Vegetation
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African vegetation zones
are closely linked to climatic zones, with the same zones occurring both north
and south of the equator in broadly similar patterns. As with climatic zones,
differences in the amount and seasonal distribution of precipitation constitute
the most important influence on the development of vegetation. Moving across
the continent into drier and drier climates, the typical sequence of vegetation
is from tropical moist forest to moist savanna, dry savanna, semidesert, and
finally desert.
Tropical Moist Forest
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Tropical moist forest
occurs in humid tropical areas, usually with 1,500 mm (60 in) or more of
precipitation and a dry season (or seasons) of three to four months or less.
West of the highlands of East Africa and centered in the basin of the Congo
River is a great tropical moist forest extending some 600 km (400 mi) north of
the equator and a similar distance south of the equator. On the west, the
forest extends to the Atlantic coast in the Congo, Gabon, and Cameroon, and
stretches in an interrupted belt along the West African coast to Sierra Leone.
Tropical moist forest also occurs along the eastern side of Madagascar.
Scientists recognize two
major subtypes of tropical forest: tropical rain forest and tropical wetland
forest. Tropical rain forests are characterized by a dense mass of evergreens,
oil palms, and numerous species of tropical hardwood trees divided vertically
into strata, or layers. The upper canopy of treetops forms a dense cover over
the middle layer of treetops and the surface layer of shrubs, ferns, and mosses
below. Rising above the canopy are scattered tall trees, known as emergents. In
dense forest environments, the shrub layer tends to be quite sparse, except
along streams, because the canopy limits the amount of light that penetrates to
the forest floor. Tropical rain forests are extremely diverse in species; pure
stands of a single tree species are rare.
Tropical wetland forests
include both freshwater and saltwater subtypes. Freshwater swamp forests cover
large parts of the Middle Congo River Basin. Saltwater swamp forests occur in
many areas between Senegal and Angola on the Atlantic coast and between South
Africa and the Red Sea on the coast of East Africa. Mangrove species, with
their characteristic tall, arched roots, are highly adapted to the fluctuating
water levels and brackish water found in estuaries and other tidal
environments. Mangrove forests are tangles of roots, tree trunks, and branches
reaching 8 to 23 m (25 to 75 ft) high. Significant areas of mangrove forest
have been lost in order to clear land for rice cultivation, particularly in
West Africa.
Tropical Savanna
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Surrounding the central
tropical forest zone on the north, east, and south is a zone of tropical
savanna vegetation that covers up to 65 percent of the continent. The savannas
have somewhat drier climates compared to the tropical forests. They typically
receive 500 to 1,500 mm (20 to 60 in) of precipitation per year, and have a
pronounced dry season, usually from three to eight months long. Moving
poleward, savanna vegetation transitions from moist woodland savanna to dry
woodland savanna.
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Moist woodland savanna
occurs close to the tropical forest, where climates are wetter and the dry
season is only three to four months. The characteristic vegetation is a mixture
of tall grasses and closely spaced trees. Vegetation is especially dense along
river courses, with trees lining the banks in gallery forests. Shrubs and
grasses are also dense in areas where intensive cultivation and past use of
fire to clear vegetation have led to the degradation of once forested lands.
Shea trees occur widely; their tough outer bark is fire-resistant and their
kernels are a source of oil for cooking and other uses.
Dry woodland savanna,
frequently called Sudan savanna, occurs where there is less precipitation and a
prolonged dry season of about five to eight months. As precipitation declines,
grass becomes shorter and sparser, and the tree cover less dense. The baobab is
the largest tree; it is widely distributed and is valued for its inner bark
(from which rope may be made) and its edible leaves and fruits. Other common
trees are the silk cotton and locust bean, and various species from the acacia
and fig (ficus) families.
