Supporting article G: Various ecosystems found in South Africa
The Biomes of South Africa and sensitive ecosystems
Biomes can be defined as the major communities of the world, classified according to their predominant vegetation and characterised by adaptations of organisms to that particular environment.
Ecosystems are communities of organisms that inhabit specific physical environments. Biomes are composed of several ecosystems and represent a regional community of organisms named after the dominant vegetation.
The four major types of biomes are aquatic, grasslands, forests, and desert. Aquatic biomes are probably the most important of all the biomes. Their medium, water, is a major natural resource. Aquatic biomes can be subdivided into freshwater, seawater and atmospheric biomes. Grasslands can be subdivided into savanna, temperate grasslands (prairie) and tundra. This classification corresponds to decreasing average temperatures. Forests receive more precipitation than other biomes and vary from boreal, to temperate, to rainforest. This classification corresponds to increasing temperatures. Deserts have the fewest species and the most extreme climate.
Effective management and care of the biosphere require that we understand how organisms interact with the physical environment to create their habitats. Management involves understanding the scale at which such associations function and the processes that control the distribution of species within such systems. Ecosystems are communities of organisms that inhabit specific physical environments, defined primarily by their climate and landforms. A number of similar ecosystems can be grouped together in a biome, a regional community of plants and animals named after the dominant type of vegetation. Biomes are characterised by a similar association of species, comparable climates, and consistent soil types.
Ecologists do not always agree on the exact number of ecosystems and biomes, as the number will vary depending upon how the biomes are defined, for instance: according to species or according to the particular climate characteristics that are considered.
Because we share the world with many other species of plants and animals, we must consider the consequences of our actions. Over the past several decades, increasing human activity has rapidly destroyed or polluted many ecological habitats throughout the world. It is important to preserve all types of biomes as each houses many unique forms of life. However, the continued heavy exploitation of certain biomes, such as the forest and aquatic biomes, may have even more severe implications.
By educating people about the consequences of our actions, we can all gain a better understanding of how to preserve the natural biomes of the earth. Although areas that have already been destroyed will probably never regain their original forms, conservation can help to keep them from deteriorating further.
The succulent Karoo is restricted to the year-round and winter rainfall areas and have the greatest summer aridity. This biome occurs mostly west of the western escarpment through the western belt of the Western Cape and inland towards the Little Karoo. This is the land of many spring flowers, which for a few weeks each year, draw large numbers of tourists from all over the world
Succulent plant species with thick, fleshy leaves are plentiful here, the diversity of which is unparalleled anywhere else in the world. This, together with many geophytes (plants that survive by means of bulbs, tubers, etc. in times of unfavorable climatic conditions) and annual plants, makes the succulent Karoo unique and of international importance in terms of conservation. Examples of animals that occur here are the bat-eared fox (Otocyon megalotis), suricate (Suricata suricatta) and the common barking gecko (Ptenopus garrulus).
Savannas are the wooded grasslands of the tropics and subtropics that account for 46% of the South African landscape. They are second only to tropical forests in terms of their contribution to terrestrial primary production. They are the basis of the livestock industry and the wildlife in these areas is a key tourist drawcard
The fact that the public are well aware of African savannas may be explained by the variety of large mammals found here. Large game species such as lion (Panthera leo), buffalo (Syncerus caffer) and elephant (Loxodonta africana) occur here. The large diversity of animals is associated with the rich plant diversity. A well-known tree species found in the Northern Province is the baobab (Adansonia digitata). Other species found here include the mopane (Colophospermum mopane), monkey-thorn (Acacia galpini) and knob-thorn (Acacia nigrescens). Savannnas also include valley bushveld, the veld type containing the greatest range of rainfall seasonality in South Africa. Fire is a crucial factor in the ecology of all savannas and is therefore a regular natural feature of this environment.
