The African Continent

• Background information: by edgardowelelo@yahoo.com

Africa, the second – largest continent (after Asia), extends from 37°N to 35°S of the equator. Bordered by the Atlantic Ocean on the west, the Mediterranean Sea on the north, and the Red Sea and Indian Ocean on the east, it is connected by land only to Asia at the Sinai Peninsula of Egypt. Africa has the highest average land elevation (Highlands) of any continent. While it lacks the splendid long mountain ranges found on other continents, it has relatively little land at or near sea level. Much of eastern, central, and Southern Africa lies above 5000’ (1,500 m) elevation. In the north, a wall of mountains dominated by the Atlas range stretches from Morocco east to northern Tunisia. The Sahara Desert is peppered with massive mountain ranges that culminate in Chad’s Tibesti Mountains, which peak at 11,204’ (3,415 m) elevation. In west Africa, which has the lowest percentage of highland area, the Guinea highlands reach up to 6,069’ (1,850 m) at Mount Nimba, in Ivory coast. The highlands of Cameroon, which stretch to the Gulf of Guinea islands, are crowned by Mount Cameroon at 13,353’ (4,070 m). Ethiopia has the highest average elevation of any large African country, with extensive mountain ranges and high plateaus on both sides of its rift valley. The high point is Ras Dashan, at 15,158’ (4,620 m), in the Semien Mountains. There are numerous isolated volcanic peaks along the eastern rift valley, such as Mount Kenya (17,058’ / 5,199 m) and Mount Elgon (14,178’ / 4,321 m) in Kenya, and Mount Kilimanjaro (Africa’s tallest, at 19,340’ / 5,895 m), Mount Meru (14,979’ / 4,566 m), and the highlands surrounding Ngorongoro Crater in Tanzania. Along the western arm of the rift valley there are both volcanic peaks, such as the recently active Nyiragongo, in DRC, and non-volcanic ranges such as the Ruwenzori, on the Uganda – DRC boundary, which peaks at 16,763’ (5,109 m) on Mount Stanley. Most of Southern Africa, as far north as Angola, Zambia, and Malawi, sits on vast plateaus of over 3,300’ (1,000 m) elevation. The South’s highest peaks are in eastern Zimbabwe and in the Drakensberg Mountains of South Africa and Lesotho which reach 11,425’ (3, 482 m). Africa’s highlands give way to coastal plains of varying widths. Wide coastal plains are a feature chiefly in the Mauritania / Senegal / Gambia / Guinea Bissau area: from Ivory coast east to Nigeria (and inland along the Niger valley; in Southern Somalia; and from Southern Tanzania to Mozambique. Coastal plains in most of eastern and Southern Africa are relatively marrow. Africa’s coastline is rarely broken up by Peninsulas or inshore archipelagos. Coral reefs flank much of the Red Sea and Indian Ocean shores but are absent on the Atlantic side. Inland of the beaches in much of tropical Africa there are strings of small lagoons flanked with mangrove swamps.

• THE GREAT RIFT VALLEY

The most dramatic geological feature of the African continent is the rift valley system of eastern Africa known as the Great Rift Valley. “Temporary” features in geological time, rift valleys form when a landmass is splitting apart due to the divergent movements of tectonic plates. When the plates separate, the land in between drops, forming a rift in the earth’s crust. Africa’s rift valley is a long strip of land extending from the Dead Sea area of Israel and Jordan south to Mozambique that is gradually dropping in elevation, causing the areas on either side to rise. The resulting friction has spawned volcanoes on the sides of the valley in certain areas. Some of the valley has been filled in by saline or freshwater lakes. The Res Sea covers most of the northern third of the valley floor. Between Southern Ethiopia and Malawi, the rift valley splits into eastern and western branches. The eastern rift valley slices through Kenya and Tanzania. The western rift valley runs through eastern DRC and the western borders of Uganda, Rwanda, Burundi, and Tanzania. The two rejoin in Malawi (under Lake Malawi / Nyasa), and the single rift extends to Mozambique and will probably one-day reach the Indian Ocean.

