Forest zone
Encyclopedia
In West Africa
, the forest zone refers to the southern part of the region once covered by tropical rainforest
. Sometimes this region is referred to as Guinea
to distinguish it from the grassland-covered Sudan
, drier Sahel
and perarid Sahara
.
and Sierra Leone
, most of Guinea
, the southern halves of Côte d'Ivoire
and Nigeria
, and parts of Ghana
, Togo
and Guinea-Bissau
.
The Dahomey Gap
splits the forest zone into two halves by producing an area of much drier climate
- Accra
receives less than 760 millimetres (30 inches) of rainfall per year - between the wetter regions capable of supporting rainforest
. The western forest zone is known as the Upper Guinea forests, and extends from Guinea to western Togo, and the eastern forest zone is known as the Lower Guinea forests, and extends from southeastern Benin through southern Nigeria and into Cameroon
.
To the north, as the length for which the region is affected by the Intertropical Convergence Zone declines, the dry season becomes too long to support rainforest except in the wettest areas of the far west. Thus the forest fades out, except on some rivers, north of about 7° N in the east and 9° N in the west.
During the Last Glacial Maximum
(and probably more severely during earlier glaciations), because the Atlantic Ocean
was up to six degrees cooler, rainfall was dramatically reduced (by up to ninety percent in the area around Freetown
) est all but vanished, probably surviving only in the extreme southeast of Nigeria and a few coastal areas of Côte d'Ivoire.
craton
s and has not been tectonically active in Phanerozoic
periods. (It is believed that these cratons came together mear the end of the Precambrian). Most of it is flat to undulating lowland, with mountains only on its northern fringe, rising to 1948 metres in the Loma Massif. Many rivers cross the forest zone, with the most important being the Niger
and the Volta
.
and around Mont Nimba, maxima are about 27 °C but minima can be relatively low at 16 °C.
The major factor governing the climate of the forest zone is rainfall. During the northern summer, a vast area of very low pressure centred on India
extends a trough across the region. This trough reaches its most northerly position between July and September driving extremely moist westerly winds onto the coast from the Atlantic and producing extremely heavy rain of as much as thirty inches per month in lowland sites in Guinea, Sierra Leone and Liberia. As this trough moves north and south, it creates two rainy seasons on the extreme southern coast: a heavy one between May and July and a lighter one in October and November.
During the northern winter, an anticyclone
develops over the Sahara and drives dry northeasterly winds over the region, creating a dry season except in the extreme southeast (where the monsoonal low over Southern Africa
has the unusual effect of producing westerly winds on its northern flank north of the equator
). This effect is sufficiently widespread that the driest months of January and February are not totally dry on the coast as they are further inland (though average rainfall is typically only 1 inch per month even in Abidjan).
Total annual rainfall decreases with distance from the coast and is also heavily influenced by the aspect
of the coastline. In the wettest areas of Guinea, Sierra Leone and Liberia, average annual rainfall ranges from 3000 to 5000 millimetres (120 to 200 inches), whilst in Abidjan
it is about 2050 millimetres (81 inches), in Lagos
1800 millimetres (71 inches) and about 1400 millimetres (55 inches) at the northern edge of the forest.
, soils are often fertile and there are large areas of subsistence farming
. Major crops include millet
, yams
and rice
, whilst plantation
agriculture
is extensive on the best soils, producing chiefly cocoa. Further west, due to the ancient geology of the region, soils are much less fertile and farming becomes chiefly confined to the raising of perennial crops, with cocoa remaining pre-eminent. Forestry, however, has devastated much of the natural rainforest in countries such as Côte d'Ivoire and Liberia, and farmers without land have been pushed onto land with soil
very marginal for agriculture by population growth, which, despite frequent warfare, continues to be among the highest in the world.
The eastern part of the forest zone is one of the most heavily populated parts of Africa, largely owing to its abundant and highly reliable rainfall and the fertile alluvial soils. Whilst this region contains numerous large cities, the most important being Lagos, Ibadan
and Port Harcourt, both of which have grown into mega-cities since the 1970s, the majority of its population remains rural and dependent upon subsistence farming. Major ethnic groups include the Igbo
and Yoruba
. The western part is less populated but is similar demographically to the east, with numerous African tribes predominating. The major cities here are Abidjan and Conakry
.
The fauna includes many endemic
mammal species, most of which are now highly endangered
because of deforestation
. The most famous is the pygmy hippopotamus
(Hexaprotodon liberiensis), whilst the royal antelope
(Neotragus pygmaeus) is one of the smallest hoofed mammals in the world and is remarkable for its ability to leap up to ten times its body size.
