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Ecoregion Description


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Species Richness


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574: Drakensberg - Maloti Highlands

Major Habitat Type:

montane freshwaters

Author:

Belinda Day, Freshwater Research Institute, Zoology Department, University of Cape Town, South Africa

Reviewers:

Paul Skelton, South African Institute for Aquatic Biodiversity (formerly J.L.B. Smith Institute of Ichthyology), South Africa

Countries:

Lesotho; South Africa

Boundaries:

The Drakensberg-Maloti Highlands are highly valued in southern Africa for their rivers’ excellent water quality and high water yield. These rivers provide water to large areas of xeric South Africa. The ecoregion encompasses the whole of Lesotho, excluding the westernmost lowland areas. It also includes small parts of South Africa just south and north of Lesotho.

Main rivers or other water bodies:

The ecoregion is heavily dissected by many small streams, most of which comprise the headwaters of the Senqu/Orange River, which is the largest catchment in the ecoregion. These rivers have eroded deep gorges through the overlying basalts and into the sandstones, and the resulting cliffs and valleys can be in excess of 1,000 m deep (Barnes 1998). The Senqu rises in the northeast and is joined by a number of tributaries in the highlands (the Senqunyane, Malibamatso, Sinqa, Makhaleng, Matsoku, and Khubela Rivers) before it flows southwest through the lowlands of Lesotho. Known as the Orange in South Africa, the river then flows westward through semi-arid and arid lands and empties into the Atlantic Ocean. The headwaters of a number of short, eastward-flowing rivers (the Tina, Keneka, Umzimvubu, Umzimkulu, and Umkomaas) also arise in the highlands (Lesotho Government 2000). 

Topography:

The whole of the ecoregion lies above 1,850 m asl and slopes upwards towards the east, where the border with the KwaZulu-Natal province of South Africa forms the rim of the southern African plateau. The steep formations along the uplifted edges of the plateau make up the Great Escarpment, of which the Drakensberg comprises the eastern portion. Within this ecoregion, the highest part of the Drakensberg Escarpment forms a ridge at a height of over 3,000 m, with spectacular drops of between 500 and 700 m (Hughes & Hughes 1992).

The terrain of the highlands ranges from undulating hills to rugged peaks and headlands intersected by deep valleys and ravines. The highest peak in southern Africa, Thabana-Ntlenyana (3,482 m), is located in this ecoregion, and the whole of the eastern half of Lesotho lies above 2,440 m (Hughes & Hughes 1992; Barnes 1998). The mountains and peaks of the Lesotho Highlands above 2,300 m consist of basalts, extruded approximately 180 million years ago during a massive series of tectonic events. Underlying the basalts are horizontal sedimentary strata topped by soft sandstones (Barnes 1998).

Climate:

The climate is temperate and strongly seasonal, with extreme temperatures of -20oC in winter and 31oC in summer recorded on the mountain peaks. The weather is also prone to sudden changes (Jacobsen 1999). The ecoregion receives summer rainfall (October to March), but precipitation is highly variable, both spatially and temporally. Mean annual rainfall averages between 1,300 and 1,900 mm per annum in the highlands, with figures of 2,000 mm recorded on the highest mountain peaks in the east. Winters are cold and extremely dry, though snow and frost are common in the eastern mountains from April to September. On most afternoons mists move westwards down from the Drakensberg Escarpment onto the highland slopes (Hughes & Hughes 1992; Barnes 1998).

Freshwater habitats:

The streams of this ecoregion tend to be steep (dropping up to 1,200 m in 60 – 70 km) and fast-flowing. Upon reaching the foothills and lowlands in the west, the rivers slow down and widen, often forming small floodplains and marshes (Hughes & Hughes 1992).