• VOLCANOES IN AFRICAN CONTINENT

Formerly active volcano zones are scattered about Africa. In the northwestern half these include the Canary and Cape Verde Islands, in the Atlantic Ocean off Morocco and Senegal, respectively; several ranges in the central Sahara; and the Cameroon line of volcano, which extends into the Gulf of Guinea islands. In the Southeastern half the major areas are along the western rift valley in eastern DRC and Rwanda; flanking the eastern rift valley in Kenya and Northern Tanzania; and an arc in the Indian Ocean from Grand Comoro Island east to Mauritius and Reunion islands. Ngorongoro Crater, along the rift valley in northern Tanzania, was once a mountain – perhaps as tall as Kilimanjaro – whose cone collapsed inward, forming a caldera, a great basin ringed by slopes.

• RIVERS AND MARSHES

Of the four (4) great river systems of Africa, only the Congo River (called the Zaire River in DRC) has a relatively constant flow. The highly seasonal rainfall distribution away from the equator causes great variability in the flow of the Nile River in northeastern Africa, the Niger River in West Africa, and the Zambezi River in the South. While Africa’s four (4) major rivers flow into the Sea, forming large deltas, other continental rivers are landlocked, flowing into lakes such as Lake Chad. The Okavango Delta of Botswana is an inland delta without a lake that is fed by rivers draining the Angolan highlands. Seasonally flooded marshes, important for wildlife, particularly birds, are found along the Nile in the SUDD area of South Sudan, along the Niger in Mali, and near the Zambezi in Zambia and northern Botswana.

• LAKES AND PANS IN AFRICAN CONTINENT

The largest lake on the continent is shallow Lake Victoria (Nyanza) in East Africa, a source of the Nile River. Several long, very deep lakes fill parts of the rift valleys, including Lake Tanganyika and Lake Malawi (Nyasa). A variety of freshwater and soda or alkaline lakes, some very important for water birds, dot other areas of the rift valleys. Soda lakes, such as Lake Natron, in Tanzania, a breeding ground for flamingos, form in interior drainage lakes (with no outlets to the sea) in dry areas that become subject to intense evaporation. Their waters become saltier in dry periods and turn highly alkaline. Some may dry out completely, leaving a wasteland crusted over with minerals. The gradual drying out of the Sahara has eliminated many former lakes, and has contributed to the reduction in size of Lake Chad to its south. The water Level in Lake Chad rises and falls drastically with variable multi annual cycles of wet and dry. In dry areas many lake beds have no water at all for long periods; these are called Chotts in northern Africa and Pans in Southern Africa. During exceptionally wet periods, freshwater may cover these lake beds.

• WATER HOLES

Many of Africa’s National parks and Game reserves have natural or man – made water holes that attract many types of animals, which come to drink and in some cases bathe. Some water holes are fed by natural springs or rainwater; others are remnant ponds in dried – out riverbeds, becoming part of the river in the wet season. Some water holes under dry streambeds reach the depth of the water table and are dug out by thirsty animals,

• AFRICAN ISLANDS

Islands of varying sizes and origins are scattered around continental Africa. Generally, islands have fewer species of wildlife than nearby continents, and those near the mainland have few or no endemic wildlife species (species not found anywhere else). Africa’s largest island, Madagascar was joined with Africa for part of the Age of Mammals (both were part of the supercontinent of Gondwanaland, along with India, Arabia, Australia, South America, and Antarctica). After Madagascar became an island it lost contact with (and ceased to be invaded by) newer land mammal groups, and its mix of wildlife evolved on its own. Today Madagascar is home to a fascinating range of chiefly endemic species. Volcanic islands that rise from the Sea and were never a part of a continent have many fewer species than would be found in similar vegetation on a continent. (The Same can be said of coral line islands or atolls, which build up over submerged volcanoes.) The chance arrivals of wildlife to such islands often lead to rapid evolution of new species. This has occurred on Sao Tome and Principe, in the Gulf of Guinea; the Comoro Islands in the Indian Ocean; and in the Canary and Cape Verde Islands in the Atlantic.

• AFRICAN CLIMATE

The climatic zones of Africa are quite predictable, except where disrupted by mountain ranges and unusual Ocean currents. In general, areas along the equator are warm and humid with rain all year (with two peaks). Proceeding northward and southward from the equator, rainfall totals gradually decrease; near the Tropics of Cancer and Capricorn, there is a single high – sun (summer) rainy season. The northwestern and southwestern extremes of the continent have low – sun (winter) rainfall. Temperatures are highest in much of Africa in the late dry season before the rains cool things down.

