| Abstract |
Bush encroachment is a phenomenon that occurs in savanna regions worldwide. It is characterized by the increase of biomass and abundance of woody plant species, accompanied by the suppression of perennial grasses and herbs. Bush encroachment is mainly ascribed to poor management of farmland, including overgrazing, the suppression of fires and the absence of browsers. Encroaching plant species are often unpalatable to grazers and domestic animals due to chemical and physical defenses, leading to a decreased livestock carrying capacity in the affected areas. This is especially problematic in countries like Namibia, where livestock keeping is a major source of income for both commercial and communal farmers. Although numerous models try to explain the occurrence of bush encroachment, there is agreement that herbivore impact is a central factor. Knowledge about plant-herbivore interactions, feeding preferences and habitat use of herbivores is thus crucial to develop sustainable land management systems. This study aims to explore the interactions between woody encroachment and herbivory in the central Namibian thornbush savanna. Vegetation and herbivore distribution on the farm Erichsfelde was assessed during the dry season 2013. One of the study sites is an established longtime monitoring observatory; therefore vegetation monitoring data from 2004 to 2009 were available. Diet composition of cattle, oryx, greater kudu, and warthog was analyzed. No increase in thorn shrub cover was observed over the last decade. Locally, high densities of juvenile acacias indicated potential future encroachment. The results suggest that the current management practices on the farm support a stable state and prevent encroachment. Habitat use of wild herbivores was not dependent on grass cover or thorn shrub cover, and was thus ascribed to large-scale factors and structural diversity. Diet composition was analyzed from feces and stomach content, with deviating results between the two methods. Results of these analyses are discussed for single herbivore species. |
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