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, and 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.
It is directly dependent on the weather. With each period of drought, the savanna loses its brightness and turns into a sea of dried grass and sultry gloom. And after a few days of rain, nature becomes unrecognizable.
The vegetation of the savannas has adapted to the dry continental climate and long droughts and has a sharply xerophytic character. All herbs usually grow in tufts. The leaves of cereals are dry and narrow, hard and covered with a wax coating. The foliage on the trees is small, protected from excessive evaporation. Many species are high in essential oils.
Of the grasses for the savanna, elephant grass (Pinnisetum purpu-reum, P. Benthami) is typical. It got its name due to the fact that elephants love to feast on its young shoots. In areas where the doge season is longer, the height of the grasses can reach three meters. During a drought, the ground part of the shoot dries up and is often destroyed by fires, however, the underground part of the plant is preserved and after the rains gives a new life.
The hallmark of the savannah is the baobab (Adansonla digitata). The height of the tree reaches 25 meters, a thick (up to 10 meters in diameter) trunk and a huge spreading crown are typical. And recently, a giant baobab was discovered in Africa, 189 meters high and with a trunk diameter of 44 meters at the base. These are long-lived trees, the age of some reaches 4-5 thousand years.
Baobab blooms for several months, but each flower lives only one night. The flowers are pollinated by bats. Baobab is also called the "monkey tree", as its fruits are a favorite food for monkeys. A person in a baobab uses everything: he makes paper from the inner layer of the bark, eats the leaves, and receives a special substance adansonin from the seeds, which he uses as an antidote for poisoning.
Also in Africa, acacia savannahs are often found. More common Senegalese, whitish, giraffe acacia and other species (Acacia albida, A. arabica, A. Giraffae). Due to its crown, which has a flattened shape, the acacia is called umbrella-shaped. The adhesives contained in the bark are widely used in industry, and the wood is used to make high-quality expensive furniture.
The acacia tree is well known throughout the world, as it not only grows in most countries, but is also a symbol of some of them, as well as the object of many legends and works of art and literature.
The white or yellow clusters of this tree that are familiar to modern people, blooming in May, actually have a thousand-year history. Acacia adorned gardens and houses, used in medicine and religious ceremonies. Probably, there are no trees on the planet that have been more revered for many centuries by representatives of different civilizations and cultures than acacia. The photo cannot convey all the beauty and aroma of this plant, which today there are more than 800 species.
History of acacia
The uniqueness of this tree was noticed by the ancient Egyptians, who believed that it simultaneously symbolizes both life and death, as it blooms with white and red flowers. It was for them a symbol of the sun god, reviving life. The goddess of war and hunting, Neith, lived in its crowns.
In many cultures, the acacia tree symbolized purity and purity, and the ancient inhabitants of the Mediterranean believed that its thorns drive away evil spirits, and decorated their homes with plucked branches. And the nomads who traveled around considered it sacred and believed that the one who broke the branch of this tree would die within a year.
Acacia, the description of which is found in the Torah, was for the ancient Jews a symbol of holiness. So from its wood the altar of the Jewish Temple and the tabernacle were made, in which the
For Christians of the Middle Ages, it symbolized purity of thoughts and innocence, so houses were decorated with its branches. Acacia oil was used in rituals by various secret societies, and the priests smeared the altar and incense burners with it.
Places of growth
The acacia tree belongs to the legume family and can reach 25-30 meters in height. The homeland of the plant is considered to be North America, although most of its species grow in the tropical and subtropical forests of Africa, Asia, Mexico and Australia.
Depending on the location, this plant can be both trees and tree-like bushes. It has been cultivated in European countries since the 18th century because of its healing properties, beauty and strong wood. Today, in many cities of Russia and the CIS, you can see its most common species - Robinia, which is known as white locust. The tree is able to withstand sub-zero temperatures as well as the more commonly known mimosa. The real white locust grows exclusively in the tropical forests of Africa.
Description of the species
Regardless of where the plant grows, acacia has features common to the entire family:
These are traits common to most members of this species, although there are exceptions.
Acacia corkscrew
This is the most common tree in city parks and streets. Acacia, although usually growing quite quickly, reaches maturity at an average speed of 40 years.