Though many national parks and strict nature reserves exist to protect what remains of the forests in this region, most of them exist only on paper because of lack of finance. Thus, the future of the forests of this region is in grave doubt.
West Africa
West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the UN definition of Western Africa includes the following 16 countries and an area of approximately 5 million square km:-Flags of West Africa:...
, the forest zone refers to the southern part of the region once covered by tropical rainforest
Tropical and subtropical moist broadleaf forests
Tropical and subtropical moist broadleaf forests , also known as tropical moist forests, are a tropical and subtropical forest biome....
. Sometimes this region is referred to as Guinea
Guinea (region)
Guinea is a traditional name for the region of Africa that lies along the Gulf of Guinea. It stretches north through the forested tropical regions and ends at the Sahel.-History:...
to distinguish it from the grassland-covered Sudan
Sudan (region)
The Sudan is the name given to a geographic region to the south of the Sahara, stretching from Western to Eastern Africa. The name derives from the Arabic bilâd as-sûdân or "land of the Blacks"...
, drier Sahel
Sahel
The Sahel is the ecoclimatic and biogeographic zone of transition between the Sahara desert in the North and the Sudanian Savannas in the south.It stretches across the North African continent between the Atlantic Ocean and the Red Sea....
and perarid Sahara
Sahara
The Sahara is the world's second largest desert, after Antarctica. At over , it covers most of Northern Africa, making it almost as large as Europe or the United States. The Sahara stretches from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean...
.
Extent
The forest zone of West Africa, in the strict sense, covers all of LiberiaLiberia
Liberia , officially the Republic of Liberia, is a country in West Africa. It is bordered by Sierra Leone on the west, Guinea on the north and Côte d'Ivoire on the east. Liberia's coastline is composed of mostly mangrove forests while the more sparsely populated inland consists of forests that open...
and Sierra Leone
Sierra Leone
Sierra Leone , officially the Republic of Sierra Leone, is a country in West Africa. It is bordered by Guinea to the north and east, Liberia to the southeast, and the Atlantic Ocean to the west and southwest. Sierra Leone covers a total area of and has an estimated population between 5.4 and 6.4...
, most of Guinea
Guinea
Guinea , officially the Republic of Guinea , is a country in West Africa. Formerly known as French Guinea , it is today sometimes called Guinea-Conakry to distinguish it from its neighbour Guinea-Bissau. Guinea is divided into eight administrative regions and subdivided into thirty-three prefectures...
, the southern halves of Côte d'Ivoire
Côte d'Ivoire
The Republic of Côte d'Ivoire or Ivory Coast is a country in West Africa. It has an area of , and borders the countries Liberia, Guinea, Mali, Burkina Faso and Ghana; its southern boundary is along the Gulf of Guinea. The country's population was 15,366,672 in 1998 and was estimated to be...
and Nigeria
Nigeria
Nigeria , officially the Federal Republic of Nigeria, is a federal constitutional republic comprising 36 states and its Federal Capital Territory, Abuja. The country is located in West Africa and shares land borders with the Republic of Benin in the west, Chad and Cameroon in the east, and Niger in...
, and parts of Ghana
Ghana
Ghana , officially the Republic of Ghana, is a country located in West Africa. It is bordered by Côte d'Ivoire to the west, Burkina Faso to the north, Togo to the east, and the Gulf of Guinea to the south...
, Togo
Togo
Togo, officially the Togolese Republic , is a country in West Africa bordered by Ghana to the west, Benin to the east and Burkina Faso to the north. It extends south to the Gulf of Guinea, on which the capital Lomé is located. Togo covers an area of approximately with a population of approximately...
and Guinea-Bissau
Guinea-Bissau
The Republic of Guinea-Bissau is a country in West Africa. It is bordered by Senegal to the north, and Guinea to the south and east, with the Atlantic Ocean to its west....
.
The Dahomey Gap
Dahomey Gap
In West Africa, the Dahomey Gap refers to the portion of the Guinean forest-savanna mosaic that extends all the way to the coast in Benin, Togo and Ghana, thus separating the forest zone that covers much of the south of the region into two separate parts...
splits the forest zone into two halves by producing an area of much drier climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
- Accra
Accra
Accra is the capital and largest city of Ghana, with an urban population of 1,658,937 according to the 2000 census. Accra is also the capital of the Greater Accra Region and of the Accra Metropolitan District, with which it is coterminous...
receives less than 760 millimetres (30 inches) of rainfall per year - between the wetter regions capable of supporting rainforest
Tropical and subtropical moist broadleaf forests
Tropical and subtropical moist broadleaf forests , also known as tropical moist forests, are a tropical and subtropical forest biome....