Semidesert and Desert
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In the semidesert, or
steppe, zone that lies between the dry woodland savanna and the desert, annual
precipitation is between 250 and 500 mm (10 to 20 in). Rainfall is limited,
localized, irregular, and often violent. Semidesert vegetation fringes the
Sahara on the south (where this zone is referred to as the Sahel savanna),
north (especially the southern slopes of the Atlas Mountains) and east (on the
Red Sea coast). It also occurs in Somalia and northeastern Kenya, in the Karoo
plateau regions of South Africa, and on the inland margin of the Namib Desert
of Namibia and Angola. In addition, the Kalahari Desert is actually a
semidesert region, despite its name. In many of these areas, vegetation occurs
in strips running along contours in the land, where there has been an
accumulation of moisture and soil. These vegetated strips are usually separated
by wide barren areas.
With increasing aridity,
the drought-resistant properties of plants become crucial for their survival.
Trees must be adapted to the prolonged dry period, with deep root systems,
thick bark, small leaves that may be shed, and thorns to discourage animals
from feeding on them. With still greater aridity, only grasses and desert
shrubs survive. Semidesert vegetation is vulnerable to damage from fire,
clearing for cultivation, and overgrazing.
Desert vegetation occurs
in the Sahara and Namib deserts, areas with less than 250 mm (10 in) of
rainfall per year. Desert plant life must adapt to the harsh conditions of
sparse, infrequent rainfall and extreme temperatures. The seeds of some species
lay dormant for prolonged periods, until there is moisture to support their
growth. Large areas of desert are essentially bare; plant growth is
concentrated in channels and depressions where water accumulates when it rains.
Environmental conditions and species found in the Sahara differ from those in
the Namib Desert of southern Africa. In the latter, cold ocean currents
facilitate the accumulation of dew on the desert, which helps to support plant
life. Succulents (plants that retain water) and annual plant species typically
account for most species found in desert ecosystems, with different plant
species characteristic of different desert types (sand, gravel, or rock). The
arid environments of southern Africa have a remarkable number of different
species. Namaqualand, a region in northwestern South Africa, is renowned for
the profusion of brilliantly colored wildflowers that appear after spring
rains.
Mediterranean Shrub Lands
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The shrub lands of the
northwestern and southern tips of the continent have Mediterranean climates,
with warm, dry summers and mild, rainy winters. Unlike most of Africa, this
climate supports distinctive types of temperate plant species. Mediterranean
vegetation is xerophytic (drought-resistant), an adaptation to the
limited rainfall and prolonged dry season that occurs during the summer months.
The tree species typical of the North African shrub lands resemble those found
elsewhere around the Mediterranean Sea, including wild olive, cork, juniper,
and oak. Large areas of North African shrub lands have been damaged or
destroyed through thousands of years of herding and agriculture. Environmental
impact was pronounced during the 20th century, when rapid population increase
and commercialization encouraged the expansion of agriculture into marginal,
environmentally sensitive lands.
The Cape region of South
Africa has a distinctive ecosystem known as fynbos, in which fine-leaved
evergreen shrubs predominate. It is one of the richest plant life biomes in the
world, with some 8,500 species of plants in a relatively small area of about
90,000 sq km (about 30,000 sq mi). Over two-thirds of the species are endemic,
meaning that they are found nowhere else in the world. Distinct subtypes of
fynbos occur along the coast and in the adjacent mountains. In several other
parts of southern Africa infertile soils, fire, and a lengthy dry season
constrain vegetation growth.
Highland Vegetation
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In Africa’s discontinuous
areas of high mountains and uplands, altitude plays a significant role in
determining climate and vegetation. On high peaks such as Kilimanjaro,
vegetation changes as altitude increases: savanna vegetation near the base,
then, in turn, zones of montane forest, bamboo, hagenia, heather, and
high-altitude alpine moorland, with rock and ice at the summits of the very
highest peaks. The montane forests include hardwood trees and many unusual
plant species, including giant heather, giant groundsel, and giant lobelia.
Growing conditions are also unusual due to the high temperatures during the day
and very low temperatures that prevail at night. Some 4,000 species are
associated with the African alpine zone, and three-quarters of these species
are found only in Africa’s montane forests.