With a height of 20 m and a width of 1.2 m, it has an asymmetric crown and white flowers with a pleasant aroma, hanging in tassels up to 20 cm in length. Often a corkscrew acacia can have two trunks, blooms from late May to early June, is not demanding to care for, and tolerates dry summers well. The elliptical leaves are bluish green in summer and bright yellow in autumn. They appear quite late, almost simultaneously with the flowers.
Acacia golden
Small, only up to 12 m in height, these trees are immediately noticeable. Acacia golden (Robinia pseudoacacia Frisia) has several trunks and beautiful light yellow leaves of an elliptical shape. On twisted, zigzag thorny branches, foliage appears late, almost before flowering: in late May - early June.
This tree was first discovered in Holland in 1935. It blooms with white fragrant inflorescences up to 20 cm in length, the fruit is brown and flat. The leaves are pinnate and alternate from 7 to 19 pieces on the petiole.
This acacia is not demanding to care, although it prefers humus dry soil. In wet and heavy soil, it can suffer from frost and die.
Acacia cone-shaped and umbrella
One of the old-timers among the trees of this species is the cone-shaped acacia (Pseudoacacia Bessoniana). It lives up to 100 years and grows up to 20 meters in height, forming offspring. Often has multiple trunks.
The foliage is openwork odd-pinnate, the crown can be either asymmetric or free, rounded. It blooms not densely, with white fragrant tassels up to 20 cm in length. From 7 to 19 leaves of an elliptical shape of a bluish-green color bloom on the petioles. Forms fruits up to 12 cm in length, in the form of flat brown beans. This acacia loves the sun very much and tolerates drought very well, it is not whimsical to the soil. If you plant such a tree in the garden, heavy and wet soil should be avoided. In frosts in such soil, acacia roots can be severely damaged.
The umbrella acacia is found in Africa and in the deserts of Israel. On the hot continent, she lives in the savannas and is loved by all her inhabitants, as she gives shade, thanks to her crown, which looks like an umbrella. In fact, this is a symbolic protection from the scorching rays of the sun, because its leaves are turned edgewise towards the luminary.
The tree has large sharp spines that protect it from the numerous herbivores that inhabit the savannah. It blooms with very small flowers with long stamens collected in a panicle. They are yellow or white.
According to legend, it was from the umbrella acacia that the Jews who left Egypt made Noah's Ark.
Acacia street
Most often in specialized stores there is street acacia, the seedlings of which are sold in flower pots.
Pseudoacacia Monophylla is slightly susceptible to environmental pollution, is a fast-growing and non-thorny tree species, reaching 25 m in height. The leaves of this acacia are pinnate and alternating: at the beginning of the petiole is small, but closer to the end they can reach 15 cm in length. Foliage is dull green in summer and yellow in autumn. It should be remembered that the leaves are very poisonous.
Branches may have a zigzag or horizontal, slightly raised appearance. It blooms with large white flowers, collected in clusters up to 20 cm in length with a pleasant aroma. This tree loves the sun and is not picky about the composition of the soil.
Acacia bristle
This name refers both to a tree-like shrub that reaches a height of more than 2 meters, and to a tree that, depending on the zone of growth, can reach from 15 to 20 m. A powerful root system and strong thorny zigzag branches make the plant wind resistant. These types of acacia bloom with beautiful large flowers of purple or pink color without aroma, collected in inflorescences of 3-6 pieces.
The name of the plant was due to the fact that its shoots are covered with reddish bristles. The leaves are dark green in spring and summer, yellow in autumn. If such an acacia grows in the garden, it attracts attention with its large and bright flowers.
Does not require additional care, prefers a quiet and sunny place, easily tolerates dry summers. Even poor soil is suitable for it.
Acacia pink
Robinia sticky (Robinia viscosa Vent.), as it is also called, pink acacia comes from the southeast of North America, is also cultivated in Ukraine. The tree can reach 7 to 12 m in height, but has a short lifespan.