• AFRICAN RAINFALL PATTERNS

In most of Africa, rainfall patterns are greatly influenced by the height of the midday Sun in the sky. Because of the tilt of the earth on its axis (at an angle of 23. 4°), the Sun is directly overhead at the Tropic of Cancer (23.4°N) on or around June 21, the first day of the Northern Hemisphere summer, and is directly overhead at the Tropic of Capricorn (23.4°S ) on or around December 21, the first day of the Southern Hemisphere summer. At the equator the Sun is directly overhead in March and September. The time at which the Sun is directly overhead at a particular place is referred to as that region’s high – Sun season. Between December and June, the Sun appears to move northward in the sky as it approaches its highest point over the Tropic of Cancer in June. Having reached this point, it then proceeds southward, arriving overhead at the Tropic of Capricorn on December 21. Areas between the Tropics, including the equator, experience high Sun twice: once when the Sun is moving northward and again when it is returning southward. The higher the Sun the more it warms the air, thereby pulling up from the earth moisture that forms clouds and then falls as rain. Generally, areas with a single high – Sun season have one rainy season, while those with two high – Sun seasons have two periods of peak rainfall. Rainfall amounts generally decrease with increased distance from the equator. In the vast swath of Africa from Senegal to Sudan, the number of months with reliable rainfall decreases from five in southerly areas to two months in the more northerly Sahara. In summer rainfall zones north of the equator, from Senegal east to Ethiopia, most of the rain falls from May through October, while to the South, from inland Namibia east to Mozambique, most of the rain falls from November through April. These areas experience a long, very dry season in the lower – Sun months. Closer to the equator there are generally two rainy seasons. These occur roughly from March through May and September through November. In much of eastern Africa, the former period is called the long rains, the latter the short rains. Rainfall is relatively constant year – round only in parts of the Congo (DRC) Basin and in the coastal strip of Kwazulu Natal in South Africa. Winter rainfall zones, which have hot dry summers and get their rains during low Sun, are found in Africa’s northern and southern extremes. Morocco and eastward along the Mediterranean Sea in the north, and in the Cape area of South Africa. During the winter months, cyclonic storms from the west, which bring rain to Europe or Sub Antarctic regions stray into these edges of Africa that are farthest from the equator. During the summer, these regions see little or no rain for many months. Other factors can affect an area’s rainfall totals. Mountains often have increased rainfall on higher elevations and windward slopes, and decreased rainfall on the highest summits, leeward slopes, and in lowlands in the downwind rain shadow. Warm offshore currents bring higher rainfall accumulations as air masses over them come ashore. In southeastern Africa, the southward – flowing Mozambique Current sweeps down along eastern South Africa, past Kwazulu Natal to southeastern Cape Province. With the much higher rainfall, humidity, and temperatures brought by this current, a wide variety of savanna and forest wildlife are able to extend their ranges southward to Kwazulu Natal.

• AFRICAN DESERT CLIMATES

The Sahara region, centered on the Tropic of Cancer, is the largest desert in the world. Stretching from Mauritania in the west to Egypt in the east, the Sahara covers about one – sixth of Africa. Most years it receives little or no rain. With rare exceptions, neither the cyclonic storms to the north nor the summer monsoon rains of the tropics to the South penetrate the region. Heat can be intense in the late dry season in areas near the deserts. The Sahara is very dry and hot in summer but can be cold in winter and at night. Dry desert climates are rare near the equator. The equatorial deserts of the Horn of Africa, sometimes called the Somali – Maasai arid zone, blanket much of Somalia, eastern Ethiopia, Djibouti, Eritrea, and northern Kenya. Two of the factors that created this desert are the rain – shadow effect of the Ethiopian highlands and the cold currents off Somalia. Along the western coast of Southern Africa, the cold, north – flowing Benguela Current is responsible for the Namib Desert, a long strip of foggy, yet nearly rain – free land that extends along the Namibia and Angola coastline, almost as far north as the equator. Inland, the Kalahari Desert of South Africa and Botswana, which gets light summer rains, blends into the Karroo, arid scrublands of interior Cape Province. During the Southern winter, nighttime temperatures in these desert regions dip to freezing.

