The vegetation and restoration potential of the arid coastal belt between Port Nolloth and Alexander Bay, Namaqualand, South Africa
Master Thesis
1996
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University of Cape Town
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Abstract
This thesis introduces the environment and the vegetation of the Namaqualand coastal belt between Port Nolloth and Alexander Bay. Aspects of the abiotic environment are discussed and related to patterns and processes observed in the vegetation of the study area. The restoration of the natural vegetation impacted by diamond mining activities is discussed. 1-4 The study area, located within the winter rainfall area of the Namib Desert, is one of four global fog deserts. The area is characterised by a near ubiquitous covering of Recent to Tertiary amorphous dunes of marine origin. The dunes can be divided into two broad categories: Recent, mobile white dunes, and Tertiary to Late Quaternary, semi-mobile red dunes. The red dune soils are considered arenosols, underlain by dorbank and calcrete hardpans, whereas the white dunes generally lack this structure, unless they are superimposed on an older dune series. The dune landscape is interrupted by outcrops of bedrock, such as river canyons (Holgat River); inselbergs (Buchu Twins); and koppies. Gravel plains and rocky outcrops cover much of the area on the south bank of the Orange River, as far south as Cape Voltas. The low rainfall ( <70 mm) is offset by frequent fog and dew. Summers are dominated by high energy, southerly winds and winters by gentle land-sea breezes interrupted by occasional, warm-easterly "berg" winds. A complete bio-inventory of higher plants of the study area was undertaken. Patterns of diversity and endemism were analysed in relation to plant growth form and habitat. 300 plant species were collected in the study area representing 40 families, with 28 being endemic to the coastal region. The flora is dominated by the Asteraceae (53 species), Mesembryanthemaceae (47), Crassulaceae (28), Poaceae (17) and Aizoaceae (15). Endemic species are over-represented in the Mesembryanthemaceae (60 endemic) and Crassulaceae (44), and under represented in the Asteraceae (8), Poaceae (0) and Aizoaceae (0). Rocky outcrops have the highest species:area ratio (3.77). They are characterised by their own distinct flora as well as representing a significant proportion ( 46) of the species from the surrounding dune landscape. Endemic species are concentrated on these, as well as on the gravel plain habitats. Dune habitats are the most widespread. However, they are characterised by a widespread, generalist flora with low species:area ratio (0.81), few endemics, and share an expected number of species with other habitat types (21 ). An endemic species in the southern Namib can be characterised as being a dwarf leaf succulent in the Mesembryanthemaceae which is most likely to be encountered on a rocky outcrop.
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Includes bibliography.
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Desmet, P. 1996. The vegetation and restoration potential of the arid coastal belt between Port Nolloth and Alexander Bay, Namaqualand, South Africa. University of Cape Town.