The bark is brown, smooth, and the branches may have small spines. The shoots of the tree are covered with a sticky mass, which gave it its name. Acacia pink blooms with large, up to 2-3 cm in length, odorless flowers. They are collected in erect brushes of 6-12 pieces and are also covered with sticky hairs that attract bees. The tree is an excellent honey plant and pollen plant.
Suitable for those gardeners who prefer to grow plants with long flowering in the garden, as it has 4-5 flowering waves lasting until mid-September, this type of acacia. The leaves of this tree are large, up to 20 cm long. Bright green above, grayish below, they are collected on a petiole in an amount of 13 to 25 pieces.
The tree is unpretentious, frost-resistant (can withstand up to -28 degrees), can grow on any soil.
Acacia silver
Mimosa, well known to all post-Soviet women, is the silver acacia, whose homeland is Australia and the island of Tasmania.
This evergreen tree can reach 45 m in its native lands, but does not exceed 12 m in other countries. Its trunk has a light gray or brown hue with vertical cracks from which gum flows.
The leaves are grayish-green in color, pinnately dissected twice, go alternately on the petiole and reach from 10 cm to 20 cm in length. The flowers are very small, in the form of yellowish balls, collected in racemose inflorescences, from which panicles are formed. They have a very strong and pleasant aroma.
Silver Acacia seeds are flat and hard, and may be dull or slightly shiny black.
White acacia
Robinia, or false acacia (Robinia pseudacacia L.) has taken root well on the European continent and is familiar to many of its inhabitants. Its white flowers emit a very strong and pleasant fragrance that attracts not only people but also bees.
This tree lives on average from 30 to 40 years, has a brownish bark, a spreading crown with green pinnate leaves. The fruits of white acacia ripen in September - October and fall off only next spring.
Acacia in medicine
The chemical composition of acacia bark and its effect on the body have not yet been fully studied, but today decoctions from it are recommended not only by traditional healers, but also by official medicine. Since the bark, flowers and fruits of this plant are often poisonous, they can be used only after consulting a doctor and in the recommended doses.
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. To study the flora and fauna of the savannas.
3. Consider the features of different types of African savannas.
4. Consider current environmental problems and ways to solve them in the savannas.
General characteristics of the savannas of Africa
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 tall grasses up to 3-5 m, among them are sparsely 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 tall 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.
In parallel with 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
The savannahs of the northern hemisphere differ from the southern savannahs in appearance and species composition of the flora. To the south of the equator, among the thickets of cereals and dicotyledons, palm trees rise: Copernicia (Copernicia spp.) - in drier places, winding Mauritia (Mauritia flexuosa) - in swampy or flooded areas. Acacias and tall tree cacti are also numerous.
Red and red-brown soil savannahs and tropical woodlands are characterized by a higher humus content and greater fertility than the soils of moist forests. Therefore, in the areas of their distribution are the main areas of plowed land with plantations of coffee trees, cotton, bananas and other cultivated plants exported from Africa.
pacific coast between 5 and 27° S and the Atacama Basin, with their constant lack of rain, have the most typical desert soils and vegetation in South America. Plots of almost barren stony soils alternate with massifs of free-flowing sands and vast surfaces occupied by saltpeter solonchaks. Extremely sparse vegetation is represented by sparsely standing cacti, thorny cushion-like shrubs and ephemera of bulbous and tuberous plants.
Australia. A much larger area is occupied in Australia tropical woodlands and savannas. They are distributed over large areas in the north of the mainland, mainly north of 20°S. In the east, light woodlands and typical savannahs penetrate much further south. They also occupy large areas in the south of the island of New Guinea.
During the wet season, the Australian savannah is covered with bright flowering plants from the buttercup, lily and orchid families, various cereals. Typical savannah trees are eucalyptus, acacia, casuarina. The leaves of the latter consist of separate segments, and from a distance these trees look like conifers with long needles. Trees with thickened trunks are also widespread, in which a supply of moisture accumulates. They are represented by several species of the genus Strecularia, the so-called bottle trees. The presence of these peculiar plants makes the Australian savanna somewhat different from the savannas of other continents.
