Regional biodiversity hotspot (Succulent Karoo)
Biological diversity in the Succulent Karoo
Large Euphorbia and other succulent Karoo, Lapalala River basin. @ C.Michael Hogan
Stretching along the Atlantic coast of Africa, from southwestern South Africa (Southern Africa and biodiversity conservation) into southern Namibia, the Succulent Karoo hotspot covers 102,691 square kilometres of desert. Some pockets of this hotspot are scattered within the Cape Floristic Region Hotspot, which borders it to the south. In fact, the Succulent Karoo exhibits a particularly strong floristic affiliation with the Cape Floristic Region, to the point that some have argued convincingly for the region's inclusion as part of a greater Cape Flora.
The Succulent Karoo, which consists primarily of winter rainfall desert, is one of only two hotspots that are entirely arid (the other being the newly recognized Horn of Africa). The region is commonly divided into two zones. The first, Namaqualand, extends along the west coast of South Africa and southern Namibia. It is a winter rainfall desert with a mild climate moderated by cold Atlantic Oceancurrents. The mild climate has contributed to the evolution of a rich array of endemic species. The second zone, the Southern Karoo, experiences peaks of rainfall in spring and autumn and has more extreme climate variations than the Namaqualand desert.
Dwarf shrubland dominated by leaf succulents is found throughout the hotspot. These drought-adapted plants have thick, fleshy leaves or stems for water storage. In the Succulent Karoo, there are about 1700 species of leaf succulents, and this dominance is unique among the world's desert s. The recent and explosive diversification of the Mesembryanthemaceae, the largest group, has been described as an event unrivaled among flowering plants. Stem succulents are also found here (around 140 species), as are seasonal bulbs and annuals that display magnificent spring blooms in the open spaces between the shrubs, particularly during the spring in the Namaqualand. Hilly topography within the southern Karoo is dotted with evergreen shrubs and tall aloes.
Unique and Threatened Biodiversity
Plants
For an arid region, the Succulent Karoo has extraordinarily high plant endemism, including the richest succulent flora in the world. In total, there are more than 6350 vascular plant species in this hotspot, nearly 2440 of which are endemic (40 percent). Local plant species richness is very high, with an average of 70 species found in 0.1 hectare test plots, and the diversity between sites in the region is also significant. Many plants in the Succulent Karoo, especially succulents, are specialists for a limited range of environmental conditions, producing a phenomenon known as point endemism. Regional endemism is notable at the genus level; 80 genera are found nowhere else in the world.
Notable plant species found in this hotspot include the botterboom (Tylecodon paniculatus), a stem succulent that has glossy leaves in winter and red flowers in summer, and the halfmens ("half human") (Pachypodium namaquanum), a stem succulent endemic to the Richtersveld that can grow up to four metres tall. Clusters of halfmens stems tend to face toward the north, giving the appearance of groups of people gazing northwards. The stems' crowns of leaves, which resemble hairy human heads, enhance the impression. The scientific explanation for this unusual orientation is that the plants, which grow on shaded slopes, lean northwards in order to ensure that their leaves and developing flowerheads, produced during the cool, foggy winter months, are maximally exposed to the sun’s warming rays.
Vertebrates
Birds
The avifauna of the Succulent Karoo includes more than 225 species, one of which is endemic: Barlow's lark (Certhilauda barlowi). Other species in the region include the black harrier (Circus maurus, VU), which has the most restricted range of the world’s 13 harrier species, Karoo bustard (Eupodotis vigorsii), Ludwig's bustard (Neotis ludwigii), Karoo chat (Cercomela schlegelii), dune lark (Certhilauda erythrochlamys), and dusky sunbird (Nectarinia fusca).
Mammals
There are roughly 75 mammal species in the Succulent Karoo hotspot, of which two are endemic: De Winton's golden mole (Cryptochloris wintoni, VU), and the Namaqua dune mole rat (Bathyergus janetta). An important flagship species in the region is the riverine rabbit (Bunolagus monticularis, CR), found in the Succulent Karoo, and whose population is thought to have declined by 60 percent over the past 70 years such that no more than perhaps 250 individual remain.
Major concentrations of large mammalian vertebrates, including elephant (Loxodonta Africana, VU), black rhinoceros (Diceros bicornis, CR), and African buffalo (Syncerus caffer), once roamed the gallery forests along the Orange River in the Succulent Karoo. These populations have now disappearedfrom the hotspot. Today, only smaller herds of gemsbok ( Oryx gazella), mountain zebra (Equus zebra), and springbok (Antidorcas marsupialis) can still be seen there.
