Location and General Description
South African thickets are similar in structure and generic composition to the thicket communities found throughout tropical and subtropical Africa (White 1983; Cowling 1984). Structurally, a predominance of evergreen, sclerophyllous species and a high cover of succulent shrubs distinguish the South African thickets from other African thicket types, which often have a strong component of orthophyllous, deciduous species. Albany thicket is easily distinguished from the complex mosaic of surrounding ecoregions as a dense, spiny shrubland rising about 2 to 2.5 m, dominated by succulents (mainly of Karooid affinity).
The ecoregion occurs along the Fish, Sundays, and Gamtoos river valleys in the eastern Cape and moves west along the intermontane valleys of the inland Fold Mountains (Kouga, Baviaanskloof and Swartberg). Towards the east, it grades into Maputaland-Pondoland Bushland and Thicket, a sparser scrub forest up to 6 m tall. The Maputaland-Pondoland Bushland and Thicket is less spinescent and less succulent, comprised of more grasses, and dominated by subtropical woody evergreen species.
The east-trending axes of the Cape Fold Belt sink beneath the sediments of the Karoo Supergroup in the eastern Cape (Du Toit 1966). Tertiary planation greatly subdued the topography of the Folded Belt, resulting in a fairly level basin, which is broken by the wide, deep valleys of the Fish, Sundays, and Gamtoos rivers. These wide valleys are the predominant geological feature of the Albany Thicket ecoregion. The soils of these valleys are well-drained, deep, lime-rich, sandy loams derived from the Uitenhage and Ecca Group shales (Low and Rebelo 1996). Towards the coast, the soils may include consolidated dune sands, with the densest thickets occuring on the deepest sandy loams. It is thought that this may be one of the factors responsible for the confined distribution of the Albany Thicket (Cowling 1984). To the west of the Sundays River are rugged quartzite mountains typical of the Cape Folded Belt. The soils of the intermontane valleys are well-drained, colluvial sandy loams that are slightly shallower than the river valley soils. They are derived from sandstone, quartzite, and shale substrata.
The Fish, Sundays, and Gamtoos river valleys are harsh environments, with high diurnal and annual temperature ranges and low, sporadic rainfall (Cowling 1983). The inland areas of these valleys are arid with non-seasonal, sporadic rainfall from 300 to 450 mm per year. The three summer months (December to February) are the driest. Annual temperatures in these inland valleys are extreme, ranging from 0oC to more than 40oC. The coastal areas of the valleys have a more moderate climate with a temperature range from 10oC to 35oC and a slightly higher annual rainfall of 450 to 550 mm per year. Valley mists are common towards the coast, providing additional moisture. The intermontane valleys have moderate temperatures, although extremes may be experienced for short periods. These valleys fall within a rain shadow, resulting in a low annual rainfall of 250-300 mm per year (Low and Rebelo 1996).
The vegetation of the Albany Thicket ecoregion can be divided into three regions: the dry, inland areas of the Fish, Sundays, and Gamtoos river valleys; the more moderate coastal areas of these river valleys; and the intermontane valleys to the north and west. The thickets of the Fish, Sundays, and Gamtoos river valleys are sparse, succulent and spinescent. The vegetation contains a high proportion of both leaf and stem-succulent shrubs such as Spekboom (Portulacaria afra), Euphorbia bothae (dominant along the Fish River Valley), Euphorbia ledienii and Noorsdoring (Euphorbia coerulescens) (dominant along the Sundays River Valley). Characteristic woody species include the Karoo cross-berry (Grewia robusta), small bitterleaf (Brachylaena ilicifolia), Maytenus capitata, and Lycium campanulatum. This inland valley thicket vegetation has been classified as Valley Bushveld and Noorsveld by Lubke et al (1986), Xeric Kaffrarian Succulent Thicket by Everard (1987) and Xeric Succulent Thicket by Low and Rebelo (1996).