Savannah is combined with sparse forests consisting mainly of various types of eucalyptus. Trees in such forests are rare, so the soil is covered with thick grasses that burn out during the dry season and lush green during the rainy season. Eucalyptus woodlands occupy most of the Cape York Peninsula and a wide strip of the northern coast of Australia. Perhaps such a wide distribution of representatives of the genus Eucalyptus is due to their resistance to the effects of fire, which for thousands of years the Australian Aborigines used during hunting. Seeds of some eucalyptus species germinate much faster after forest fires.
Since the beginning of the colonization of Australia, immigrants from Europe burned out woody vegetation of savannahs and eucalyptus woodlands to use the land as pasture or arable land. Burning was also carried out in order to preserve moisture in the soil, since eucalyptus trees evaporate a large amount of moisture and in arid areas they cause damage to agriculture.
Soils Australian savannahs are of the red ferralitic type, and in drier places - red-brown highly leached and red-brown slightly leached soils.
The most humid areas of the north and east of Australia are gradually replaced by drier areas of the central and western parts of the mainland. When moving from east to west and from north to south, the forests become thinner and take more and more xerophytic appearance. Gradually, they turn into a kind of shrubby thickets, which in Australia are called " scrub"- these are thickets of thorny shrubs or stunted trees with small leathery foliage.
They consist mainly of eucalyptus and acacia. Depending on the predominance of certain plants in them or a more or less uniform combination of eucalyptus and acacia, different types of scrub are distinguished. The scrub also contains a lot of protea and casuarina. Scrub thickets cover large areas in the Central Plain and in the extreme west of the mainland, corresponding to the climatic conditions of semi-deserts. Soils under them are reddish-brown, often saline, turning into structureless soils of desert regions.
Individual features of the nature of South America, distinguishing it from other continents.
The main climate-forming factors of South America.
Geographical position between 12°N. and 56° S causes high values solar radiation almost throughout South America. Most of it receives 5000-6700 120-160 kcal / cm 2 per year, and only in the extreme south this value decreases to 80 kcal / cm 2.
An important factor in climate formation in South America, as well as in North America, is its orography. Air currents coming from the Atlantic Ocean freely penetrate westward up to the foot of the Andes. In the west and partly in the north, the Andean barrier influences the air currents coming from the Pacific Ocean and the Caribbean Sea.
Great value also currents
trade wind circulation
On the eastern outskirts On the mainland, south of the equator, there are trade winds of the northern and southern hemispheres, and in more western regions in the summer for each hemisphere, there is a transition of trade winds to the other hemisphere and the formation of monsoon winds.
Western edge The mainland is exposed to the eastern periphery of the South Pacific High and the associated southerly and southwesterly winds and trade wind inversion for a significant distance. The extreme south of the mainland is affected by the western transfer of temperate latitudes.
The North Atlantic High is somewhat shifted to the south, and the air flow flowing along its southern periphery in the form of a northeast trade wind captures the northern part of South America. It leaves a significant amount of precipitation on the eastern slopes of the Guiana Highlands and on the Guiana Lowlands.
Monsoonal winds blow from the side of the South Atlantic High towards the heated mainland, bringing rain to the southeastern outskirts of the Brazilian Highlands and the La Plata Lowland. Most of the western coast, from 30° almost to the equator, is under the influence of the eastern periphery of the South Pacific High and receives no precipitation.
In July the entire northern part of the mainland is under the influence of humid equatorial air brought by the southwest monsoon, and no less humid tropical marine air coming from the Atlantic Ocean.
In the subtropical and temperate latitudes of the southern hemisphere dominates western carry and cyclonic rains fall.
Peculiarities of climate formation in the subequatorial and equatorial belts of South America.
An important factor in climate formation in South America is its orography.
Air currents coming from the Atlantic Ocean freely penetrate westward up to the foot of the Andes. In the west and partly in the north, the Andean barrier influences the air currents coming from the Pacific Ocean and the Caribbean Sea.
Great value also currents Atlantic and Pacific Oceans off the coast of the mainland. The Guiana and Brazilian branches of the South Trade Wind Current in the Atlantic Ocean create a winter positive anomaly of the order of 3 °C off the coast of South America. The Peruvian cold current in the Pacific Ocean, penetrating almost to the very equator, carries masses of cold water from Antarctica to the north and reduces the temperature in the equatorial zone by 4 °C compared to the average value for these latitudes.
