Description
Location and General Description
Distributed in a narrow band along the eastern South African coastline, this ecoregion represents the coastal tropical and subtropical forest of South Africa. It extends from Cape St Lucia (about 32°E), south along the eastern narrow coastal plain to Cape St Francis (26°S 33°E). Its inland boundary lies at the foothills of the Drakensberg Escarpment, from 450 m in elevation in the north, dropping to about 300 m in the south (Acocks 1953).
Topography in the north is steeply rolling, forming a maze of deep ridges between rivers. There are few rocky outcrops and soils are stable with very little erosion. Dunes, estuaries and woodlands are all represented in this ecoregion (Geldenhuys 1992). As one moves south, woodlands tend to become less frequent as coastal platforms and gorges become more prevalent. There are deep rocky valleys in some areas but on the whole the south is less steep. The frost-free coastal plain of Kwazulu-Natal contributes to the forest’s subtropical nature. In the southern portion of this ecoregion, frosts occur but maritime influences modify both winter and summer temperature regimes. Mean maximum temperatures range between 15° and 24°C, and mean minimum temperatures between 10° and 15°C.
Coastal forest is confined to higher rainfall areas, receiving between 900 mm to1,500 m per annum. The northern extent receives more rain, primarily in the summer, while the south has lower rainfall, falling predominantly in the winter. The combination of high rainfall, inland proximity to the towering Drakensberg escarpment, Grootwinterhoek and Baviaanskloof Mountains, and the relatively narrow coastal plain, results in many large rivers bisecting the ecoregion. There are 18 large rivers flowing through valleys to the coast, from the Umfolozi in the extreme north to the Gamtoos in the south. River number and size decreases southwards as the coastal plain broadens and climate becomes more mesic. The rivers further south tend to be narrower, flowing in steep river gorges.
Coastal forest develops on deep, consolidated, calcareous sands with poor soil development (Lubke and McKenzie 1996). Soils are generally alkaline and range from medium to coarse-grained. The underlying lithology of KwaZulu-Cape Coastal Forest Mosaic predominantly includes sediments of the Karoo sequence interspersed by islands of Natal Group sandstones, and basement rocks (granites, gneisses, and schists). At the northernmost limits KwaZulu-Cape Coastal Forest Mosaic is found on ancient Precambrian rocks (Moll and White 1978). Inland and southwards, these are replaced by Cretaceous rocks. At the coast, these basal layers are overlain by calcareous Quaternary sands (composed of Cretaceous and Caenozoic marine sediments), forming dunes (Moll and White 1978). Coastal dune soils are sandy, with sand deposition and erosion roughly in equilibrium. Further inland, dunes sands tend to have higher clay content and support taller forests (Tinley 1985). Geldenhuys (1992) typifies the geology of this region as being mostly dune sands, alluvium (mud), and river in the north, but consisting of dune sands, shale, mudstone, and dolerite towards the south.
Forest species have a wide distribution in southern Africa (Palgrave 1977) and fall into two main floristic regions: the Tongaland-Pondoland forests of the Indian Ocean Coastal Region and the Afromontane forests of the Drakensberg escarpment, Natal and eastern Cape midlands, the southern and southwestern Cape mountains, and coastal plateau. The vegetation of KwaZulu-Cape Forest Mosaic consists of the narrower (minimum 8 km), southern part of Moll and White’s (1978) Tongaland – Pondoland regional mosaic. This regional mosaic is part of a greater Indian Ocean Coastal Belt extending down from the extreme southeastern corner of Somalia. The composition of the flora of the KwaZulu-Cape coastal forest mosaic, and the affinities of the species, is related to changes in the rainfall that tends to decline to towards the south. In addition, the generally colder temperatures of the southern portion limit distribution of subtropical species such as Natal wild banana (Strelitzia nicolai) that grows down near Port Elisabeth.
The KwaZulu-Cape Coastal Forest Mosaic vegetation grades into the more mesocline vegetation of Maputaland-Pondoland Bushveld and Thicket ecoregion where river valleys meet the coast. In the north, coastal forest grades into a more tropical forest that contains elements of the Zanzibar-Inhambane Regional Mosaic that gradually replaces it (Moll and White 1978). Inland, it mixes with Afomontane forest at the base of the Drakensberg escarpment, while in the south, towards the xeric end of its distribution, KwaZulu-Cape coastal forest grades into subtropical thicket.
