Why are the savannahs replace deserts? What is Savannah and where it is the formation of savannah and desert.

1. Name the natural zones of Africa. What are the features of their placement on the mainland?
2. What connection exists between climatic belts and natural zones?
3. Name the essential signs of the zones of equatorial forests, savannah, tropical deserts.

Equatorial forests are located on both sides of the Equator in the Congo River Basin (Zaire) and along the Guinean Bay north of the equator. The formation of the zone is due to a large amount of heat and moisture throughout the year.

Equatorial forests of Africa are diverse in composition. Only trees are about 1000 species. The upper tier form ficuses, palm trees, etc. In the lower tiers, bananas grow, tree ferns, lianas, which, hanging garlands from trees, make forest trap in places impassable.

Equatorial forest is the birthplace of many valuable plants, such as the most common of all palm trees - oilseed, from the fruits of which palm oil is obtained. The wood of many trees goes to the manufacture of expensive furniture and in large quantities are exported outside the mainland, such as an ebony tree having wood black or dark green.

Many animals of equatorial forests dwell on trees. In addition to birds, rodents and insects, numerous monkeys - marty, chimpanzee, etc. live in trees.

Turning inhabitants include pigs, small hoofs (African deer, etc.). On the forest edges and the coast of the reservoirs there are the rarest animals on Earth - dwarf hippo (growth of up to 80 cm) and the relatives of the Giraffe - Ogolai, dwelling only in Africa. A large predator of equatorial forests - leopard. In the deaf, low-cost places preserved the largest human monkeys - gorillas that are no longer found anywhere. In loose soil and forest litter, snakes are found, lizards.

Fig. 56. Rhino in one of the National Parks of African Savann

In all forest tiers, ants are common. Some types of ants (the so-called worst ants) move long columns, exterminating all the living on their way. Numerous insects are termites that feed on plant residues.

Great harm to the population brings Fly Tsetse. It is a carrier of the causative agent of a disease that causes diseases and death of cattle and horses, in humans - life-threatening sleepy disease.

Not only vegetation and animal world of equatorial forests, but also other natural phenomena are unusual for us. There reigns the eternal summer, eternal equinox. And we have only two days a year, when the day is equal to the night. In low latitudes, it gets rapidly, as fast in the morning the sun awakens the whole nature. No less unusual and view of the star sky. Southern Cross rushes to eyes, and the polar star is close to the horizon.

Savannes in Africa occupy huge spaces - about 40% of the continental area. Such a large percentage of Savannan Square is not on any continent. In the appearance of Savannah differs sharply from equatorial forests. A man in the forest is cut off from the light and the sun, he surrounds huge trees and shrub pigs, it is like on the bottom of the Green Sea, in the eternal twilight. People who fell after the dark, gloomy forest in Savannah are affected by the abundance of light and open cheerful spaces. Forest and savanna are two different worlds.

Soil and vegetation Savannnes depend on the duration of the season of the rain. Closer to Equatorial forests, where the rainy season lasts 7-9 months, red ferallic soils are formed. Herbs reach 3 m in height. Among the solid seas of herriads, the groves with rack-started trees are scattered, huge baobabs with splashing branches, oilseed palms, palm dum.

Where the duration of the season of rains is less than 6 months, typical savannate with red-brown soils, with not very high herbs. On a vast grassy space, various acacias with a flat umbrella-shaped crown are highlighted.

Fig. 57. The animal world of Africa has been unique.

On the border with semi-deserts, where scarce rains fall out only 2-3 months, sabotanes are formed with dry spiny shrubs and rare rigid herbs. There are also Mokhodi - tree plants having fleshy stems and branches, devoid of leaves and spiny-covered, which, adapting to dry climates, accumulate moisture supply in them.

A rainy time that comes after the anti-sentence of the sun comes suddenly. As in the magic maroon, the savanna is covered with luxurious grass, and the trees awaken to life after sleep. The herds of antelope, rhinos, elephants, zebras, etc. appear.

