Effects of grazing pressure, age of enclosures and seasonality on bush cover dynamics and vegetation composition in southern Ethiopia

This study evaluated the dynamics of bush cover in relation to the role played by seasonally grazed traditional enclosures compared to grazed rangelands. The result showed that herbaceous biomass was higher in enclosures than in the open grazed areas. Enclosures also showed more diversity and evenness of herbaceous species than open grazed areas. Herbaceous species richness declined with increased age of enclosures compared to the recent and medium age of enclosures. The frequencies of herbaceous species were relatively similar in both management and across enclosures age. A total of 26 herbaceous and 29 woody species were recorded within both enclosures and open grazed sites. Of the total woody plants, 38% of the species were invasive, while the rest (i.e. 62%) were non-invasive. Generally, grazed areas were less threatened by invasive species than enclosures. The density of invasive woody population (63.4% of the total density of woody population) was 2665 stems ha(-1). Commiphoro africana accounted for most of the increase in cover of woody population, on average contributing 86% to the total invasive woody cover in the study area. A reintroduction of fire is recommended together with the integration of traditional range enclosures in order to control invasion of bush encroachment. (C) 2009 Elsevier Ltd. All rights reserved.