Wet equatorial forests otherwise called permanently wet forests. From the name it becomes obvious that they are located mainly in the equatorial regions of the planet. Equatorial forests cover the territory of the Amazon in South America, the Congo and Lualaba river valleys in Africa, and are also located on the Great Sunda Islands and on east coast Australia. This natural area mainly accompanies the equatorial climatic zone... This is due to the fact that the formation of these forests requires enormous moisture - more than 2000 mm of precipitation per year and a constantly hot air temperature - more than 20 ° C. Therefore, they are usually located near the coasts of continents, where warm currents flow. Constantly wet forests are impenetrable jungles, according to various estimates, up to 2/3 of all species living on Earth live here, millions of them have not yet been discovered and studied. The largest area of rainforest is located in South America, where it is called selva (pictured), which means "forest" in Portuguese.
Wet equatorial forests are characterized by the presence of several layers of plants. The height of the trees here on average reaches 30-40 meters, and in Australia there are huge eucalyptus trees, up to 100 meters high. In the treetops of the equatorial forest, perhaps 40% of all animals on the planet live! Its research is especially difficult, so the canopy of the equatorial forest was figuratively called another unknown living "continent". The plants in these forests are characterized by very large leaves, often dissected or perforated to prevent heavy equatorial rains. Plants never completely shed their leaves, remaining green all year round. For this reason, there are no seasons in the year, their stems grow evenly, and there are no tree rings on the tree cuts. The fauna is characterized by a huge number of snakes, lizards, frogs, spiders and insects. The animals that live here are usually small in size, many of them, like koalas in Australia or sloths in South America, spend most of their lives in trees. Large animals simply could not move through the rugged wilderness of the equatorial jungle. This is also very difficult for humans. Pioneers often had to simply hack their way through the wall of vines using saber machetes. But even today, many parts of these forests remain unexplored and untouched by man. Unfortunately, civilization is attacking forests, destroying them for crops of cultivated plants, paving roads or extracting timber. The preservation of these forests is a very important task for humanity, because their massifs have a huge impact on the regulation of the planet's climate.
Despite the large amount of organic matter and plant litter, the soil is moist equatorial forests poor in humus. This is due to the fact that a very large amount of rain is constantly washing it out of their composition. The soils of the equatorial forests are predominantly red-yellow ferralite.
Brazil rain forest
Humid equatorial forests
Wet equatorial forests
evergreen forests, mainly in the equatorial, less often in subequatorial belts in the north South America, in Central America, in Western Equatorial Africa, in the Indo-Malay region. Into the bass. Amazons they got the name helium, selva... Distributed in areas with annual precipitation of more than 1500 mm, relatively evenly distributed over the seasons. Characteristically big variety species of trees: from 40 to 170 species are found per hectare. Most trees have straight, columnar trunks, branching only in the upper part. The tallest trees reach heights. 50-60 m, trees avg. tier - 20-30 m, lower - approx. 10 m. Many trees have board-like roots, sometimes rising to a height. 8 m. In swampy forests, trees have stilted roots. Change of foliage different types trees happen in different ways: some shed their leaves gradually throughout the year, others only at certain periods. Opening young leaves initially hang as withered, sharply differing in color, which is characterized by a wide range of colors - from white and pale green to crimson and burgundy. Flowering and fruiting also occur unequally: continuously throughout the year or periodically - once or several times a year. Often on the same tree you can see branches with fruits, flowers and young leaves. Many trees are characterized by caulifloria - the formation of flowers and inflorescences on the trunks and leafless areas of the branches. The dense crowns of trees almost do not allow sunlight to pass through, so there are very few grasses and shrubs under their canopy.
In the equatorial forests there are many lianas, mainly with woody stems, less often grassy ones. Their trunks reach a diameter of. 20 cm, and the leaves are raised to the height of the tree crowns. Some vines, for example. rattan palms, resting on tree trunks with short shoots or special outgrowths; others, ex. vanilla, are fixed by adventitious roots; however, most tropical vines are curly. There are often cases when the trunk of a vine is so strong, and the crown is so closely intertwined with several trees that the tree braided by it does not fall after death.
Epiphytes are very diverse and numerous - plants growing on trunks, branches, and epiphylls - on tree leaves. They do not suck out nutritious juices from the host plant, but use it only as a support for growth. Epiphytes from this. bromeliads accumulate water in the rosettes of leaves. Orchids store nutrients in the thickened areas of the shoots, roots or leaves. Breeding epiphytes, for example. ferns "bird's nest" and "antlers" accumulate soil between roots, epiphytes-sconces - under the leaves adjacent to tree trunks. In America, even some types of cacti are epiphytes. The humid equatorial forests were being exterminated by predators and continue to be exterminated. By now, their area has already halved and continues to decrease at a rate of 1.25% per year. They are inhabited by St. 2
/ 3 of all species of plants and animals of the Earth, many of which perish, even not yet being discovered and explored by man. In place of the destroyed primeval forest, low-growing and very species-poor forests of fast-growing trees begin to grow. With regular fires and clearings, secondary forests are replaced by savannas or pure thickets of cereals.
Geography. Modern illustrated encyclopedia. - M .: Rosman. Edited by prof. A.P. Gorkina. 2006 .
See what "humid equatorial forests" are in other dictionaries:
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Often called the lungs of the entire planet, and there is a lot of truth in this. A huge number of green plants, thanks to every minute, convert carbon dioxide into the oxygen necessary for all living things. What explains the riot of vegetation observed in these places?
One of the reasons is the large annual quantity precipitation (more than 2000 mm) and a favorable temperature regime - from +25 to +28 degrees Celsius. Although in summer in many countries the thermometer often rises above 30 degrees, due to the high humidity level of +25 in equatorial forests, it is subjectively perceived as extremely uncomfortable and hot weather.
