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TheAfrotropical realm is one of the Earth's eightbiogeographic realms. It includesSub-Saharan Africa, the southernArabian Peninsula, the island ofMadagascar, and the islands of the westernIndian Ocean.[1] It was formerly known as theEthiopian Zone orEthiopian Region.
Most of the Afrotropical realm, except for Africa's southern tip, has atropical climate. A broad belt ofdeserts, including theAtlantic andSahara deserts of northern Africa and theArabian Desert of theArabian Peninsula, separates the Afrotropic from thePalearctic realm, which includes northern Africa and temperateEurasia.
South of theSahara, two belts oftropical grassland and savanna run east and west across the continent, from theAtlantic Ocean to theEthiopian Highlands. Immediately south of the Sahara lies theSahel belt, a transitional zone of semi-arid shortgrassland andvachellia savanna. Rainfall increases further south in theSudanian Savanna, also known simply as theSudan region, a belt of tallergrasslands andsavannas. TheSudanian Savanna is home to two greatflooded grasslands: theSudd wetland inSouth Sudan, and theNiger Inland Delta inMali. Theforest-savanna mosaic is a transitional zone between the grasslands and the belt oftropical moist broadleaf forests near theequator.
South Arabia, which includesYemen and parts of westernOman and southwesternSaudi Arabia, has few permanent forests. Some of the notable ones areJabal Bura, JabalRaymah, and Jabal Badaj in the Yemeni highland escarpment and the seasonal forests in eastern Yemen and theDhofar region of Oman. Otherwoodlands that scatter the land are small, predominantlyJuniperus orVachellia forests.
Theforest zone, a belt of lowlandtropical moist broadleaf forests, runs across most of equatorial Africa'sIntertropical Convergence Zone. TheUpper Guinean forests of West Africa extend along the coast fromGuinea toTogo. TheDahomey Gap, a zone of forest-savanna mosaic that reaches to the coast, separates the Upper Guinean forests from theLower Guinean forests, which extend along theGulf of Guinea from easternBenin throughCameroon andGabon to the westernDemocratic Republic of the Congo. The largest tropical forest zone in Africa is theCongolian forests of theCongo Basin in Central Africa.
A belt of tropical moist broadleaf forest also runs along the Indian Ocean coast, from southernSomalia toSouth Africa.
In northeastern Africa, semi-aridAcacia-Commiphora woodlands, savannas, and bushlands are the dominant plant communities. This region is called the Somali-Masai center ofendemism or Somali-Masai region. It extends from centralTanzania northwards through theHorn of Africa and covers portions ofTanzania,Kenya,Ethiopia,Somalia,Djibouti, andEritrea. Thorny, dry-seasondeciduous species ofVachellia andSenegalia (formerlyAcacia) andCommiphora are the dominant trees, growing in open-canopied woodlands, open savannas, dense bushlands, andthickets. This region includes theSerengeti ecosystem, which is renowned for its wildlife.[3]
TheAfromontane region extends from theEthiopian Highlands to theDrakensberg Mountains of South Africa, including theEast African Rift. This region is home to distinctive flora, includingPodocarpus andAfrocarpus, as well as giantLobelias andSenecios.
TheZambezian region includes woodlands, savannas, grasslands, and thickets. Characteristic plant communities includeMiombo woodlands, driermopane andBaikiaea woodlands, and higher-elevationBushveld. It extends from east to west in a broad belt across the continent, south of therainforests of theGuineo-Congolian region, and north of the deserts of southeastern Africa, the countries areMalawi,Angola,Botswana,Mozambique,Zambia, andZimbabwe, and the subtropical.[4]
Southern Africa contains several deserts. TheNamib Desert is one of the oldest deserts in the world and extends for over 2,000 kilometers along the Atlantic coasts ofAngola,Namibia, andSouth Africa. It is characterized by toweringdunes and a diversity ofendemic wildlife. Further inland concerning the Namib Desert, theKalahari Desert is a semi-arid savanna spanningBotswana,Namibia, andSouth Africa. The Kalahari is known for its diversity of mineral resources, particularlydiamonds, as well as a variety of flora. South of the Namib and Kalahari deserts is theKaroo. A semi-desert natural region, the Karoo desert spans across parts of the Western and Eastern Cape in South Africa and contains vast open spaces and unique vegetation, such as certain species ofAsteraceae flowering plants. Within the boundaries of the larger Karoo, theTankwa Karoo is a more arid sub-region known for harsher conditions and starker landscapes. Further to the west, theRichtersveld, a mountainous desert in the northwestern corner of South Africa, presents a rugged landscape. It is celebrated as aUNESCO World Heritage Site for its uniquebiodiversity and cultural significance to the localNama people.