The most important type of atmospheric circulation for much of South America is trade wind circulation both hemispheres. Along the western periphery of the Atlantic highs, masses of relatively humid tropical air are carried out, which transforms, moving deep into the mainland and giving up a significant part of its moisture to the marginal uplifts of the Brazilian and Guiana highlands.
A distinctive feature of the subequatorial climate - seasonality in the distribution of precipitation - is quite clearly expressed in this territory. In the southern hemisphere - in the Brazilian Highlands, in the south of the Amazonian lowland and in the lower reaches of the Amazon - the period of rains associated with the action of the equatorial monsoon lasts approximately from December to May, and its duration increases towards the equator. In the north, the rainy season lasts from May to December. In winter, during the action of the trade winds, precipitation does not fall. Only in the northern segment of the coastal part of the Brazilian Highlands, where the trade winds, coming from the warm ocean, meet mountains on their way, does it rain even in winter.
Comparative analysis of tectonics and orography of South America.
The main part of the territory of South America is composed of the Precambrian tectonic belt, which is represented by the South American platform consisting of shields and syneclises. Between the Precambrian and Paleozoic tectonic belts, there is the Baikal folded structure, which is represented by separate areas on the mainland. The Paleozoic tectonic belt is represented by the epihercynian plate and the Hercynian folded structure in the south of the mainland. The Cenozoic tectonic belt is represented by the Alpine folded structure and pre-Alpine foredeep (in the east and south of the mainland).
Precambrian: South Amer platf. -Shields: a) Guianan (Guiana flat), b) East-Brazil (east part of Brazil flat, flat Barbarena, Serra Dumar), c) West-Brazil (western part of Brazil flat, matu-gros plateau, sulfur du- kashimba, sera dos espinhasus, sera dos paresis). –Syneclises: a) Orinokskaya (Orinok lowland), b) Amazonian (Amazon lowland), c) Parnaita, d) Laplatskaya (Laplatskaya lowland), e) Parana (Parana river basin).
Baikalskaya skl building (Serra Buenos Aires, Serra De Cordova)
Paleozoic:-Epihercynian plate (Patagonia Plateau), -Hercynian skl building (De Cordillera).
Cenozoic:- Alpine slope (Andes (center of the Andes, center of the Cordillera, Ecuadorian Andes, Caribbean Andes, subtropical Andes, Patagonian Andes)), - Pre-Alpine foredeep (equal to Beni Mamore, Granchakka, Pampa).
Patterns of spatial changes in the soil and vegetation cover of South America.
The vegetation cover of South America is especially characterized by tropical rainforests.
Humid tropical (equatorial) forests of South America on ferrallitic soils, named by A. Humboldt hylaea, and in Brazil called selva, occupy a significant part of the Amazonian lowland, adjacent areas of the Orinok lowland and the slopes of the Brazilian and Guiana highlands. Thus, tropical rainforests cover areas with an equatorial climate, but, in addition, they grow on the slopes of the Brazilian and Guiana highlands facing the Atlantic Ocean, in higher latitudes, where there are abundant trade winds for most of the year. However soil under this richest plant community in terms of volume of organic mass, they are thin and poor in nutrients. Decay products, continuously coming to the ground, quickly decompose in a uniformly hot and humid climate and are immediately absorbed by plants without having time to accumulate in the soil.
As the climate changes, i.e. with the advent of the dry season, tropical rainforests are moving into savannas and tropical woodlands. In the Brazilian Highlands, between the savannahs and the tropical rainforest, there is a strip of almost pure palm forests. Savannahs are common in a large part of the Brazilian Highlands, mainly in its interior regions. In addition, they occupy large areas in the Orinok Lowland and in the central regions of the Guiana Highlands. In Brazil, typical savannahs on red ferralite soils are known as campos. Their herbaceous vegetation consists of representatives of the legume and Compositae families. Woody forms of vegetation are either completely absent, or are found in the form of individual specimens of mimosa with an umbrella-shaped crown, tree-like cacti, spurges and other xerophytes and succulents.
