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Southern Africa: Southern Namibia into South Africa

The Succulent Karoo’s botanical diversity is unparalleled by any other arid region on earth. This ecoregion is home to greater than 5,000 higher plant species, nearly 40 percent of which are endemic, and 18 percent of which are threatened. It has the richest succulent flora in the world, harboring about one-third of the world’s approximately 10,000 succulent species. Other unique features include the diversity of miniature succulents (435 spp.) and geophytes (630 spp.). The ecoregion is also a center of diversity and endemism for reptiles and many invertebrate taxa, especially monkey beetles (Rutelinae: Hoplinii). However, less than 3 percent of the ecoregion is conserved in ten statutory reserves. Overgrazing, especially on communal lands, and mining continue to transform this landscape. The existing biodiversity is threatened by expansion of communal lands and associated overgrazing, new mining ventures, and the illegal harvesting of succulents.

  • Scientific Code
    (AT1322)
  • Ecoregion Category
    Afrotropical
  • Size
    39,700 square miles
  • Status
    Critical/Endangered
  • Habitats

Description
Location and General Description
This ecoregion extends down the western coast of Namibia from the town of Luderitz into South Africa, and then penetrating further inland. It comprises two major biogeographical domains, the Namaqualand-Namib Domain and the Southern Karoo Domain (Jürgens 1991). The Namaqualand-Namib Domain encompasses the fog-affected coastal plain and adjacent escarpment in the west. It is made up of several sub-regions: the Sperrgebiet of southern Namibia; the Richtersveld, which is a desert mountain region adjacent to the Orange River; the Sandveld, or sandy coastal plain, south of the Orange River; the Hardveld, or granitic uplands, of the Great Escarpment; the Kamiesberg, a granite massif of 1,800 m along the escarpment; and the quartz-strewn plains of the Knersvlakte in the extreme south. This domain receives most of its rain in winter.

The Southern Karoo Domain is located to the east of the Namaqualand-Namib Domain, is not subject to fog, and receives most of its rain in spring and autumn. It includes three subregions: the Western Mountain Karoo comprising the southwestern sector of the Great Escarpment; the Tanqua Karoo, a large, arid basin located between the Western Mountain Karoo and the fynbos-clad Cape Fold Mountains; and the Little Karoo, a basin to the southeast, surrounded entirely by Cape Fold Mountains.

The most succulent vegetation on Earth is found in the Succulent Karoo (van Jaarsveld 1987). The Succulent Karoo has a predominance of low, succulent-leaved shrubs, few grasses, and a scarcity of tall shrubs and trees. It is easily distinguished from its neighboring ecoregions by its climate, soils, and the resultant vegetation and flora. The Namib Desert ecoregion to the north is characterized by extremely low and variable summer rain (less than 50 mm per year), and extremely sparse plant cover, dominated by ephemerals. To the east lies the Nama Karoo ecoregion, a low open shrubland with variable grass cover and highly variable rain that falls mainly in the late summer months. To the south of the Succulent Karoo lie the fire-prone, hard-leaved shrublands of the Lowland and Montane Fynbos and Renosterveld ecoregions. They are associated with predominantly winter rainfall and sandy, infertile soils.

The distinctive climatic characteristics of the Succulent Karoo make it different from all other deserts in the world (Desmet and Cowling 1999a). Rainfall is reliable and predictable, falling mostly in winter, and prolonged droughts are rare. The mean lowest minimum temperature for the coldest month is above -40C, while the same temperature index for the Namib Desert is above 20C, and that for the Nama Karoo ranges from 00C to -90C (Rutherford 1997). The climate is mild compared to other arid areas, particularly in the Namaqualand-Namib Domain, where frosts are extremely rare. This domain receives annual rainfall ranging from 20 mm in the drier northwest to more than 400 mm in the escarpment zone, but the majority receives less than 150 mm. The winter rains are associated with cold fronts. Precipitation is supplemented by heavy dewfalls and fog. Fog is generated by the cold Benguela Current of the Atlantic Ocean, and tempers summer heat in coastal parts of this domain. Surprisingly, some of the hottest days, when temperatures up to 40oC are recorded, occur in winter as a result of hot "berg," or mountain winds.

