Savannahs and deserts are vast territories of our planet, which differ sharply from each other in flora and fauna and are similar only in a hot climate. Zones of equatorial forests on Earth are replaced by savannahs, they turn into semi-deserts, and already semi-deserts are replaced by deserts - with quicksand and a minimum of vegetation. These territories are of great interest to researchers; many expeditions go there every year to study the natural diversity of our planet. What are savannas and deserts and how they differ from the steppes of the temperate zone, you will learn on this page
What are savannahs and what plants grow in them
Savannahs are grassy plains located between rainforests and deserts. They differ from the steppes of the temperate zone in that trees and shrubs are found everywhere in them, sometimes single, and sometimes forming entire groves. So the savanna can also be called a forest-steppe. Acacias, baobabs and cereals grow there. There are savannahs in America, where they are called "llanos", and in Africa, and in Asia.
The main feature of the savannas is that the rainy and dry seasons are clearly distinguished here.
As you can see in the photo, the savannas look completely different in different seasons. Both plants and animals have adapted to many months of drought. The leaves of savanna plants are usually narrow, they can be rolled up into a tube, and sometimes covered with a waxy coating. In the dry season, the vegetation freezes, and numerous animals - zebras, buffaloes, elephants - make long migrations (transitions from one place to another) in search of water and food. And in the rainy season, on the contrary, the savannah is full of life.
Candelabra spurge grows only in Somalia and eastern Ethiopia. Its branches resemble a candelabra, that is, a candlestick for several candles. The tree reaches a height of 10 m, and even elephants find shelter in its shadows.
Speaking of what grows in the savannah, one cannot fail to mention the favorite delicacy of giraffes - acacia. These trees have a broad, flat crown that provides shade for the leaves below, preventing them from drying out. These are quite tall trees, and their leaves and branches serve as food for the inhabitants of those places. Acacia is very fond of giraffes - the tallest land animals on our planet. With a growth of 6 m, a third of which is the neck, the giraffe finds plant food for itself at a height where it has no competitors. And the long 45-meter tongue allows it to capture the farthest branches.
Savannah perennial grasses have underground shoots, and the roots grow and form a woody tuberous body. It persists in the dry season and produces new shoots as soon as the wet weather sets in.
Interesting facts about deserts and desert plants
Deserts occupy almost a fifth of the land. All of them, except for the Arctic and Antarctic, occur in a hot, dry climate. Not all lands in the deserts are bare and dull. There are also xerophytic plants, the roots, stems and flowers of which are able to extract and conserve water, hide from the merciless sun and catch its life-giving rays. And some of them - ephemera - grow, bloom and fade in just a few weeks under favorable conditions for life.
The desert saxaul plant can be a shrub or a small tree. Its roots go into the ground at 10-11 m. These plants form desert-tree thickets - saxaul forests.
Tamarisk grows along the banks of rivers, but also lives in deserts, salt marshes and sands. This plant is widely used to fix moving sands in forest plantations and in desert and semi-desert zones, especially on saline soils.
Camel's thorn is a thorny shrub. It is helped to successfully exist in the sands by a long root system, going to a depth of 3-4 m, where the water is. And the plant itself rises above the ground by no more than 1 m.
Ephedra is found in dry areas around the world. Its leaves are small, scale-like, which reduces water loss, and its roots are strong and long. It is a poisonous plant, but it has been used for several thousand years to make medicines for asthma and other diseases.
One of the most interesting facts about deserts is the presence of magnificent oases in these seemingly dead territories. An oasis in the desert is a place where groundwater comes to the surface and forms a spring or lake. Birds fly there to drink, and they carry seeds, from which trees, grasses and shrubs later grow. As long as there is water, the oasis also lives. It can be a small pond with a few palm trees or a whole city with rich agricultural land. Thus life flourishes among the sands.
Deserts are not only sandy, but also rocky, and rocky, and saline. Their vegetation serves as food for animals, even large ones like camels. They feed on branches and leaves of saxaul, desert acacia, although the leaves of these plants are small and hard. The main delicacy of the “ship of the desert” is camel thorn. Its branches are prickly and inedible, but the leaves are very juicy and tasty.
Desert plants cacti and their photos
Among the plants of the southern deserts and semi-deserts, cacti stand out. They do not have leaves, but there is a thick stem in which reserves of water and nutrients are created. Such plants are called "succulents". Desert cacti are very diverse: among them there are both large, like trees, and medium, like shrubs, and low, like grasses.
Cacti are native to North and South America and can be found from Canada to Patagonia. Therefore, cacti are a sign of American deserts and semi-deserts. Cacti in the desert differ from other succulents in that they have areoles, that is, modified buds with scales that have turned into thorns and hairs or only thorns.
Pay attention to the photo: cacti in the desert sometimes form real cactus thickets, which are not so easy to get through. In Australia, they even erected a monument to the moth. The fact is that a South American cactus catastrophically bred there in the 1920s, and only a compatriot moth could cope with it.
The plant of the desert cactus saguaro, or giant carnegia, reaches a height of 1.5 m by the age of 20. But it continues to grow, and 7-8 m high cacti have side shoots that look like hands. The cactus has nowhere to hurry, since its average life expectancy is 75 years, but there are also 150-year-old centenarians. They grow up to 15-20 m, weigh about 10 tons, and 90% of their weight is water. The roots of the saguaro are short, but very tenacious, so that he is not afraid of any hurricanes.
In the Galapagos Islands, off the coast of South America, you can see tree-like cacti reaching a height of 12 m. Surprisingly, these trees are cacti. These are prickly pear, which most often grow as shrubs on the mainland.
Savannahs are located in the subequatorial zone on both sides of the equator on all continents except Antarctica and North America. Savannah is characterized by the presence of two climatic seasons: dry and rainy. And, as a rule, it is located on high platforms with a sharply continental climate. Where there is not enough moisture for variable forests, savanna appears.