Other comparatively high-altitude
regions have distinctive plant life. The highlands of Ethiopia contain
scattered patches of montane forest with many species that resemble temperate
deciduous trees. At higher elevations, tree cover largely disappears—except in
deep valleys—and grasses, sedges, and heathers prevail. In the highlands of
South Africa above 1,100 m (3,500 ft), vast expanses of temperate grasslands
occur. In the highest parts of the Ahaggar and Tibesti mountains of the Sahara,
some plant species resemble those of the Mediterranean region, isolated there
when the region’s climate became drier thousands of years ago.
Soils
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Like vegetation zones,
soil regions in Africa are closely linked to climatic zones. Rainfall and
temperature determine the growth of vegetation, which inhibits soil erosion and
enriches soil with nutrients from decaying organic material, called humus. The
luxuriant vegetation of tropical forest environments produces large quantities
of humus, which is concentrated on the forest floor. In savanna grasslands,
humus extends to a greater depth in the soil. The sparse vegetation of
semidesert and desert regions gives rise to soils with little organic content.
Rainfall and temperature also determine the intensity of chemical weathering,
physical weathering, and leaching—all of which affect the development of soil
types.
Soil development is highly
influenced by the soil’s parent material—the rock from which it is derived—and
by topographic relief. Much of Africa’s soil is derived from ancient,
quartz-rich rocks that produce generally infertile soils with high sand
content. Soils formed in areas of younger volcanic bedrock tend to have higher
clay and mineral content, and are therefore more fertile. Relief plays a major
role in soil erosion, especially by water. Erosion removes topsoil from upper
slopes and deposits eroded materials downslope. These erosion and deposition
processes often create a gradation of soil types along a slope. African farmers
take advantage of these variations in soil type and soil fertility by planting
different crops at different levels of the slope.
Soil-Forming Processes
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Hot, humid tropical climates
provide ideal conditions for chemical weathering, which gradually brings about
the disintegration of parent rock material into soil particles. In drier
climates, physical weathering—the breakup of parent material by the force of
moving water and wind—is more important than chemical weathering.
Soils in humid tropical
regions are especially subject to leaching, the process in which smaller
particles and minerals are carried by groundwater downward through the soil.
When the upper layers of soil have been leached of critical nutrients, they are
left primarily with iron and aluminum compounds, accounting for both their
infertility and their typical brick-red or yellow color.
Salinization and calcification
are important processes in the development of soils in arid and semiarid
regions. Salinization occurs when salts, dissolved in soil water, are carried
upward through the soil and deposited on or near the surface as a result of evaporation.
Few species of plants are adapted to survive in soils with high salt
concentrations. Calcification is prevalent in moderately dry to semiarid
environments, generally in grassland areas. Calcification involves development
of a subsurface layer of calcium carbonate, carried downward from the upper
soil layers.
Major Soil Types
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Despite the richness of
vegetation, soils in the tropical forests of Central and West Africa are poor.
The heavy rainfall of these areas is acidified as it passes through organic
material on the forest floor and leaches most of the mineral content from the
upper soil layers. The resulting soils—classified as oxisols—are quite
infertile, forcing plants to gain most of their nutrient needs from decaying
vegetation. Oxisols are reddish or yellowish in color, reflecting the high
concentrations of iron and aluminum compounds in them.
The soils of the moist
boundary areas between the forests and savanna are subject to high levels of
chemical weathering. The resulting ultisols are highly leached (but less
so than oxisols), have low to moderate organic content, and are generally
infertile.
In savanna regions where
there are moderate levels of seasonal rainfall, chemical weathering is less
pronounced than in moister environments. Calcification occurs where calcium
carbonate levels are high. The resulting soils are called alfisols. The
organic content of alfisols is relatively high, and they are generally quite
fertile.
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In Africa’s arid and semiarid
regions, low rainfall and sparse vegetation gives rise to aridisols.
These soils are poorly developed, with little chemical weathering, infrequent
leaching, and low organic content. Salinization is widespread, resulting in the
concentration of mineral salts at or near the surface. In areas with less
saline soils, irrigated agriculture is possible. Without proper management,
however, irrigated aridisols may become infertile as a result of salinization
or waterlogging.
