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Addis Ababa University (2009)

Bush Encroachment and its Impacts on Plant Biodiversity in the Borana Rangelands

Adisu, Abebe

Titre : Bush Encroachment and its Impacts on Plant Biodiversity in the Borana Rangelands

Auteur : Adisu, Abebe

Université de soutenance : Addis Ababa University

Grade : Master Degree in Environmental Science (2009)

Until few decades ago the Borana rangeland was considered as one of the finest grazing areas in East Africa. However, the pastoral system has recently shown symptoms of destabilization because of the shift in the natural balance between trees and grasses, and bush-tree cover has become dominant in the rangeland. In order to assess the major encroaching woody plant species and their advancement under three land use units (Kalo, Worra & Foora) ; the impact on plant biodiversity ; as well as possible causes of the encroachment and their challenges to the pastoral community ; a comprehensive vegetation and household survey was conducted. The results of the study revealed that the density of woody species in the study area is 4185 ha ̄ ¹, which is far beyond the critical limit. Species such as Acacia drepanolobium, A. mellifera, A. bussi, A. bresvispica, and A. senegal were found to be the major encroaching species. The mean density of total woody species significantly differed across the land use units (P < 0.05). Relatively higher densities of woody plants occurred at Kalos that might associate with reduced grazing pressure in Kalos compared to other land use units provide suitable environment for seeds to germinate. Diversity of herbaceous grass species negatively correlated with woody density(r=-0.520, p<0.01). The pastoralists asserted that encroachment of woody species to their prime grazing land has been the major challenge to their livelihoods. The pastoralists also perceived that restriction of indigenous rangeland management system and climate change in terms of erratic rainfall and drought were among the main factors that caused woody plant encroachment. Thus interventions in the range management need to be in consultation with local communities and in harmony with traditional systems


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