• AFRICAN VEGETATION (FLORA)

The annual and seasonal distribution of rainfall and latitudinal and elevational temperature gradients largely determine the vegetation of an area. The vegetation of Africa can be categorized in several distinct zones, but much of the landscape is transitional or a mosaic of types; in places it has been greatly altered by the activities of humans, including farming, logging, and grazing of domestic animals. Here is a simple breakdown of the continent’s plant geography. An equatorial belt of rain forest runs along the Gulf of Guinea coast of West Africa, expanding into a broader zone from Gabon through much of the Democratic Republic of Congo (DRC). Extending away from the rain forest to the north, east, and south are belts of gradually drier vegetation. The forest savanna mosaic belt ranges from rain forest in the better – watered soils to forest mixed with wooded savanna in better – drained soils. Next is a zone of Savanna woodland and grassland. Beyond this are regions of sub desert, which has scattered small bushes, and steppe, sparse grassland without trees. These zones give way in some areas to true desert, which is nearly devoid of vegetation. Far from the equator, in the winter rainfall areas near the Mediterranean and Cape Town, macchia scrub, typical Mediterranean – type vegetation, dominates. Mountainous areas, scattered throughout the continent, are complicated in vegetation. Many have high forests (montane forests) and are topped with specialized flora and alpine grasslands and deserts.

• TROPICAL RAIN FOREST  

These lowland forests receive more than 60” (1,500 mm) of rain, well distributed year – round. They (Tropical Rain Forest) can be subdivided into tropical rain forests, with no dry season, and tropical evergreen forests, which have most of the characteristics of rain forests but experience three or so drier months. Unlike temperate – zone forests, tropical rain forests have many dozens, sometimes more than 100, species of trees. The interlocking canopy of branches – which may be 65 – 100’ (20 – 30 m) high, with scattered emergent giant trees reaching 200’ (60 m) – allows very little light to reach the forest floor. Most rain – forest trees have smooth trunks with few branches at lower and middle levels; their branches typically support a rich array of epiphytic plants, including Orchids. Lengthy climbing woody vines called lianas snake from tree to tree. In uncut primary (virgin) rain forest there is little undergrowth, and it is relatively easy to walk about. In forest that has been partly cut, and around clearings in forests, a dense tangle of undergrowth forms. These areas have quick – growing but short – lived trees and are often rich in fruiting and flowering species of interest to birds and mammals. While significant blocks of rain forest, known as Congolese forest, survive in Gabon, Congo, and DRC, very little forest remains west of Cameroon. Great conservation efforts are needed to save the small remnants in Sierra Leone, Liberia, and Ivory Coast. There is a great diversity of species in the African rain forests, which are little visited by tourists. Most birds, mammals, and reptiles of the rain forest are hard to see because of the dense foliage and their innate shyness, nocturnal habits, and low population densities. The few large mammals, such as small antelopes and treetop monkeys, are heavily persecuted by bush meat – gatherers. Photography is difficult, due to the dark forest interior and the distance to the treetop haunts of the animals.

• FOREST – SAVANNA MOSAIC

A hybrid vegetation zone, the forest – savanna mosaic forms a transition between the rain forest and savanna. It receives somewhat less rainfall than the rain forest, but rain forest survives along its rivers and floodplain swamps and in some hilly areas. There may be patches or strips of forest penetrating into and among neighboring areas of wooded savanna and luxuriant grassland. Derived savanna, poor, shrubby grassland, occurs in areas of moist forest that have been cleared or eroded. The forest – savanna mosaic is expanding in area as humans clear more and more of the rain forest.