Where are savannas located and what are they called in different parts of the world?
Savannah in Africa
Most often, the African steppe-like zone is called the savannah. The word "savannah" is the Spanish word "sabana", which is distorted in the English manner, which means treeless space. A typical savannah zone in Africa is the territory of Kenya, Tanzania, South Sudan, Ghana, Mali, Angola, Zambia and several other smaller states. The flora and fauna vary greatly from north to south. If on the border with the Sahara this is a huge grassy space with rare baobabs, then closer to the equator there is an abundance of shrubs, and the floodplains of the rivers are densely occupied by trees.
Where are the savannahs in Australia?
Savannah here is called "bush", which means bush. Indeed, unlike our steppes, in the savannah of the southern mainland, a significant part is occupied by shrubs and groups of trees. The savannah area is the north of the country.
Where are the savannahs in South America?
Here the savannah is called the pampa. And it has a difference not only in the name, but also in natural expression. For example, in Brazil, the savannah is a light and very rare forest, and you can move freely in it in any direction. But the real territory of the pampas is Argentina. Probably, many have heard about fat herds of many thousands grazing in this territory. In the USA it would be called a prairie.
India also has savannas, but they have a slightly different specificity associated with the powerful influence of the Indian Ocean.
The season in the savannah is divided into rainy and dry for about half a year each. And if, during a drought, grasses as tall as human beings dry up, and some animal species fall into symbiosis, then during the rainy period there are whole floods.
Fires often occur in the savannah, largely because of people. The fact is that hunters from time immemorial drove prey simply by setting fire to grass. Therefore, in the African savannah, vegetation remained exclusively with fire-resistant seeds and bark, for example, like the baobab.
Introduction
Today, grassy plains occupy a quarter of all land. They have many different names: steppes - in Asia, llanos - in the Orinoco basin, veld - in Central Africa, savannah - in the eastern part of the African continent. All these areas are very fertile. Individual plants live up to several years, and when they die, they turn into humus. Leguminous plants, vetch, daisies and small flowers hide among the tall grasses.
The name "grass" combines a wide variety of plants. This family is perhaps the largest in the entire plant kingdom, it includes more than ten thousand species. Herbs are the product of a long evolution; they are able to survive fires, droughts, floods, so they only need an abundance of sunlight. Their flowers, small and inconspicuous, are collected in small inflorescences at the top of the stem and are pollinated by the wind, requiring no services from birds, bats or insects.
Savannah is a community of tall grasses and woodlands with low to medium sized, fire resistant trees. It is the result of the interaction of two factors, namely soil and rainfall.
The significance of the savanna lies in the conservation of rare species of animals and plants. Therefore, the study of the African savannas is relevant.
The object of study is the African savannas
The subject of the research is the study of the natural features of the African savannas.
The purpose of this course work is a comprehensive study of the types of African savannas.
The main tasks of the work are the following:
1.Consider the geographical location of the African savannas.
2.Explore the flora and fauna of the savannas.
.Consider the features of different types of African savannas.
.Consider modern environmental problems and ways to solve them in the savannas.
Chapter I. General characteristics of the savannas of Africa
.1 Geographical location and climatic features of the African savannas
Savannah is a zonal type of landscape in tropical and subequatorial belts, where the change of the wet and dry seasons is clearly expressed at consistently high air temperatures (15-32°C). As you move away from the equator, the period of the wet season decreases from 8-9 months to 2-3, and precipitation - from 2000 to 250 mm per year. The violent development of plants in the rainy season is replaced by droughts of the dry period with a slowdown in the growth of trees, grass burning out. As a result, a combination of tropical and subtropical drought-resistant xerophytic vegetation is characteristic. Some plants are able to store moisture in the trunks (baobab, bottle tree). The grasses are dominated by high grasses up to 3-5 m, among them are rarely growing shrubs and single trees, the occurrence of which increases towards the equator as the wet season lengthens to light forests.
Vast expanses of these amazing natural communities are found in Africa, although there are savannahs in South America, Australia, and India. The savannah is the most widespread and most characteristic landscape in Africa. The savannah zone surrounds the Central African rainforest with a wide belt. In the north, the tropical forest is bordered by the Guinean-Sudanese savannas, stretching in a strip 400-500 km wide for almost 5000 km from the Atlantic to the Indian Ocean, interrupted only by the White Nile Valley. From the Tana River, savannas in a belt up to 200 km wide descend south to the valley of the Zambezi River. Then the savannah belt turns to the west and, now narrowing, now expanding, extends for 2500 km from the shores of the Indian Ocean to the Atlantic coast.
The forests in the frontier strip are gradually thinned out, their composition becomes poorer, patches of savannas appear among the massifs of continuous forest. Gradually, the tropical rainforest is limited only to river valleys, and on the watersheds they are replaced by forests shedding leaves for the dry season, or savannahs. Vegetation change occurs as a result of a shortening of the wet period and the appearance of a dry season, which becomes longer and longer as one moves away from the equator.
The savannah zone from northern Kenya to the sea coast of Angola is the largest plant community on our planet in terms of area, occupying at least 800 thousand km 2. If we add another 250,000 km2 of the Guinean-Sudanese savannah, it turns out that more than a million square kilometers of the Earth's surface is occupied by a special natural complex - the African savannah.
A distinctive feature of the savannas is the alternation of dry and wet seasons, which take about half a year, replacing each other. The fact is that for the subtropical and tropical latitudes, where the savannahs are located, the change of two different air masses is characteristic - humid equatorial and dry tropical. Monsoon winds, bringing seasonal rains, significantly affect the climate of the savannahs. Since these landscapes are located between the very humid natural zones of the equatorial forests and the very dry zones of the deserts, they are constantly influenced by both. But moisture is not long enough present in the savannahs for multi-tiered forests to grow there, and dry "winter periods" of 2-3 months do not allow the savannah to turn into a harsh desert.
