Responses of vegetation, small mammals and large herbivores to human induced pressures in the Savannah Plains of Nech Sar National Park, South Ethiopia Rift Valley
25 February 2016
UAntwerp, Campus Middelheim, A.143 - Middelheimlaan 1 - 2020 Antwerpen
Simon Shibru Cheche
Herwig Leirs & Karen Vancampenhout
PhD defence Simon Shibru Cheche - Faculty of Science, Department of Biology
The objective of this study was to develop better understanding on how the vegetation and small and large herbivore mammals respond to human induced pressures in the savannah plains of Nech Sar National Park. We studied the effects of exclusion of large herbivores on vegetation and found that ungrazed plots had better vegetation condition compared to grazed plots, the worst being in plots grazed by cattle.
We also assessed the effects of exclusion of large herbivores on abundance and diversity of small mammals and found that the small mammals were more abundant in ungrazed plots. We evaluated whether the abundance and diversity of rodents correlate with changes in vegetation along an altitudinal gradient and showed that rodent abundance and diversity vary with vegetation and altitude. We identified three rodent communities, with Acomys wilsoni, Arvicanthis sp. and Gerbilliscus nigricaudus as respective indicator species. However, due to their localized distribution A. wilsoni and Lemniscomys macculus may serve better as ecological indicators for habitat condition in the Park. We also documented the woody species density in the plains of the Park and investigated its effect on distribution of large mammals.
We showed that woody plants density had exceeded the critical threshold level of encroachment. Dichrostachys cinerea was the most visible encroaching species. We surveyed the population size of the Swayne’s Hartebeest and document the threats bringing the species on the verge of local extinction; we found evidence of a dramatic decline of density from 65 in 1974 to 1 individual per 100 km2 in 2014, hunting and habitat loss being the main causes for local extinction. We also investigated if endozoochory could explain the changing vegetation in the plains and showed that lesser kudu, cattle, greater kudu, Grant’s gazelle and goats had the potential to dispersing D. cinerea and Acacia nilotica seeds.
In conclusion, the plains of the Park serve as an example where resources are being depleted. A cryptic shift from more palatable grazing sensitive to less palatable grazing tolerant grass species, increasing percentage of bare ground, increasing density of encroaching woody species, and a declining population of mammals particularly Swayne’s Hartebeest were indicators of such resource depletion. This is a challenge for conservation and tourism and calls for urgent intervention.