KwaZulu-Cape coastal forest includes three of Acock’s (1953) five subdivisions of the Indian Ocean forest and Thornveld, namely: Typical Coastal-belt Forest, Transitional Coastal Forest, and Dune Forest. He described the more xeric southwest extension of KwaZulu-Cape coastal forest across the Keiskamma River as Alexandria Forest. These different forest types correspond roughly to Everard et al.’s (1994) Coastal Lowlands Forest, Sand Forest, and Dune Forest. In all of these classification systems, these forest types are evergreen with varying proportions of semi-deciduous species, except for some of the largest trees in the dry seasons (Ficus natalensis, Calodendrum, Celtis, Erythrina caffra, and E. lyssistemon) and have structural similarities based on seaward distribution. Towards the coast, wind and sea spray restrict forest distribution and structure on exposed dunes so that elements are short (5 m to 10 m high), dense, and tangled. Inland, against seaward facing hills, the forest becomes taller (approximately 20 m high) and less tangled. KwaZulu-Cape Coastal Forest no longer exists as a continuous belt of forest down the east coast of Africa. The mosaic comprises numerous and extensive patches of forest on a back drop of more or less open thornveld. This grassveld constituent displays strong successional movement towards forest by being scrubby, full of tall herbs, shrubs, and tall coarse grasses, rather than purely uniform grassland (Acocks 1953). In comparison with the adjacent Afromontane forests, regeneration- and growth-rates are good in the KwaZulu-Cape coastal forests (Moll and White 1978). Another important distinguishing feature of the coastal forests is that woody lianas are very common in disturbed areas.
Common trees in the Typical Coastal-belt Forest include Millettia grandis and Protorhus longifolia, which are indicator species for this forest type, as well as Vepris undulata, Combretum kraussii, and Rhus chirindensis. Widespread shrubs and climbers are Uvaria caffra, Dalbergia obovata, and Tricalysia lanceolata. The family Acanthaceae is well represented in the sub-canopy and forest margin as well as Oplismenus hirtellus and Centella asiatica. Some species noted as having a lower general occurrence by Acocks (1953), e.g. the tree Strelitzia nicolai and the shrub Indigafera micrantha, still have a high relative abundance which suggests that despite their low general occurrence they are still important and these species may give some indication of the differences between forest patches. Species of Typical Coastal-belt Forest do not usually occur south of the Great Kei River where species more typical of Transitional Coastal Forest such as Ptaeroxylon, Schotia spp., Cassine spp. and Euphorbia granidens replace them. Typical Coastal-belt Forest is interspersed by scrubby thornveld that only very rarely becomes an open grassy savanna. These grasses tend to consist of tall forms such as Themeda triandra, and Digitaria spp. Thornveld replacing Transitional Coast Forest is similar to that found inland except that it contains tropical species such as Dalbergia obovata (Acocks 1953).
Dune Forest occupies a narrow belt on high dunes running down the coast. Principle trees include Mimusops caffra, Euclea natalensis, and Psydrax obovata obovata. Lianas are less important in this forest, with common shrubs and climbers including Scutia myrtina, Allophylus natalensis and Dracaena hookeriana. In rocky coastal areas, the forest extends down to the high tide level. M. caffra and A. natalensis are diagnostic of Dune Forest. Where dunes directly face the beach, the lower seaward edge of the forest usually consists of pioneer stages. On half stabilized dunes, these species comprise Chrysanthemoides monilifera, Metalasia muricata, and Passerina rigidia. With Mariscus congestus, Sporobolus virginicus, Scaevola plumieri, Ipomoea pes-caprae brasiliensis and other trailing and stoloniferous plants on recently formed dunes. At the edge of the beach one finds Gazania rigens uniflora, Arctotheca populifolia, and Heteroptilis suffrutiosa. Thornveld associated with Dune Forest is subtropical, dominated by Themeda triandra and Digitaria natalensis but also contains a number of species of fynbos affinity e.g. Stipagrostis zeyheri., especially southwards on loose, disturbed sand.