Nowhere in the world there is no such cluster of large animals, as in African savannah: a variety of antelopes, striped zebras, giraffes that, pulling long necks, eat leaves with high trees. Other large herbal animals are found in Savannah and other large herbal animals - elephants (weight up to 4.5 tons), buffaloes, rhinos, which are almost exterminated by man. In the shores of rivers and lakes there are hippos (weight up to 3 tons). Such a cluster of large animals is possible due to the abundance of a variety of food. Numerous predators - cheetahs, leopards, sacking, hyenas are accompanied by herbivores. Among them is the strongest and terrible - lion. Crocodiles live in rivers, the largest of them are Nile - reach a length of 5-6 m.

Africa savannah is extremely rich in birds. Here and the smallest is a beautiful notic, and the largest bird on Earth - African Ostrich, Marabou Bird, which is found only in Africa. From the predatory, it stands out by their appearance and housings of a bird secretary with long, like a crane, legs. She hunts the minor rodents reptiles, especially for snakes. The bird catches the snake and hinds her legs.

Extremely many termites in the savanna, their durable high buildings of a variety of shapes - fracthers - a characteristic detail of the zone.

In the dry period of the year, large animals, birds are invened to wet places, invertebrates, amphibians flow into hibernation or hide in shelters.

Natural conditions Savannan are favorable for growing cultural plants of hot countries: Manica (evergreen shrub, whose roots are rich in starch), bathata (sweet potato), corn, peanuts, in the eastern part of Savannan - cotton, and in more wet places - rice.

Tropical deserts in Africa occupy a huge area. The desert and savannah accounts for a large area of \u200b\u200bthe mainland. Therefore, Africa is called the mainland of the classical development of Savannnes and deserts.

The greatest area of \u200b\u200bthe desert is occupied in North Africa. The annual amount of precipitation in the Sahara almost everywhere is less than 100 mm. In the inner parts of precipitation sometimes does not happen for several years. The clouds are a rare phenomenon, so the sun's rays are particularly heated by the earth's surface. In the summer, the heat reaches 40-50 ° C in the shade. Flying from the scorching sun, the local population puts on loose long clothes. It is especially difficult to endure heat because of hot and dry winds, the heat dries the skin. A person feels strong fatigue, thirst, deprivates appetite.

Fig. 58. Sand Desert in Sahara

Large daily and significant annual temperature amplitudes cause severe physical weathering. Often in Sahara you can hear explosions that resemble a crash of remote canonada. These rock rocks crack and destroy, turning into pile of stones, rubble and sand. In sugar huge areas occupy stony deserts. The clay and sandy deserts alternate with them, where dunes and verakhans are praying.

The vegetation of the Sahara is extremely scarce, and in some places, especially in the central part, it is not at all. Some of the separate bunches of herbs and spiny shrubs grow. Only in oases is developing rich vegetation. Animals Sahara, like other deserts, are adapted to the conditions of the desert climate. So, the antelopes are capable of searching for water and food run long distances. Lizards, turtles and snakes can do without water for a long time. Numerous various beetles, locust, scorpions. From predators there are hyenas, sacking, foxes.

In South Africa, the desert zone takes the coast of the Atlantic Ocean (Namib Desert). It is characterized by a unique and amazing plant of Velvichia. A short trunk rises above the ground only 50 cm. Two dense leaf leaf departs from its top, reaching up to 3 m. The leaves grow continuously, dying at the ends. The age of Velvichia can reach 150 years. To the east and the north of the South African deserts are transferred to semi-deserts, where spiny pillow-shaped plants prevail, as well as the Mokhod and Aloe. Wild watermelons with juicy fruits are also characteristic, often replacing the local population and animal water.

1. On the map, determine which climatic belts are tropical deserts and semi-deserts.
2. Using cards, determine the climatic conditions of the desert zone.
3. Why are the savannahs replace deserts?
4. What are the features of rivers in the zone of tropical deserts?

The article gives the definition of what Savannah is. The climatic features of the natural zone are described, the characteristic of soils, vegetable and animal world is given.