Reptiles
Reptile diversity is relatively high in the Succulent Karoo, with more than 90 species, about 15 of which are endemic. All of the endemics are geckos and lizards, representing about a quarter of the nearly 60 gecko and lizard species in thehotspot. These endemics include seven species of girdled lizards of the genus Cordylus, including the armadillo girdled lizard ( Cordylus cataphractus, VU). This lizard has a heavily armored body and spiny tail and is known for rolling into a tight ball when threatened.
As in the rest of South Africa, tortoise diversity is very high in the Succulent Karoo, with seven taxa, two of which are endemic: the Namaqualand tent tortoise (Psammobates tentorius trimeni) and the Namaqualand speckled padloper (Homopus signatus signatus).
Amphibians
Amphibians are poorly represented in the Succulent Karoo with just over 20 species. All of these species are frogs, including one endemic, the desert rain frog (Breviceps macrops, VU), which occurs along the Namaqualand coast of South Africa north to Luderitz in coastal southwestern Namibia.
Freshwater Fishes
There are around 26 species of freshwater fish in the Succulent Karoo, none of which are endemic.
Invertebrates
Invertebrate diversity is quite high in the Succulent Karoo, and evidence suggests that more than half of the species in some insect groups are endemic. Of the 70 species of scorpions found in the hotspot, nearly 20 are endemic. Monkey beetles, which are almost exclusively found in southern Africa, are concentrated in the area. Along with many types of wasps and bees, these beetles pollinate the hotspot's diverse plant species. Perhaps the most unusual invertebrates found here are the long-tongued flies (Memestrinidae), which can have mouthparts up to 50 millimetres long. The flies are the exclusive pollinators of 28 different plant species in Namaqualand.
Human Impacts
The vegetation of the Succulent Karoo is in somewhat better shape than in other hotspot. A sparse human population of only 300,000 people and the fact that more than 90 percent of the hotspot is used for natural grazing (a form of land use that is, theoretically, compatible with maintenance of biodiversity) have eased the conversion pressures on this region as compared to the other hotspots. It is difficult to arrive at accurate estimates of the amount of vegetation remaining intact, but at least five percent has been irreversibly lost to overgrazing, mining and agriculture, with about two-thirds of the land having been seriously overgrazed, especially in Namaqualand. Consequently, only an estimated 30,000 km, or 29 percent, of the hotspot remains in a relatively pristine state.
Diamond mining has had a very heavy impact on the Namaqualand coastline and alluvial terraces of the lower Orange River Valley. Approximately two-thirds of the South African coastline, and almost all the Namibian coastline in this hotspot, has been mined for diamonds. This mining is now supplemented by the large-scale extraction of heavy minerals, including gypsum, marble, monazite, kaolin, ilmenite, and titanium, which threatens to vastly increase the impact of mining on the region's biodiversity.
Farming in the Succulent Karoo hotspot depends on irrigation infrastructure, like dams, that transform the natural habitats of river valleys. The cultivation of grapes, citrus, tobacco, alfalfa, and vegetables is practiced throughout the hotspot in areas that get as little as 150 millimetres of annual rainfall. Several dam projects and new irrigation schemes have been proposed for the last remaining wild rivers in the Succulent Karoo. Dryland farming also accelerates desertification as fragile soils are blown away during the dry season without the natural flora to keep them in place. Furthermore, the rise of the ostrich farming industry has resulted in the degradation of thousands of hectares of veld in the Little Karoo.
Finally, the illegal collection of succulents and bulbs is an increasing problem throughout the area. Spectacular diversity, including miniature succulents and many flowers, attract unscrupulous plant collectors who harvest without regard for the integrity of this unique ecosystem. The problem is likely to grow as the public knowledge of the region's spectacular plant diversity increases.
Conservation Action and Protected Areas
Remarkably, especially for a country like South Africa with its well-established network of reserves, only about 2,560 km of the Succulent Karoo, or 2.5 percent of the land area, is protected, with only 1890 km (1.8 percent) in IUCN categories I to IV. The largest of the statutory reserves, the 1624 km2 Richtersveld National Park, is governed by an arrangement between the South African government and the community that lives there. Economic benefits and grazing rights are granted to the community in exchange for national park status of the communally owned land.
There are more than 900 nationally threatened plant species in the hotspot, and the present system of protected areas is inadequate for the preservation of all its biodiversity. Two new developments, however, are positive signs for the region's future. First, the reserve system is expanding throughout the hotspot. The creation of the Namaqua National Park (600 km) in the central uplands of Namaqualand is an example of one such positive development, and the park is set to expand westwards to encompass Sandveld habitats on the coastal plain.