The thickets of the coastal areas of the Fish, Sundays and Gamtoos river valleys are extremely dense and often impenetrable, with a canopy cover of about 90 percent. These species-rich, dense thickets are composed of spinescent shrubs, woody creepers and succulents. Characteristic succulent species include the Uitenhage aloe (Aloe africanai), bitter aloe (Aloe ferox), Euphorbia ledienii, and Euphorbia grandidens. Common woody species are white milkwood (Sideroxylon inerme), dune kokotree (Maytenus procumbens), and Septemberbush (Polygala myrtifolia). This coastal valley thicket vegetation has been classified as coastal Kaffrarian succulent thicket by Everard (1987) and as Mesic succulent thicket by Low and Rebelo (1996).
The thicket vegetation of the intermontane valleys to the north and west of the ecoregion is a dense shrubland dominated by Spekboom (Portulacaria afra). Other species include Kerky bush (Crassula ovata), large honeythorn (Lycium austrinum), jacketplum (Pappea capensis), Euclea undulata, Rhizogum obovatum, Grewia robusta, Aloe spp., R hus spp., and Schotia afra. Many species of Plakkies (Crassula spp.) as well as succulent herbs and grasses also occur. Towards the western limits of the ecoregion Spekboom becomes overwhelmingly dominant and can form pure stands. This intermontane valley thicket vegetation is called Spekboomveld by Acocks (1953) and Lubke et al. (1986) and Spekboom succulent thicket by Low and Rebelo (1996).
The distribution of Albany thicket communities is determined by a complexity of interrelated factors. The most important of these appears to be soil type. Albany Thicket is restricted to deep, well-drained, fertile sandy loams with the densest thickets occurring on the deepest soils (Cowling 1984). Soil moisture is another important limiting factor. The vegetation is adapted to grow in hot, dry river valleys where soil moisture is limited for extended periods. Soil moisture increases towards the east, resulting in thickets that are more open, less succulent and less thorny. They include more grasses and more subtropical species. The thickets then grade into the Maputaland-Pondoland Bushland and Thicket, which in turn grades into forest and savanna. Towards the west, the thickets become sparse, highly succulent and spiny (xeric thickets), eventually grading into the open shrublands of the succulent Karoo.
Thickets are similar to forests in that their distribution is restricted to fire-protected sites such as river valleys, screes and ravines (Trollope 1974). Large browsers such as elephant (Loxodonta africana), rhinoceros (Diceros bicornis, Ceratotherium simum) and greater kudu (Tragelaphus strepsiceros) have historically played a part in limiting its spread. Where large browsers have been removed from the system, thicket is becoming invasive and is spreading into other vegetation types in the Eastern Cape (particularly into savanna and grassland) (Low and Rebelo 1996). Yet, thicket communities have low resilience. They regenerate slowly after disturbance and are eliminated if these disturbances occur at intervals of less than a few decades.
The Eastern Cape (defined broadly as the area south of 31oS and between 24oE and 29oE) has long been recognized by botanists as being a complex transition zone where four major phytochoria converge (Goldblatt 1978, Gibbs Russell & Robinson 1981, White 1983, Cowling 1983, Cowling and Hilton-Taylor 1994, Lubke et al. 1986). It has major climatic, topographic and geological variation on a fine scale and is the meeting point of a mix of taxa reaching the limits of their distributions. Tongaland-Pondoland forests and thickets enter the region along the coast and penetrate up the river valleys. Succulent and dwarf shrublands of the Karoo-Namib phytochorion extend down the dry river valleys from the arid interior. Because of increased latitude compensating for elevation, Afromontane elements are found at sea level, especially in the southwest where the coastal forests are almost entirely composed of Afromontane species. Fynbos taxa of the Cape Region occur on the infertile sandy soils derived from Cape supergroup rocks.