Pans (areas without external drainage, some of which seasonally dry out), marshes (often with reedbeds), tarns (shallow pools and pans that typically form on sandstones), and bogs and sponges (some of which have been re-classified as midslope and valleyhead fens) are common in the highlands (Lesotho Government 2000). They are especially prevalent in the northeast, where rainfall is highest, and decrease in both size and frequency to the south and west. Most occur in the soft sandstone of the alpine regions above 2,300 m. Bogs and sponges collectively cover thousands of hectares but most are individually small (Hughes & Hughes 1992; Barnes 1998). They are found at all altitudes, wherever there is a continuous or semi-continuous source of water. This distribution extends to extremely high altitudes, such as on the plateau along the rim of the Drakensberg Escarpment and on summits of peaks such as Thabana Ntlenyana. Pans are found in a few places in the highveld grasslands both at lower altitudes and on several of the plateaus, whereas marshes are less common due to harvest of reeds. Marshes remain at Tebeteben, Mohlaka-oa-tuka, and Koro-Koro (Lesotho Government 2000). Tarns occur in depressions in soft sandstones, such as those found in the Sehlabathebe National Park (Hughes & Hughes 1992).

The Drakensberg-Maloti Highlands contain rare examples of Afromontane and Afro-alpine rivers and other wetlands (Lesotho Government 2000). The high altitude wetlands found in this ecoregion have limited occurrences in the Eastern Cape and are found nowhere else in southern Africa (Wetlands International 2002).

Terrestrial Habitats:

The Drakensberg-Maloti Highlands ecoregion falls within the Afromontane and Afro-alpine bioregions (Stuart et al. 1990). The Lesotho Government (2000) classifies the vegetation into three types: Highveld grassland (1,400 – 1,800 m), Afromontane grassland (1,800-2,500 m), and Afroalpine grassland (above 2,500 m). Each of the various types of wetlands in the ecoregion is characterized by a different vegetation community. For example, montane sandstone pools are characterized by aquatic species such as Limosella spp., Utricularia spp., Ilysanthes confertiflora, and Aponogeton ranunculiflorus, whereas gravel-filled pools tend to support Crassula galpinii. Crassula natans, Aponogeton spathaceum, and Limosella maior are found in sandstone pools in the foothills.

Fish Fauna:

There are ten fish species in the ecoregion, not including introduced rainbow and brown trout (Oncorhynchus mykiss, Salmo trutta), among other introduced fish species. Other fish species include Barbus aeneus, B. kimberleyensis, B. anoplus, Labeo capensis, L. rubromaculatus, L. umbratus, Anguilla mossambica, Clarias gariepinus and Austroglanis sclateri. The rock catfish (A. sclateri) is considered to be a rare/intermediate species (Lesotho Government 2000).

Description of endemic fishes:

The only endemic, the Maloti minnow, Pseudobarbus quathlambae, is known only from six high-altitude tributaries of the Orange River. It is critically endangered due to habitat degradation and alteration, and competition with and predation by alien trout species (Stuart et al. 1990; Rall & Skelton 2001).

Other noteworthy aquatic biotic elements:

The wetland fauna of this ecoregion is depauperate in comparison to other large river catchments in southern Africa, in part as a result of a long history of disturbance and human use (Jacot-Guillarmod 1963)(Jacot-Guillarmod 1963; Du Plessis 1969 as cited in Ferreira 1999). There are no records of the historical distribution of the aquatic fauna of Lesotho, thus it is impossible to accurately estimate changes in biodiversity or abundance, although it is certain that there has been a reduction in abundance and extirpations may have occurred (Jacobsen 1999). Furthermore, very few studies have investigated population size, distribution, life history, or habitat requirements of the wetland fauna, particularly the invertebrates. What is known about the invertebrates, however, indicates that in contrast to the vertebrates, they may be very rich in species and include montane palaeogenic representatives. For example, there are 23 species of odonates in the ecoregion, including the endemic Chloroestes draconicus (Samways, personal communication). Little has been published about the levels of endemism of wetland plant species but the aquatic species Aponogeton ranunculiflorus is endemic to the ecoregion (Jacobsen 1999).

There are only a few large wetlands in the Drakensberg-Maloti Highlands that can support a diversity of wetland birds, with the result that there are only twelve water-dependent bird species. Two riverine mammals (the marsh mongoose, Atilax paludinosus, and the Cape clawless otter, Aonyx capensis (Ferreira 1999) live in the rivers of this ecoregion.