In contrast, the inland Southern Karoo Domain experiences a more extreme climate with frequent summer maximum temperatures greater than 40oC. Dew is an important source of moisture here and rainfall is reliable, with 150 mm to 300 mm falling each year, although less reliable than in the Namaqualand-Namib domain. Rain falls mainly in the spring and autumn months, associated with post-frontal events.

The Namaqualand-Namib Domain is part of the Namaqualand Metamorphic Province, comprising granites and gneisses that are from 1 to 2 billion years old (Watkeys 1999). The coastal plain is covered by Tertiary and recent sands of marine and aeolian origin. The Knersvlakte is an ancient delta of the palaeo Orange River, characterized by relatively recent sediments and quartz lag gravels.

In the Southern Karoo Domain, the Tanqua Karoo is a large basin between the Great Escarpment and the Cape Folded Belt underlain by Mesozoic sediments of the Karoo cycle (Watkeys 1999). Soils are mainly stony and shallow. The Western Mountain Karoo forms part of the Great Escarpment, a mountainous landscape comprising mainly of Karoo rocks with dolerite intrusions forming many of the peaks and ridges. The Little Karoo is an intermontane basin nestled within the Cape Folded Belt. Predominant rocks are Cape Supergroup sediments (Palaeozoic), especially shales of the Bokkeveld Group. There are also residual deposits of Cretaceous sediments.

There are several special geological and geomorphological features of the ecoregion:

•The Richtersveld Mountains contain extremely ancient sediments, more than 2.6 billion years old, which are among the oldest sedimentary rocks of the world (Cowling and Pierce 1999).
•The quartz lag gravels of the Knersvlakte and Little Karoo are associated with high endemism of miniature succulents, especially Argyroderma spp. in the former area and Gibbaeum spp. in the latter, both genera in the Mesembryanthemaceae family (Schmiedel and Jürgens 1999).
•The succulent-rich quartz mountains and hills in Namaqualand-Namib Domain contain extremely high levels of point endemics among many succulent and bulb lineages (Desmet and Cowling 1999b).
•The limestones of the Knersvlakte have high numbers of edaphic endemics in genera such as Antimima (Mesembryanthemaceae) (Desmet et al.1999).
•The sand movement corridors along the Atlantic Coast are edaphically complex, associated with soil development from mobile sand to old red sands underlain by duricrusts (Cowling et al. 1999a).
•The Kamiesberg Massif has high levels of endemism especially among bulb genera, namely Babiana, Lapeirousia, Moraea, and Romulea (Iridaceae) (Hilton-Taylor 1996).
There are only three major perennial river systems in the Succulent Karoo, all of which have their source in wet mountain areas distant from the ecoregion. The Orange, or Gariep, River, the longest perennial river in South Africa, originates in the uplands of Lesotho, and forms the boundary between the Sperregebiet and Richtersveld in the Namaqualand-Namib Domain. The Sperregebiet is completely devoid of ephemeral rivers, so the Orange River is a vital resource. The southern boundary of this domain comprises the Olifants River, which, along with its tributary, the Doring River, originates in the fynbos covered Cape Fold Mountains. In the Southern Karoo Domain, the Olifant-Gourits-Groot River System bisects the Little Karoo, and is sustained by run-off from the adjacent Cape Fold Mountains.

The perennial rivers are important in providing corridors of productivity dominated by trees that are derived from the distant savannas, such as Acacia karroo. In earlier times large mammals, including elephants (Loxodonta africana), black rhinoceroses (Diceros bicornis) and hippos (Hippopotamus amphibius), occupied these habitats. On the sandy coastal plain of the Namaqualand-Namib Domain, the numerous seasonal river courses are associated with exposed bedrock. These provide stepping-stone corridors for succulents to extend across the plain from the rocky coast to the inland hills and mountains.

The vegetation of this ecoregion may be divided into six broad types (Cowling and Pierce 1999), determined primarily by soil depth and texture, moisture and temperature regime.