Soils in certain seasonally
dry areas are heavy and have a high clay content. The clay in these vertisols
expands when it is wet, then shrinks and cracks when dried. These soils are
associated with river floodplains and former lake bottoms, notably the middle
Nile Valley and Lake Chad Basin. Vertisols are quite fertile due to their high
mineral content, and are used extensively to grow cotton and grain crops.
Younger, less developed
soils are classified as inceptisols. Included are the thin, rocky soils
derived from younger volcanic deposits on the Ethiopian Plateau, young beach deposits
in coastal regions, and active sand dunes in semiarid areas. Inceptisols are
generally infertile.
Animal Life
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Africa teems with animals
of all shapes and sizes. The continent has thousands upon thousands of species
of mammals, fish, reptiles, amphibians, birds, and insects. Many of these
animals are linked in an intricate food web. For example, hippopotamuses
deposit large amounts of nutrients in bodies of water where they rest and
defecate; these nutrients support abundant growth of plants, insects, and other
smaller creatures that in turn provide food for species higher in the food
chain. Other animals are linked in symbiotic relationships, such as between big
game animals and birds known as oxpeckers. These birds eat the ticks that
pester the large animals.
F1
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Continental Forest Animals
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African tropical forests
offer many niches and habitats for different species. With a wide array of
different types of food resources available year-round, they allow large
numbers of species to coexist.
Different habitats occur
at different heights of the forest. Each of these habitats harbors a distinct
set of animal species. The ground layer is strewn with nutrient-rich organic
litter, providing a rich environment for many arthropods and insects, as well
as creatures that feed on them, such as moles and rats. The forest canopy
supports numerous species of mammals, including many kinds of monkeys and
flying squirrels. Species of birds, reptiles, bats, and insects also abound.
The forest floor tends to be less diverse, although its wildlife includes some
of the largest and most fascinating species in Africa, including elephants,
lowland and mountain gorillas, and okapis, giraffe-like animals found in the
Congo Basin. Other species include duikers, bushbucks, forest pigs, giant
pangolins (a type of armored anteater), and drills and mandrills (two species
of baboon).
Different areas of the
African tropical forest vary in species diversity: For example, the relatively
undisturbed forests of Gabon are more diverse than those in Nigeria, where
there have been major human impacts on forest ecosystems. Overall, Africa’s
forests appear to support less biodiversity than the larger, more heterogeneous
forests of the Amazon and Southeast Asia.
Animal Life on Madagascar
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Despite its proximity
to the continental mainland, Madagascar’s animal life developed in isolation
after the island broke away from the rest of Africa about 135 million years
ago. It is estimated that 90 percent of the species inhabiting its tropical
forests are endemic, meaning that they are found nowhere else in the world.
Madagascar has some 25 species of lemurs and 30 species of tenrecs, a type of
insectivore. Other native mammal species include several civets and the fossa,
a member of the cat family measuring almost 1.5 m (5 ft) in length.
Madagascar’s bird and insect populations are equally rich and are also largely
endemic.
Because more than 90 percent
of Madagascar’s forests have been affected by human activity, many species on
the island face extinction because of loss of habitat. Many other notable
species have already vanished, including the giant lemur, giant tortoise, and
elephant bird.
Savanna Animals
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The savannas offer a narrower
range of habitats than the forested regions, but nevertheless support
exceedingly rich animal populations. The savannas of eastern and southern
Africa are renowned for their big game animals, huge herds of herbivores, and
abundant bird species. West African savanna regions tend to have less diverse
fauna and smaller animal populations, primarily because of long-standing
pressures from hunting and loss of habitat. Many species are adapted in
particular ways to their environment. Giraffes, for example, have long necks
and therefore can graze on vegetation higher than other animals can reach.
Because rainfall and food supply are highly seasonal, numerous species are
migratory.