Alexandria Forest is a short (10 m), very dense forest with key species such as Ochna arborea var. arborea, Apodytes dimidiata dimidiata and Cassine aethiopica. Less common trees include Euclea natalensis, Pittosporum viridiflorum, and Rapanea melanophloes. In this short forest, shrubs are particularly important and a large proportion are scramblers. Scutia myrtina, Azima tetracantha, and Grewia occidentalis are all found here and undergrowth species include various Acanthaceae spp., Panicum deustum, and Sansevieria spp.
Biodiversity Features
The Tongaland-Pondoland Regional Mosaic is a regional center of floral endemism. According to White (1978) this coastal belt supports a rich flora of about 3,000 species, with approximately 40 percent of larger woody species considered endemic to the region. There are a large number of plants endemic or near-endemic to the sandstone islands and these taxa comprise a significant proportion of the Tongaland-Pondoland Regional Mosaic endemics (Van Wyk 1990). Species of these monotypic, woody taxa are found in one family (Rhynchocalyceae) and at least six genera (Dahlgrenodendron, Eriosemopsis, Jubaeopsis, Pseudosalacia, Pseudoscolopia, and Rhynchocalyx). Moll and White (1978) attributed Tongaland-Pondoland Regional Mosaic with 23 endemic genera, many of which are paleoendemics. These endemics fall within the Pondoland Center (Midgley et al. 1997) and are associated with outcrops of Cape Supergroup sandstone. Van Wyk (1990) suggests that reduced competition on unfertile substrata allowed this relictual flora to persist. This view is opposed by Cawe (1994), who attributes high levels of endemism to the high rainfall in the area.
There are three plant genera that are confined to the Tongaland-Pondoland Regional Mosaic in Africa but are found elsewhere: Atalaya (Indochina, Malaysia, Australia), Alberta (2 spp. in Madagascar) and Protorhus (20 spp. in Madagascar) (Moll and White 1978). Some genera that are widespread in Africa, e.g. Bersama, Diospyros, Euclea and Rhoicissus, have their center of variation in Tongaland-Pondoland Regional Mosaic. Others, such as Cassine spp. and Eugenia spp., are more widespread in Africa and elsewhere, and have markedly high concentrations of species in the area (Moll and White 1978).
Coastal forests, particularly dune forest, are species rich and have high woody species diversity (Everard et al. 1994). Species richness is particularly high in trees, shrubs, lianas, and vines (Geldenhuys and MacDevette 1989). While alpha diversity (number of species within a homogenous community) is high, beta diversity (species turnover) is relatively low (Geldenhuys and MacDevette 1989). The Sand Forest component, like Afromontane Forests, tends to be dominated by few species, whereas Dune Forest has a mix of species (Everard et al. 1994). Forest patch size is not an important determinant of species richness but other variables that explain dispersal patterns include proximity to other forests, number of dispersal corridors, landscape types, and mean altitude (Geldenhuys 1992). Plant species richness decreases with increasing altitude and latitude. This progressive southward reduction in numbers of tree and shrub species as climatic conditions become drier and more temperate is true for most forests in southern Africa (Tinley 1985). In addition, species at higher latitudes tend to have broader distribution ranges. Many of the endemic/near endemic species of the sandstone islands of KwaZulu-Cape Coastal Forest Mosaic are taxonomically isolated and approaching natural extinction. Specific examples of these plant species include Rhynchocalyx lawsonioides, Dahlgrenodendron natalensis, and Rinorea dematiosa.
The high degree of similarity between southern African forests is thought to have been established before major fragmentation of continuous forest belt (Geldenhuys 1992). In southern Africa, Indian Ocean coastal belt forest was probably established after the last glacial maximum (Tinley 1985). These forests appear to have a Tropical origin (Midgley et al. 1997). These authors argue that the distribution of these forests is likely to be a result of biotic interactions rather than narrow habitat requirements, while others (e.g. Tinley 1985, Geldenhuys 1992), attribute the strong southward attenuation of species to the subtropical temperate transition. Moll and White (1978) suggest that Tongaland-Pondoland Regional Mosaic has served as a refugia for genera that were formerly more widespread on the African mainland, and that it has also been a region of recent diversification.