•Vygieveld is the most widespread vegetation type – a dwarf to low shrubland ranging from less than 25 cm to less than 50 cm in height dominated by leaf succulents, notably Crassula spp. and members of the Mesembryanthemaceae family (known in the vernacular as the vygie family). Vygieveld, is invariably associated with shallow soils, and can be further classified into subtypes depending on substrate type:
•vygieveld on quartz fields supports Argyroderma spp., Conophytum spp., Monilaria spp., and Oophytum spp. in the Namaqualand-Namib Domain, and Gibbaeum spp. and monotypic Muirii in the Little Karoo
•vygieveld in heuweltjie-pocked areas (heuweltjies are termite mounds) with Ruschia spp., Drosanthemum spp., Cephalophyllum spp., all in the family Mesembryanthemaceae.
•vygieveld on bedrock supports genera in Mesembryanthemaceae, notably Crassula spp., Anacampseros spp., and Tylecodon spp.
•vygieveld on gravel plains contains Dracophilus spp., Juttadinteria spp., Psammophora spp., Lithops spp. (all Mesembryanthemaceae) in the Sperrgebiet and Richtersveld, and species in the following genera in the Tanqua Karoo: Augea, Cephalophyllum, Crassula, Pleiospilos, Psilocaulon, Hereroa, Rhinephyllum, Ruschia, and Sphalmanthus.
•Strandveld is an open shrubland of 0.5 m to 2.0 m high that grows on the coastal plain of the Namaqualand-Namib Domain on deep sands of marine origin. Its species complement is relatively modest with low succulent creeping shrubs (Cephalophyllum spp.), dwarf forms in rocky sites (e.g the monotypic endemic Wooleya farinosa – Mesembryanthemaceae), succulent shrubs (Stoebaria spp., Ruschia spp., Zygophyllum spp.), as well as non-succulent shrubs (e.g. Eriocephalus spp., Hermannia spp.). In autumn, amaryllid bulbs of Brunsvigia and Haemanthus produce brilliant blooms, while in spring the space between the showy perennial shrubs is ablaze with flowering ephemerals.
•Broken Veld, a widespread vegetation type in this ecoregion, is found on rocky terrain in the escarpment zone of the Namaqualand-Namib Domain, and is the predominant vegetation of the Little Karoo. Its name refers to the scattered individuals of tall shrubs and small trees (2 m to 3 m in height) that "break" the uniformity of the low shrub layer, which is rich in succulents, especially those in the families Mesembryanthemaceae and Euphorbiaceae. In the Namaqualand-Namib Domain, Broken Veld is found mainly on granite landscapes; the tree dominants are Ozoroa spp., Rhus spp., Boscia foetida, and Ficus ilicina as well as the characteristic Aloe dichotoma. In the Little Karoo, Broken Veld grows on exposed shale ridges as well as on the stony plains. The tree stratum is dominated by Euclea undulata and Pappea capensis. The low shrub stratum includes a wealth of succulents (Crassula spp., Ruschia spp., Tylecodon spp.) and non-succulents (Pteronia spp., Rhigozum spp., Osteospermum spp.) alike.
•Renosterveld grows in the uplands of the Hardeveld, Little Karoo, Richtersveld, and the Western Mountain Karoo with rainfall varying from 250 mm to more than 400 mm per year. This is a dense and taller shrubland dominated by Asteraceae, especially Elytropappus spp., Euryops spp., Didelta spp., Pteronia spp., Eriocephalus spp., and Athanasia spp.. The renosterveld of the Succulent Karoo shows strong similarities with, and grades into, the renosterveld of the adjacent Lowland and Montane Fynbos and Renosterveld ecoregions.
•Fynbos, the characteristic vegetation of these two ecoregions, is also found in the Namaqualand-Namib Domain, patchily distributed on infertile, wind-blown sands along the coast, as well as in the highest and wettest reaches of the Kamieberg.
The Sperregebiet part of the ecoregion has a dominance of low perennial shrubs that bear succulent leaves, branches and stems. This growth form is found extensively throughout the families Aizoaceae, Crassulaceae, Liliaceae, and Euphorbiaceae (Pallett 1995). The coastal zone of the Sperregebiet is made up of numerous hummocks formed by the tough woody shrub, Salsola nollothensis and the spiky desert grass Cladoraphis cyperoides, which trap windblown sand. Scattered among these hummocks are numerous rocky outcrops on which grow wind-shaped, low-growing woody succulents such as Othonna furcata, Pelargonium spp., Salsola spp., Lycium decumbens, Drosanthemum luderitzii, and Osteospermum crassifolium (White 1983). Lichens are also found along this coastal zone, growing on wood, rocks and soil. The orange lichen Xanthoria turbinata is common and mostly grows on dead Salsola plants. Further inland are sand plains that have a low plant density. Hummocks are formed on these plains by the nara plant (Acanthosicyos horrida), a large, spiny, leafless shrub. To the east are gravel plains that support a fairly dense shrubby flora made up of a mosaic of dominant plants, including several Euphorbia and Zygophyllum species. The 1.5m tall succulent shrub Euphorbia gummifera is common. The low mountains in the region support some of the oddest and rarest trees in the Succulent Karoo, the halfmens (Pachypodium namaquanum), the quiver tree (Aloe dichotoma) and the bastard quiver tree (Aloe pillansii). To the extreme east of the Sperregebiet there is a well-developed grass plain with Stipagrostis spp., Erharta pusilla and Eragrostis nindensis as the dominant species (Pallett 1995).

