eragrostis papposa.