In the dry northeast of the Brazilian Highlands, a significant area is occupied by the so-called caatinga, which is a sparse forest of drought-resistant trees and shrubs on red-brown soils. Many of them lose their leaves during the dry period of the year, others have a swollen trunk in which moisture accumulates, for example, a milkweed. The trunks and branches of Caatinga trees are often covered with creepers and epiphytic plants. There are also several types of palm trees.
On the Gran Chaco plain, in especially arid regions, on brown-red soils, thickets of thorny bushes and sparse forests. In their composition, two species belong to different families, they are known under the common name "quebracho".
The savannahs of the northern hemisphere differ from the southern savannahs in appearance and species composition of the flora. To the south of the equator, among the thickets of cereals and dicotyledons, palm trees rise: copernicia - in drier places, winding mauricia - in swampy or flooded areas.
Red and red-brown soil savannahs and tropical woodlands are characterized by a higher humus content and greater fertility than the soils of moist forests.
pacific coast between 5 and 27° S and the Atacama Basin, with their constant lack of rain, have the most typically pronounced in South America desert soils and vegetation. Plots of almost barren stony soils alternate with massifs of free-flowing sands and vast surfaces occupied by saltpeter solonchaks. Extremely sparse vegetation is represented by sparsely standing cacti, thorny cushion-like shrubs and ephemera of bulbous and tuberous plants.
subtropical vegetation occupies relatively small areas in South America.
The extreme southeast of the Brazilian Highlands, which receives abundant rainfall throughout the year, is covered subtropical forests from araucaria with an undergrowth of various shrubs.
The second type of subtropical vegetation of South America is subtropical steppe, or pampas, characteristic of the eastern, most humid parts of the La Plata lowland south of 30 ° S, is a herbaceous cereal vegetation on fertile reddish-black soils formed on volcanic rocks. To the west and south, as precipitation decreases, vegetation of dry subtropical steppes and semi-deserts appears on gray-brown
The extreme southeast (Patagonia) is characterized by vegetation dry steppes and semi-deserts of the temperate zone. Gray-brown soils predominate, salinization is widespread. The vegetation cover is dominated by tall grasses, and various xerophytic shrubs, often cushion-shaped, undersized cacti.
In the extreme southwest of the mainland, with its oceanic climate, insignificant annual temperature differences and an abundance of precipitation, moisture-loving evergreen subantarctic forests, multi-tiered and very diverse in composition. They are close to tropical forests in the richness and diversity of plant life forms and the complexity of the forest canopy structure. They abound with vines, mosses, lichens. Along with various high-stemmed conifers from the genera Fitzroya, Araucaria and others, evergreen deciduous species are common, for example, southern beeches (Nothofagus spp.), Magnolia, etc.
Patterns of spatial change and features of the animal world of South America.
The modern fauna, like the flora of the mainland, was formed starting from the end of the Cretaceous period. in isolation and little climate change. The antiquity of the fauna and the presence in its composition of a large number of endemic forms are associated with this. In addition, there are some common features of the fauna of South America and other continents of the southern hemisphere, which indicates a long-standing relationship between them. An example is marsupials, preserved only in South America and Australia. All monkeys of South America belong to the group of broad-nosed ones, which are absent in the fauna of the Old World. The very rich and peculiar fauna of South America (together with Central America) belongs neotropical region and is included within its two subregions - Brazilian and Chile-Patagonian.