The Nama-Karoo, the Highveld Grassland, the Drakensberg Montane Grassland, Woodland and Forest, the KwaZulu-Cape Coastal Forest Mosiac, the Maputaland-Pondoland Bushland and Thicket, the Knysna-Amatole Montane Forest and the Montane Fynbos and Renosterveld all converge in the Eastern Cape. This mosaic of ecoregions provides a mix of taxa in the area, giving the Eastern Cape a very high level of species richness and diversity. The area, however, represents the distribution limits for most of these ecoregions, which have their centers elsewhere in South Africa. Consequently, the Eastern Cape is a region of low endemism and biological distinctiveness relative to rich endemic centers such as the Cape Floristic Region (73 percent of flora is endemic) and the Namib Desert (35 percent of flora is endemic). The diversity of taxa in the Eastern Cape is due, therefore, to combinations of species from different phytochoria meeting at the ends of their distribution ranges, and is not a result of speciation taking place in the area (Cowling 1984). In contrast, Albany Thicket, which is confined to the Eastern Cape, contains high levels of endemism and is recognized as a Center of Plant Diversity (WWF and IUCN 1994). Albany Thicket is species-rich (as a result of the mix of converging taxa) and ranks as an important center of endemism for the Karooid succulent flora (Lubke et al. 1986). Endemic succulents include sheep fig (Delosperma echinata), Delosperma ecklonis, Lampranthus productus, Euphorbia fimriata, Euphorbia gorgonis, Gasteria armstrongii, Aloe africana, Senecio pyramidatus and Haworthia fasciata (Cowling 1983).
Croizat (1965) recognized the Albany area as a center of endemism for succulent Euphorbia species, with 14.5 percent of southern African Euphorbia species being confined to this area. The Albany area is also a center of endemism for certain geophytes including Cyrtanthus, Albuca and Ornithogallum (Cowling 1983). The succulent Karooid elements have had a lengthy history in the Eastern Cape valleys. It was only during the onset of a warmer, wetter Holocene climate (after the last glaciation, 12,000 years ago) that the valleys were invaded by subtropical and Cape taxa. The low annual rainfall of this ecoregion is an important constraint on the southwards migration of subtropical flora. Only those species with long-lived sclerophyllous leaves (e.g. Sideroxylon, Euclea, Cassine, Diospyros) have penetrated the region, and of these, only a few are endemics. The full list includes Cussonia gamtooensis, Cassine reticulata, Rapanea gilliana and Smellophyllum capense. Both soil and climatic barriers restrict the northward migration of the Cape flora, with the flora closely following infertile, sandy soil distributions and a winter rainfall pattern. There are few endemics of Cape origin in the Albany Thicket. The Albany Thicket has a total of 61 endemic plant species (of which, 31 are threatened). Most of these are found in the mesic thicket type, which has the highest percent endemism (9.2 percent) of the three thicket types.
While the Albany Thicket is an important center of floral endemism, its level of faunal endemism is relatively low. It has two near-endemic bird species, the orange-breasted sunbird (Nectarinia violacea) and the Cape siskin (Serinus totta), and one near-endemic mammal, Duthie’s golden mole (Chlorotalpa duthieae). There are no endemic amphibians, but six reptile species are considered to be strictly endemic, including Tasman’s legless skink (Acontias tasmani), Tasman’s girdled lizard (Cordylus tasmani), and the snake Bitis albanica.
The ecoregion has a relatively low level of faunal species richness. The mammalian fauna of the Albany Thicket is characterized by different species of antelope including bushbuck (Tragelaphus scriptus), grey rhebok (Pelea capreolus), mountain reedbuck (Redunca fulvorufula), eland (Taurotragus oryx), greater kudu (Tragelaphus strepsiceros), red hartebeest (Alcelaphus buselaphus), cape grysbok (Raphicerus melanotis) and common duiker (Sylvicapra grimmia). It is also home to birds which occur in both forest and thicket habitats, for example the gymnogene (Polyboroides typus), the knysna lourie (Tauraco corythaix), the black sparowhawk (Accipiter melanoleucus), Klaas’s cuckoo (Chrysococcyx klaas), the blackheaded oriole (Oriolus oriolus) and a number of doves including the red-eyed, laughing and green-spotted dove (Streptopelia semitorquata, S. senegalensis, Turtur chalcospilos).