Biodiversity Features
The Succulent Karoo is the world’s only plant hotspot (sensu Mittermeier et al. 1999) that is entirely arid. By far the most distinctive feature of the Succulent Karoo is the diversity of succulents, especially dwarf and contracted leaf succulents (Cowling et al. 1999b). The ecoregion includes some 1,700 species of leaf succulents, 700 of which are stone plants and their allies (Conophytum, Lithops etc.). The major families contributing to this group are Mesembryanthemaceae, Crassulaceae and Aloaceae. Certain succulent genera are extremely speciose – e.g. Ruschia (Mesembryanthemaceae: 136 spp.); Conophytum (Mesembryanthemaceae: 85 spp.), Euphorbia (Euphorbiaceae: 77 spp.), Othonna (Asteraceae 61 spp.), and Drosanthemum (Mesembryanthemaceae: 55 spp.) (Hilton-Taylor 1996).

Another outstanding feature of the Succulent Karoo is the high diversity of geophytes or bulblike plants. Most of the 630 species of geophytes are petaloid monocots in the families Hyacinthaceae (Lachenalia, Ornithogalum), Iridaceae (Babiana, Lapeirousia, Moraea, Romulea), Amaryllidaceae (Brunsvigia, Hessea, Strumaria) and Asphodelaceae (Bulbine, Trachyandra). No other desert region has this diversity and splendor of bulbs.

Despite the world-renowned displays of spring annuals, this plant group comprises a low proportion (8 percent) of the Succulent Karoo flora, and includes few endemics. However, at 390, the number of annual species is nevertheless impressive. Tree richness is poor, comprising only 35 species, but this paucity is offset by the presence of charismatic endemics such as bastard quiver tree (Aloe pillansii), quiver tree (Aloe dichotoma), and halfmens (Pachypodium namaquanum).

Levels of plant endemism are extremely high in the Succulent Karoo. Some 67 genera and 1,940 species are endemic to this ecoregion. Endemics are concentrated in four centers of endemism (three in the Namaqualand-Namib Domain and one in the Southern Karoo Domain) (Hilton Taylor 1994), although local and point endemics are found throughout the region (Desmet and Cowling 1999b).

The Gariep Center encompasses the Richtersveld and extends northwards into Namibia’s Sperrgebiet. This area is home to about 355 endemic species, and three endemic genera, namely Juttadinteria, Dracophilus, and Arenifera (Mesembryanthemaceae). This center of endemism and high species richness experiences large climatic variability, caused by coastal fogs, zones of local aridity due to rain shadow effects, and the combination of summer and winter rainfall. Together with local topographic variability, the variation in climate has produced a wide range of conditions and habitats that have resulted in the evolution of an extremely rich and endemic fauna and flora (Simmons et al. 1998). Included in this center are lichen fields that have the highest cover, density, and diversity of lichens in the world. Limited to a few fog-soaked coastal ridges with fine-grained soils, these bizarre communities include 29 species of lichens and 41 higher plants, including minute embedded succulents such as Fenestraria rhopalophylla, Lithops herrei (both Mesembryanthemaceae), and Euphorbia stapelioides.

The Kamiesberg Center, home to 86 endemics, includes the peaks and upper slopes of the Kamiesberg Massif. The predominant vegetation types are fynbos and renosterveld, and most of the endemics are geophytes, especially irids in the genera Babiana, Moraea, Romulea, and Lapeirousia. Endemic dwarf succulents include species of Cheiridopsis, Conophytum, and Lithops.