. The western forest zone is known as the Upper Guinea forests, and extends from Guinea to western Togo, and the eastern forest zone is known as the Lower Guinea forests, and extends from southeastern Benin through southern Nigeria and into Cameroon
Cameroon
Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the...
.
To the north, as the length for which the region is affected by the Intertropical Convergence Zone declines, the dry season becomes too long to support rainforest except in the wettest areas of the far west. Thus the forest fades out, except on some rivers, north of about 7° N in the east and 9° N in the west.
During the Last Glacial Maximum
Last Glacial Maximum
The Last Glacial Maximum refers to a period in the Earth's climate history when ice sheets were at their maximum extension, between 26,500 and 19,000–20,000 years ago, marking the peak of the last glacial period. During this time, vast ice sheets covered much of North America, northern Europe and...
(and probably more severely during earlier glaciations), because the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
was up to six degrees cooler, rainfall was dramatically reduced (by up to ninety percent in the area around Freetown
Freetown
Freetown is the capital and largest city of Sierra Leone, a country in West Africa. It is a major port city on the Atlantic Ocean located in the Western Area of the country, and had a city proper population of 772,873 at the 2004 census. The city is the economic, financial, and cultural center of...
) est all but vanished, probably surviving only in the extreme southeast of Nigeria and a few coastal areas of Côte d'Ivoire.
Geography
Except for the extreme east near Mount Cameroon, the forest zone is entirely with a series of PrecambrianPrecambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...
s and has not been tectonically active in Phanerozoic
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...
periods. (It is believed that these cratons came together mear the end of the Precambrian). Most of it is flat to undulating lowland, with mountains only on its northern fringe, rising to 1948 metres in the Loma Massif. Many rivers cross the forest zone, with the most important being the Niger
Niger River
The Niger River is the principal river of western Africa, extending about . Its drainage basin is in area. Its source is in the Guinea Highlands in southeastern Guinea...
and the Volta
Volta River
The Volta is a river in western Africa that drains into the Gulf of Guinea. It has three main tributaries—the Black Volta, White Volta and Red Volta...
.
Climate
Being so close to the equator, the forest zone experiences almost no variation in temperatures across the year. The climate is consistently hot, with maxima typically being about 31 °C and minima around 24 °C. In the Fouta DjallonFouta Djallon
Fouta Djallon is a highland region in the centre of Guinea, West Africa. The indigenous name is Fuuta-Jaloo...
and around Mont Nimba, maxima are about 27 °C but minima can be relatively low at 16 °C.
The major factor governing the climate of the forest zone is rainfall. During the northern summer, a vast area of very low pressure centred on India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
extends a trough across the region. This trough reaches its most northerly position between July and September driving extremely moist westerly winds onto the coast from the Atlantic and producing extremely heavy rain of as much as thirty inches per month in lowland sites in Guinea, Sierra Leone and Liberia. As this trough moves north and south, it creates two rainy seasons on the extreme southern coast: a heavy one between May and July and a lighter one in October and November.
During the northern winter, an anticyclone
Anticyclone
An anticyclone is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere"...
develops over the Sahara and drives dry northeasterly winds over the region, creating a dry season except in the extreme southeast (where the monsoonal low over Southern Africa
Southern Africa
Southern Africa is the southernmost region of the African continent, variably defined by geography or geopolitics. Within the region are numerous territories, including the Republic of South Africa ; nowadays, the simpler term South Africa is generally reserved for the country in English.-UN...
has the unusual effect of producing westerly winds on its northern flank north of the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
). This effect is sufficiently widespread that the driest months of January and February are not totally dry on the coast as they are further inland (though average rainfall is typically only 1 inch per month even in Abidjan).
Total annual rainfall decreases with distance from the coast and is also heavily influenced by the aspect
Aspect (geography)
In physical geography, aspect generally refers to the horizontal direction to which a mountain slope faces. For example, a slope on the eastern edge of the Rockies toward the Great Plains is described as having an easterly aspect...
of the coastline. In the wettest areas of Guinea, Sierra Leone and Liberia, average annual rainfall ranges from 3000 to 5000 millimetres (120 to 200 inches), whilst in Abidjan
Abidjan
Abidjan is the economic and former official capital of Côte d'Ivoire, while the current capital is Yamoussoukro. it was the largest city in the nation and the third-largest French-speaking city in the world, after Paris, and Kinshasa but before Montreal...
it is about 2050 millimetres (81 inches), in Lagos
Lagos
Lagos is a port and the most populous conurbation in Nigeria. With a population of 7,937,932, it is currently the third most populous city in Africa after Cairo and Kinshasa, and currently estimated to be the second fastest growing city in Africa...