TheCape floristic region at Africa's southern tip is aMediterranean climate region that is home to a significant number of endemictaxa, as well as to plant families like theproteas (Proteaceae) that are also found in theAustralasian realm.
Madagascar and neighboring islands form a distinctive sub-region of the realm, with numerous endemictaxa, such aslemurs. Madagascar and theGranitic Seychelles are old pieces of the ancientsupercontinent ofGondwana, and broke away from Africa millions of years ago. OtherIndian Ocean islands, like theComoros andMascarene Islands, arevolcanic islands that formed more recently. Madagascar contains various plant habitats, from rainforests to mountains and deserts, as its biodiversity and ratio of endemism are extremely high.
The Afrotropical realm is home to several endemic plant families.Madagascar and the Indian Ocean Islands are home to ten endemic families of flowering plants; eight are endemic to Madagascar (Asteropeiaceae,Didymelaceae,Didiereaceae,Kaliphoraceae,Melanophyllaceae,Physenaceae,Sarcolaenaceae, andSphaerosepalaceae), one toSeychelles (Medusagynaceae), and one to theMascarene Islands (Psiloxylaceae). Twelve plant families are endemic or nearly endemic to South Africa (includingCurtisiaceae,Heteropyxidaceae,Penaeaceae,Psiloxylaceae, andRhynchocalycaceae) of which five are endemic to theCape floristic province (includingGrubbiaceae). Other endemic Afrotropic families includeBarbeyaceae,Dirachmaceae,Montiniaceae,Myrothamnaceae, andOliniaceae.
TheEast African Great Lakes (Victoria,Malawi, andTanganyika) are the center of biodiversity of many freshwater fishes, especiallycichlids (they harbor more than two-thirds of the estimated 2,000 species in the family).[4] The West African coastal rivers region covers only a fraction of West Africa, but harbors 322 of West Africa's fish species, with 247 restricted to this area and 129 restricted evento smaller ranges. The central riversfauna comprise 194 fish species, with 119 endemics and only 33 restricted to small areas.[5]
The Afrotropic has various endemicbird families, includingostriches (Struthionidae), thesecretary bird (Sagittariidae),guineafowl (Numididae), andmousebirds (Coliidae). Several families ofpasserines are limited to the Afrotropics, includingrock-jumpers (Chaetopidae) androckfowl (Picathartidae).
Africa has three endemic orders of mammals, theTubulidentata (aardvarks),Afrosoricida (tenrecs andgolden moles), andMacroscelidea (elephant shrews). TheEast-African plains are well known for their diversity of large mammals.
Four species ofgreat apes (Hominidae) are endemic to Central Africa: both species ofgorilla (western gorilla,Gorilla gorilla, andeastern gorilla,Gorilla beringei) and both species ofchimpanzee (common chimpanzee,Pan troglodytes, andbonobo,Pan paniscus).Humans and their ancestors originated in Africa.
The tropical environment is rich in terms of biodiversity. Tropical African forest is 18 percent of the world's total and covers over 3.6 million square kilometers of land in West, East, and Central Africa. This total area can be subdivided to 2.69 million square kilometers (74%) in Central Africa, 680,000 square kilometers (19%) in West Africa, and 250,000 square kilometers (7%) inEast Africa.[6] InWest Africa, a chain of rain forests up to 350 km long extends from the eastern border ofSierra Leone toGhana. In Ghana, the forest zone gradually dispels near theVolta river, following a 300 km stretch ofDahomey savanna gap. The rain forest of West Africa continues from east of Benin through southern Nigeria and officially ends at the border ofCameroon along theSanaga river.
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Semi-deciduous rainforests in West Africa begin at the fringed coastline ofGuinea Bissau (via Guinea) and run through the coasts of Sierra Leone,Liberia,Ivory Coast, Ghana, continuing through Togo,Benin, Nigeria and Cameroon, and ending at theCongo Basin. Rainforests such as these are the richest, oldest, most prolific, and most complex systems on Earth, are dying, and in turn, are upsetting the delicate ecological balance. This may disturb globalhydrological cycles, release vast amounts ofgreenhouse gases into the atmosphere, and lessen the planet's ability to store excesscarbon.
The rainforest vegetation of the Guinea-Congolian transition area, extending fromSenegal to westernUganda is constituted of two main types: The semi-deciduous rainforest is characterized by a large number of trees whose leaves are left during the dry season. It appears in areas where the dry period (rainfall below about 100 mm) reaches three months. Then, the evergreen or the semi-evergreen rainforest climatically adapted to somewhat more humid conditions than the semi-deciduous type and is usually there in areas where the dry period is shorter than two months. This forest is usually richer inlegumes and a variety of species and its maximum development is around theBight of Biafra, fromEastern Nigeria to Gabon, and with some large patches leaning to the west from Ghana to Liberia and to the east of Zaïre-Congo basin.