This information will be useful for schoolchildren and students, when preparing for a lesson, report or exam.

What is savannah

Savannes are called extensive territories occupying a significant part of the subequatorial belt covered with high herbal vegetation and rare trees.

From the description of the Natural Zone, Savannnes and the Raffeles should be noted the main items:

1. Herbal cover is higher than in the steppes, and in its basis, there are severe cereals.
2. The density of vegetation cover is high, and it is low, so the soil is visible.
3. Trees may not be at all, but there are sites that are almost sparse forest.

Geographical position

The location is a subequatorial belt in the north, and in the southern hemisphere. On the map of natural zones, it is clear that herbaceous spaces capture almost 40% of Africa Square, and separate territories are located in Australia, Northeast Asia, America.

In South America, the natural zone captures the Brazilian Highlands and the plains of the Orinoca River. In Brazil, the square is occupied predominantly by a parel, in the pool of the Orinoco Wood vegetation there is almost no. South American savannahs wear different names: Brazilian - Campos, Venezuelan - Lianos.

In Asia, the natural zone occupies individual sections of India, Burma, Ceylon, Indochina.

In Australia, grassy territories are located in the northeast, differed by a pronounced arid period.

Plants savanna

The plant world is represented by a high cereal cover with separate trees and shrubs, small groups of trees.

Ivory grass

Most of the plants are hydrophitis, there are also xerophytes adapted to the dry season. In the arid months, cereals burn out, many trees are losing the foliage. The grass is pulled up to 3 m, and in lowlands up to 5 m.

Characteristic plants:

• ivory grass;
• oil palm;
• palma Dum;
• pandanus;
• baobab is a thick tree with an unusual shape barrel.

In more wet places, cereal cover becomes lower (up to 1.5 m), complemented by acacia - trees with a thick spreader crown, resembling an umbrella.

For more arid places are characterized by spiny semi-free. The trees are almost all year without leaves, the cereal carpet is rare, low (up to 1 m).

Flora is represented by low spiny wood species, succulents, pillow-shaped shrubs. Some scientists call these sections of the African steppe.

Soil

The mains are the red-brown and latheric soils, characterized by sufficient content of humus, due to the abundant decomposition of grass.

Because of the periodic moistening in the soil layers, the saturation of metal oxides is actively proceeded, so peels are often appear on the ground surface.

Seasonality of moisturizing affects the processes of soil formation. In the wet season, the soil layers are intensively leached, in dry - due to heating the surface of the Earth, the soil solutions rise. Therefore, the accumulation of humus, the evidence of the soil, the formation of chernozems is characteristic of dry savannah, where the period without precipitation is long.

Relief

On the African continent, the Zone Savannan and the Step Falcals occupies a plateau of East Africa, the Zamfisi River Waterproof Plateau, Congo, Limpopo, separate sections of high plains of Calahari.

Savannah in Tanzania

In South America, Savannah are located in Brazilian and Guiangian Plateau, the Plain Chaco Plain, in the Orinoco Pool.

In Australia - on the northeastern plains.

Climate and climatic belts

Savannes are located in the sub-screen climatic belt. Two seasons are clearly detected: winter dry and summer wet. Annual temperature ranges from 18 to 32 ° C. Temperature oscillations are slow, unfinished.

The dry cool period lasts from November to April. The average temperature is 21 ° C. Weather solar, frequent fires. Not more than 4 inches (100 mm) of precipitation drops out.

Dry season - migration time. Huge herds of hoofs are sent to search for food and water, predators rushed behind them. Wood species survive in dry time, due to the deep root system and a dense refractory crust.

The hot wet period begins in May, lasts October. The amount of precipitation for the period reaches 10 - 30 inches (250 - 750 mm). Abundant rains go after noon.

In the rainy season, the life of Savannah boils, the Earth is reborn after drought, rushing a lush green carpet.

Residents savanna

Fauna Savannan is unique. Nowhere on the planet there is no longer such a variety of large hoofs and predatory animals.