Tropical rainforests
The greatest originality and wealth are characterized by tropical rainforests, animals there hide in dense thickets or spend most of their time on tall trees. American (broad-nosed) monkeys live in the tropical forests of South America. Spider monkeys with long flexible limbs are widespread. sloths. They are sedentary and spend most of their time hanging in trees, feeding on leaves and shoots. Sloths climb trees confidently and rarely fall to the ground. Some are also adapted to life on trees. anteaters. In tropical forests there are predators from the family feline: ocelots, small jaguarundis, as well as large and strong jaguars. Ungulates, few in South America, are represented in the forests by only a few genera. Among them are tapir (Tapirus terrestris), a small black peccary pig and small South American pointed deer. Several species live in the forests of South and Central America. marsupial rats, or opossums. Some of them are equipped with a tenacious tail and climb trees well. The Amazonian forests are teeming with bats, among which there are species that feed on the blood of warm-blooded animals. Reptiles and amphibians are very richly represented in the forests. From reptiles stand out water boa anaconda Many poisonous snakes, lizards. There are crocodiles in the rivers. From amphibians many frogs in the forests many different birds, especially brightly colored parrots. The largest of the parrots, the macaw, is the most typical. One of the features of the tropical forests of the mainland is a large number insects, many of which are endemic. Diurnal and nocturnal butterflies, various beetles, ants abound
Savannas, woodlands and steppes
Fauna more dry and open spaces South America - savannas, tropical woodlands, subtropical steppes - different than in dense forests. Of the predators, in addition to the jaguar, the cougar, ocelot, and pampa cat are common. The southern part of the mainland is characterized by a maned wolf from the canine family. On the plains and in mountainous regions, the pampa fox is found almost throughout the mainland, in the extreme south - the Magellanic fox. Of the ungulates, a small pampas deer is common. armadillos- animals equipped with a strong bone shell. From rodents in the savannahs and steppes there are viscacha and tuko-tuko living in the land. From birds in addition to numerous parrots and hummingbirds, there are also nandu (genus Rhea) - South American representatives of the ostrich order, some large birds of prey. There are many snake and lizards. A characteristic feature of the landscapes of South America is a large number termite mounds. Some areas of South America periodically suffer from locust invasions.
Andes South American representatives of the camelid family - llamas - are common throughout the mountainous region. Also found in the Andes spectacled bear, some marsupials. Small endemic rodents used to be widespread chinchillas(Chinchilla). Birds. Of the predators, the condor is interesting - the largest representative of this detachment.
Comparative analysis of the zone of moist equatorial forests of Africa and South America.
Zone humid equatorial forests covers the coast of the Gulf of Guinea to the north of the equator and the basin of the Congo River, stretching for 1600 km from north to south and 5000 km from west to east. This natural area is original and unique. There are practically no seasons here: in winter and summer the air temperature is the same and is approximately +24 °C. More than 2000 mm of precipitation falls per year. It rains every day, usually in the afternoon. Water and heat create ideal conditions for the development of all living things, so moist equatorial rainforests grow here - hylaea .
In the zone of humid equatorial forests, rivers are always full-flowing. During floods, they often flood low banks, and water covers vast areas.
In the conditions of the equatorial forest formed red-yellow ferrallitpy soils. It is iron compounds that give them their red color. These soils are very poor in nutrients, since organic residues are quickly decomposed by microorganisms under conditions of moisture and heat, and nutrients are quickly absorbed by plants. Therefore, deforestation here leads to a real environmental disaster. The soil in bare areas is washed away by rains, and the sun turns the surface of the earth into a dry crust, where nothing can grow.
In the equatorial forests of Africa, there are over 25,000 species of plants, only trees - about 1,000 species. These forests are always stuffy, humid and dark. The forest is so dense that it is impossible to see anything not far from you, everything around is obscured by bushes, lianas that braid trees, fallen trees and oxen of giant trees. The equatorial forest has two characteristic features: it is evergreen and multi-tiered.
Evergreen the forest is due to the fact that the plants never completely shed their leaves. Warm and humid weather, hovering all year round, allows the leaves to exist on the shoot for 2-3 years. The leaves, of course, are replaced, but in turn.
Layering is the distribution of plants in height according to the need for light, water and nutrition. In the forests of the temperate zone there are 3-4 tiers of plants, in their hylaea - 6-8 (Fig. 58). At the very bottom - the realm of shade-loving mosses and creeping plants. Shrubs and young trees that are undemanding to light rise higher. There are many tree ferns,bananas. The third tier is trees 15-20 m high, which need more light. Among them are many valuable breeds, such as red, ebony, sandalwood,yellow trees. There are also bread,nutmeg trees. Reign even higher ficuses and various types palms. The highest are light-loving, up to 60-80 m high, ceiba with spreading crowns. Due to their extraordinary height, they are called "upstart trees". In such tall trees, the leaves are very hard and evaporate little water, because it is difficult to raise it to such a height even for the most powerful root system. Wide root-supports help keep the trunk in an upright position.