The Drakensberg-Maloti Highlands ecoregion is rich in amphibians at all altitudes. Jacobsen (1999) postulates that the high rainfall and diversity of aquatic habitats contribute to the high species count. Twenty-one aquatic-dependent frogs are known from this ecoregion, of which three are endemic and several are near-endemic. These restricted-range species include Rana vertebralis, R. dracomontana, Strongylopus hymenopus, Arthroleptella hewitti, and Heleophryne natalensis (Stuart et al. 1990; Jacobsen 1999). According to the Lesotho Government (2000), the aquatic or umbraculate river frog, Rana vertebralis, and the Lesotho or Drakensberg river frog, Rana dracomontana, are imperiled. Four species of snake are often found in wetland habitats in the Drakensberg-Maloti Highlands, but the only true wetland species is the common brown water snake, Lycodonomorphus rufulus.

Justification for delineation:

The delineation of this ecoregion follows the boundaries of the Drakensberg-Maloti Highlands and comprises the middle sub-region of the Montane-escarpment aquatic region (Skelton 1993). The Drakensberg-Maloti Highlands are a residual portion of the peripheral uplands of the Great Escarpment that has progressively been eroded and dissected northward and westward by the rivers on the southern and eastern southern African coasts (Truswell 1977; Corbett 1979 in Skelton 1986) (Trusw. Relict fauna and flora of Afromontane species are present in the highlands and a comprehensive treatment of the fish biogeography of the region is presented by Skelton (1994)(Skelton 1994).

Level of taxonomic exploration:

Little is known about the historical distribution, habitat requirements, biology, or life history of most of the wetland taxa, particularly the invertebrates, in the Drakensberg-Maloti Highlands. It seems likely however, from the results of the few taxa that have been studied, that further investigation may reveal a diverse fauna that could include endemic or relict species. As many of the taxa in Lesotho are seriously threatened, it is essential that research, monitoring, and conservation are made a priority before ecosystems are permanently degraded and destroyed.

References/sources:

Barnes, K. N. (1998)"Important Bird Areas of Lesotho" In Barnes, K.N. (Ed.). The important bird areas of southern Africa. (pp. 281-294) Johannesburg, South Africa: BirdLife International.

Ferreira, S. (1999) "Specialist report: Wildlife and birds. Consultancy Report No: LHDA 648-F-19 (Vol 1). Consulting Services for the Establishment and Monitoring of the Instream Flow Requirements for River Courses Downstream of LHWP Dams". Lesotho. Metsi Consultants and Lesotho Highlands Water Project for the Lesotho Highlands Development Authority.

Hughes, R. H.,Hughes, J. S. (1992). "A directory of African wetlands" Gland, Switzerland, Nairobi, Kenya, and Cambridge, UK: IUCN, UNEP, and WCMC.

Jacobsen, N. (1999) "Specialist report: Herpetofauna. Consultancy Report No: LHDA 648-F-19 (Vol 2). Consulting services for the establishment and monitoring of the instream flow requirements for river courses downstream of LHWP dams". Lesotho. Metsi Consultants and Lesotho Highlands Water Project for the Lesotho Highlands Development Authority.

Jacot-Guillarmod, A. (1963). "Further observations on the bogs of the Basutoland Mountains" South African Journal of Science 58(6) 179-182.

Lesotho, Government (2000) "Biological diversity in Lesotho: A country study". Maseru, Lesotho. National Environment Secretariat.

Rall, J.,Skelton, P. H. (2001) "Conservation of the Maloti minnow (Phase 1): Distribution and conservation status. Final report, contract 1041". Maseru, Lesotho. Lesotho Highlands Development Authority.

Skelton, P. H. (1993) A complete guide to the freshwater fishes of Southern Africa. South Africa: Southern Book Publishers, Halfway House.

Skelton, P. H. (1994). "Diversity and distribution of freshwater fishes in East and Southern Africa" Annals of the Royal Central Africa Museum (Zoology) 275 95-131.

Skelton, P. H. (1986). "Distribution patterns and biogeography of non-tropical southern African freshwater fishes" , Rotterdam.

Stuart, S. N., Adams, R. J., et al. (1990) Biodiversity in Sub-Saharan Africa and its islands: Conservation, management and sustainable use, Occasional Papers of the IUCN Species Survival Commission No. 6. Gland, Switzerland: IUCN.

Truswell, J. F. (1977). "The geological evolution of South Africa" Cape Town, South Africa: Purnell.

Wetlands, International (2002) "Ramsar Sites Database: A directory of wetlands of international importance" <http://www.wetlands.org/RDB/Ramsar_Dir/_COUNTRIES.htm>(2003)

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