Once upon a time, humid equatorial forests posed a serious question for botanists: why, with such a variety of vegetation, local soils are relatively poor in humus? But the answer was found. It turned out that due to frequent rains, the fertile layer cannot accumulate indefinitely - it is washed off into rivers by streams of water. In addition, the plants themselves immediately absorb the remaining trace elements.
Currently, many environmental organizations warn: if humid equatorial forests continue to be cut down at the same rate as now, then people of the next generation may not see all the beauties of evergreen forests. Just a hundred years ago, these forests occupied no less than 12% of the total land area of the earth, and now this figure barely exceeds 5%. It is easy to calculate that, while maintaining the same intensity, after 60-70 years, instead of trees, only grass will remain in the clearings. And since rainfall is determined by the evaporation of moisture from forests, even grass can become rare when the rains disappear. Climate and plants form a very complex interdependent system, so thoughtless human intervention can lead to tragic consequences. More detailed information on the results of studies of environmental organizations can be found on their websites or in print media.
The humid equatorial forests of Africa stretch in the central part of the continent as well as in the area along the equator. However, it would be a mistake to say that such forests are the prerogative of only Africans. Much more extensive are the humid equatorial forests of South America. Here they occupy almost 30% of the land area.
Why are humid forests so attractive to scientists? The answer lies in the enormous variety of life forms. Thus, in forests with a temperate climate on an area of one hectare, relatively few tree species can be counted. For example, a pine forest (pines predominate), a birch grove, etc. Everything is completely different in relation to wet forests- over 80 species coexist on the same area. Their life cycles are so closely intertwined that even distinguished researchers rainforest recognize that it is still very far from a complete understanding of all interrelationships. Of course, it is not limited to only one. These forests are home to many arthropods, reptiles and mammals. After all, the abundance of plants guarantees food for a variety of herbivores. Let's give an example: if we take the area of an equatorial forest with a side of a square of 10 sq. km, then on it you can count over 100 species of butterflies, more than 120 species of mammals and at least 400 - birds.
The portion of air that enters our lungs with each breath contains a portion of the oxygen "born" in the equatorial "green lungs" of the planet. How can you protect them from logging? Of course, simply organizing demonstrations and rallies is ineffective, but ancient wisdom claims that a long journey begins with just one small step. The same applies to forests: respect for nature in their places of residence is that very small step.
) a zone represented by more or less closely growing trees and shrubs of one or more species. The forest has the property of constantly renewing itself. Mosses, lichens, grasses, and shrubs play a secondary role in the forest. Plants here influence each other, interact with the habitat, forming a commonwealth of plants.
A significant area of forest with more or less clear boundaries is called a forest massif. There are the following types of woodlands:
Gallery forest... It stretches out in a narrow strip along the river flowing among treeless spaces (in Central Asia it is called tugai forest, or tugai);
Tape bur... This is the name of the pine forests growing in the form of a narrow and long strip on the sands. They are of great importance for water protection, their felling is prohibited;
Park forest... This is an array of natural or artificial origin with rare, singly scattered trees (for example, a park forest of stone birch in Kamchatka);
Coppice... These are small forests connecting woodlands;
Grove- a section of the forest, usually isolated from the main massif.
The forest is characterized by tiering - the vertical division of the forest, as it were, into separate floors. One or several upper tiers form the crowns of trees, followed by tiers of shrubs (undergrowth), herbaceous plants, and, finally, a tier of mosses and lichens. The lower the tier, the less demanding on the light are the species composing it. Plants of different tiers interact closely and are mutually dependent. Strong growth of the upper tiers reduces the density of the lower ones, up to their complete disappearance, and vice versa. There is also an underground layer in the soil: the roots of plants are located here at different depths, so numerous plants get along well in one area. Man, by adjusting the density of crops, makes those layers of the community that are valuable for the economy to develop.
Depending on climatic, soil and other natural conditions various forests arise.
This is a natural (geographic) zone stretching along the equator with some displacement south of 8 ° N. to 11 ° S The climate is hot and humid. All year round average air temperatures are 24-28 C. The seasons are not expressed. At least 1500 mm of precipitation falls, since here is an area of low pressure (see), and on the coast the amount atmospheric precipitation increases to 10,000 mm. Precipitation falls evenly throughout the year.
Such climatic conditions in this zone contribute to the development of a lush evergreen with a complex layered forest structure. Trees branch little here. They have disc-shaped roots, large leathery leaves, tree trunks rise like columns and only spread their dense crown above. The shiny, as if varnished surface of the leaves saves them from excessive evaporation and burns of the scorching sun, from the blows of rain streams during heavy downpours. In plants of the lower tier, the leaves, on the contrary, are thin and delicate.
The equatorial forests of South America are called selva (port - forest). This zone occupies much larger areas here than in. Selva is more humid than African equatorial forests, richer in plant and animal species.
The soils under the forest canopy are red-yellow, ferrolite (containing aluminum and iron).
Equatorial forest- the homeland of many valuable plants, such as the oil palm, from the fruits of which palm oil is obtained. The wood of many trees is used for the manufacture of furniture and is exported in large quantities. These include ebony, whose wood is black or dark green. Many plants of the equatorial forests provide not only valuable wood, but also fruits, sap, and bark for use in technology and medicine.
Elements of equatorial forests penetrate the tropics along the coast of Central America, at.
The main share of equatorial forests is located in Africa and South America, but they are found in, mainly on the islands. As a result of significant felling, the area under them is sharply reduced.
Stiff-leaved forests
Stiff-leaved forests are developed in a Mediterranean climate. It is a moderately warm climate with hot (20-25 ° C) and relatively dry summers, cool and rainy winters. The average amount of precipitation is 400-600 mm per year with a rare and short-lived snow cover.
Mostly hard-leaved forests grow in the south, in, in the southwest and southeast. Some fragments of these forests are found in America (Chile).
They, like equatorial forests, have a tiered structure with lianas and epiphytes. In hard-leaved forests, there are oaks (stone, cork), strawberry trees, wild olives, heather, myrtle. Stiff-leaved plants are rich in eucalyptus trees. There are giant trees with a height of more than 100 m. Their roots go 30 m into the ground and, like powerful pumps, pump moisture out of it. There are undersized eucalyptus and eucalyptus shrubs.