• SAVANNA WOODLAND AND GRASSLAND

There is an enormous variety of Savanna habitats, which together cover about 40 percent of the African landscape. The savannas are divided by the equator into northern savanna and southern savanna. With annual rainfall accumulations ranging from 12 to 60” (300 – 1500 mm), savannas are often subdivided into moister and drier types. Moist savanna, usually covered with broad – leafed deciduous woodland, receives 35 – 60” (900 – 1,500 mm) of rainfall yearly, with one very dry season (two near the equator). Fires sweep through in the dry season, but they rarely kill the thick – barked trees. The moist savanna north of the equator in higher – rainfall areas, called the Guinea savanna, has broad – leafed deciduous woodlands (Isoberlinia is a dominant tree genus) with tall (10’/3m) coarse grasses. In south – central Africa, the wooded moist savanna is called Miombo woodland. Dominated by trees of the Brachystegia genus, which often form a canopy overhead, Miombo woodland covers vast areas of Zambia and Zimbabwe. Wildlife is fairly conspicuous (visible) in these habitats, particularly in the drier months. In the wetter months, access and visibility are restricted by muddy roads and the high grasses, which may grow to 12’ (3.5 m) tall. The drier savannas, characterized by scattered thorny trees and bushes, typically have a yearly rainfall of 12 – 35” (300 – 900 mm), with a long dry season. These savannas extend in a broad belt from Senegal to southern Somalia, southward through Tanzania, and from Angola and western Zambia south to South Africa. North of the equator this zone is called Sudan savanna. Dry woodland, grassland with bushes, and open grassland steppe predominate. Feather – leafed acacias are common; various deciduous broad – leafed trees and enormous – trunked baobabs predominate in certain areas. The thin strip of these drier savannas and steppe habitats extending across the continent at the southern boundary of the expanding Sahara is called the Sahel. This greatly degraded zone is subject to long periodic droughts and suffers from severe overgrazing by domestic animals. In South – central Africa, the drier savanna is covered with a leguminous, open woodland called Mopane woodland, which has fewer species of shorter, thinner trees than Miombo woodland. Mopane woodland occurs in badly drained clay soils from central Zambia south to Transvaal and west to southwestern Angola. During wet seasons (Rainy seasons) in drier savannas, both north and south of the equator, the grass may grow several feet tall; grassfires here are less severe than those in the moist savanna. Many of the great eastern and southern wildlife reserves are located in drier savanna regions, where nutritious grasses, leaves, and the seedpods of trees attract wildlife. The good visibility in the driver savannas makes them excellent areas for viewing and photographing wildlife.

• SUB DESERT AND STEPPE

Between the savanna and the true desert are areas that receive 6 – 12” (150 – 300 mm) of rain a year (on average). This scant rain usually is concentrated in one or two months, followed by ten or more dry months. Plant life in sub desert – also called semi – desert or semi – arid desert usually consists of scattered dwarf shrubs, irregular growths of short grasses (depending on rains), and a sparse line of trees along the intermittent streambeds. This habitat extends along the southern edge of the Sahara, making up much of the area known as the Sahel, and is the dominant vegetation in the sub deserts of the Horn of Africa, which are known as the Somali – Maasai arid zone and cover the lowlands of Somalia, Djibouti, Eritrea, eastern Ethiopia, northern Kenya, and northeastern Uganda, with fingers reaching south into Tanzania. The Kalahari Desert of much of Botswana, eastern Namibia, and South Africa, along with the Karroo region of interior Cape Province, South Africa, are of similar vegetational structure. Steppe is a term for dry grasslands neighboring true deserts. There is a swath of steppe on the northern edge of the Sahara, south of the Atlas and other mountain ranges of North Africa.

• TRUE DESERT

In true desert, most of the land is devoid of plant life of any kind, and annual rainfall ranges from none to 6” (0 – 150 mm). African deserts occur in three main areas; the vast Sahara, in the north from Mauritania east to the Red sea; some of the Horn of Africa in Somalia, Djibouti, and neighboring Ethiopia; and the coastal Namib Desert of Namibia. Plants are scarce in such places, but seeds, lying dormant for years, do sprout when erratic rains soak the ground. Barren sand dunes, gravel, and rocks blanket vast areas of true deserts. The Sahara has been getting drier and expanding in size steadily since the time of the Roman Empire. In this century the misuse by humans (and their domestic animals) of the fragile ecosystems of the sub deserts and steppes is causing more rapid expansion of the desert in a process termed desertification.

• MACCHIA SCRUB

Macchia scrub is a term applied to the common vegetation associated with Mediterranean regions. It covers areas poleward from either tropic (Cancer or Capricorn) that have a single rainy season in winter. Globally it occurs only on the western sides of continents, in southern Europe, southwestern Australia, central Chile, California, and two areas of Africa: along the Mediterranean from Morocco east to Tunisia, and in the southern Cape Province of South Africa. The cool wet winters are followed by long, hot, rainless summers. The dominant vegetation consists of dense evergreen shrubs, stunted trees, and superb spring wildflowers. The isolated macchia scrub vegetation zone in South Africa’s Cape Province is so rich in endemic plant species that it is called the “Cape Floral Kingdom”.