Unfortunately, since the beginning of the 20th century, wildlife seriously suffers from the activities of poachers and irrepressible hunters, gaskets, the leads of significant territories under cattle breeding and agriculture.

Horsepie antilop.

The list of animals that disappeared due to hunting activities are made:

• white GNU;
• horsepie antilope;
• zebra Kvagga.

Hoofs

The most numerous group of savanna hoofs lives in Africa.

Most common:

• blue GNU;
• zebras;
• thompson Gazelles;
• gazelle Grant;
• imphala;
• cannes;
• cow antelopes;
• rusties;
• giraffes;
• buffaloes;
• warts;
• african elephants.

Antelope Kuda

Rare hoofs, found only in reserves, are Kudo, sulfasses.

On the verge of extinction are black and white rhinos. Their luxurious, as seen in the photo, the horn is valuable mining for poachers.

In reserves are huge efforts to preserve these animals.

Predators

Painted animals are as diverse as herbivores.

African leopards

In African plains are common:

• lions;
• spotted hyenas;
• hyenoid dogs;
• leopards;
• cheetahs;
• caracals;
• nile crocodiles.

In the American steppes dwell:

• jaguars;
• oceloti;
• grivist wolves;
• puma.

Ding Dingo

In Australia:

• varana;
• dingo dogs.

Birds

The variety of African birds amazes, attracts tourists from around the world.

African Ostrich

Baboins and numerous types of monkeys are adjacent on the trees with birds. Decoration of water bodies are flamingo.

Nanda ostrises are residents of Brazilian steppes, Ostrich Ema - Australian.

Insects

Among the insects eating green parts of plants, you can note:

• locust (the most common family);
• bronze;
• cycad;
• rugging;
• caterpillars;
• sheets;
• rags;
• distributions.

From the processors of dead organicists are common:

• termites (in savannas the largest number of meters, often a huge value);
• crickets;
• worms;
• cockroaches;
• multi-like;
• chernotelki;
• ground mollusks.

Termites are the main source of food for the Australian and South American amusements.

Every year the deserts are growing at the savanna. This is especially noticeable in Africa. The main reason why savannahs are replaced by deserts is human activity. A person for his needs takes too much water from the reservoirs, which is why the vegetation is experiencing a hard deficit of moisture.

Another reasons of desertification are global warming and intensive cattle breeding. Pashed cattle eats the grass so actively that herbal cover does not have time to recover.

Savanns and deserts on the continents where they exist are almost always near and replace each other. This is due to the fact that each of them is located in one climatic zone. Under the influence of the system of precipitation of zones, they become a savanna or desert.

Formation of savannah and desert

The savannahs are formed in the territories where there are two clearly dedicated season of the year: rainy and dry. Also in this zone almost always retains a high temperature of about 30 ° C. Almost always, similar conditions are observed in the subequatorial or in tropical zones.

Savanns are on four continents:

• Africa.
• Asia (India, Pakistan).
• Australia.
• South America.

The deserts, in turn, are most often formed in the tropical zone, since here the temperature is almost the same or even higher than in the subequatorial zone. However, winds that bring precipitation will be afraid of a tropical zone, so precipitation here falls very little.

This explains why on continents two these natural zones replace each other.

Change of savanna desert

In some parts of the Earth, especially in the northern part of Africa, there is a tendency to expand the desert through the territory of Savannah. This happens for several reasons.

First, in the consequence of global warming Recently, the drought season is delayed. Therefore, in the transition zone between the savannahs and deserts, the sands of the Sahara covers fertile soil, having a plants to climb after the rains seasons.

Secondly, the human factor plays a major role here, since people in the Savannan zone graze too much livestock, which eats all the grass. Including their food becomes cereals with seeds. And in the savannah ecosystem, it is designed so that local herbivores (zebra, an antilope GNU, etc.) eat different parts of the plants, which gives the last time for distribution.

Thirdly, a person uses groundwater for different purposes. Since these waters in the drought season help root systems of perennial plants live to the rainy season when a person takes them away, herbs die and the desert expands.