Swartland Shale Renosterveld
Distribution: Western Cape Province: Large, generally continuous areas of the Swartland and the Boland on the West Coast lowlands, from Het Kruis in the north, southwards between the Piketberg and Olifantsrivierberge, widening appreciably in the region around Moorreesburg between Gouda and Hopefield, and encompassing Riebeek-Kasteel, Klipheuwel, Philadelphia, Durbanville, Stellenbosch to the south and Sir Lowry’s Pass Village near Gordon’s Bay. Altitude 50–350 m. 9.8% of this vegetation type occurs within and 90.2% outside the City. Similar transformation rates occur nationally (92%) and inside City borders (91%).
Vegetation & Landscape Features: Moderately undulating plains and valleys supporting low to moderately tall leptophyllous shrubland of varying canopy cover as well as low, open shrubland dominated by renosterbos. Heuweltjies are a very prominent local feature of the environment, forming ‘hummockveld’ near Piketberg and giving the Tygerberg Hills their name. Stunted trees and thicket are often associated with the heuweltjies. Disturbed areas are dominated by Athanasia trifurcata and Otholobium hirtum. Patches of Cynodon dactylon ‘grazing lawns’ also occur in abundance.
Geology & Soils: Clay soils derived from Malmesbury Group shales (specifically the Porterville Formation in the north and east and the Moorreesburg Formation in the west). The soils contain prismacutanic and pedocutanic diagnostic horizons and Glenrosa and Mispah forms are predominant.
Climate: Winter-rainfall regime, with MAP 270–670 mm (mean: 430 mm), peaking from May to August. Mean daily maximum and minimum temperatures 29.6°C and 6.3°C for February and July, respectively. Frost incidence 3 or 4 days per year. Mists are common in winter.
Endemic Taxa: Low Shrubs: Leucadendron verticillatum, Aspalathus acanthophylla, A. horizontalis, A. pinguis subsp. longissima, A. pinguis subsp. occidentalis, A. puberula, A. rectistyla, Cliffortia acockii, Lotononis complanata, Serruria incrassata. Succulent Shrubs: Erepsia ramosa, Ruschia patens, R. pauciflora. Herb: Indigofera triquetra. Geophytic Herbs: Aristea lugens, Babiana angustifolia, B. latifolia, B. odorata, B. secunda, Hesperantha pallescens, H. spicata subsp. fistulosa, Lachenalia liliflora, L. mediana var. rogersii, L. orthopetala, Lapeirousia fastigiata, Moraea gigandra, M. tulbaghensis, Oxalis fragilis, O. involuta, O. leptocalyx, O. levis, O. macra, O. perineson, O. strigosa, Pelargonium viciifolium.
Conservation: This is a critically endangered vegetation unit. Target 26%, but since 90% of the area has been totally transformed (mainly for cropland), the target remains unattainable. The remnants are found in isolated pockets, usually on steeper ground. So far only a few patches have been included in conservation schemes (e.g. Elandsberg, Paardenberg). Aliens include Acacia saligna (very scattered over 65%), A. mearnsii (very scattered over 62%) as well as several species of Prosopis and Eucalyptus. Alien annual grasses (species of Anagallis, Avena, Briza, Bromus, Lolium, Phalaris and Vulpia) are a primary problem in remnant patches. Other serious aliens include herbs such as Erodium cicutarium, E. moschatum, Echium plantagineum and Petrorhagia prolifera.