Since the Pliocene, climatic change (increasing aridity), increased fire frequency, and ‘natural’ fragmentation have all contributed to the highly fragmented nature of forests in southern Africa generally (Geldenhuys 1989). Until the Cretaceous period, mixed evergreen forest covered most of Africa. During the Cretaceous the eastern escarpment formed separating the moist forested coastal belt from the arid forest-less interior (Geldenhuys and MacDevette 1989). During the Holocene, climatic and landscape changes further complicated forest distribution (Scholtz 1986). Although there is evidence that the grasslands found among forest patches today were present during the Holocene (Feely 1980), the relictual nature of forests within grassland has been attributed to the destructive activities of man in the relatively recent past (100 to 300 years) (Acocks 1953).
Disturbance, or lack thereof, plays a large role in maintaining the diversity of KwaZulu-Cape coastal forest. Everard et al. (1994) established that coastal forest is coarse-grained, containing predominantly shade-intolerant canopy species. Recruitment in these forests occurs mainly by colonization and rapid growth of shade-intolerants to canopy level. In the absence of relatively large-scale disturbance (periodic gaps between 100 m2 and 10,000 m2) these shade-intolerant species tend to be rare and beta diversity decreases. Geldenhuys and MacDevette (1989) found a general pattern that suggests the opposite. They and several other authors found that undisturbed forest is slightly more species rich than disturbed forest and that mature forest is richer than regrowth or seral forest. Forest margins are also affected, with unburnt margins having definite margin-associated species and higher species richness. There are no large blocks of intact habitat where natural disturbances predominant outside conservation areas, anthropogenic disturbances are the main influencing factors.
Because this ecoregion is a mosaic of forest and interspersing thornveld, the ecoregion is rich in faunal species that live in both elements. It is relatively rich in mammalian species, with some 40 Insectivores represented, including 23 bat species. The Lagomorpha (hares and rabbits) and Rodentia are also well represented. Primates and Ungulates are less well represented with only three and nine species, respectively. Carnivores are well-represented by some 22 species (Skinner and Smithers 1990). Faunal species do not differ widely between southern African forests. There is a large measure of intra- and inter-continental similarity in forest litter fauna diversity (Endrödy-Younga 1989). Endemic mammals include Duthie’s golden mole (Chlorotalpa duthieae, VU), dark-footed forest shrew (Myosorex sclateri, VU), and the strictly endemic giant golden mole (Chrysospalax trevelyani, EN). Other mammals found here include Samango monkeys (Cercopithecus albogularis) and the thick-tailed bush baby (Galago crassicaudatus), both of which are dependent on forested habitat. The blue duiker (Cephalophus monticola) and the red Natal duiker (Cephalophus natalensis) are both found here, in both forest and thicket. The leopard (Panthera pardus), caracal (Felis caracal), African wildcat (Felis sylvestris), and the black-backed jackal (Canis mesomelas) are the top predator species in this ecoregion.
Rare bird species are primarily confined to the forest components of the Kwazulu-Cape Coastal Forest Mosaic, but there are no strictly endemic species. There are a number of bird species occurring which are found only in the forests and bushlands of the southern African coasts, including brown scrub-robin (Cercotrichas signata), Knysna turaco (Tauraco corythaix), Knysna woodpecker (Campethera notata), Knysna scrub-warbler (Bradypterus sylvaticus, VU), Chorister robin-chat (Cossypha dichroa), and forest canary (Serinus scotops). Other bird species of note in this ecoregion include the African fish eagle (Haliaeetus vocifer), Ayres’ eagle (Hieraaetus ayresii), southern bald ibis (Geronticus calvus, VU), crowned eagle (Stephanoaetus coronatus), cuckoo hawk (Aviceda cucloides), forest buzzard (Buteo oreophilus), green coucal (Ceuthmochares aereus), green twinspot (Mandingoa nitidula), Gurney’s sugarbird (Promerops gurneyi), longcrested eagle (Lophaetus occipitalis), martial eagle (Polemaetus bellicosus), southern banded snake eagle (Circaetus fasciolatus), wattled crane (Grus carunculatus, VU), and wattle-eyed flycatcher (Platysteira peltata).
The Natal diving frog (Natalobatrachus bonebergi) is found only in this ecoregion, together with five other near-endemic amphibians. In the reptiles the Transkei dwarf chamaeleon (Bradypodion caffrum), Günther's burrowing skink (Scelotes guentheri), the skink Acontias poecilus and the gecko Cryptactites peringueyi are all regarded as strictly endemic to this ecoregion.