Diversity of plant life
South Africa is characterised by a wide diversity of plant life and is ranked as the third most biologically diverse country in the world (mainly due to the richness of plant life). Over 18 000 species of vascular plants occur in South Africa, of which over 80% occur nowhere else. This diversity is caused by variations in climate, geology, soils and landscape forms. However, South Africa also has the highest concentration of threatened plant groups in the world. Approximately 3 435 of South African plant groups are considered to be globally threatened by extinction. A further 204 groups are estimated to be threatened at a local level.
Fynbos occupies 5,3 % of South Africa, occurring almost exclusively in the south-western and southern parts of the Western Cape Province. Fynbos comprises evergreen heathlands and shrublands in which fine-leafed low shrubs and leafless tufted grasslike plants are typical. Trees are rare and grasses comprise a relatively small part of the biomass.
Fire is a very important component in fynbos. Most fynbos is highly flammable due to the common presence of flammable oils. Finely wooded fynbos plants are obligate seeders, which means that the whole plant dies after fire and can only reproduce through seed. This distinguishes fynbos from the other ecosystems where fire is common. Many plant species are dependent for pollination on small mammals or birds such as the Cape sugarbird (Promerops cafer).
Fynbos, with its complement of at least 8 578 species of flowering plants, is now recognised as supporting one of the most diverse and distinctive floras in the world. All in all, 5 832 or 68 % of the plant species are endemic. Many of the fynbos plant species are restricted to extremely small distribution ranges, a fact which has rendered them dangerously susceptible to extinction.
Economic utilisation of fynbos vegetation is limited to selective grazing by small stock on newly burned lowland areas and to wild-flower production. Most commonly utilised are the protea species, which are exported fresh or dried.
The floristic diversity of the fynbos is not paralleled by an equally rich fauna due to the absence of grass and berry-producing plants. Fauna includes species such as the leopard (Panthera pardus) and geometric tortoise (Psammobates geometricus).
Fynbos products such as rooibos tea, buchu, veld flowers and thatching-reed are also harvested while table and wine grapes, wheat, fruit and olives are important agricultural products. South Africa’s oldest city, Cape Town, at the foot of Table Mountain, is located in the fynbos biome.
Invasive alien plants
In South Africa, invasive plants cause billions of rands of damage each year. Over 160 plant species introduced into South Africa have become invasive. If left unchecked, these species will spread at an alarming rate, doubling within 15 years. Invasive alien plants have the following impacts:
• They use about 7% of our scarce water resources.
• Their impact on agricultural resources and indigenous natural resources is significant.
• They increase the likelihood of flooding and bush fires.
• They cause erosion, siltation of dams and estuaries and adversely affect water quality.
They lead to the extinction of indigenous plants and animals and undermine the ecological functioning of natural systems.
The grasslands cover the high central plateau of South Africa, inland areas of Kwazulu-Natal and the mountain areas of the Eastern Cape Province. Grasslands are defined as those areas where grasses dominate the vegetation and where woody plants are absent or rare. They occupy 24,1% of the country’s surface area. Most grassland occurs in high-rainfall areas, where thunderstorms and hail are common in summer and frost is common in winter.
The grassland biome is regarded as the third-richest area in terms of plant species diversity, with a total number of 3 788 species. The most noteworthy species with a wide distribution is, Themeda triandra, more commonly referred to as ‘rooigras’. In the past the ungulate fauna (hoofed animals) of the Highveld grasslands included vast herds of blesbok (Damaliscus dorcas phillipsi), black wildebeest (Connochaetes gnou) and the springbok (Antidorcas marsupialis). A surprisingly rich variety of birds are found in the grasslands, including the blue crane (Anthropoides paradiseus), black korhaan (Eupodotis afra) and helmeted guineafowl (Numida meleagris).
The forests of South Africa include the indigenous evergreen and semi-deciduous closed forests of the coastal lowlands and escarpment slopes and cover only about 0.25% of the land area.