1800 millimetres (71 inches) and about 1400 millimetres (55 inches) at the northern edge of the forest.
Land use and demographics
In the eastern part of the forest zone, because of the influence of Mount CameroonMount Cameroon
Mount Cameroon is an active volcano in Cameroon near the Gulf of Guinea. Mount Cameroon is also known as Cameroon Mountain or Fako or by its native name Mongo ma Ndemi ....
, soils are often fertile and there are large areas of subsistence farming
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
. Major crops include millet
Millet
The millets are a group of small-seeded species of cereal crops or grains, widely grown around the world for food and fodder. They do not form a taxonomic group, but rather a functional or agronomic one. Their essential similarities are that they are small-seeded grasses grown in difficult...
, yams
Yam (vegetable)
Yam is the common name for some species in the genus Dioscorea . These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America and Oceania...
and rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
, whilst plantation
Plantation
A plantation is a long artificially established forest, farm or estate, where crops are grown for sale, often in distant markets rather than for local on-site consumption...
agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
is extensive on the best soils, producing chiefly cocoa. Further west, due to the ancient geology of the region, soils are much less fertile and farming becomes chiefly confined to the raising of perennial crops, with cocoa remaining pre-eminent. Forestry, however, has devastated much of the natural rainforest in countries such as Côte d'Ivoire and Liberia, and farmers without land have been pushed onto land with soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
very marginal for agriculture by population growth, which, despite frequent warfare, continues to be among the highest in the world.
The eastern part of the forest zone is one of the most heavily populated parts of Africa, largely owing to its abundant and highly reliable rainfall and the fertile alluvial soils. Whilst this region contains numerous large cities, the most important being Lagos, Ibadan
Ibadan
Ibadan is the capital city of Oyo State and the third largest metropolitan area in Nigeria, after Lagos and Kano, with a population of 1,338,659 according to the 2006 census. Ibadan is also the largest metropolitan geographical area...
and Port Harcourt, both of which have grown into mega-cities since the 1970s, the majority of its population remains rural and dependent upon subsistence farming. Major ethnic groups include the Igbo
Igbo people
Igbo people, also referred to as the Ibo, Ebo, Eboans or Heebo are an ethnic group living chiefly in southeastern Nigeria. They speak Igbo, which includes various Igboid languages and dialects; today, a majority of them speak English alongside Igbo as a result of British colonialism...
and Yoruba
Yoruba people
The Yoruba people are one of the largest ethnic groups in West Africa. The majority of the Yoruba speak the Yoruba language...
. The western part is less populated but is similar demographically to the east, with numerous African tribes predominating. The major cities here are Abidjan and Conakry
Conakry
Conakry is the capital and largest city of Guinea. Conakry is a port city on the Atlantic Ocean and serves as the economic, financial and cultural centre of Guinea with a 2009 population of 1,548,500...
.
Flora, fauna and conservation
Because of its history of glacial epochs, and also the strong seasonality of rainfall, the West African forest zone is not nearly so rich in plant species as other tropical forest areas. There are, however, many species unique to the area, and numerous valuable plants native to the region, including such timber trees as iroko (Chlorophora excelsa).The fauna includes many endemic
Endemic (ecology)
Endemism is the ecological state of being unique to a defined geographic location, such as an island, nation or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, all species of lemur are endemic to the...
mammal species, most of which are now highly endangered
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
because of deforestation
Deforestation
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....
. The most famous is the pygmy hippopotamus
Pygmy Hippopotamus
The pygmy hippopotamus is a large mammal native to the forests and swamps of western Africa . The pygmy hippo is reclusive and nocturnal...
(Hexaprotodon liberiensis), whilst the royal antelope
Royal Antelope
The Royal Antelope is a West African antelope, only 25–30 cm high at the shoulder and weighing only 3.2–3.6 kg — it is the smallest of all antelopes. Their calves are small enough to fit into the average person's open hand...
(Neotragus pygmaeus) is one of the smallest hoofed mammals in the world and is remarkable for its ability to leap up to ten times its body size.
Though many national parks and strict nature reserves exist to protect what remains of the forests in this region, most of them exist only on paper because of lack of finance. Thus, the future of the forests of this region is in grave doubt.