The annual rhythm of the life of the savannas is associated with climatic conditions. During the wet period, the riot of grassy vegetation reaches its maximum - the entire space occupied by savannahs turns into a living carpet of herbs. The picture is violated only by thickly low trees - acacias and baobabs in Africa, fan palms of Ravenal in Madagascar, cacti in South America, and in Australia - bottle trees and eucalyptus trees. The soils of the savannas are fertile. During the rainy period, when the equatorial air mass dominates, both the earth and the plants receive enough moisture to feed the numerous animals that live here.
But now the monsoon leaves, and dry tropical air takes its place. Now the time for testing begins. Grasses grown to human height are dried up, trampled down by numerous animals moving from place to place in search of water. Grasses and shrubs are very susceptible to fire, which often burns large areas. This is also “helped” by the indigenous people who make a living by hunting: by specially setting fire to the grass, they drive their prey in the direction they need. People did this for many centuries and greatly contributed to the fact that the vegetation of the savannas acquired modern features: an abundance of fire-resistant trees with thick bark, like baobabs, a wide distribution of plants with a powerful root system.
The dense and high grass cover provides abundant food for the largest animals, such as elephants, giraffes, rhinos, hippos, zebras, antelopes, which in turn attract such large predators as lions, hyenas and others. The largest birds live in the savannas - the ostrich in Africa and the South American condor.
Thus, the Savannahs in Africa occupy 40% of the continent. The savannas frame the forested areas of Equatorial Africa and extend through the Sudan, East and South Africa beyond the southern tropic. Depending on the duration of the rainy season and the annual amount of precipitation, tall grass, typical (dry) and desert savannas are distinguished in them.
In savannah areas:
the duration of the rainy period ranges from 8-9 months at the equatorial borders of the zones to 2-3 months at the outer borders;
the water content of rivers fluctuates sharply; in the rainy season, there is a significant solid runoff, slope and planar runoff.
parallel to the decrease in annual precipitation, the vegetation cover changes from tall grass savannas and savanna forests on red soils to desert savannas, xerophilic light forests and shrubs on brown-red and red-brown soils.
savannah africa climatic geographic
1.2 Flora of the savannas
An abundance of tall grasses gilded by the sun, rare trees and shrubs, found more or less depending on the area - such is the savanna that occupies most of sub-Saharan Africa.
The savannah zones are quite extensive, therefore, on their southern and northern borders, the vegetation is somewhat different. The savannas bordering the desert zone in the north of the zone in Africa are rich in drought-resistant low grasses, spurges, aloes and acacias with highly branched roots. To the south, they are replaced by moisture-loving plants, and along the banks of the rivers, gallery forests with evergreen shrubs and lianas, similar to humid equatorial forests, enter the savanna zone. In the rift valley of East Africa, the largest lakes of the mainland are located - Victoria, Nyasa, Rudolf and Albert lakes, Tanganyika. Savannahs on their banks alternate with wetlands where papyrus and reeds grow.
The African savannas are home to many famous nature reserves and national parks. One of the most famous is the Serengeti, located in Tanzania. Part of its territory is occupied by the crater highlands - a well-known plateau with ancient craters of extinct volcanoes, one of which, Ngorongoro, has an area of about 800 thousand hectares.
The vegetation of the savannah corresponds to the hot, with long dry periods, the climate that prevails in tropical places. Because the savannah is common in different parts of the world, including South America and Australia. But it occupies the most extensive territories, of course, in Africa, where it is represented in all its diversity.
The general appearance of the savannahs is different, which depends, on the one hand, on the height of the vegetation cover, and on the other hand, on the relative amount of cereals, other perennial grasses, semi-shrubs, shrubs and trees. The herbaceous cover is sometimes very low, even pressed to the ground.
A special form of savannas is the so-called llanos, where trees are either completely absent or are found in a limited number, with the exception of only damp places where palm trees (Mauritia flexuosa, Corypha inermis) and other plants form entire forests (however, these forests do not belong to savannahs). ); in llanos there are sometimes single specimens of Rhopala (trees from the Proteaceae family) and other trees; sometimes the cereals in them form a cover as tall as a man; Compositae, leguminous, labiate, etc. grow between cereals. Many llanos in the rainy season are flooded by the floods of the Orinoco River.
The vegetation of the savannas is generally adapted to a dry continental climate and to periodic droughts, which occur in many savannas for whole months. Cereals and other grasses rarely form creeping shoots, but usually grow in tufts. The leaves of cereals are narrow, dry, hard, hairy or covered with a waxy coating. In grasses and sedges, young leaves remain rolled up into a tube. In trees, the leaves are small, hairy, shiny (“lacquered”) or covered with a waxy coating. The vegetation of the savannas generally has a pronounced xerophytic character. Many species contain large quantities of essential oils, especially those of the Verbena, Labiaceae, and Myrtle families of the Flaming Continent. The growth of some perennial grasses, semi-shrubs (and shrubs) is especially peculiar, namely, that the main part of them, located in the ground (probably, the stem and roots), grows strongly into an irregular tuberous woody body, from which then numerous, mostly unbranched or weakly branched, offspring. In the dry season, the vegetation of the savannas freezes; savannahs turn yellow, and dried plants are often subjected to fires, due to which the bark of trees is usually scorched. With the onset of rains, the savannahs come to life, covered with fresh greenery and dotted with numerous different flowers.
In the south, on the border with the equatorial tropical forests, a transitional zone begins - the forest savannah. There are not very many herbs, the trees grow densely, but they are small. Then comes the sparsely forested savanna - vast expanses overgrown with tall grasses, with groves or isolated trees. Baobab dominates here, as well as palm, spurge and various types of acacia. Gradually, trees and shrubs become more and more rare, and grasses, especially giant cereals, thicken.
And finally, near the deserts (Sahara, Kalahari), the savannah gives way to the withered steppe, where only tufts of dry grass and stunted thorny bushes grow.
