The dynamics of savanna ecosystems and management in Borana, Southern Ethiopia.
The dynamics of savanna ecosystems and management in Borana, southern Ethiopia was studied by investigating the roles played by rainfall variability and the impact of cattle population under the communal rangelands and ranch system. The variability in terms of impact of multi-year droughts on livestock of different reproductive classes and their recovery patterns, comparing the traditional and ranch management systems, was considered. The importance of using herder environmental knowledge in understanding historical changes in patterns of land use and shifts in vegetation with implications for pastoral production was also investigated. Household interview and field based data collected between 2002 and 2005 were used. Household cattle data (21 years) and the ranch cattle data (15 years) were related to long-term rainfall variability. Breeding cows in the key resource tula well rangelands showed longer reproductive life than the non-key resource pond-water rangelands. Average calving rates were greater in the communal rangelands than in the ranch system. Higher densities of invasive woody species were observed in enclosures as opposed to the open grazed areas. The use of the state-and-transition model showed complex successional pathways of changes with regard to variability in rainfall, management interventions and timescales (i.e., the age chronosequence of enclosures) that are relevant for making management decisions. Tree cutting, fire and grazing treatment were more effective in controlling coppicing after disturbance. Different woody species showed varied adaptation strategies in response to disturbances by either adapting to increased seedling recruitment or coppicing after disturbance. The disturbance control treatment had no advantage in terms of herbaceous biomass and basal cover over other treatments, while herbaceous species richness was enhanced.