The Van Rhynsdorp Center, a large expanse of coastal plain with the Knersvlakte as its hub, includes at least 150 endemic species, most of which are dwarf succulents and geophytes (with new species discovered regularly). This center includes all ten species of Argyroderma and all three species of Oophytum (both Mesembryanthemaceae). As is the case with the aforementioned genera, most endemics, including several species in each of Conophytum, Tylecodon, and Crassula, are exclusively associated with quartz field habitats.

In the Southern Karoo Domain, the Little Karoo is recognized as a distinct center of endemism. Current estimates place the number of strict endemics between 200 to 300 species. As is the case throughout the Succulent Karoo, Mesembryanthemaceae are disproportionally over-represented among endemics (Cowling and Hilton-Taylor 1999). Endemic genera include Cerochlamys, Gibbaeum, and the monotypic Muirii and Zeuktophyllum. Glottiphyllum and Pleiospilos have their centers of species richness and endemism in the Little Karoo.

Succulent Karoo plant communities are extremely rich at both the local and regional scales (Cowling and Hilton-Taylor 1999). On average, 1,000 m2 plots support 74 species (with a range from 32 to 115 species). This is almost double the number recorded for Sonoran Desert communities, regarded as the most species-rich vegetation in North America. At the regional scale, from 10 km2 to 10,000,000 km2, the Succulent Karoo has almost four times the number of species as winter-rainfall deserts in North America. This extraordinarily high regional-scale richness is a consequence of high local richness (alpha diversity), high compositional turnover along environmental gradients (beta diversity), and high compositional change between equivalent environments along geographical gradients (gamma diversity) (Cowling et al. 1998).

The explosive speciation of the Mesembryanthemaceae, comprising approximately 1,800 species and 120 genera, is centered in the Succulent Karoo. This relatively recent phenomenon is probably unrivaled among angiosperms (Ihlenfeldt 1994). There has also been considerable diversification in many other succulent plant lineages, including the Crassulaceae (Crassula and Tylecodon), Aloaceae (Haworthia and Aloe), Apocynaceae (Stapelieae), and Euphorbia.

Pollinators, especially insects, have played a vital role in shaping flower morphology and thus driving speciation in the Succulent Karoo (Cowling and Pierce 1999). This is thought to be a consequence of pollinator limitation, which results from generally unsuitable conditions for insect activity during the cool and windy winter and spring flowering season. A good example of pollinator-driven speciation is the long-tongued flies Proseca peringuyei and Proseca sp. nov. (Nemestinidae) (Manning and Goldblatt 1996). With mouthparts up to 50 mm long, these hovering flies are the exclusive pollinators of 28 species of Geraniaceae and Iridaceae in the Namaqualand-Namib Domain. Strong convergence is seen in the corresponding lengths of the floral tubes and the mouthparts insect species.

The Succulent Karoo includes 851 Red Data Book plant species, 685 of which are endemic to this ecoregion (Hilton-Taylor 1996). Many of these species are endangered, largely because they occupy extremely small ranges. Others are becoming increasingly vulnerable to overgrazing, mining activities and illegal harvesting for horticulture. Charismatic species that have declining populations include halfmen, giant quiver trees, and Aloe ramossisima.

The fauna of the Succulent Karoo has a rich complement of endemics, especially among the arachnids, hopliniid beetles, aculeate Hymenoptera and reptiles (Vernon 1999). Fully 22 of the ecoregion’s 50 scorpion species are endemic. Monkey beetles (Rutelinae:Hoplini), largely endemic to southern Africa, are concentrated in the Succulent Karoo and are important pollinators of the flora (Goldblatt et al. 1998). So, too, are the Hymenoptera and masarine wasps, and colletid, fideliid, and melittid bees, all of which have centers of diversity and endemism in the ecoregion. The melittid bees include species of Rediviva, oil-collecters which exclusively pollinate species of Nemesia and Diascia (Scrophulariaceae) (Steiner and Whitehead 1990).