Plants of hard-leaved forests are very well adapted to lack of moisture. Most have small gray-green leaves obliquely in relation to the sun's rays, and the crown does not shade the soil. In some plants, the leaves are modified, reduced to thorns. Such are, for example, scrubs - thickets of thorny bushes of acacia and eucalyptus. Scrubs are located in Australia, in areas almost devoid of and.
Peculiar and animal world zones of hard-leaved forests. For example, in the eucalyptus forests of Australia, you can find the koala marsupial. He lives in trees and leads a sedentary nocturnal lifestyle.
The climatic features of this zone are favorable for the growth of deciduous trees with a wide leaf plate. Moderate continental rainfalls bring precipitation from the oceans (from 400 to 600 mm), mainly in the warm season. average temperature January -8 ° -0 ° C, July + 20-24 ° C. Beech, hornbeam, elm, maple, linden, ash grow in the forests. The broadleaf forests of eastern America are dominated by trees similar to some East Asian and European species, but there are also species that are unique to this area. In terms of their composition, these forests are one of the richest in the globe... Most of all in them are American species of oak, chestnut, linden, plane trees are common with them. Dominated by tall trees with a powerful, spreading crown, often entwined with climbing plants - grapes or ivy. To the south, magnolias and tulip trees can be found. For European deciduous forests, oak and beech are the most typical.
The fauna of deciduous forests is close to taiga, but there are some animals unknown in the forests. These are black bears, wolves, foxes, minks, raccoons. A characteristic ungulate in deciduous forests is the white-tailed deer. It is considered an undesirable neighbor for settlements, as it eats up young crops. In the deciduous forests of Eurasia, many animals have become rare and are under human protection. Bison and Ussuri tiger are listed in the Red Book.
The soils in deciduous forests are gray forest or brown forest.
This forested area is densely populated and largely depleted. It has survived only in highly rugged, inconvenient areas for arable farming and in nature reserves.
Temperate mixed forests
These are forests with various tree species: coniferous-broad-leaved, small-leaved, small-leaved pine. This zone is located in the north of North America (on the border with the United States), in Eurasia, forming a narrow strip lying between the taiga and the zone of deciduous forests, and in the Far East. The climatic features of this zone differ from the zone of deciduous forests. The climate is temperate, with continental intensification towards the center of the continent. This is evidenced by annual amplitude fluctuations in temperature, as well as the annual amount of precipitation, varying from oceanic regions to the center of the continent.
The diversity of vegetation in this zone is explained by the differences in climate: temperature, amount of precipitation and the regime of their fallout. where precipitation falls all year round thanks to westerly winds from the Atlantic, European spruce, oak, linden, elm, fir, beech are widespread, that is, coniferous-deciduous forests are located here.
In the Far East, where precipitation is brought only in summer by monsoons with, mixed forests have a southern appearance and are distinguished by a wide variety of breeds, multi-tiered, abundant lianas, and on the trunks - mosses and epiphytes. Pine, birch, aspen with an admixture of spruce, cedar, and fir prevail in deciduous forests. In North America, the most common conifers are white pine, reaching a height of 50 m, and red pine. Of the deciduous trees, birch with yellow hardwood, sugar maple, American ash, elm, beech, linden are widespread.
Soils in the zone mixed forests gray forest and sod-podzolic, and in the Far East brown forest. The fauna is similar to the fauna of the taiga and the zone of deciduous forests. Elk, sable, brown bear live here.
Mixed forests have long been subject to heavy deforestation and fires. They are best preserved in and in the Far East, while in Eurasia they are used for field and pasture lands.
Taiga
This forest zone is located within temperate climate in the north of North America and in the north of Eurasia. There are two types of taiga: light coniferous and dark coniferous. Light coniferous taiga are pine and larch forests that are the least demanding on soil and climatic conditions, the thin crown of which allows the sun's rays to pass to the ground. Pine forests, having a branched root system, acquired the ability to use nutrients from infertile soils, which is used to consolidate soils. This feature of the root system of these forests allows them to grow in areas with permafrost... The shrub layer of the light coniferous taiga consists of alder, dwarf birches, polar willow, berry bushes. Mosses and lichens are located under this layer. This is the main food for reindeer. This type taiga is widespread in.
Dark coniferous taiga are forests represented by species with dark, evergreen needles. These forests are composed of numerous types of spruce, fir, Siberian pine (cedar). The dark coniferous taiga, in contrast to the light coniferous, has no undergrowth, since its trees are tightly closed by crowns, and it is gloomy in these forests. The lower layer is made up of shrubs with hard leaves (lingonberry) and dense fern. This type of taiga is widespread in the European part of Russia and in Western Siberia.
Peculiar vegetable world these types of taiga is explained by differences in territories: and quantity. The seasons stand out clearly.
The soils of the taiga forest zone are podzolic. They contain little humus, but when fertilized they can provide a high yield. In the taiga Of the Far East- acidic soils.
The fauna of the taiga zone is rich. There are numerous predators - valuable game animals: otter, marten, sable, mink, weasel. Large predators include bears, wolves, lynxes, and wolverines. V North America in the taiga zone, buffalo and wapiti deer were previously encountered. Now they live only in nature reserves. Taiga is also rich in rodents. The most typical of them are beavers, muskrats, squirrels, hares, chipmunks, and mice. The taiga world of birds is also very diverse: nutcrackers, blackbirds, bullfinches, wood grouses, black grouse, hazel grouses.