Among rainforest areas in other continents, most of the African rainforest is comparatively dry and receives between 1600 and 2000 mm of rainfall per year. Areas receiving more rain than this mainly are in coastal areas. The circulation of rainfall throughout the year remains less than in other rainforest regions in the world. The average monthly rainfall in nearly the whole region remains under 100 mm throughout the year. The variety of the African rainforest flora is also less than the other rainforests. This lack of flora has been credited to several reasons such as the gradual infertility since theMiocene, severe dry periods duringQuaternary, or therefuge theory of the cool and dry climate of tropical Africa during the last severe ice age of about 18,000 years ago.[6]
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The Tropical African rainforest has rich fauna, commonly smaller mammal species rarely seen by humans. New species are being discovered. For instance, in late 1988 an unknown shrub species was discovered on the shores of the Median River in Western Cameroon. Since then many species have become extinct. However, undisturbed rainforests are some of the richest habitats for animal species. Today, undisturbed rainforests are remnant but rare.Timber extraction not only changes the edifice of the forest, but it also affects the tree species spectrum by removing economically important species and terminating other species in the process. The species that compose African rainforests are of different evolutionary ages because of the contraction and expansion of the rainforest in response to global climatic fluctuations.[6]
Thepygmy hippopotamus, thegiant forest hog, thewater chevrotain,insectivores, rodents, bats, tree frogs, and bird species inhabit the forest. These species, along with a diversity of fruits and insects, make a special habitat that allows for a diversity of life. The top canopy is home to monkey species like thered colobus, Black-and-white Colobus, and many other Old-World monkey species. Many of these rare and unique species are endangered or critically endangered and need protection from poachers and provided ample habitat to thrive.
In Tropical Africa, about 8,500 plant species have been documented, including 403orchid species.[7]
Species unfamiliar with the changes in forest structure for industrial use might not survive.[6] If timber use continues and an increasing amount of farming occurs, it could lead to the mass killing of animal species. The home of nearly half of the world's animals and plant species are tropical rainforests. The rainforests provide economic resources for over-populated developing countries. Despite the stated need to save the West African forests, there are varied opinions on how best to accomplish this goal. In April 1992, countries with some of the largest surviving tropical rainforests banned a rainforest protection plan proposed by theBritish government. It aimed at finding endangered species of tropical trees to control their trade. Experts estimate that the rainforest of West Africa, at the present rate ofdeforestation, may disappear by the year 2020.[6]
Africa's rainforest, like many others emergent in the world, has a special significance to theindigenous peoples of Africa who have occupied them for millennia.[6]
Many African countries are in economic and political change, overwhelmed by conflict, making various movements of forest exploitation to maintain forest management and production more and more complicated.
Forest legislation of ATO member countries aims to promote the balanced utilization of the forest domain and of wildlife and fishery to increase the input of the forest sector to the economic, social, cultural, and scientific development of the country.[6]
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The rate ofdeforestation in Africa is less known than the rate of other tropical regions. A lack of dependable data and survey information in some countries has made change in areas of unbroken forest difficult to ascertain.
The cultivation of variouscash crops has led to forest depletion. West African countries depend on products like gum,copal,rubber,cola nuts, andpalm oil as a source of steady income.Land use change spoils entire habitats with the forests. The conversion of forests into timber is another cause of deforestation. Over decades, the primary forest product was commercialtimber. Urbanized countries account for a great percentage of the world's wood consumption, which increased greatly between 1950 and 1980. Simultaneously, preservation measures were reinforced to protect European and American forests.[6] Economic growth and growing environmental protection in industrialized European countries caused increased demand for tropical hardwood from West Africa. In the first half of the 1980s, an annualforest loss of 7,200 km2 (2,800 sq mi) was noted down along theGulf of Guinea, a figure equivalent to 4-5 percent of the total remaining rainforest area.[6] By 1985, 72% of West Africa's rainforests had been transformed into fallow lands and an additional 9% had been opened up by timber exploitation.[6]
Tropical timber was used in Europe followingWorld War II, as trade with East European countries stopped and timber noticeably became sparse in western and southernEurope. Despite efforts to promote lesser-known timber species use, the market continued to focus on part of the usable timber obtainable. West Africa was prone to selective harvesting practices; whileconservationists blamed the timber industry and the farmers for felling trees, others believe rainforest destruction is connected to the problem of fuel wood.[6] The contribution of fuel wood consumption to tree stock decline in Africa is believed to be significant. It is generally believed thatfirewood provides 75% of the energy used in sub-Sahara Africa.[6] With the high demand, the consumption of wood for fuel exceeds the renewal offorest cover.