Approximately 15 amphibians are found in this ecoregion, including three endemics, Boulenger’s short-headed frog (Breviceps macrops), Namaqualand short-headed frog (B. namaquensis), and Bufo robinsoni. Among the region’s 115 reptile species, 48 are endemic and 15 are strict endemics. The genus Cordylus (spinytail lizards) includes six strict endemics. Other strict endemics are Broadley’s lance skink (Acontias litoralis), Richtersveld dwarf leaf-toed gecko (Goggia gemmula), Smith’s sand lizard (Meroles ctenodactylus), Calvinia thick-toed gecko (Pachydactylus labialis), Namaqua thick-toed gecko (P. namaqua), and Meyer’s legless skink (Typhlosaurus meyeri). The Sperregebiet region is a hotspot for endemic reptiles, including an unusual endemic tortoise, the Namba padloper (Homopus bergeri, VU) (Hilton-Taylor 2000).

Endemism is less pronounced among the Succulent Karoo’s bird and mammal faunas (Vernon 1999). Only five of the ecoregion’s 226 birds are endemic, the Karoo chat (Cercomela schlegii), Tractrac chat (Cercomela tractracs), long-billed lark (Certhilauda curvirostris), the bank cormorant (Phalacrocorax neglectus), and the recently described Barlow’s lark (Certhilauda barlowi) (Ryan et al. 1999). This strictly endemic bird has an extremely restricted distribution of only 18,000 km2, falling within the Sperregebiet region (Sinclair and Hockey 1996, Ryan et al. 1999). Only 7 out of the 78 mammals found in the ecoregion are endemic. Three are entirely restricted to the Succulent Karoo, including a subspecies of the pygmy rock mouse, Petromyscus collinus barbouri, Van Zyl’s golden mole (Cryptochloris zylii), and De Winton’s golden mole (Cryptochloris wintoni). The other species considered endemic include Namaqua dune molerat (Bathyergus janetta), river rabbit (Bunolagus monticularis), Cape golden mole (Chrysochloris asiatica), Grant’s golden mole (Eremitapia granti), and Brant’s whistling rat (Parotomys brantsii).

Current Status
Large tracts of the Succulent Karoo are still fairly intact, in spite of general overgrazing. The Little Karoo has seen the most transformation by agriculture due to the proximity of perennial streams draining into the major basin. Large tracts of the higher and hence wetter areas of the Namaqualand-Namib Domain have also been converted for agriculture.

Given its global significance as a biodiversity hotspot (Cowling and Pierce 1999), and its long-standing recognition as a regional conservation priority (Hilton-Taylor 1994, Rebelo 1997), the current conservation status of the Succulent Karoo is woefully inadequate. As of 1998, only 2,352 km2 or approximately 2 percent of its original extent was conserved in seven statutory reserves (Cowling and Lombard 1998). Larger reserves (greater than 100 km2) were located in only four of the Succulent Karoo’s 12 sub-regions and conserved only 80 plant species, or 9 percent, of the 851 species in the Red Data List of Southern African Plants (Lombard et al. 1999).

The Sperregebiet is enclosed in a Protected Diamond Area of 26,000 km2, which can be entered only by permit. This area has been sealed off from public access since 1910 and is therefore mostly undisturbed, with the only disturbance resulting from mining. Mining Area No. 1, the narrow coastal belt from the Orange River to Affenrucken (about 28°S), is the main area of disturbance and covers about 1 percent of the Sperregebiet. In this area, hummocks, which form wind barriers, have been completely removed. Their removal has allowed for excessive inland sand movement (Williamson 1997). Other areas that show a high level of disturbance are diamond valleys within the area. These valleys were mined by the old German diamond companies and have been completely stripped of their sparse vegetation cover. While the diamond mining areas are receiving protection by being highly restricted areas, this protection is only temporary. The lease for the Sperregebiet diamond mining area expires in 2020.

A game-proof fence was constructed along the eastern boundary of the Sperregebiet in 1989 by the then Department of Nature Conservation. This fence was seen as the only way to protect the gemsbok herds from poaching. This fence has prevented the eastwards migration of large mammals such as kudu (Tragelaphus strepsiceros) to the eastern Sperregebiet after times of good rain when this area becomes a lush grassland (Pallett 1995).