According to Low and Rebelo (1996), about 51 percent of the Albany Thicket has been transformed to other land uses. These include goat farming, crop production and urban expansion. Crop production and urban expansion are both highly destructive land uses, causing large-scale habitat loss and consequently, habitat fragmentation. These two land-use transformations mainly affect the mesic thicket vegetation type, which occurs in the coastal areas of the Fish, Sundays, and Gamtoos river valleys. The mesic thicket is under severe threat and is suffering major habitat fragmentation. This is a major threat to the conservation of taxa in the Albany Thicket ecoregion because the mesic thicket has the highest levels of species richness and diversity and the highest level of endemism of the three thicket types. The xeric thickets of the dry inland valleys and the Spekboomveld of the intermontane valleys are largely intact. The major land-use activity in these areas is goat farming, which may lead to habitat degradation, but does not cause direct habitat loss or fragmentation. The human population in these inland areas is low, and consequently there is little or no urban expansion to threaten these habitats.
The xeric thickets of the inland river valleys are well protected within the Addo Elephant National Park (Greyling and Huntley 1984). This park, which covers an area of 513 km2, is home to 120 elephants (Loxodonta africana, EN), 15 black rhinoceroses (Diceros bicornis, CR) and many antelope. The Groendal wilderness area, which was established in 1896, is situated 15 km from Uitenhage on the Swartkops River. This reserve is important because it contains an area of the threatened mesic thicket vegetation type. It also contains three animal species which are threatened in South Africa: leopard (Panthera pardus), blue duiker (Cephalophus monticola), and the samango monkey (Cercopithecus mitis). The Kouga/ Baviaanskloof Mountain Catchment Area includes the Baviaanskloof Valley, which contains a large area of dense Spekboomveld. Leopards are also present in this protected area. The Silaka Wildlife Reserve (4 km2) and the Kabeljousriver Nature Reserve (2 km2) are of less importance because of their small size.
These conservation areas contain each of the three thicket types recognized within the Albany Thicket ecoregion. This may be adequate for the xeric thickets and Spekboomveld vegetation types as they are not under serious threat from land-use transformations. The existing reserves are, however, not adequate for the mesic thickets which are the most important vegetation type in terms of species richness, endemism and potential threats. Conservation areas need to be established in the larger mesic thicket habitat blocks, for example along the coastal areas of the Fish, Sundays or Gamtoos river valleys. It should also be noted that the most inland areas of the river valleys (the portion of the xeric thicket identified as "Noorsveld" by Acocks (1953)) are not represented in any of the conservation areas. These areas contain highly succulent xeric thickets that grade into the Succulent Karoo in the north.
Types and Severity of Threats
Lubke et al. (1986) rated Albany Thicket as highest among the plant communities of the eastern Cape in order of priority for conservation, on the basis of conservation status of the plants, the percentage of the vegetation under conservation, uniqueness of the vegetation, and threat. It is considered to be the most threatened vegetation type in the eastern Cape, containing 125 threatened species. Within the Albany Thicket, the mesic thicket vegetation type has the highest number of threatened species.
Goat farming and overgrazing has lead to the reduction of plant cover (and therefore erosion) and to changes in species composition within thicket communities. These effects are most noticeable in the more arid areas (xeric thickets and Spekboomveld). It is estimated that about 1,500 km2 of thicket in the Uitenhage District is so badly overgrazed that it will never recover (Everard 1988). Bush-clearing for crop cultivation is another major threat to the Albany Thicket vegetation. Land has been cleared along the rivers, and lucerne and other crops are grown under irrigation. Land has also been cleared for orange orchards in the Addo region. The mesic thicket type is under the most threat from bush-clearing. This thicket type is extremely dense, making it unsuitable for goat farming, and as a result clearing for agriculture is the main land-use activity.
The mesic thickets are also under threat from urban expansion and resort developments along the coast. In addition, collectors exploit the high succulent diversity and high numbers of endemic succulents in the mesic thickets. Euphorbia species and species of the Mesembryanthemaceae are under particular threat from plant collectors.