.3 Savannah wildlife
The fauna of the savannah is a unique phenomenon. In no corner of the Earth in the memory of mankind has there been such an abundance of large animals as in the African savannas. As early as the beginning of the XX century. countless herds of herbivores roamed the expanses of the savannas, moving from one pasture to another or in search of watering places. They were accompanied by numerous predators - lions, leopards, hyenas, cheetahs. Carrion eaters followed the predators - vultures, jackals.
The seasonally dry tropical regions of Africa, from light deciduous forests and light forests to low-growing spiny forests and the sparse Sahelian savannah, differ from evergreen forests, first of all, by the presence of a well-defined dry period unfavorable for animals. This determines the clear seasonal rhythm of most forms, synchronous with the rhythm of moisture and vegetation vegetation.
During the dry season, most animals stop breeding. Some groups, mainly invertebrates and amphibians, take shelter during drought and hibernate. Others store food (ants, rodents), migrate (locusts, butterflies, birds, elephants and ungulates, predatory animals) or concentrate on small areas - survival stations (surroundings of water bodies, drying up channels with closely spaced groundwater, etc.). P.).
Animals appear in large numbers, constructing solid shelters. Strong cone-shaped termite mounds are striking, which are more than 2 m high. The walls of these structures seem to be made of cement or baked clay, and they can hardly be broken through with a crowbar or a pickaxe. The above-ground dome protects the numerous chambers and passages below from both dryness in the hot season and showers during the wet season. Termite passages in depth reach aquifers of the soil; during a drought, a favorable moisture regime is maintained in the termite mound. Here the soil is enriched with nitrogen and ash elements of plant nutrition. Therefore, trees often regenerate on destroyed and near residential termite mounds. Of vertebrates, a number of rodents and even predators build burrows, ground and tree nests. The abundance of bulbs, rhizomes and seeds of grasses and trees allows them to harvest these feeds for future use.
The tiered structure of the animal population, characteristic of evergreen forests, in seasonally dry forests, light forests, and especially in savannahs, is somewhat simplified due to a decrease in the proportion of tree forms and an increase in those living on the surface and in the grass layer. However, the significant heterogeneity of vegetation, caused by a mosaic of tree, shrub and herbaceous phytocenoses, causes a corresponding heterogeneity of the animal population. But the latter is dynamic. Most animals are alternately associated with one or another plant group. Moreover, movements are not only on the scale of seasons, but even within a day. They cover not only herds of large animals and flocks of birds, but also small animals: mollusks, insects, amphibians and reptiles.
In the savannas, with their huge food resources, there are many herbivores, especially antelopes, of which there are more than 40 species. Until now, in some places there are herds of the largest wildebeests with a large mane, a powerful tail and horns bent down; Kudu antelopes with beautiful helical horns, elands, etc. are also common. There are also dwarf antelopes, reaching a little more than half a meter in length.
Remarkable are the animals of the African savannas and semi-deserts saved from extinction - giraffes, they are preserved mainly in national parks. The long neck helps them to get and gnaw young shoots and leaves from trees, and the ability to run fast is the only means of protection from pursuers.
In many areas, especially in the east of the continent and south of the equator, African wild zebra horses are common in the savannas and steppes. They are hunted mainly for their strong and beautiful hides. In some places, domesticated zebras are replacing horses, as they are not susceptible to tsetse bites.
Until now, African elephants have been preserved - the most remarkable representatives of the fauna of the Ethiopian region. They have long been exterminated for their valuable tusks, and in many areas they have completely disappeared. Elephant hunting is currently banned throughout Africa, but this ban is often violated by ivory poachers. Now elephants are found in the least populated mountainous areas, in particular in the Ethiopian highlands.
In addition, they live in the national parks of East and South Africa, where their population is even increasing. But still, the existence of the African elephant as a biological species in recent decades has been under a real threat, which can only be prevented by the active joint activities of national and international organizations. Among the endangered animals are rhinos that lived in the eastern and southern parts of the mainland. African rhinos have two horns and are represented by two species - black and white rhinoceros. The latter is the largest of modern species and reaches a length of 4 m. Now it has been preserved only in protected areas.
Hippos are much more widespread, living along the banks of rivers and lakes in different parts of Africa. These animals, as well as wild pigs, are exterminated for their edible meat and also for their skin.
Herbivores serve as food for numerous predators. In the savannahs and semi-deserts of Africa, lions are found, represented by two varieties: the Barbary, living north of the equator, and the Senegal, common in the southern part of the mainland. Lions prefer open spaces and almost never enter forests. Hyenas, jackals, leopards, cheetahs, caracals, servals are common. There are several members of the civet family. In the plain and mountain steppes and savannahs there are many monkeys belonging to the group of baboons: real Raigo baboons, geladas, mandrills. Of the thin-bodied monkeys, Gverets are characteristic. Many of their species live only in a cool mountain climate, as they do not tolerate the high temperatures of the lowlands.
Among rodents, mice and several types of squirrels should be noted.
Birds are numerous in the savannas: African ostriches, guinea fowls, marabou, weavers, a very interesting secretary bird that feeds on snakes. Lapwings, herons, pelicans nest near water bodies.
There are no less reptiles than in the northern deserts, often they are represented by the same genera and even species. Many different lizards and snakes, land turtles. Some types of chameleons are also characteristic. There are crocodiles in the rivers.
The great mobility of animals makes the savannah highly productive. Wild ungulates are almost constantly on the move, they never overgraze the way livestock do. Regular migrations, i.e., movements, of herbivorous animals of the African savanna, covering hundreds of kilometers, allow the vegetation to fully recover in a relatively short time. Not surprisingly, in recent years, the idea has arisen and strengthened that the rational, scientifically based exploitation of wild ungulates promises greater prospects than traditional pastoralism, primitive and unproductive. Now these questions are being intensively developed in a number of African countries.