Tropical forests
They are located along the east of Central America, in the Caribbean islands, on the island, in the east of Australia and in the southeast. The existence of forests in this dry and hot climate is possible thanks to the abundant rainfall, which is brought in by the monsoons in the summer from the oceans. Depending on the degree of moisture among tropical forests, there are permanently humid and seasonally humid forests. In terms of species diversity of flora and fauna, humid tropical forests are close to equatorial ones. These forests include many palms, evergreen oaks, and tree ferns. There are many lianas and epiphytes from orchids and ferns. The rainforests of Australia differ from others in the relative poverty of the species composition. There are few palms here, but eucalyptus, laurels, ficuses, and legumes are often found.
The fauna of the equatorial forests is similar to the fauna of the forests of this belt. The soils are mostly lateritic (lat. Later - brick). These are soils, which include oxides of iron, aluminum and titanium; they are usually reddish in color.
Subequatorial forests
These are deciduous evergreen forests that are located along the eastern outskirts of South America, along the coast, in the northeast of Australia. There are two distinct seasons here: dry and wet, the duration of which is about 200 days. Equatorial humid masses of air dominate here in summer, and dry tropical air masses in winter. air masses, which leads to the falling of leaves from the trees. constantly high, + 20-30 ° С. Precipitation decrease from 2000 mm to 200 mm per year. This leads to a lengthening of the dry period and to the replacement of evergreen constantly moist forests with seasonally moist deciduous ones. During the dry season, most deciduous trees do not shed all their foliage, but few species remain completely naked.
Mixed (monsoon) forests of the subtropical belt
They are located in the southeastern United States and eastern China. These are the wettest of all areas. subtropical belt... They are characterized by the absence of a dry period. Annual precipitation is greater than evaporation. The maximum amount of precipitation usually falls in the summer, as the monsoons, which bring moisture from the oceans, have an effect; winters are relatively dry and cool. Inland waters rich enough groundwater mostly fresh, shallow.
High-trunk mixed forests grow here on brown and gray forest soils. Their species composition can vary depending on soil and ground conditions. In the forests, you can find subtropical species of pines, magnolia, camphor laurel, camellia. On the flooded coasts of Florida (USA) and in the lowlands, cypress forests are common.
The mixed forest zone of the subtropical belt has long been mastered by man. In the place of deforested forests in America, there are field and pasture lands, gardens, plantations. In Eurasia - forestry lands with areas of field lands. Rice, tea, citrus fruits, wheat, corn and industrial crops are grown here.
In terms of ecological conditions and basic features, the nature of these forests differs little from the giles of South Asia, but on the southern continents their area is much larger. They occupy vast areas in the Western Amazon and the central parts of the Congo Basin, as well as the eastern slopes of the Guiana, Brazilian and East African highlands, the highlands of South Africa, the southern slopes of the North Guinean highlands, and the lower mountain belt on the western slopes of the Northern Andes. On the Australian continent, there are such forests only in the extreme northeast, where they have many common flora elements with the South Asian ones.
The humid equatorial and tropical forests of the southern continents, like all gileas, grow in conditions of constantly high temperatures (average monthly - 24-28 ° С) and excessive moisture... The amount of precipitation, uniform throughout the year, usually exceeds 2000 mm. In most cases, the substrate for such forests is loose weathering crusts of various surface deposits, which were formed for a long time with an abundance of heat and moisture. The conditions for the existence of organisms here do not change much over time, but they are very different in different layers of forest vegetation.
The Gilei of the Amazon is the largest area of equatorial humid forests on the globe. They have their own name - selvas.
Their floristic composition is diverse: there are up to 4500 species of tree species alone, and the total number of flowering plant species reaches 15 thousand. It is difficult to find two identical plants next to each other. Many endemics. The upper tiers of selvas form a continuous canopy: the tallest trees (seibas, copifers, bertholletias, Mauritius palms, etc.) are slightly inferior in height to various legumes. Epiphytes from bromeliads, aroids, cactus, orchids are extremely rich (about 1/3 of all types of flowering plants), there are epiphytic ferns. Real selvas, which in the Amazon are called ete, occupy more or less drained areas - watersheds and slopes (the local name of these lands is terra-firm). On the flooded, swampy floodplains of the river. The Amazon and its tributaries grow poorer in species composition and relatively stunted forests. They are called varzea - forests on high floodplains, and igapo - on constantly flooded low floodplains. The Igapo Formation resembles the mangroves of the seaside. Plants have respiratory roots and all kinds of props. As in mantras, rhizophores and avicennias are not uncommon here. An interesting participant in these biocenoses is myrmecophilous (living in symbiosis with ants) cecropia, which grows on the floodplains of the rivers of the Western Amazon (riu-brancus). Palms - raffia - are also abundant here.
On the eastern slopes of the Brazilian and Guiana Highlands and in the lower belts of the Northern Andes, forests grow, in terms of the diversity of their floristic composition and structure, very similar to the Amazonian selvas. The differences are explained by the fact that they grow on well-drained slopes. Only at the foot of the mountains, on a relatively narrow strip of coastal lowlands, conditions practically do not differ from those of the Amazon. On the slopes up to an altitude of 1000-1200 meters, gileas dominate with a dominance of palm trees.
The humid equatorial and tropical forests of Africa resemble the Amazonian varzea: the upper tiers in them are thinned out, and the crowns are closed only in the lower tiers. African gileas are inferior to selva in terms of species diversity.
There are much fewer flowering plants here - about 11 thousand species. 70% of them are trees, and only 30% are other life forms. These forests are characterized by powerful ficus “suffocators”. They settle like epiphytes on the branches of other plants, give aerial roots, gradually reaching, take root, and the plant that originally served them as a support dies due to a lack of moisture and nutrients. There are such “stranglers” in South American forests, but they belong to other families (clusia, kusapoya, etc.) and are inferior to ficuses in power. In the flooded gileas of the Congo Basin, muses (a special genus of Cecropiaceae), mitragines and other endemic genera and plant species with stilted and aerial roots grow.
In Australia, rainforests are very small on the northeast coast.
They differ from the South Asian gili in the complete absence of diptera, widespread in Asia. These forests are rich in tree ferns, and eucalyptus trees dominate the south of the tropics.