Justification of Ecoregion Delineation
This ecoregion occurs along the Sundays, Gamtoos, and Fish River valleys in the Eastern Cape, as well as mountain slopes in the eastern portion of the Western Cape. The linework delineates portions of Low and Rebelo’s ‘mesic thicket,’ ‘xeric succulent thicket,’ and ‘Spekboom succulent thicket,’ with further refinement of the lines made to follow those Broad Habitat Units (BHUs), within the Cape Floristic Region, that are associated with thicket vegetation (Cowling and Heijnis 2001). BHUs are surrogates for plant and animal biodiversity that were identified on the basis of concordant patterns of geology, topography, climate and, in some cases, vegetation types (sensu Low and Rebelo). Albany Thicket is comprised of Gamtoos mesic succulent thicket, Sundays mesic succulent thicket, Aloes mesic succulent thicket, Spekboom xeric succulent thicket, Willowmore xeric succulent thicket, Addo xeric succulent thicket, and Alexandria Indian Ocean forest BHUs.
Acocks, J.P.H. 1953. Veld Types of South Africa. Memoirs of the Botanical Survey of South Africa 28.
Cowling, R.M. 1983. Phytochorology and vegetation history in the south-eastern Cape, South Africa. Journal of Biogeography 10: 393-419.
Cowling, R,M. 1984. A syntaxonomic and synecological study of the Humansdorp region of the Fynbos Biome. Bothalia 14: 283-298.
Cowling, R.M. and C. Hilton-Taylor. 1994. Patterns of plant diversity and endemism in South Africa: an overview. In Botanical Diversity in Southern Africa. Pages 31-52 in B.J. Huntley, editor. Strelitzia 1. Pretoria: National Botanical Institute.
Croizat, L. 1965. An introduction to the subgeneric classification of Euphorbia L. with stress on the South African and Malagasy species. Webbia 20: 573-706.
Du Toit, A.L. 1966. The geology of South Africa. 3rd edition. Edinburugh & London: Oliver and Boyd.
Everard, D.A. 1987. A classification of the subtropical transitional thicket in the eastern cape, based on syntaxonomic and structural attributes. South African Journal of Botany 53(5): 329-340.
Everard, D.A. 1988. Threatened plants of the eastern Cape: a synthesis of collection records. Bothalia 18(2): 271-277.
Gibbs Russell, G.E. and E.R. Robinson. DATE. Phytogeography and speciation in the vegetation of the Eastern Cape. Bothalia 13:467-472.
Goldblatt, P. 1978. An analysis of the flora of southern Africa: it’s characteristic, relationships and origins. Annals of the Missouri Botanical Garden 65: 369-436.
Greyling, T. and B.J. Huntley. 1984. Directory of southern African conservation areas. South African National Scientific Programmes Report 98.
Hall, A.V., M. De Winter, B. De Winter and S.H.M. Van Oosterhout. 1980. Threatened Plants of Southern Africa. South African National Scientific Programmes Report No. 45.
Low, A.B. and A.G. Rebelo, editors. 1996. Vegetation of South Africa, Lesotho and Swaziland. Department of Environmental Affairs and Tourism, Pretoria.
Lubke, R.A., D.A. Everard, and S. Jackson. 1986. The biomes of the eastern Cape with emphasis on their conservation. Bothalia 16(2): 251-261.
Trollope, W.S.W. 1974. Role of fire in preventing bush encroachment in the eastern Cape. Proceedings of the Grassland Society of Southern Africa 9: 67-72.
White, F., editor. 1983. Vegetation of Africa. Paris: UNESCO/AETFAT/UNSO
WWF and IUCN. 1994. Davis, S.D., V.H. Hayward and A.C. Hamilton, editors. Centres of Plant Diversity: A Guide and Strategy for their Conservation. Volume 1. Europe, Africa, Southwest Asia and the Middle East. Cambridge: IUCN Publications Unit.
Prepared by: Amy Spriggs
Reviewed by: In progress