Thus, the fauna of the savannah for a long time developed as a single independent whole. Therefore, the degree of adaptation of the entire complex of animals to each other and each individual species to specific conditions is very high. Such adaptations include, first of all, a strict division according to the method of feeding and the composition of the main feed. The vegetation cover of the savannah can only feed a huge number of animals because some species use grass, others use young shoots of shrubs, others use bark, and others use buds and buds. Moreover, different types of animals take the same shoots from different heights. Elephants and giraffes, for example, feed at the height of the tree crown, the giraffe gazelle and the large kudu reach the shoots located one and a half to two meters from the ground, and the black rhinoceros, as a rule, breaks the shoots near the ground. The same division is observed in purely herbivorous animals: what the wildebeest likes does not attract the zebra at all, and the zebra, in turn, nibbles grass with pleasure, past which the gazelles pass indifferently.
Chapter II. Features of the types of African savannas
.1 Tall grass wet savannas
Tall grass savannas are various combinations of grassy vegetation with forest islands or individual tree specimens. The soils that form under these landscapes are referred to as red or ferrallitic soils of seasonal rainforests and tall grass savannahs.
Tall grass savannas are wet. They grow very tall cereals, including elephant grass, which reaches 3 m in height. Among these savannahs are scattered arrays of park forests, gallery forests stretch along the riverbeds.
Tall grass savannas occupy an area where the annual precipitation is 800-1200 mm, and the dry season lasts 3-4 months, they have a dense cover of tall grasses (elephant grass up to 5 m), groves and massifs of mixed or deciduous forests on watersheds, gallery evergreen ground moisture forests in the valleys. They can be called a transition zone from forest vegetation to a typical savannah. Among the continuous cover of high (up to 2-3 m) grasses, trees (as a rule, deciduous species) rise. The tall grass savannah is characterized by baobabs, acacias, and terminalia. Red lateritic soils are most common here.
There is an opinion that the wide distribution of moist tall-grass savannahs, replacing deciduous-evergreen forests, is associated with human activity, which burned vegetation during the dry season. The disappearance of the dense tree layer contributed to the appearance of countless herds of ungulates, as a result of which the renewal of tree vegetation became impossible.
The Sahelian savannas and, to a lesser extent, the spiny forests of Somalia and the Kalahari are faunistically depleted. Many of the animals that are close or common with the forest disappear here.
2.2 Typical grass savannas
From the border of the hylae, the zone of cereal savannah begins. Typical (or dry) savannas are replaced by tall grasses in areas where the rainy season lasts no more than 6 months. The grasses in such savannahs are still very dense, but not very tall (up to 1 m). Grassy spaces alternate with light forests or individual groups of trees, among which numerous acacias and giant baobabs, or monkey bread trees, are especially typical.
Typical grass savannahs are developed in areas with an annual rainfall of 750-1000 mm and a dry period of 3 to 5 months. In typical savannahs, a continuous grass cover is not higher than 1 m (species of bearded man, temedy, etc.), palm trees (fan, hyphena), baobabs, acacias are characteristic of tree species, and in East and South Africa - euphorbia. Most of the wet and typical savannas are of secondary origin. In Africa, north of the equator, the savannahs extend in a wide strip from the Atlantic coast to the Ethiopian highlands, while south of the equator they occupy the north of Angola. The height of wild-growing cereals reaches 1-1.5 m, and they are mainly represented by hyperrhenium and bearded vultures.
A typical grass savanna is an area entirely covered with tall grasses, with a predominance of grasses, with sparsely standing individual trees, shrubs or groups of trees. Most of the plants have a hydrophytic character due to the fact that during the rainy season the air humidity in the savannas resembles a tropical forest. However, plants of a xerophytic character also appear, adapting to the transfer of a dry triode. Unlike hydrophytes, they have smaller leaves and other adaptations to reduce evaporation.
During the dry period, the grasses burn out, some types of trees drop their leaves, although others lose it only shortly before the new one appears; savanna becomes yellow; dried grass is annually burned to fertilize the soil. The damage that these fires bring to vegetation is very great, since it disrupts the normal winter dormancy cycle of plants, but at the same time it also causes their vital activity: after a fire, young grass quickly appears. When the rainy season comes, cereals and other herbs grow amazingly quickly, and the trees are covered with leaves. In the grass savanna, the grass cover reaches heights of 2-3 m. , and in low places 5 m .
Of the cereals here are typical: elephant grass, species of Andropogon, etc., with long, wide, hairy leaves of a xerophytic appearance. Of the trees, the oil palm 8-12 m should be noted. heights, pandanus, butter tree, Bauhinia reticulata is an evergreen tree with broad leaves. Baobab and various types of doum palm are often found. Along the river valleys stretch several kilometers wide gallery forests resembling giley, with many palm trees.
Cereal savannas are gradually replaced by acacia. They are characterized by a continuous cover of grasses of lower height - from 1 to 1.5 m. ; of the trees they are dominated by various types of acacias with a dense umbrella-shaped crown, for example, species: Acacia albida, A. arabica, A. giraffae, etc. In addition to acacias, one of the characteristic trees in such savannahs is the baobab, or monkey breadfruit, reaching min diameter and 25 m height, containing a significant amount of water loose fleshy trunk.
In the cereal savanna, where the rainy season lasts 8-9 months, cereals grow 2-3 m high, and sometimes up to 5 m: elephant grass (Pennisetum purpureum), bearded vulture with long hairy leaves, etc. Individual trees rise among the continuous sea of grasses : baobabs (Adansonia digitata), doom palms (Hyphaene thebaica), oil palms.
To the north of the equator, the cereal savannahs reach approximately 12°N. In the southern hemisphere, the zone of savannas and light forests is much wider, especially off the coast of the Indian Ocean, where it extends in places to the tropic. The difference in moisture conditions in the northern and southern parts of the zone suggests that mesophilic deciduous forests grew in the more humid northern regions, while xerophytic light forests with a predominance of representatives of the legume family (Brachystegia, Isoberlinia) occupied only the southern regions of their modern distribution. To the south of the equator, this plant formation was called the "miombo" woodlands. The expansion of its range can be explained by resistance to fires, high rate of renewal. In eastern South Africa, woodlands occur in combination with other types of vegetation well south of the tropic.