With a few exceptions such as the forests of the Knysna area and the KwaZulu-Natal coastal dune systems, forests are small, usually occupying less than 1 000 ha. These forests amount to little more than patches scattered through the higher rainfall areas. The total area of forests in South Africa is probably less than 2 000 km². The forest structure results in reduced light levels in the area beneath the canopy where species such as tree ferns are common. Typical mammals include the bushbuck (Tragelaphus scriptus), bush pig (Potamochoerus porcus) and blue duiker (Philantomba monticola). Birds found in forests include the Knysna lourie (Tauraco corythaix) and rameron pigeon (Columba arquatrix). Despite the small land surface area that they occupy, forests have relatively high species richness. Only fynbos exceeds the species richness found in forests.
The Nama-Karoo covers most of the vast central plateau region of the Western and Northern Cape Provinces. The area forms an ecotone or transition between the Cape flora to the south, and the tropical savanna in the north. Many of the plant species of the Nama-Karoo also occur in the savanna, grassland, succulent Karoo and fynbos biomes.
Species that occur in the Nama-Karoo include the sweet-thorn (Acacia karroo), stone plant (Lithops ruschiorum) and blue Karoo daisy (Felicia australis). The former vast migratory herds of springbok (Antidorcas marsupialis) have been replaced by domestic stock, particularly sheep and goats. A rich variety of rodents and reptiles, also occurs in the Nama-Karoo. The few, endemic or near-endemic bird species include the Sclaters lark (Spizocorys sclateri). Sheep-farming is the main agricultural activity in this region.
Marine and coastal ecosystems
The South African coastline covers a distance of over 3 000 km, more than 80% of which consists of sandy beaches and sand dunes. Other ecosystems include rocky shores, coral reefs, kelp beds and the open sea. Two hundred and seventy of the world’s 325 fish families occur in South African waters.
The east coast waters are characterised by the warm waters of the southward flowing Agulhas Current, while those of the west coast are characterised by the upwelling of cold, nutrient-rich waters of the Benguela Current. Along the southwest and south coast, there is an extensive mixing of water masses. The currents influence the composition of the animal and plant communities along this coastline.
Sandy beaches consist of an unstable sandy bottom layer that is continually modified by waves and currents, resulting in an absence of plants between the tide marks. Yet, a few animal species have adapted to live in this harsh environment. For example, the plough snail (Bullia sp.) and white mussel (Donax sp.) have adapted by burrowing in the sand. These animals emerge to feed when conditions are relatively mild, or they sit tight in the sand and filter food particles from the seawater with siphons or strainers. The pink ghost crab (Ocypode ryderi) burrows deeply by day, emerging by night to feed on deposited carrion and small animals. Other animals, such as the leatherback turtle (Dermochelys coriacea), merely visit the intertidal zone to lay their eggs.
Some 63 ocean outfalls are located along the South African coast. Daily these outfalls discharge approximately 800 000 cubic metres of sewage and industrial effluent into the sea. Most large pipelines discharge into deeper waters, but 27 of the older pipelines discharge above the high water mark. This is very dangerous to human health as bathing waters are contaminated, and edible species such as mussels may become contaminated. Apart from their impact on human health, sewage and industrial effluence also harm the marine environment. Untreated stormwater from urban areas along the coast also possess a pollution risk. In 1991 the total volume of stormwater run-off entering the marine environment in South Africa was estimated to be about 876 000 cubic metres per day.
The rocky shores that are scattered along the coastline provide a firm foundation for the attachment of plants and animals, but are exposed twice a day by the tides and are often lashed by a strong wave action. These shores support a great diversity of marine organisms, some of which are commercially significant, for example, mussels, oysters and seaweed. The intertidal and the subtidal zones provide feeding grounds for many species of fish, some of which are important angling species.