Under the humid equatorial and tropical forests of all three continents, red-yellow ferralite soils are formed mainly on the weathering crusts of various rocks.
They are all rich in minerals. However, organic matter decomposes quickly at high temperatures. Decomposition products - mobile mineral forms - are immediately consumed by plants or carried by abundant waters into the lower soil horizons. Residual low-mobile hydroxides of iron, aluminum, manganese are deposited in the illuvial horizon, usually in the form of nodules. Humus does not accumulate. For the vast floodplains of the rivers of the Amazon and Congo basins, swamping processes are characteristic: gleying, the formation of peat horizons.
On the sandy terraces above the floodplain, powerful illuvial-humus podzols with signs of soil moisture are formed. The soils of humid equatorial (tropical) forests are usually acidic and infertile (the humus content in the upper horizons is 2-3%).
The fauna of the tropical rainforest zone is unusually rich and diverse. All layers of vegetation are densely populated, although at first glance the forest may seem uninhabited: animals hide in the crowns of trees, among numerous epiphytes and lianas, in hollows, under fallen trunks and in various other shelters. Their presence is betrayed by loud sounds, which are emitted by many animals with a powerful vocal apparatus.
South American selvas are distinguished by a particularly rich fauna.
It is home to a huge number of insect species, most of which are endemic to the mainland. Butterflies and beetles sometimes reach gigantic proportions, many of them are brightly colored. A variety of ants live in all layers of the forest.
A small number of ungulates - tapirs, small mazam deer, baker-pigs - lead a terrestrial way of life. Representatives of endemic families of rodents live here: paca, agouti, capybara - the largest of the rodents. The body length of the capybara reaches 120 cm. All land animals are adapted to life near the water. Of the predators, a bush dog is found in the ground tier.
Most of the forest fauna of South America live in trees. In general, sloths do not descend to the ground. They lead a "hanging" lifestyle, clinging to branches with all four limbs, equipped with strong claws. In a relaxed state, the muscles support the fingers with claws in a closed position. The animal must contract its muscles to open its claws and move its paw, so sloths can sleep in a hanging position. Some anteaters - tamandua and a small anteater with a prehensile tail - freely climb trees. The same tails, which help to move through the trees, have the marsupial rats-stossums, and porcupines-koendu, and raccoon-kinkajou, and many of the wide-nosed monkeys characteristic of South American gilis. Bats, among which there are bloodsuckers, are widespread. Of the predators, some felines prey on the inhabitants of both terrestrial and arboreal tiers - jaguars, jaguarundi, ocelots, as well as noses (coati) from raccoons, marten-taira.
In the jungle, birds are numerous, usually with bright plumage and loud voices. Parrots are especially varied. Hummingbirds, characteristic of South American forests, feed on the nectar of flowers and participate in their pollination.
From reptiles, large boas stand out - the water anaconda and the land boa constrictor. There are many lizards and poisonous snakes. The rivers are home to caimans and some species of real crocodiles.
Amphibians - frogs are diverse. Many of them live in trees and differ in peculiar ways of reproduction.
Ungulates are more widely represented in the African gilea than in the South American one.
There are forest antelopes, water deer, some types of pigs, buffaloes, hippos, okapi (from the giraffe family). Of predators, leopards, jackals and civet are widespread, and of rodents, the brush-tailed porcupine and spiny-tails capable of gliding "flight". There are two types of lemurs and many monkeys - baboons, monkeys, mandrills, gwerets (colobus). The African forests are home to great chimpanzees and gorillas. There are many types of birds. Brightly colored bananoids (turaco) are endemic. There are several types of parrots. The ecological niche of hummingbirds is occupied by sunbirds. As in all gileys, there are many species of reptiles, amphibians, insects. The rivers are inhabited by blunt-nosed crocodiles, there is a giant frog - goliath.
The fauna of the tropical forests of Australia, like that of the entire continent, is very distinctive. The forests are inhabited by marsupial mammals, which lead mainly an arboreal lifestyle.
These are koala, ossums, tree kangaroo. Platypus (from monotreous) settle along the rivers, spending a lot of time in. A very large number of endemic birds: lyrebirds, birds of paradise, cassowaries, weed chickens. There are various parrots. American hummingbirds and African sunbirds are being replaced by honey suckers. Common snakes and some species of tree frogs. In the rivers there is a horntooth fish from the relict detachment of the same name.
The indigenous types of gili on all three Southern Tropical continents have been significantly altered by human activities. Only in some remote regions of Africa and South America (in the Western Amazon and in the east of the Congo Basin) areas of virgin forests with undisturbed vegetation cover are still preserved. The composition and structure of forest communities are changing as a result of selective felling of valuable tree species, the exploitation of rubber plants and other wild plants that provide valuable products. Big changes are being made by slash and fire methods of farming, which are still widespread in these areas. If small areas of the forest are destroyed, they quickly become covered with very dense thickets (clearings receive a lot of light and heat). However, the recovering forest communities differ significantly from the native type in a different species composition and low height. It takes a very long time for biocenoses close to the original type to appear in the place of disturbed forests. Forests suffer the most from clear felling for plantation farming, industrial construction and laying transport highways... As a result of the reduction of significant areas of the forest, the heat and moisture circulation of the soil is disturbed, nutrients are washed out, in loose surface sediments not fixed by the roots of plants, processes of solifluction and suffusion are rapidly developing, landslides are formed on the slopes. Thus, the lithogenic base itself is disrupted and even destroyed. natural complexes... This impedes the recovery of forest communities. Biocenoses are dying. The process in some cases can become irreversible. The vulnerability of giles threatens their very existence under intense unregulated exploitation.
Seasonally humid monsoon rainforests
As you go climatic conditions from equatorial to subequatorial with a distinct dry period, constantly moist forests give way to seasonally moist ones. They are often called monsoon. Deciduous plants appear in these forests, losing their foliage during the dry season. In terms of diversity and phytomass, seasonally humid tropical forests are slightly inferior to gilea. South America is especially rich in them, where they are often combined with typical jungle.