Under grass savannahs and light forests, special types of soils are formed - red soils under savannahs and red-brown soils under forests.
In drier areas, where the rainless period lasts from five to three months, dry spiny semi-savannahs predominate. Most of the year the trees and shrubs in these areas stand without leaves; low grasses (Aristida, Panicum) often do not form a continuous cover; among cereals grow low up to 4 m heights, thorny trees (Acacia, Terminalia, etc.)
This community is also called the steppe by many researchers. This term is widely used in the literature on the vegetation of Africa, but does not fully correspond to the understanding of our term "steppe".
Dry prickly semi-savannahs are replaced with the distance from the acacia savannahs to the so-called thorny-shrub savannah. It reaches 18-19 ° S. sh., occupying most of the Kalahari.
2.3 Desert savannas
In areas with a wet period of 2-3 months. typical savannahs turn into thickets of thorny bushes and hard grasses with sparse turf. As the wet period is reduced to 3-5 months. and a general decrease in precipitation, the grass cover becomes more sparse and stunted, various acacias predominate in the composition of tree species, low, with a peculiar flat crown. Such plant communities, called desert savannas, form a relatively narrow band in the northern hemisphere north of the typical savannas. This strip expands from west to east in the direction of decreasing annual precipitation.
In the deserted savannahs, scanty rains are rare and occur only for 2-3 months. The strip of these savannahs, stretching from the coast of Mauritania to Somalia, expands to the east of the African continent, and this natural zone also covers the Kalahari basin. The vegetation here is represented by turf grasses, as well as thorny shrubs and low leafless trees. In typical and deserted savannas, tropical red-brown soils are developed, not rich in humus, but with powerful alluvial horizons. In places of development of basic rocks and lava covers - in the southeast of Sudan, in Mozambique, Tanzania and the Shari River basin - significant areas are occupied by black tropical soils related to chernozems.
Under such conditions, instead of a continuous herbaceous cover, only turf grasses and leafless and thorny shrubs remain. The belt of semi-deserts or deserted savannahs on the Sudanese plains is called "sahel", which in Arabic means "shore" or "edge". This is really the outskirts of green Africa, beyond which the Sahara begins.
In the east of the mainland, desert savannahs occupy especially large areas, covering the Somali peninsula and extending to the equator and south of it.
Deserted savannahs are typical for areas with an annual rainfall of no more than 500 mm and a dry period of 5 to 8 months. Deserted savannahs have a sparse grass cover, thickets of thorny bushes (mainly acacias) are widespread in them.
Despite a number of common features, savannahs are distinguished by considerable diversity, which makes it very difficult to separate them. There is a point of view that most of the savannahs of Africa arose on the site of exterminated forests and only deserted savannahs can be considered natural.
Chapter III. Ecological problems of African savannas
.1 Human role in the savannah ecosystem
Among biocenoses of dry land, the steppes produce the largest biomass of animals per unit of surface, therefore, from time immemorial, they have attracted a person who lived mainly by hunting. This upright primate was created by nature itself to live in the steppes, and it was here that in the struggle for food and shelter, escaping from enemies, he turned into a rational being. However, improving, man increasingly complicated his weapons and invented new methods of hunting herbivores and predatory animals, which played a fatal role for many of them.
Whether ancient man was already involved in the extermination of a number of animal species is a moot point. There are various, very conflicting opinions on this matter. Some scientists believe that many inhabitants of the African savannahs and steppes were already destroyed in the early Paleolithic, characterized by the use of a hand ax (the so-called Acheulean culture). According to supporters of this opinion, the same thing happened in North America, when about 40 thousand years ago man first entered this continent through the Bering Bridge. At the end of the Ice Age, 26 genera of African and 35 genera of North American large mammals disappeared from the face of the Earth.
Proponents of the opposite point of view insist that ancient man, with his still extremely imperfect weapons, cannot be considered guilty of their destruction. Mammals that went extinct at the end of the Ice Age were most likely victims of global climate change that affected the vegetation that served them as food or their prey.
It has been established that when, much later, well-armed people appeared in Madagascar, whose animal world did not know natural enemies, this led to very sad consequences. In Madagascar, in a relatively short period of time, at least 14 species of large lemurs, 4 species of giant ostriches were exterminated, and, in all likelihood, the same fate befell the aardvark and pygmy hippopotamus.
However, it was only when the white man used firearms that this led to a catastrophic imbalance between him and the world of large animals. By now, in all corners of the Earth, man has almost completely destroyed the large animals of the savannas, turning the once endless grassy plains into arable land or pastures for livestock.
The destruction of the original vegetation led to the disappearance of many small and medium-sized animals. Only in national parks and other protected areas are the remains of a unique community of living creatures that have been formed over millions of years. The man-hunter destroyed his steppe ancestral home and many animals generated by the amazing savannah ecosystem.
A hundred years ago, Africa was represented as a continent of untouched nature. However, even then, nature was significantly changed by human economic activity. At the beginning of the 21st century, environmental problems that arose during the predatory campaigns of European colonialists escalated.
Evergreen forests have been cut down for centuries for redwoods. They were also uprooted and burned for fields and pastures. Burning of plants in slash-and-burn agriculture leads to a violation of the natural vegetation cover and deterioration of the soil. Its rapid depletion forced to leave cultivated land after 2-3 years. Now almost 70% of Africa's forests have been destroyed, and their remains continue to disappear rapidly. In place of forests, plantations of cocoa, oil palm, bananas, and peanuts arose. Deforestation leads to many negative consequences: an increase in the number of floods, increased droughts, the occurrence of landslides, and a decrease in soil fertility. Reproduction of forests is very slow.
