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Editor: Ben J. Strohbach
- Preliminary account of the floristic zones of the Sperrgebiet (Protected Diamond Area) in southwestern Namibia. G. Williamson
- Grazing gradients in the Highland savanna of Namibia. D.F. Joubert
- Human impacts on woody vegetation, and multivariate analysis: a case study based on data from Khowarib settlement, Kunene Region. Sian Sullivan and Tracey L. Konstant
- Looking into the past: Interpretations of vegetation change in western Namibia based on matched photography. R.F.Rhode
The Sperrgebiet (Protected Diamond Area), a little known part of southern Namibia, can only be entered by permit. To date no complete account of the Sperrgebiet flora exists and no full plant list has been compiled. Due to strict security it has been especially difficult to obtain permission to collect in the closed coastal diamond mining area No. 1.
This preliminary account covers the whole Sperrgebiet. The floristic zones are described in relationship to climate (wind conditions and sea fogs) and geomorphology. Notes on plant collecting are included and biodiversity and endemism discussed. A list of plants occurring in the Sperrgebiet, with known distribution, is annotated. Two tables covering an analysis of total families, species and endemics are set out. Two maps display the floristic zones relating to topographical contours and the position and orientation of wind-corridors and sand-dune systems. Various aspects of the flora, including revegetation of waste mine dumps are illustrated by the inclusion of 25 photographs. A bibliography is appended.
The Sperrgebiet is situated in the south-west corner of Namibia and is roughly rectangular in shape with a narrow triangular spur north of Liideritz. The north-south length is about 250 km and east-west width varies from 100 km to 70 km at the narrowest covering about 26.000 km². The orientation of the area is roughly in a south-east direction from Lüderitz to Oranjemund. The north-west point at Lüderitz is located at approximately 26°40'S x 15°4'E and the north-east close to Aus at 26°40'S x 16°10'E. The south-west corner close to Oranjemund is approximately 28°36'S x 16°28'E and the south-east corner close to Dreigratberg 28°5'S x 16°52'E.
The north spur is approximately 65 km long. The area is administered jointly by Namdeb (Pty) Ltd. and the Ministry of Wildlife, Conservation and Tourism except for the designated mining area which is wholly the responsibility of Namdeb. To date, entry is by permit issued by Namdeb and the Diamond Branch of the Namibian Police. The vegetation can be classified into several floristic zones which overlap and are demarcated by the topography.
The flora in relation to rainfall, fog, wind and geomorphology:
a) Rainfall and fog The whole Sperrgebiet falls within the west coast winter rainfall region with the central Namib area north of the Sperrgebiet receiving the lowest rainfall in Southern Africa. The southern two thirds of the Sperrgebiet can expect an average rainfall of 11-88 mm 90% of the time and the northern section an average of 3-38 mm 90 % of the time. The gradient towards the lower rainfall of the northern area is reflected in the lower biodiversity and density of plants. Because of the exceptionally low rainfall, the vegetation is largely dependent on sea fog generated by the presence of the cold, north-flowing Benguela current which bathes the Atlantic seaboard.
Due to the differential between the cold sea and the higher inland temperatures, cool moisture-laden fog drifts inland towards a lower pressure belt and condenses over the entire area, but especially on rocky inselbergs and protected mountain slopes. The effective humidity on the high inselbergs is probably in excess of the expected recorded maximum (possibly about 88 mm) for the area. The section least influenced by the sea fog is the highland of the north-east corner of the Sperrgebiet, including the Kuckaus and Tsaus massifs. Here the flora is partly derived from the climatic zone towards the east, intermediate between summer and winter rainfall.
b) Wind The prevailing winds blow from the south-west and increase in intensity from south to north. Due to the centre of the constant Atlantic anticyclone situated off the mid-Sperrgebiet coast, the strongest winds are experienced around Pomona, where the highest wind velocities in the subcontinent occur**. [...]