South Africa’s only coral reefs occur in the subtropical waters off the coast of northern KwaZulu-Natal and Maputaland. These particularly fragile environments support an abundant growth of Indian Ocean corals that harbour diverse Indo-Pacific fish fauna. These reefs form a vital link in the overall food web of southeast Africa and play an important role in the distribution of migratory fish. Commercially important species such as the larger mackerels, couta and kingfishes migrate along the narrow belt of the coral reefs of Maputaland, to reach southern African waters during the summer months.
The west coast is dominated by dense beds of the giant kelps or sea bamboo (such as Ecklonia maxima), which form a calm underwater forest-like habitat and can extend to as much as 3 km offshore. These kelps are extremely productive. Not only are they a major source of food, but they also provide shelter for fish, animals and plants that inhabit calm waters such as the commercially important rock lobster and abalone stocks.
In the open sea, there is no firm base, and organisms must either drift or be able to swim. Examples include the bottlenose dolphin (Tursiops truncatus), the blue-and-gold fusillier (Caesio caerulaureus), the Cape moony (Monodactylus falciformis) and the Japanese bigeye (Pristigenys niphonia), phytoplankton and zooplankton. The east coast waters are characterised by a greater biotic diversity than the southwest and south coast waters where fewer species occur but in greater numbers. The main focus of commercial fisheries is therefore centered in the more productive waters of the southwest and south coasts.
The term “wetlands” groups together a wide range of inland and coastal habitats – from mountain sponges and midland marshes to swamp forests and estuaries – linked by rivers and streams. These wetlands share common and important functions in river catchments by providing a regular water supply, by filtering the water naturally, by reducing the effects of floods and droughts, and by providing a vital wildlife habitat and superb recreational areas for people.
Most wetlands are characterised by a high water table, water-carrying soil and hydrophytes (water-loving plants), but in semi-arid Southern Africa there are numerous pans that support few if any hydrophytes and that may contain shallow water only once in five or more years.
Wetlands play an important role in maintaining biodiversity since they support an extraordinary variety of plant and birdlife e.g. the red bishop (Euplectes orix), the South African shelduck (Tadorna cana), insects, mammals, reptiles, amphibians, e.g. the striped stream frog (Strongylopus fasciatus), fish and invertebrate species.
Wetland plants such as the bulrush (Typha capensis), play an important role in the healthy functioning of a wetland ecosystem by generating organic matter, the primary element for any foodweb. They also provide the soil and water with oxygen, prevent erosion and serve as a filter that purifies the water. These plants provide food, shelter and breeding sites for many birds and aquatic animals such as the hippopotamus. Attractive plant species such as the arum lily (Zantedeschia aethiopica) and the red-hot poker (Kniphofia caulescens) are common to wetlands.
Wetlands are currently under immense pressure. In the United States 51% of all wetlands have disappeared, while the State of California has already lost 91% of its wetlands. More than 50% of South African wetlands have also been lost. In the Province of KwaZulu-Natal St Lucia has been declared a World Heritage Site, the only wetland in Africa to receive this status.
For more information: http://www.ccwr.ac.za/wetlands/ http://www.epa.gov/owow/wetlands/ http://www.wetlands.org/
Wetlands are likely to occur in the catchment of all river systems in South Africa, but their form and abundance vary considerably owing to regional differences in topography, climate, vegetation, soil, land use and hydrological conditions. South African wetlands, being at the southern tip of the continent, host a number of endemic and highly isolated bird species, e.g. the Cape shoveller (Anas smithii). A number of paleoarctic migrants visit Southern African wetlands during the northern hemisphere’s winter, some of which come all the way from the Taimyr Peninsula in Siberia (a distance of approximately 15 000 km). South Africa extends into the tropics, providing the southern limits to a number of tropical species such as the pink-backed pelican (Pelecanus rufescens), the rufous-bellied heron (Butorides rufiventris), the dwarf bittern (Ixobrychus sturmii), the open-billed stork (Anastomus lamelligerus) and the pygmy goose (Nettapus auritus).