Vegetation of the Thornbush Savanna of Central Namibia: Baseline description of the present vegetation at Farm Erichsfelde, Otjozondjupa Region
Keywords:Acacietea, Livestock Farming Suitability Index, Modified TWINSPAN, Nonmetric Multidimensional Scaling, Phytosociology, Veld degradation
The Vegetation Survey of Namibia project has been initiated to provide baseline data in support of sustainable land-use planning. The finding of historical data from the Farm Erichsfelde initiated a long-term monitoring programme. This study serves as a baseline description of the vegetation associations. Regular Braun-Blanquet type sampling was done in April 1999, and additional relevés were obtained from the BIOTA project from 2002 and 2005. The entire data set comprised 232 relevés with 379 species. The data were classified using the modified TWINSPAN procedure. Eleven associations, grouped into five habitat types, were identified from the classification. These habitat types are linked to landscape facets, being wetlands, rocky habitats, plains, soils on calcretes as well as riverine and related habitats. The associations are described in terms of their composition, general position in the landscape and structure. The relevé data were subjected to an NMS ordination. The main environmental gradients identified were the topography, the soil pH and the slope of the landscape. It is, however, very clear from the ordination that the various associations identified are closely related, and in many respects ecotonal to each other. The vegetation associations were mapped using aerial images as well as the GPS position of the relevés as baseline. In addition, a Livestock Farming Suitability Index was calculated for each association, based on its habitat, composition and structure. Only the Ziziphus mucronata—Dichanthium annulatum association was rated highly suitable for livestock farming. The two plains associations, Ondetia linearis—Acacia mellifera and Aristida congesta—Acacia mellifera were rated moderately suitable, whilst all other associations were rated with a low suitability for livestock farming. The main reason for these fairly low ratings is a high degree of bush encroachment and low perennial grass cover.
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