• MONTANE VEGETATION (FLORA)

In Africa the forest above 5,000’ (1,500 m) elevation are often called Montane forests (In Latin America these would be called subtropical and temperate – zone cloud forests). Africa’s Montane forests thrive in cool, moist areas with frequent cloud cover or fog. They are usually not as tall as lowland rain forests, and have a smaller average leaf size. Those on a mountain’s windward side tend to be evergreen, while those on the leeward side, in the rain shadow, tend to be deciduous. Long strands of Usnea lichensii) – similar to Spanish moss of the Americas) hang from the limbs on – moister ridges. Above the tree line afro – alpine vegetation occurs, including giant Lobelias and Senecio plants in moister areas of the equatorial mountains and alpine grassland in some drier areas. Coniferous and Oak forests cover moister areas of the Atlas Mountains in northwestern Africa. Patches of broad – leafed forest extend from East Africa down through Malawi, eastern Zimbabwe, and the Drakensberg Mountains of South Africa, to the coast of Cape Province near Knysna. Because montane forests tend to occur in isolated pockets interrupted by intervening lowland forests or savannas, they have given rise to a large number of endemic plant and animal species with restricted ranges. Such species need careful protection if they are to survive. The isolated relict montane forests of the Guinea highlands, Cameroon, Angola, and various islands are of particular concern to conservationists.

 

• WATERSIDE HABITATS

Although most vegetation zones are at the mercy of rainfall, Africa also has several important habitats that have little dependence on rainfall. Riverine (or gallery) forests grow along most rivers and streambeds. Their trees and undergrowth, whose roots have access to water levels normally found in much wetter regions, are much more luxuriant than would be found in the surrounding area away from the watercourses. These – conditions allow many plant and animal species usually found in wetter areas to survive in relatively arid regions. Among the permanent vegetation found in marshy areas in both wet and dry regions is papyrus, a marsh plant with large clumps of fine tassels at the top. Along the coasts of tropical Africa – Mangrove swamps are common. Unlike other trees, mangroves with their tangles of stilted roots, thrive in brackish and salty water. They provide an important habitat for wildlife.

• MIGRATION PATTERNS

 For millions of years there have been annual migrations of large numbers of mammals – herds of herbivores and some of the carnivores that fed on them – in drier zones of Africa. The herds take advantage of temporary good grazing in one area part of the year and move to other areas the rest of the year. Excessive hunting, fencing, grain field production, and competition with domestic livestock have eliminated some of Africa’s migrations, but significant migrations of large grazing mammals still occur in the Sudd region and Boma National Park of SOUTH SUDAN; between the Okavango Delta and Chobe National Park in Botswana, and in the Kalahari Desert. The present – day wildebeest and zebra migration of Tanzania’s Serengeti and Kenya’s Maasai Mara reserves is a unique circular migration pattern. The animals move clockwise, grazing in the short – grassy plains of the southeast from December to April, in the wooded savanna of the west – from May to July, and in the taller grassy hills to the north from August to October. This migration has not been interrupted by human activity and has increased in recent years to more than a million animals.

• AFRICA’S BIRD MIGRATION

Bird migration takes place over all of Africa and its islands. Vast numbers of birds that breed in Europe and Asia fly to Africa to spend the fall, winter, and spring. The Sahara is an enormous barrier, yet a number of birds store up body fat and cross it twice a year in a broad front. Soaring birds that ride thermal air currents over land avoid crossing large expanses of water as they would use up too much energy flapping their wings. These larger birds enter and leave Africa at four(4) sites: the Tangier area of Morocco; Cap Bon, Tunisia; the Sinai area of Egypt; and the Ras Siyan Peninsula, Djibouti. Shorebirds are found widely around the continent, while most ducks from Eurasia winter north of the equator. The grassland parks of eastern Africa are winter home to impressive numbers of wheatears, yellow wagtails, and Caspian plovers. Eagles (especially steppe eagles), common buzzards, and various falcons follow the rains southward to Southern Africa, returning northward with the rains in the spring. Many intra – African migrants breed during the rains north of the equator and then winter south of the equator during the Southern Summer Rains.