Changes in vegetation structure and aboveground biomass in response to traditional rangeland management practices in Borana, southern Ethiopia

Abstract

This study aimed to determine vegetation structure, species diversity and aboveground herbaceous biomass and browse yields in Borana rangelands of southern Ethiopia. Sampling through random allocation of quadrats within replicated sample plots was undertaken in communally grazed areas, grazing enclosures and rangelands managed by prescribed fire for five years and grazed only post-fire during dry seasons. A total of 57 herbaceous species (24 grasses and 33 non-grasses) and 39 woody species (12 trees and 27 shrubs) were identified. Of the 24 grass species identified, 16.7% were highly desirable, 62.5% desirable and 20.8% less desirable by grazers. Biomass of both trees and shrubs was significantly higher (p < 0.001) in grazing enclosures than in other treatments, whereas herbaceous vegetation biomass was higher, but not significantly, in prescribed fire managed rangeland units. Importantly, fire-managed areas also contained the highest densities of some of the most desirable grassland species, including Cenchrus ciliaris, Chrysopogon aucheri and Digitaria milanijiana. We conclude that in the absence of fire, the increasing prevalence of enclosures in Borana pastoralist systems may be encouraging the proliferation of woody shrubs and trees at the expense of more desirable pasture species.