They predominate in the Eastern Amazon, where there is a short dry period, and some plants of tropical rainforests can survive only along rivers in the so-called gallery forests. Plakors, on the other hand, are occupied by seasonally humid forests and in places - tall-grass savannas. The more xerophytic variant is widespread in southeastern Brazil, in the basin of the upper and middle Parana, in combination with woodlands and savannas.
In Africa, seasonally humid forests border the gilli area. They are park forests dominated by pandanus and ficuses. On the northern border of the gili zone, seasonally moist forests are apparently of a secondary nature.
Here, the conditions are "boundary" for the existence of tropical rainforests: the lush evergreen vegetation of the gili can survive a short dry period due to microclimatic features, within the community, where there is shading, evaporation is reduced, the soils are initially overwetted, etc. The biocenosis in its former form is not restored if the vegetation cover is disturbed by felling and fires. Those plants survive that have been able to adapt to the changed conditions, for example, the oil palm, lofira, kaya, terminalia and some others. They are often represented here as species other than in the giley, having adaptations for experiencing unfavorable periods. Evergreen trees usually occupy the lower tiers in such forests, and deciduous species dominate in the upper ones. By southern border African giles are dominated by sparse light forests, they are called myombo.
In woodlands Northern Australia dominated by eucalyptus. Many have vertical leaflets to reduce evaporation during the dry season. Under their canopy, dense undergrowth, shrub and grass layers develop.
The fauna of seasonally humid forests differs little from giles. Many species have either adapted to experiencing a short dry period, or migrate during a drought to gallery forests along rivers or to neighboring wetter areas.
Savannah and woodlands
With the increase in the duration of the dry season in areas of the subequatorial climate, more and more areas are occupied by savannas. This type of vegetation is very widespread on the southern continents: 85% of the total world area of the zone is concentrated here. In Africa, savannas and woodlands occupy almost half of the mainland (46%), in South America - more than a third (36%), and in Australia - more than a quarter (26%).
The structure and appearance of the vegetation in the zone depend on the duration of the dry season and the total amount of precipitation. But on all three continents, as a rule, these are areas with a predominance of herbaceous vegetation and with groves or free-standing trees of a characteristic xerophytic appearance.
The zone of savannas and woodlands is characterized by high average monthly temperatures (15-32 ° С) and a fairly large annual amount of precipitation (up to 2500 mm). However, the amount of precipitation varies greatly within the zone and on the border with deserts drops to 250-300 mm.
Most important factor, which determines all the features of the soil and vegetation cover of the zone, is the change of dry and wet seasons at constant high temperatures air. During humid summers with almost daily downpours, vegetation grows rapidly and multiplies. A leaching regime is established in the soil cover. In the dry season, evaporation significantly exceeds the amount of precipitation. The terrestrial organs of plants die off, the trees shed their foliage - the savannahs acquire the appearance of lifeless, sun-scorched spaces of red-brown color. The processes of physical weathering and deflation are intensifying. Soil solutions experience capillary uplift, which contributes to salinity. In the upper horizons, iron oxides are also deposited, which cement soil particles. This results in the formation of soils typical of savannahs with a relatively low humus content, usually enriched with iron oxides, sometimes saline.
The land cover of savannahs depends on the length of the dry season. It ranges from 2-3 to 8-9 months. Such differences determine the intrazonal heterogeneity of the soil and vegetation cover.
Where the dry period is short, tall grass savannas or woodlands dominate. Of the grasses, cereals dominate throughout the zone. Trees have devices to protect them from lack of water.
Under tall-grass savannas, mainly red and yellow soils are formed with a humus content of 2-4%, but sometimes up to 8%, with an acid reaction, enriched with iron and aluminum hydroxides. The parent rock for them is often ancient weathering crusts with laterite shells located at a depth of several tens of centimeters to the very surface. With the increase in the duration of the dry season, savannas acquire an increasingly xeromorphic appearance: the grass cover becomes lower and very thinned, succulents appear among the woody elements, and tree forms are often replaced by shrubs. The soils here are reddish-brown - low-humus (less than 1.5%), with a poorly differentiated profile, enriched with iron oxides and carbonates. Under typical savannas, occupying territories with an average duration of the dry period, there are red-brown soils with a humus content of 2-3%, an abundance of ferruginous secretions in the form of films and nodules, usually with a carbonate horizon at a depth of 20-30 cm.
The different types of savannah replace each other gradually, as the duration of the dry and wet seasons changes. There are no sharp boundaries between them. However, with a certain degree of conventionality, three subzones with different plant formations can be distinguished: tall-grass savannas and light forests; typical savannas and dry woodlands; deserted savannas, xerophytic light forests and shrubs. To one degree or another, they are common on all Southern Tropical continents, but each of them has its own characteristics and differ in floristic composition.
In Africa, savannas and woodlands occupy the largest territories (more than half of the global area of the zone). Savannah formations successively replace each other from the border of the forest zone to deserts. The boundaries in the northern part of the continent run almost sublatitudinally, in the east and south they have a more complex configuration: in some places different types of savannah replace each other when moving from west to east.
The strip of savannahs, as well as seasonally humid forests, along the border with the gileae in places, is probably of secondary origin. Light woodlands with a fairly large species diversity are combined here with tall grasses. The trees are evergreen (usually in the lower tiers) and deciduous (in the upper tiers). The grass cover of this type of savannah and woodland is dominated by tall grasses, the main type of which is the herb of the impera. Areas covered with woody vegetation are similar to miombo or other types of seasonally moist woodlands. Gallery forests along rivers are similar to gileas.
In North, South and East Africa, large areas within the subequatorial and partly tropical belts occupy typical savannahs. These are vast expanses of grasses with separate groups of trees of a characteristic xerophytic appearance. In the grass cover there are bearded and aristides, many bulbous and rhizome plants from lily, amaryllis, etc. Typical trees include baobabs with thick trunks and powerful bark, mimosa, mainly acacia with umbrella-shaped crowns. There is a dum palm with a branching trunk and a fan palm. During the dry season, the trees shed their foliage and the terrestrial organs of the grasses dry out and burn out.