The nature of the savannas has also been significantly changed. Huge areas are plowed up there, pastures. Due to overgrazing of cattle, sheep and camels, cutting down trees and shrubs, the savannas are increasingly turning into deserts. Especially negative consequences of such use of land in the north, where the savannah turns into desert. The expansion of desert areas is called desertification.
Aerospace images taken from artificial Earth satellites have convincingly shown that in the last half century alone, the Sahara has moved south by 200 km. and increased its area by thousands of square kilometers.
Protective forest belts are planted on the border with deserts, cattle grazing is limited in areas with sparse vegetation, and dry areas are watered. Great changes in natural complexes occurred as a result of mining.
The long colonial past and the irrational use of natural resources have led to a serious imbalance between the components of natural complexes. Therefore, in many countries of Africa, the problems of nature protection have become acute.
3.2 Economic role of savannas
Savannas play a very important role in human economic life. According to climatic and soil conditions, the savannas are favorable for tropical agriculture. At present, significant areas of savannas have been cleared and plowed up. Significant areas are plowed up here, cereals, cotton, peanuts, jute, sugar cane and others are grown. Animal husbandry is developed in drier places. Some species of trees growing in savannahs are used by humans for their own purposes. So, teak wood gives solid valuable wood that does not rot in water.
At present, it can be said with full confidence that a significant part of the wet and dry savannahs of Africa arose as a result of human activity on the site of mixed forests, almost extinct deciduous forests and light forests. Since man learned how to make fire, he began to use it for hunting, and later for clearing thickets for arable land and pastures. For millennia, farmers and pastoralists set fire to the savanna before the start of the rainy season to fertilize the soil with ash. Arable land, which quickly lost fertility, was abandoned after several years of use, and new areas were prepared for crops. In pasture areas, vegetation suffered not only from burning, but also from trampling, especially if the number of livestock exceeded the fodder "capacity" of pasture lands. The fire destroyed most of the trees. For the most part, only a few tree species that have adapted to fires, the so-called "fire-loving" ones, have survived, the trunk of which is protected by thick bark, charring only from the surface.
Plants that reproduce by root shoots or have seeds with a thick shell have also survived. Among the fire-lovers are thick-bodied giant baobabs, the shea tree, or karite, called the oil tree, since its fruits give edible oil, etc.
The fencing of private properties, the construction of roads, steppe fires, the opening of large areas and the expansion of cattle breeding aggravated the plight of wild animals. Finally, the Europeans, unsuccessfully trying to fight the tsetse fly, staged a grandiose massacre, and more than 300 thousand elephants, giraffes, buffaloes, zebras, wildebeest and other antelopes were shot from rifles and machine guns from vehicles. Many animals also died from the plague brought with cattle.
3.3 Conservation action to protect the African Savannahs
The fauna of the African savannah is of great cultural and aesthetic importance. Untouched corners with pristine rich fauna literally attract hundreds of thousands of tourists. Each African reserve is a source of joy for many, many people. Now you can drive hundreds of kilometers across the savannas and not meet a single large animal.
Once virgin forests are being developed by man and gradually uprooted to clear land, or cut down for the purpose of harvesting building materials. Further, the soil, which is no longer reinforced by plant roots and protected by tree crowns, is washed away during tropical rains, and the natural landscape, rich in the recent past, becomes impoverished, transforming into a barren desert.
Often the interests of the wild inhabitants of Africa run counter to the needs of the local population, which makes the protection of wildlife in Africa complicated. In addition, environmental protection measures are also more expensive, and not every country's government can afford to finance them.
However, some African states are concerned about the state of wild flora and fauna on their territory, so nature protection is given increased attention. Wild animals are protected in the national parks of such countries, water bodies are to be cleaned for fish breeding, and comprehensive measures are being taken to restore forests.
The governments of the newly independent states of Africa, which have thrown off the yoke of colonialism, have strengthened and expanded the network of such reserves - the last refuges for wild animals. Only there can one still admire the view of the primeval savannah. For this purpose, protected areas are being established - nature reserves and national parks. They protect the components of natural complexes (plants, animals, rocks, etc.) and carry out research work. Reserves have a strict environmental regime, and tourists who are required to comply with established rules can visit national parks.
In Africa, protected areas cover large areas. They are arranged in various natural complexes - in the mountains, on the plains, in humid evergreen forests, savannahs, deserts, on volcanoes. Serengeti, Kruger, Rwenzori national parks are world-wide.
Serengeti National Natural Park- One of the largest and most famous in the world. Translated from the Maasai language, its name means boundless plain. The park is located in East Africa. It is called the African paradise for animals. Herds of thousands of large ungulates (various species of antelopes, zebras) and predators (lions, cheetahs, hyenas) live in its open spaces, which have been preserved in an untouched state as they have been since time immemorial.
Kruger National Park- One of the oldest on the mainland. It originated in southern Africa as early as 1898. Buffaloes, elephants, rhinos, lions, leopards, cheetahs, giraffes, zebras, various antelopes, marabou, secretary birds reign supreme in this region of the savannah. Each type of animal has thousands of individuals. By their diversity, the park is often compared to Noah's Ark.
Ngorongoro National Parklocated in the crater of an extinct volcano. Buffaloes, rhinos, antelopes, giraffes, hippos, and various birds are protected there.
At Rwenzori parkchimpanzees and gorillas are protected.
The creation of reserves and national parks contributes to the conservation of rare plants, unique wildlife and individual natural complexes of Africa. Thanks to protective measures, the number of many species of animals that were on the verge of extinction has been restored. The world's largest diversity of species makes Africa a real paradise for ecotourists.
Conclusion
The African savannas are the Africa of our imagination. Huge expanses of the earth, unusually amazing fauna, the greatest herds on the planet. And everything seems to exist here outside of time.
Savannah is incredibly changeable, fickle. A dense forest may appear in this place in a few years. But there may be another development of events: all the trees will disappear, only grass will remain.