The overall conservation situation has improved recently with the establishment of the approximately 500 km2 Namaqua National Park and the initial phase of the Knersvlakte Nature Reserve (74 km2) in the Namaqualand-Namib Domain. The Anysberg Nature Reserve was recently expanded by more than 200 km2 and Groenefontein Nature Reserve (47 km2) was created in the Little Karoo (Southern Karoo Domain). Formal (statutory) reserves now cover 2.79 percent of the Succulent Karoo, including the multiple use Richtersveld National Park, where nomadic herders graze livestock, and the Goegab and Vrolikheid Nature Reserves. These initiatives have been directed by the outcomes of systematic conservation plans (Cowling and Lombard 1998, Desmet et al. 1999, Lombard et al. 1999).

Types and Severity of Threats
Although more than 90 percent of the Succulent Karoo is in a natural or semi-natural state where the principal form of land use is extensive pastoralism, much of this habitat has been severely degraded by overgrazing. Land-use practices that will further threaten the ecoregion’s biodiversity are listed below, in their order of importance.

•The expansion of communally-owned land and associated overgrazing and desertification.
•Overgrazing of commercial (privately–owned) rangelands.
•Agriculture, especially in the valleys of perennial rivers.
•Mining for diamonds, heavy minerals, gypsum, limestone, marble, monzite, kaolin, ilmenite, and titanium. For example, 65 percent of the Namaqualand coastline is or has been mined.
•Illegal and large scale collection of succulents and geophytes.
In addition, climate change is likely to have a major negative influence on the biodiversity of the Succulent Karoo, given the specialized habitat requirements of the numerous local and point plant endemics (Rutherford et al 1999).

Justification of Ecoregion Delineation
The northern and eastern (outer) boundaries are according to Low and Rebelo (1996) Succulent Karoo biome, which is, in turn, based on Rutherford and Westfall's (1986) biome concepts. The inner boundary (with the fynbos ecoregions) is according to Cowling and Heijnis’ (2001) delimitation of the Cape Floristic Region. This was established by concordant patterns of geology, topography, climate and, in some cases, vegetation types (sensu Low and Rebelo 1996). 

References
Barnard, P., C.J. Brown, A.M. Jarvis, and A. Robertson. 1998. Extending the Namibian protected areas network to safeguard hotspots of endemism and diversity. Biodiversity and Conservation 7: 531-547.

Cowling, R.M., and C.E. Heijnis. 2001. Broad Habitat Units as biodiversity entities for conservation planning in the Cape Floristic Region. South African Journal of Botany (in press).

Cowling, R.M. and A.T. Lombard. 1998. A strategic and systematic framework for conserving the plant life of the Succulent Karoo. IPC Report 9802 submitted to the Trustees of the Leslie Hill Succulent Karoo Trust. Institute for Plant Conservation, University of Cape Town.

Cowling, R.M., P.W. Rundel, P.G. Desmet, and K.J. Esler. 1998. Extraordinarily high regional-scale plant diversity in southern African arid lands: subcontinental and global comparisons. Diversity and Distributions 4: 27-36.

Cowling, R.M., K.J. Esler, and P.W. Rundel 1999b. Namaqualand, South Africa – an overview of a unique winter-rainfall desert ecosystem. Plant Ecology 142: 3-21.

Cowling, R.M. and C. Hilton-Taylor. 1999. Plant biogeography, endemism and diversity. Pages. 42-56 in W.R.J. Dean, and S.J. Milton, editors. The Karoo: ecological patterns and processes. Cambridge University Press, Cambridge.

Cowling, R.M. and S.M. Pierce. 1999. Namaqualand. A succulent desert. Fernwood Press, Cape Town.

Cowling, R.M., R.L. Pressey, A.T. Lombard, P.G. Desmet, and A.G. Ellis. 1999a. From representation to persistence : requirement for a sustainable reserve system in the species rich mediterranean-climate deserts of southern Africa. Diversity and Distributions 5: 1-21.

Desmet, P.G. and R.M. Cowling. 1999a. The climate of the karoo – a functional approach. Pages 3-16 in W.R.J. Dean and S.J. Milton, editors. The Karoo: ecological patterns and processes. Cambridge University Press, Cambridge.

Desmet, P.G. and R.M. Cowling. 1999b. Biodiversity, habitat and range-size aspects of a flora from a winter rainfall desert in north-western Namaqualand, South Africa. Plant Ecology 142: 23-33.

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Prepared by: Shirley Cowling
Reviewed by: In progress

 

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