Deserted savannas have a sparse grass cover of dense sod grasses with the participation of ephemeroids. Of the trees, acacia and arboreal milkweed are common. Thickets of thorny bushes, often called bush, are widespread here. The savannahs of the Sahel zone along the border with the Sahara, the Somali Peninsula, the east of the Ethiopian Highlands, the Kalahari region, and the veldy of southeastern Africa have such a character.
South American savannas are half the size of African ones. Due to the influence of orography and lithological composition of surface rocks, they are represented by separate isolated massifs. Their boundaries are rather submeridional than sublatitudinal.
Tall grass savannas in South America are common on the plains of Orinoco (here they are called llanos), Mamore, Gran Chaco. Depending on local conditions, they are combined with woodlands and are called campos serrados. The most studied llanos Orinoco. Savannahs are formed here in low flooded areas not so much due to periodic droughts, but as a result of seasonal waterlogging. Tall grasses: bearded, aristides, as in the savannas of Africa, are the basis of the grass cover of the Low Llanos. They are joined by sedges, cyperus and other species growing in swamps. There are few trees - mostly Mauritius palm, which tolerates flooding well. On the better drained Vysokye Llanos, the dry period is well pronounced. The grass cover consists of lower grasses, bearded, paspalum. Low-growing acacias and chaparro (curatella) grow. Similar formations are common in the so-called campos-serrados of the Brazilian Highlands. Cacti and other succulents play a prominent role here. In drier conditions, grassy savannas are formed without the participation of trees - campos-limpos. In the western part of the Chaco plains, the monte formations are common with the predominance of acacias and an abundance of succulents: cacti, agaves, milkweed, terrestrial bromeliads and even lianas. Also characteristic are sparse forests of kebracho (quebracho) trees with unusually hard and heavy wood.
The largest variety of succulent and "barrel" or "bottle" forms with swollen trunks grows in the arid northeast of the Brazilian Highlands in the so-called caatinga. It is characterized by the absence of grass cover for almost the entire year. Herbs emerge from bulbs and tubers only during a short rainy season. There is a layer of undersized cacti, agaves, caesalpines and bromeliads. Sometimes they are joined by dwarf palms. Kaatinga changes its appearance unusually quickly In dry weather, on the bare rocky soil, there are trees and shrubs devoid of leaves, thorny cacti, prickly pears, and agaves. But once the rain passes, in a few hours the foliage unfolds, ephemeroids germinate, and the caatinga turns green. They say that you can fall asleep in the scorched dry landscape, I wake up in the green world of tall grasses, bushes and trees.
In Australia, the zone of savannas and open woodlands almost in a closed ring covers desert territories from the north, west and east. Tall grass savannas of the north and northeast of the mainland are gradually turning into shrub thickets, and along the border with deserts they acquire especially xerophytic features of deserted savannas. They are called scrubs.
The grass cover of the Australian savannas and woodlands, as well as on other continents, is dominated by cereals with the participation of a special species of bearded vulture - blue grass and endemic genera of temeda. Of the tree species, the most common are acacias from mimosa, eucalyptus and other myrtle. Casuarins with reduced leaves and xanthorrhea or herbaceous trees close to liliaceae are characteristic. Both are Australian endemics.
The sparse forests of the northeast are called bigelow scrub. In them, plants from other families, including bottle trees of the endemic genus Brachychiton from Sterculiaceae, are added to acacias, casuarins and eucalyptus trees. In drier areas, savannas with acacias are common - mulga-scrub, and in deserted savannas with shrubs (mally-scrub), shrub eucalyptus prevails.
In the presence of similar features (growing conditions, adaptive properties of plants, external appearance, structure of communities) savannas and woodlands of the southern tropical continents also have great differences. They are especially pronounced in the floristic composition of communities and in the distribution different types savannahs within each of the continents.
The fauna of the savannah has a clear seasonal mode of life. During the dry season, many herbivorous animals take refuge in shelters and either hibernate or live off supplies made in the summer. Others migrate to neighboring zones or accumulate near water bodies. They also often adapt to a change in the type of food and move from one phytocenosis to another. Many species can travel long distances quickly in search of food and water. Predators follow herbivores.
Adaptations to living conditions in animals of the savannahs of Africa, South America and Australia are similar, but the fauna of each of the continents is very peculiar.
There are few ungulates in the savannas of South America. The ecological niche of antelopes and dukers is occupied only by mazam deer. But there are many rodents, including endemic whiskach and tuko-tuko. Hamsters are characteristic. Nutria lives along the shores of reservoirs. Armadillos and anteaters from edentulous and marsupial possums are widespread. Carnivores are not as diverse as in Africa. They are represented by jaguars, pumas, ocelots from felines, and from canines - by maned wolves, savannah foxes and bush dogs. Noses (coati) from raccoons are endemic.
In Australia, almost all ecological niches are occupied by marsupials. Instead of ungulates, savannahs are inhabited by various kangaroos and wallabies, rodents are replaced by wombats and other herbivorous marsupials. There are also some types of common rodents - mice and rats. The trees are home to koalas, feeding on the leaves of certain types of eucalyptus, and ossums. Predators are few in number. The marsupial wolf and the marsupial devil appear to be completely extinct. There is a marsupial cat and several types of carnivorous marsupial rats. The role of predators is performed mainly by wild dingo dogs and introduced by humans to combat the introduced and highly multiplied fox rabbits. It is believed that the dingo dog entered the mainland together with the ancient man in a semi-domesticated state and became feral.