Africa is famous for its
huge herds of savanna animals. In areas such as the Serengeti Plain in northern
Tanzania, herds of herbivores, several thousand zebras or gnus (wildebeests)
strong, can stretch for miles. Besides gnus, the savannas support a rich
variety of other antelopes, from huge elands to tiny duikers; others include
hartebeests, impalas, topis, oribis, kobs, and waterbucks. These animals
provide the main food source for carnivores, including lions, leopards,
cheetahs, and hyenas. Other species of large herbivores include elephants,
black and white rhinoceroses, African buffaloes, giraffes, and hippopotamuses.
Many smaller animals, including baboons, several species of monkeys, and a
multitude of small carnivores and rodents, are also found.
Africa’s savannas harbor
rich bird life. With more than 1,000 bird species, Kenya has one of the most
diverse bird populations in the world. Birds of prey, including numerous hawks,
eagles, and falcons, feed on smaller birds and other fauna, while vultures seek
out carrion as a source of food. Brightly colored rollers, kingfishers, and
bee-eaters are commonly seen in the air. Larks and pipits are widespread in the
grasslands, as are flycatchers, bulbuls, babblers, warblers, and swallows.
Other distinctive birds of the region include the crowned-crane, guinea fowl,
ground hornbill, and marabou stork. Some species congregate in huge flocks,
among them flamingos and red-billed queleas. The quelea is considered a pest by
farmers because of the damage it does to crops.
Savanna regions are also
rich in reptile life. Nile crocodiles, as well as other smaller crocodile
species, inhabit waterside environments. Various lizards abound, among them
large Nile monitors and smaller species of chameleons and geckos. The savannas
have many types of snakes, the most feared of which are various species of
vipers, as well as cobras and mambas. The rock python is the largest snake,
being known to attain a length of 8 m (25 ft).
Desert and Semidesert Animals
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Animals in arid environments
must adapt to conditions such as water shortages, high temperatures, and a high
risk of food scarcity. Some species adapt by migrating to other climes, while
others are able to survive for prolonged periods without water. Sizes of animal
populations vary from area to area, depending on food abundance; and from time
to time, due to unpredictable and scarce rainfall.
Rodent species, including
the Nile rat, jerboa, gerbil, and hare, are common in arid and semiarid
regions. Several species of gazelles are also found. Rodents and gazelles serve
as prey for fennecs, other foxes, jackals, and hyenas. Ostriches, the world’s
largest birds, are also found in arid and semiarid regions. Other birds
restricted to the deserts and their fringes include sand grouse and coursers.
Freshwater Fish
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The rivers and lakes of
the northern semiarid and savanna regions—such as the Sénégal, Niger, and Nile
rivers, and Lake Chad—have similar fish populations. Several species of catfish
and the huge Nile perch are the mainstays of the fishing industry. Some fish
species, such as the lungfish, survive the prolonged dry season by burrowing
into the mud of drying streambeds and reemerging the following rainy season.
Such is the biological
diversity of fish in Lakes Victoria, Tanganyika, and Malawi that biologists
consider these lakes critical to the study of evolution. Despite their
relatively young age and close geographical proximity, these lakes have
developed distinct and highly varied fish populations. Lake Malawi alone has
about 540 species of fish—including some 500 species of cichlids—and 99 percent
are endemic. To date, 290 species have been identified in Lake Victoria, half
of them endemic. Lake Tanganyika has about 140 cichlid and 110 other fish
species.
Marine Life
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The Atlantic Ocean off
Africa’s west coast has two cold ocean currents—the Benguela south of the
equator and the Canaries to the north—as well as several areas where cold water
rises to the surface. These zones of upwelling are rich in nutrients and
support large fish populations. Fishing fleets off the coasts of southern and
northwest Africa harvest species such as sardines, herrings, and tuna. Shrimp
are harvested on the coasts of several West African countries.