Current Status
Today, KwaZulu-Cape Coastal Forest Mosaic is a highly fragmented ecotype. There are some large forest complexes interspersed by large areas of non-forest, but the majority of remaining vegetation is found in small, isolated patches amounting to approximately 9,468 km2 (Lubke and McKenzie 1996). This is little more than half of its previous extent, as some 43 percent of the original extent of coastal forest has been transformed. In South Africa, ownership and resulting levels of conservation management range from forests in private and tribal ownership, to those in conservancies and natural heritage sites, through to forests in nature reserves and wilderness areas as proclaimed under the Forest Act (Geldenhuys and MacDevette 1989). Presently an estimated 9.5 percent of KwaZulu-Cape Coastal Forest Mosaic is conserved in some form or other (Low and Rebelo 1996), mostly in a large number of small reserves that are not interconnected. Only one of these, Amatikulu Nature Reserve, falls under IUCN category II. Other protected areas include the following Nature Reserves: East London Coast, Great Fish River, Geelkrans, Sunshine Coast, Vernon Crookes, and Woody Cape, as well as Hluleka Wildlife Reserve.
While this conservation network protects elements of the KwaZulu-Cape Coastal Forest Mosaic, it still does not adequately conserve large intact blocks of forest and interspersed thornveld as single units. Many of the forest patches and corridors existing outside conservation areas are not protected. These provide avenues of gene flow between protected areas and may therefore be vital for continued conservation of forest species in conserved areas (Geldenhuys and MacDevette 1989).
Types and Severity of Threats
The main threat to the KwaZulu-Cape Coastal Forest Mosaic is both the direct and indirect use of forest as a resource. Traditional uses of forests by local populations include building materials, traditional medicines (muti), food, water, and grazing. With burgeoning populations and decreased employment prospects resulting from political instability in South Africa, demands for these resources have increased. The natural fragmentation of the forests has been aggravated by land use practices such as clearing for agriculture, forestry, subsistence utilization, and burning practices for grazing and improved water runoff in catchments (Feely 1980). Much of the northern, inland distribution of KwaZulu-Cape coastal forest in Natal, particularly the thicket component, has been replaced by sugarcane. Informal housing is also an ever-increasing threat to the integrity of the ecoregion.
Coastal dunes are especially sensitive to human interference. The worst disturbances to dunes by human activities are: material developments e.g. mining and holiday resort expansion; alien plant invasion e.g. deliberate planting for dune stabilization; recreational activities e.g. unrestricted vehicle access; and inappropriate planning, zoning, and ineffective administrative control (Tinley 1985). Where dune forest has been disturbed by urban development, Brachylaena discolor, Strelitzia nicolai, and/or Chrsanthemoides monilifera tend to dominate the secondary vegetation.
The important invasive forest species are mainly fast-growing tree species of the forest fringe such as Casuarina equisetifolia. There is some evidence that alien infestations can aid forest development. Fast-growing alien trees planted in forest gaps and plantations along forest margins protect the forest against fires, aid in their rehabilitation after disturbance, and provide resources such as timber, fiber, and firewood (Geldenhuys et al. 1986). There are few true indigenous pioneer forest trees (e.g. Trema orientalis, Acacia karoo). Alien trees supplement these in ameliorating disturbed sites and allowing succession to proceed in a similar way to indigenous pioneers. The initial pure stand of alien pioneers is gradually colonized and enriched by the shade-tolerant species of middle to late seral stages (Huntley 1965, Wiesser and Marques 1979, Knight et al. 1987). In addition, there is some evidence that small mammal species richness increases through successional stages to the intermediate stage and then declines again during climax stage (Rowe-Rowe and Meester 1968).
Justification of Ecoregion Delineation
This ecoregion follows the southern part of Moll and White’s (1978) Tongaland–Pondoland regional mosaic and the southern extent of a greater Indian Ocean Coastal Belt. Bordered to the north by the more tropical Zanzibar-Inhambane Coastal Mosaic (White 1983) and to the south by subtropical evergreen and semi-evergreen bushland and thicket, it contains affinities to both tropical and subtropical species distributed as rainfall and temperature declines towards the south. It is also distinguished as part of the South African Forests Endemic Bird Area (Stattersfield et al. 1998) and Maputaland-Pondoland center of plant diversity (WWF and IUCN 1994).
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Prepared by: Charlotte Heijnis
Reviewed by: In progress