Desertification of savannas. The xerophytic features of the vegetation cover of savannas increase with the duration of the dry season. Savannahs are gradually replaced by semi-deserts and deserts. The position of the border between them shifts one way or the other, depending on climate fluctuations. If abnormally dry years in some period follow one another, savanna communities degrade - desertification occurs. It also happens the other way around: years with an abnormally high amount of precipitation follow in a row. In this case, the border of the savannah shifts towards the zone of deserts and semi-deserts. The desertification process is more active: savannah communities under conditions unfavorable for plants are preserved for some time due to their own microclimate. The restoration of a destroyed community is only due to improving external conditions, and this is a long and difficult process. Desertification is very actively promoted by human activities. Savannah vegetation degrades and is destroyed as a result of land cultivation, overgrazing, burning grasses in a dry period in order to improve pastures: ash fertilizes the soil, besides, livestock more readily eats young grass. Trees and shrubs are cut down as this is a source of firewood. As a result, the process of desertification is spreading to all three Southern Tropical continents.
Tropical semi-deserts and deserts
This zone forms where the band begins, in which precipitation falls irregularly. By average annual number rainfall these territories may not yield to the savannah zone, but the rainy season does not happen here every year.
Deserts and semi-deserts are widespread in Africa and Australia. The area of the zone is especially large in Africa. This continent accounts for more than half of the global area of the zone. Various types of deserts occupy a wide strip on the plains and plateaus of northern and southwestern and central South Africa.
The largest tracts of desert landscapes are located in the north of the African continent. There are huge spaces (about 7 million km 2) from Atlantic Ocean to the Red Sea are occupied by deserts, which are united under the general name of the Sahara. These territories are heterogeneous in terms of relief, composition of surface rocks and vegetation.
The vegetation of the Sahara is close to that of the Arabian deserts. It is characterized by milkweed, perennial thorny shrubs (retam, camel thorn, etc.), wormwood and saltwort on saline soils. As in the Asian deserts, the Jericho rose grows here - an ephemeral that uses periods of brief irregular rains for breeding. Stony placers and rocky outcrops are covered with lichens.
Animal world... In terms of the composition of the animal world, the Sahara is very similar to Western Asia and the Mediterranean and is included with them in the Holarctic zoogeographic region.
Various antelopes live here, overcoming large spaces in search of water and food (Addax, Oryx, Bubal, Mendes, etc.), some species of gazelles, from predators - jackals, hyenas, cheetahs, fennec fox, etc. There are birds - African ostrich , bustard, desert raven, etc. There are many reptiles: snakes, lizards, turtles. In rare permanent reservoirs, crocodiles have been preserved - a legacy of the pluvial eras. Among the numerous insects that can tolerate the loss of moisture and heat, there are pests (for example, locusts) and poisonous ones - scorpions, phalanges.
There are desert territories in South Africa... The coastal (“cold”, “wet”) Namib Desert occupies the western South African plateaus and plateaus, and in the Kalahari Basin it turns into deserted and dry savannas with endemic flora and fauna.
The area of the zone in Australia is large: 1/5 of all the deserts in the world are located on this small continent. They are common in the West Australian Highlands and in the plains of Central Australia.
Vegetation... Where at least a small amount of precipitation falls, spinifex deserts dominate, occupied by rare bushy holly grasses (from the genera spinifex and triodium), which have a dense turf. In the driest areas of the center of the continent, large areas are generally devoid of vegetation and are stony placers or mobile sands.
In the West Australian Highlands, rocky deserts form on thick ferruginous crusts (a legacy of the humid ages). Their bare surface has a characteristic bright orange color. On the Nullarbor Plain, composed of fractured limestones, the desert extends to the southern coast of the mainland. In some places, you can see rare quinoa bushes and some hodgepodge or thickets of dwarf eucalyptus.
Animal world. In the Australian deserts, as in the entire fauna of Australia, among mammals the leading place belongs to the lowest.
The giant kangaroo can traverse large areas. In the shrub thickets, the echidna from monotremes is found. There are many endemic species of reptiles, lizards are widespread (for example, moloch and frilled).
In South America, the territories occupied by tropical desert biocenoses are negligible. Only by west coast between 5 ° and 30 ° S NS. there is a strip of coastal deserts. Small areas of desert landscapes are found in intermontane depressions (in the Precordillera, in the longitudinal valleys between the Coastal and Western Cordilleras, for example, Atacama).
Natural complexes of deserts are extremely vulnerable. Any impact on their components, including biotic ones, can lead to unpredictable consequences and the disappearance of not only individual plant and animal species, but also entire biocenoses. Intervention in natural processes here must be carefully thought out from a scientific point of view and taking into account the long-standing experience of the population of areas with similar conditions.
Altitudinal zonality
This pattern is most pronounced in the Andes of South America. The structure of the altitudinal zonation is different depending on the distribution of heat and moisture in this mountain system, which has a huge length from north to south and large differences in the moisture content of slopes of different exposure. In the Andes, there are all types of zonal landscapes - from humid tropical forests to deserts, both hot and periglacial, which are represented by mountainous, including alpine variants. Some formations are found throughout the entire mountain system, for example mountain meadows - paramos, others are locally distributed.
The spectrum of altitudinal zonality is most fully expressed in the Northern Andes, especially on the western slopes of high ridges, where the landscapes of the true giles of the lower belt are replaced by mountain giley, in which there are almost no palms, tree ferns, bamboos, etc. dominate. The belt of low-growing evergreen forests and shrubs begins even higher. with an abundance of ferns, lyes, mosses, lianas and epiphytes (nephelogylea - "forest of mists"). At altitudes of more than 3000 meters, a belt of mountain meadows and shrubs of a xerophytic appearance - paramos begins, and higher, in the periglacial zone, rocky placers are sometimes covered with mosses and lichens. Such a zonal spectrum is also found in other Andean regions, but in many parts of the system, the structure of the altitudinal zonality is completely different.
Thus, Southern continents are distinguished by the dominance of zonal landscapes of humid and variable-humid equatorial and tropical forests, savannas and woodlands of various types and tropical deserts... Formations in other zones have a more limited distribution.