Second, public awareness of the rich natural heritage of the Succulent Karoo is growing, thanks in large part to the Succulent Karoo Ecosystem Programme (SKEP). SKEP is the result of a one-year planning exercise that combined a rigorous scientific process with broad land-user participation to identify and generate consensus for a 20-year Conservation and Sustainable Land-use Strategy for the Succulent Karoo Hotspot. SKEP aims to meet quantitative targets for the conservation of vegetation types and globally threatened and endemic species at particular sites, as well as critical ecological and evolutionary processes that must be conserved to ensure the persistence of these species. The increased public awareness that SKEP has raised, of the importance and fragility of the Succulent Karoo, has yielded increased efforts of landowners to adopt biodiversity-friendly land-use patterns, and, fortunately, funds have become available to help fuel this interest.
Building on the SKEP framework, the Critical Ecosystem Partnership Fund has allocated $8 million over five years to support civil society groups and conservation initiatives in the Succulent Karoo. A key objective is to test and expand innovative approaches that will involve people of the region to support sustainable development and promote conservation of this unique treasure.
Further Reading
- Desmet, P., Ellis, A. & Cowling, R. 1998. Speciation in the Mesembryanthemaceae. Aloe 35(2): 38-43.
- Driver, A., Desmet, P. G., Rouget, M., Cowling, R. M. & Maze, K. E. 2003. Succulent Karoo Ecosystem Plan Biodiversity Component Technical Report. Cape Town, Cape Conservation Unit, Botanical Society of South Africa.
- Harrison, J.A., Allan, D.G., Underhill, L.G., Herremans, M., Tree, A.J., Parker, V., & Brown, C.J. (Eds.). 1997. The Atlas of Southern African Birds. Johannesburg: BirdLife International.
- Hoffman, M.T., Cousins, B., Meyer, T., Petersen, A., & Hendricks, H. 1999. Historical and contemporary land use and the desertification of the Karoo. In W. R. J. Dean & S. J. Milton. (Eds.), The Karoo: Ecological Patterns and Processes.Cambridge: Cambridge University Press. ISBN: 0521554500.
- Hogan, C.Michael, Cooke, Mark L. and Helen Murray. 2006. The Waterberg Biosphere, Lumina Technologies
- Ihlenfeldt, H.D. 1994. Diversification in an arid world: The Mesembryanthemaceae. Annual Review of Ecology and Systematics 25:521-546.
- van Jaarsveld, E. 1987. The succulent riches of South Africa and Namibia. Aloe 24:45-92.
- Jurgens, N. 1986. Untersuchungen zur okologie sukkulenter pflanzen des sudlichen Afrika. Mitteilungen aus dem Institut fur Allgemeine Botanik Hamburg 21:139-365.
- Jurgens, N. 1991. A new approach to the Namib region. I: Phytogeographic subdivision. Vegetation 97:21-38.
- Klak, C., Reeves, G. & Hedderson, T. 2004. Unmatched tempo of evolution in Southern African semi-desert ice plants. Nature 427:63-65.
- Lombard, A.T., Hilton-Taylor, C., Rebelo, A.G., Pressey, R.L. & Cowling, R.M. 1999. Reserve selection in the Succulent Karoo, South Africa: Coping with high compositional turnover. Plant Ecology 142(1-2): 35-55.
- Meadows, M. E. & Watkeys, M.K. 1999. Palaeoenvironments In W. R. J. Dean & S. J. Milton. (Eds.), The Karoo: Ecological Patterns and Processes.Cambridge: Cambridge University Press. ISBN: 0521554500.
- Milton, S.J., Yeaton, R., Dean, W.R.J. & Vlok, J.H.J. 1997. Succulent Karoo. In R.M. Cowling, D.M. Richardson & S.M. Pierce. (Eds.), Vegetation of Southern Africa. Cambridge: Cambridge University Press. ISBN: 0521548012.
- Rebelo, A. G. 1997. Conservation. In R.M. Cowling, D.M. Richardson & S.M. Pierce. (Eds.), Vegetation of Southern Africa. Cambridge: Cambridge University Press. ISBN: 0521548012.
- Rundel, P.W., Cowling, R.M., Esler, K.J., Mustart, P.J., van Jaarsveld, E. & Bezuidenhout, H. 1995. Winter growth phenology and leaf orientation in Pachypodium namaquanum (Apocynaceae) in the Succulent Karoo of the Richtersveld, South Africa. Oecologia 101: 472-477.
- Vernon, C.J. 1999. Biogeography, endemism and diversity of Animals in the Karoo. In W. R. J. Dean & S. J. Milton. (Eds.), The Karoo: Ecological Patterns and Processes.Cambridge: Cambridge University Press. ISBN: 0521554500.
- Vlok, J.H.J., Euston-Brown, D. I. W. & Cowling, R. M. 2003. Acocks Valley bushveld 50 years on: New perspectives on the delimitation, characterisation and origin of thicket vegetation. South African Journal of Botany 69: 27-51.
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