Savannah life is subject to the weather, which is very capricious here. Every year there is a dry, hot season. But no year is like the previous one.
The significance of the savannas is enormous. This is, first of all, the biological value of the community as a habitat for many species of animals and plants, including those that are endangered. Also, savannahs, after the forest zone, give the highest yield of plant products.
Sadly, African wildlife was once even more diverse. Currently, unfortunately, part of the species of wild flora and fauna is completely destroyed, and some more are under the threat of extermination.
A great misfortune for the inhabitants of the African savannahs are hunters who harass commercial species of animals under the root. But the advance of civilization on the original natural habitats of representatives of the wild fauna of Africa has become no less a problem. The traditional routes of migration of wild animals are blocked by roads, and new human settlements appear in places of wild thickets.
Now mankind understands the need to protect nature on Earth - it can be hoped that in the near future the wildlife of Africa will not only not suffer even more from human activity, but will also restore to some extent its impoverished flora and fauna, returning to it its former splendor and diversity. .
List of sources
1. Boris Znachnov Radio Africa / Around the World No. 4, 2008 S. 84-92
Boris Zhukov Eden at the bottom of the boiler / Vokrug Sveta No. 11, 2010 P. 96-101
Vlasova T.V. Physical geography of continents and oceans: a textbook for students. higher ped. textbook institutions / T.V. Vlasova, M.A. Arshinova, T.A. Kovalev. - M.: Publishing Center "Academy", 2007. - 487p.
Vladimir Korachantsev. Moscow. Armada-press, Africa-land of paradoxes (Green series 2001. Around the world), 2001- 413s.
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Savannahs and woodlands are a natural zone found mainly in the subequatorial belts of both hemispheres, although savannah areas are also found in the tropics and subtropics. The most characteristic feature of this zone is a seasonally humid climate with a clear change in the period of rains and drought, which determines the seasonal rhythm of all natural processes, the predominance of ferrallitic soils and herbaceous vegetation with rare, isolated groups of trees.
Characteristics and description of the natural zone of savannas and woodlands.
See geographical position zones of savannas and light forests on the map of natural zones.
The largest territory of the savannas is located in Africa, occupying approximately 40% of its total area. They are also common in South America (in the valleys of the Orinoco River they are called llanos, and on the Brazilian plateau - campos), Australia, in the north and east of the mainland and in Asia (on the Indo-Gangetic plain, the Deccan plateau and the Indochina peninsula).
Climate. The natural zone of savannahs and woodlands is characterized by the trade wind-monsoon circulation of air masses, where dry tropical air dominates in winter, and humid equatorial air in summer. With distance from the equatorial belt, the duration of the rainy season is reduced from 8-9 months to 2-3 months at the outer boundaries of the zone. The annual amount of precipitation also decreases in the same direction (from 2000 mm to 250 mm per year). Also, a characteristic feature of the savannas is the relatively small seasonal temperature fluctuations (from 15 to 32 degrees), but the daily amplitudes can be significant, reaching 25 degrees. All these characteristic climatic features are reflected in all components of the natural environment of savannahs and light forests.
Soils savannahs directly depend on the duration of the rainy season and are characterized by a flushing regime. Closer to the equatorial forests, where this season lasts up to 9 months, red ferralitic soils form. In the territory where the rainy season is less than 6 months, typical red-brown savannah soils are characteristic, and on the borders with semi-deserts, the soils are unproductive and with a thin layer of humus.
The natural zone of savannahs and light forests is very actively developed by man, which often leads to its irreparable changes (for example, desertification processes).
Video: "African Savanna" by Pim Niesten.
An abundance of tall grasses gilded by the sun, rare trees and shrubs, found more or less depending on the area - such is the savanna that occupies most of sub-Saharan Africa.
The vegetation of the savannah corresponds to the hot, with long dry periods, the climate that prevails in tropical places. Because the savannah is common in different parts of the world, including South America and Australia. But it occupies the most extensive territories, of course, in Africa, where it is represented in all its diversity.
In the south, on the border with the equatorial tropical forests, a transitional zone begins - the forest savannah. There are not very many herbs, the trees grow densely, but they are small. Then comes the sparsely forested savanna - vast expanses overgrown with tall grasses, with groves or isolated trees. Baobab dominates here, as well as palm, spurge and various types of acacia. Gradually, trees and shrubs become more and more rare, and grasses, especially giant cereals, thicken.
And finally, near the deserts (Sahara, Kalahari), the savannah gives way to the withered steppe, where only tufts of dry grass and stunted thorny bushes grow.
desert
Deserts are areas where precipitation is extremely rare. However, some plants have adapted to such conditions. Some have a very fast vegetation cycle: a small "willow" is enough for them to produce seeds in ten days. Others have a mainly root system: after rain, they immediately release a few leaves, and then flowers appear. Cereals can also be found in the Sahara and several species of gorse.Finally, some plants survive in drought by accumulating water in their stems and leaves.Such are the well-known cacti, especially common in the desert places of Central and North America.
The roots of some shrubs, for example sahara acacia, go very deep into the soil, sometimes even more than 20 m, to get to the underground reserves of the moisture they need.
Tuareg Drinn
constantly keeps the leaves rolled groove. Its very long roots, protected by a sand muff, extract moisture at great depths.
Baobab has a huge trunk, in the fibers of which there is a lot of moisture.
Euphorbia ("candelabra")
The Euphorbiaceae family has more than 300 genera: some of them are tree-like, like this plant, others resemble cacti.
Prickly pear("Indian fig tree")
Although this plant belongs to the cactus family, it is very similar to a tree with a solid and branched trunk, sometimes more than 3 m high.
Thanks to their succulent stems and leaves, cacti (below "cocker boom" from South Africa) are drought tolerant.
Saguaro or "giant candle", - a huge cactus (up to 10-15 m) of the desert regions of America.