The waters of the Red
Sea and Indian Ocean are considerably warmer than those of the Atlantic,
supporting the development of coral reefs. These reefs provide for a great
variety of fish species. Local fishers harvest many types of fish, but
large-scale commercial fishing remains relatively unimportant. One famous rare
species of Indian Ocean fish is the coelacanth, characterized as a “living
fossil.” Before it was discovered in 1938, experts believed it had been extinct
for 70 million years.
Insects
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Africa has a vast insect
population. As on other continents, insects play a critical role in African
ecosystems. Some insects are of particular importance to humans as either
transmitters of diseases, soil modifiers, or threats to crops.
Insects as Carriers of Disease
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In colonial times, Europeans
referred to Africa as the “white man’s grave,” reflecting the fear of
life-threatening tropical diseases for which non-Africans lacked natural
resistance. The leading cause of death—among colonists and Africans alike—was
malaria. The malaria parasite is transmitted to humans by the bite of the
female Anopheles mosquito. The World Health Organization (WHO) launched
a worldwide campaign to eradicate malaria during the 1960s by spraying homes
with insecticides, draining breeding sites, and dispensing antimalarial drugs.
The campaign failed: Parasites developed genetic resistance to drugs,
mosquitoes became resistant to insecticides, and impoverished governments
lacked the resources to develop a comprehensive strategy against the disease.
Today, malaria remains Africa’s leading cause of death.
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Various species of tsetse
fly are another scourge of Africa. The tsetse transmits the Trypanosoma
parasite, which causes the often-fatal disease trypanosomiasis, also known as
sleeping sickness in humans and nagana in livestock. The prevalence of tsetse
is believed to be a major factor in settlement patterns in Africa, including
the low population densities of large areas of the savanna. Because cattle are
especially vulnerable to trypanosomiasis, the full economic potential of vast
areas of fertile grassland has not been realized. Certain colonial policies
heightened the tsetse scourge: The creation of game reserves increased
populations of wild animals that serve as natural reservoirs of the Trypanosoma
parasite; and resettlement schemes increased human contact with tsetse and
brought about major epidemics of sleeping sickness. An epidemic in the early
20th century wiped out some two-thirds of the population of what is now Uganda.
Colonial control programs eventually succeeded in limiting, but not
eliminating, the tsetse and the diseases it transmits.
The black fly Simulium
damnosum has had a major impact on settlement in Burkina Faso and several
other countries in West Africa. This insect, which breeds in fast-flowing
streams, transmits a parasitic worm that is responsible for onchocerciasis,
also known as river blindness, which causes blindness and severe skin problems.
As rates of infection and blindness increased in villages close to fly-breeding
sites, local economies were weakened and eventually the village sites were
abandoned. The WHO initiated a control program during the 1970s, using
insecticides to kill larvae of the fly, and chemotherapy to treat infected
people. This program has succeeded in interrupting the transmission of the
disease in most of the affected areas.
Termites
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The forests and savannas
of Africa are home to some 400 species of termites. Termite mounds vary in
size, depending on the termite species and on soil conditions: Some may be up
to 9 m (30 ft) tall, with nests extending up to 15 m (50 ft) underground. Vast
numbers of termites inhabit these nests; densities as high as 9 million
termites per hectare (4 million per acre) have been recorded.
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Termites are both friend
and foe to humans. Termite colonies enhance soil fertility by transporting and
concentrating fertile subsoil clays near the surface and by increasing soil
aeration. African farmers seek out termite mounds and plant crops around
them—yields are usually higher from crops in these sites. Conversely, termites
consume vast quantities of organic matter, and are blamed for increased soil
erosion that may occur around termite mounds.
Locusts
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Three main types of locusts
are found in the dry savanna and semidesert areas of Africa: the desert locust
and the African migratory locust, found north of the equator, and the red
locust, which occurs in south central Africa. These locusts occasionally
congregate in large swarms to migrate in search of food. Following the
direction of prevailing winds, they devour everything green in their path,
including entire crop harvests. Spraying programs to control populations and
routine monitoring to detect the first signs of swarming have reduced the
serious threat that locusts once posed to agriculture. However, locusts can
still sometimes cause significant damage at a local or regional scale.