Other observed changes in these forests are forest disintegration (changing the spatial continuity and creating a mosaic of forest blocks and other land cover types), and selective logging of woody species for profitable purposes that affect the forest subfloor and the biodiversity.[6]
The rainforests that remain in West Africa now greatly differ in condition from their state 30 years ago. In Guinea, Liberia, and the Ivory Coast, there is almost no primary forest cover left unscathed; in Ghana, the situation is much worse, and nearly all of the rainforest is being removed.Guinea-Bissau loses 200 to 350 km2 (77 to 135 sq mi) of forest yearly, Senegal 500 km2 (190 sq mi) of wooded savanna, and Nigeria 6,000,050,000 of both. Liberia loses 800 km2 (310 sq mi) of forests each year. Extrapolating from present rates of loss,botanist Peter Raven pictures that the majority of the world's moderate and smaller rainforests (such as in Africa) could be destroyed in forty years. Tropical Africa comprises 18% of the world's total land area covering 20 million km2 (7.7 million sq mi) of land in West and Central Africa.[6] The region has been facing deforestation in various degrees of intensity throughout the recent decades. The actual rate of deforestation varies from one country to another and accurate data does not exist yet. Recent estimates show that the annual pace of deforestation in the region can vary from 150 km2 (58 sq mi) inGabon to 2,900 km2 (1,100 sq mi) inCôte d'Ivoire. The remaining tropical forests still cover major areas in Central Africa but are abridged by patches in West Africa.
The African Timber Organization member countries eventually recognized the cooperation between rural people and their forest environment. Customary law gives residents the right to use trees for firewood, fell trees for construction, and collect of forest products and rights for hunting or fishing and grazing or clearing of forests for maintenance agriculture. Other areas are called "protected forests", which means that uncontrolled clearings and unauthorized logging are forbidden. After World War II, commercial exploitation increased until no West African forestry department was able to make the law. By comparison with rainforests in other places of the world in 1973, Africa showed the greatest infringement though in total volume means, African timber production accounted for just one-third compared to that ofAsia.[6] The difference was due to the variety of trees in Africa forests and the demand for specific wood types in Europe.
Forestry regulations in East Africa were first applied by colonial governments. The Tropical Forestry Action Plan was conceived in 1987 by theWorld Resources Institute in cooperation with theFood and Agriculture Organization, theUnited Nations Development Program, and theWorld Bank with hopes of halting tropical forest destruction.[6] In its bid to stress forest conservation and development, theWorld Bank provided $111,103 million to developing countries, especially in Africa, to help in developing long-range forest conservation and management programs meant for ending deforestation.
In early 2007, scientists created an entirely new proxy to determine the annual mean air temperature on land—based on molecules from the cell membrane of soil-inhabiting bacteria. Scientists from the NIOZ,Royal Netherlands Institute for Sea Research conducted a temperature record dating back to 25,000 years ago.[8]
In concordance with their German colleagues at theUniversity of Bremen, this detailed record shows the history of land temperatures based on themolecular fossils of soil bacteria. When applying this to the outflow core of theCongo River, the core contained eroded land material and microfossils from marine algae. That concluded that the land environment of tropical Africa cooled more than the bordering Atlantic Ocean during the last ice age. Since the Congo River drains a large part of tropical central Africa, the land-derived material gives an integrated signal for a very large area. These findings further enlighten natural disparities in climate and the possible costs of a warming earth on precipitation in central Africa.[8]
Scientists discovered a way to measure sea temperature—based on organic molecules from algae growing off the surface layer of the Ocean. These organisms acclimatize the molecular composition of their cell membranes to ambient temperature to sustain regular physiological properties. If such molecules sink to the sea floor and are buried in sediments whereoxygen does not go through, they can be preserved for thousands of years. The ratios between the different molecules from the algal cell membrane can approximate the past temperature of the sea surface. The new “proxy” used in this sediment core obtained both a continental and asea surface temperature record. In comparison, both records show that ocean surface and land temperatures behaved differently during the past 25,000 years. During the last ice age, African temperatures were 21 °C, about 4 °C lower than today, while the tropicalAtlantic Ocean was only about 2.5 °C cooler. Lead author Johan Weijers and his colleagues concluded that the land-sea temperature difference has by far the largest influence on continental rainfall. The relation of air pressure to temperature strongly determines this factor. During thelast ice age, the land climate in tropical Africa was drier than it is now, whereas it favors the growth of a lush rainforest.[8]