The branches of the trees of the lower tier are so densely intertwined that because of them the crowns of the trees of the upper tier are not visible. At the very surface of the earth there is complete darkness. Only 1/120 of the sunlight gets here, so there is no grass at all. Instead, they rise from the ground creepers- trees with a flexible and long (up to 300 m) stem, which, wrapping around the trunks, bring their leaves and flowers to the light. Making your way through such a forest without a path is a difficult and dangerous business.
The equatorial forests of South America are called selva(port. - forest). This zone here occupies much larger areas than in Africa. The selva is wetter than the African equatorial forests, richer in plant and animal species.
The soils under the forest canopy are red-yellow, ferrolitic (containing aluminum and iron).
selva is located on the territory of countries such as Brazil, Peru, Suriname, Venezuela, Guyana, Ecuador, Bolivia, Colombia. Selva is located in the equatorial and subequatorial belts (selva in the broadest sense - and in the tropical zone) on vast lowland areas of land in conditions of constant freshwater moisture (1800-2300 mm of precipitation per year), as a result of which the soil of the selva is extremely poor in minerals washed out by tropical rains .
Like all tropical rainforests, the selva has several tiers of plants. Trees grow in 3-5 tiers, but the undergrowth is weakly expressed. Due to the diversity of tree species (at least 2500 species of trees grow in the Amazon basin), and, accordingly, the diversity of leaf color, the surface of the selva has a spotted green color. The effect is enhanced by flowering trees, creating white or colored spots. There is a lot of extra-tiered vegetation - lianas and epiphytes, a lot of orchids. Unflooded territories (terra firma) are especially rich in epiphytes.
Most of the numerous and diverse animals of the selva live mainly on trees, there are even a lot of arboreal amphibians. There are few land animals, among them - a giant armadillo, a large anteater, peccaries that look like small pigs, noses, a bush dog, and guinea pigs. Capybara (the largest rodent on Earth) and tapir live near the water. Many mammals for life on trees have a tenacious tail: pygmy anteater and four-toed anteater, opossum, tenacious-tailed porcupine, kinkajou, three-toed sloths and chain-tailed monkeys (howler monkeys, capuchins, uakari, arachnid, etc.); small marmosets are very numerous. Predatory mammals of the selva are felines - jaguar, puma, ocelot, which are also well adapted to life on trees.
Among the richest fauna of birds - toucans (endemic), hoatzin, gokko, urubu vulture, macaw parrot, Amazon parrot and other parrots, hummingbirds (among them the smallest birds of the Earth) are represented here by more than 300 species. In addition to birds, many bats fly here.
Lots of reptiles. Representatives of snakes are boas, including the anaconda, the largest snake. There are many poisonous snakes among them: bushmaster, asps. Examples of lizards are iguanas, skinks, gilatooth.
Comparative analysis of climate types in the northern and southern tropical zones of Africa.
The tropical belt of Africa occupies very large areas, especially in its northern part. Most of the Sahara is characterized by a hot arid climate of tropical deserts and is even sometimes referred to as "Saharan". Continental tropical air dominates there throughout the year. In the summer season, the territory of North Africa is subject to strong heating, conditions are created for the formation of a baric minimum, and the northeast trade wind rolls here, which brings air with a humidity of 20-25%. During this period, blind rainfall is often observed. This is when it rains from the clouds, but it does not reach the earth, as it evaporates. In winter, due to relative cooling in North Africa, an anticyclone is formed, during which descending air currents are established throughout the Sahara and no precipitation occurs at all. The daily amplitude is large and can be up to 50°. This is due to the complete absence of clouds, vegetation and dryness of the climate. Even frosts can occur over the Sahara at night. The coast of the Red Sea and the territory of the Gulf of Aden are also located in tropical latitudes. But, proximity to the water basin does not mean that precipitation falls there. There are practically no deposits. This is because the summer, moisture-saturated monsoon that goes to the Sudan region lingers on the slopes of the Ethiopian highlands, giving precipitation to this area. But the areas of the Gulf of Aden and the Red Sea, this monsoon blows in the form of a foehn, which, according to the rules of meteorology, never gives precipitation.