Environmental Issues
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Africa is widely seen
as a “devastated continent,” where inappropriate human use of land has caused
deforestation, desertification, and soil erosion on a massive scale. This view
of Africa has greatly influenced academic research agendas and international
aid programs, as well as public perceptions of the continent. But some
scientists are increasingly questioning this view of environmental degradation.
They emphasize the need to ascertain whether degradation is actually occurring,
how human actions affect the process, and what conservation measures are
needed. In some cases, Western viewpoints and ideas have led to misguided
attempts at conservation that had no effect or even an adverse effect on the
environment. At the same time, some African conservation methods were
discovered to be much more effective. Going forward, many experts argue that
conservation strategies must be sensitive to regional and temporal variations
and should seek to preserve and build upon local indigenous knowledge.
Soil Erosion and Desertification
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Until recently, there
was widespread consensus among scientists and policymakers that African soils
were threatened by ill-advised traditional farming methods that increased soil
erosion and desertification (the process in which soil dries out until almost
no vegetation grows on it). Policy documents used limited, often flawed case
studies to produce continent-wide generalizations in which worst-case scenarios
were too often presented as typical. In reality, the nature and extent of soil
erosion and desertification varies greatly throughout Africa and much of it is
unrelated to human activity. For example, savanna regions are subject to wind
erosion in the dry season, which is the primary cause of soil erosion in arid
and semiarid environments.
The Sahel, a semiarid
savanna region located to the south of the Sahara, experienced a severe drought
from the late 1960s to the early 1970s. In reaction, Western scholars
propagated a popular view that the Sahara was expanding year by year,
relentlessly enveloping once-productive land. Further research has shown that,
while soil degradation was confirmed in some areas, in many parts of the Sahel
there was little evidence of degradation, and none of steady desert expansion.
During the colonial era, the perception of imminent crisis led to policy
initiatives designed to preserve the soil. Colonial administrators attempted to
control the perceived problem of erosion by enforcing restrictions on herding
and agriculture, restricting the use of fire to clear land for agriculture, and
installing grass and stone barriers along slope contours. These measures were
generally resented by the local African population, and they had little impact
on erosion rates. Similarly, attempts to control desertification through
policies such as planting shelter belts of trees and restricting nomadic
herding have had limited effect.
Scientific research has
demonstrated that indigenous African farming and herding practices are much
less harmful to the soil than was formerly believed. Methods such as retaining
farmland trees, growing crops on ridges, and interplanting different crops
densely in a single field significantly reduce soil erosion. On the other hand,
modern cultivation methods—involving the use of mechanical equipment, row
cropping, and weed control with herbicides—greatly increase the risk of soil
loss. Similarly, problems of soil erosion and degradation are greater in areas
with fenced cattle ranches than in places where traditional livestock practices
are followed, with animals grazing less intensively over a very large area.
Human Impact on Vegetation
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Little of Africa’s vegetation
is natural in the sense of being virtually unaltered by humans. Areas near
settlements bear the particular marks of human impact: People plant trees for
fruit, shade, and other uses; preserve beneficial wild species; and selectively
clear less desired vegetation.
Humans have had a major
impact on the loss and degradation of Africa’s tropical forests. Between 1990
and 2000 an estimated 5 million hectares (13 million acres) of forest were lost
in Africa. The destruction has been especially significant in Madagascar and in
West African countries such as Nigeria, Ghana, and Côte d’Ivoire, where
population growth and agricultural development have been rapid and forest area
is relatively small. Economic development schemes have harmed forests in many
countries. Forests have been cleared for large-scale plantation agriculture,
flooded under reservoirs by the construction of dams, and, in the case of the
Niger Delta, harmed by development and pollution related to petroleum
exploitation.
While agricultural expansion
has resulted in forest loss in many areas of Africa, traditional agricultural
practices are not necessarily the cause. Recent studies in Guinea have
documented significant expansions of forest cover during the 20th century
through the deliberate interventions of humans, including the strategic burning
of patches of forest. When practiced in moderation, burning helps replenish
soil with nutrients from burnt vegetation and provides new seedlings with the
space to flourish. Similar results have been found elsewhere in West Africa.
Threats to Freshwater Ecosystems
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Overfishing, pollution,
habitat changes, and the ill-advised introduction of exotic species all pose a
significant threat to the biodiversity of Africa’s major lakes and rivers.
Human impact has been especially severe in Lake Victoria. Signs of
overfishing—declining size and volume of catch—have been evident in the lake
since the 1920s. One response was to introduce new species to enhance the
fishing industry: Four species of tilapia and the Nile perch were released into
Lake Victoria in the 1950s and 1960s. While the fisheries initially benefited,
the ecosystem was devastated. The Nile perch displaced the traditional
predators, and by the 1990s about 60 percent of Lake Victoria’s cichlid species
had become extinct. Many rivers and lakes—particularly Lake Victoria—have also
suffered from the introduction of the water hyacinth, a large ornamental water plant
native to South America. The water hyacinth spreads rapidly and threatens fish
and other water life in the rivers and lakes by depriving them of oxygen and
causing significant changes in aquatic habitats.
Wildlife Conservation and Management
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Africa’s animal life is
under pressure, facing threats that include habitat loss from forest clearance,
agriculture, and herding; hunting for food and profit; pollution from
agricultural and industrial sources; and disturbance by tourists. As spaces for
wildlife shrink and corridors linking areas of habitat are cut, the survival of
healthy species populations—especially of larger animals and highly specialized
species—becomes more tenuous. Addressing these problems is a very complex
issue, especially because indigenous peoples have diverse needs for, and claims
to, these resources. Thus, the need for protected spaces for wildlife often
seems at odds with human needs.
Wildlife protection has
had a long history in Africa. Colonial conservation measures were imposed on
African societies without consultation or consideration of the impact on local
economies. Indigenous conservation measures, practiced for centuries, were
ignored and sometimes undermined. In more recent times, threats to habitat and
to wildlife have come increasingly from large-scale projects, such as dams,
reservoirs, and irrigation schemes. Yet the solutions proposed to protect
wildlife have generally continued to impose significant costs on local
communities.
Game reserves were first
established by Africa’s colonial rulers in the 1890s. Concern about the effects
of hunting on big game led to the establishment of several national parks for
wildlife conservation in the 1930s. The establishment of new parks and reserves
continued throughout the colonial era, and postcolonial regimes followed suit.
A sometimes uneasy mix of conservation and economic concerns—especially
tourism—continues to provide the rationale for such initiatives. Some 5 percent
of Africa’s land area is designated as protected. However, protected areas vary
between countries: While 30.2 percent of Botswana is designated as protected,
the figure is only 2.6 percent for Madagascar. Also, some environments, such as
semidesert and marine sites, remain underrepresented.
Indigenous populations
often remain ambivalent about wildlife conservation programs that restrict
their access to farmland and pastures and set limits on killing wild animals
for food. Governments have begun to experiment with comanaged protected areas,
in which local communities are consulted about decisions, given priority access
to jobs as guards and guides, and allowed limited access to the protected areas
for hunting and other activities. The objective of these programs is to ensure
that local communities feel they have a stake in successful conservation. The
most effective
of these programs—notably, Zimbabwe’s Communal Areas Management Programme for Indigenous Resources (CAMPFIRE)—have succeeded in reducing poaching and increasing local incomes.
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There has been much controversy
over the best way to stop the poaching of big game animals, particularly
elephants, which are killed for their ivory tusks. In 1989 the Convention on
International Trade in Endangered Species (CITES) voted to enforce a total ban
on the ivory trade. Kenya and other African countries that had been severely
affected by poaching were strong supporters of this ban. On the other hand,
South Africa, Zimbabwe, and Botswana argued for limited elephant hunting and a
controlled ivory trade as the best way to protect elephants. These countries
have large and growing elephant populations, and have traditionally culled
their herds periodically to maintain the health of herds and of the ecosystems
supporting them.
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