What are the plants in humid tropical l. Wet tropical forests. Brief physical and geographical characteristics. Tropical moist evergreen forests

Structure and structure. It is almost impossible to give a generalized description of the structure of a tropical rainforest: this most complex plant community reveals such a variety of types that even the most detailed descriptions... A few decades ago, it was believed that a humid forest is always an impenetrable thicket of trees, shrubs, ground grasses, vines and epiphytes, since it was mainly judged on the descriptions of mountain humid forests. Only relatively recently it became known that in some humid tropical forests, due to the dense closure of the crowns tall trees sunlight almost does not reach the soil, so the undergrowth is scarce here, and through such forests it is possible to pass almost unhindered.

It is customary to emphasize the species diversity of the tropical rainforest. It is often noted that there are hardly two specimens of trees of the same species in it. This is a clear exaggeration, but at the same time, it is not uncommon to find 50-100 species of trees on an area of ​​1 hectare.

But there are also relatively poor species, "monotonous" humid forests. These include, for example, special forests, consisting mainly of trees of the Dipterocarpaceae family, which grow in areas of Indonesia that are very rich in rainfall. Their existence indicates that in these areas the stage of optimal development of humid rainforest already passed. The extreme abundance of precipitation makes it difficult to aerate the soil, as a result, a selection of plants has taken place that have adapted to living in such places. Similar living conditions can also be found in some of the damp regions of South America and the Congo Basin.

The dominant component of tropical rainforest is various trees appearance and different heights; they make up about 70% of all higher plant species found here. There are three tiers of trees - upper, middle and lower, which, however, are rarely clearly expressed. The upper tier is represented by individual giant trees; their height, as a rule, reaches 50-60 m, and the crowns develop above the crowns of trees below the located tiers. The crowns of such trees do not close together; in many cases, these trees are scattered in the form of individual specimens, which seem to be overgrown. On the contrary, the crowns of middle-tier trees with a height of 20-30 m usually form a closed canopy. Due to the mutual influence of neighboring trees, their crowns are not as wide as those of the trees of the upper tier. The degree of development of the lower tree layer depends on the illumination. It is made up of trees reaching an average of about 10 meters in height. A special section of the book will be devoted to the lianas and epiphytes found in different layers of the forest (pp. 100-101).

Often there is also a layer of shrubs and one or two layers of herbaceous plants; they are representatives of species that can develop under minimal illumination. Since the humidity of the surrounding air is constantly high, the stomata of these plants remain open throughout the day and the plants are not threatened with wilting. Thus, they are constantly assimilating.

According to the intensity and nature of growth, tropical rainforest trees can be divided into three groups. The first consists of species whose representatives grow rapidly, but do not live long; they are the first to develop where in the forest, either naturally or as a result of human activity, lightened areas are formed. These light-loving plants stop growing after about 20 years and give way to other species. Such plants include, for example, the South American balsa tree ( Ochroma lagopus) and numerous myrmecophilous species of cecropia ( Cecropia), African species Musanga cecropioides and representatives of the Euphorbia family that grow in tropical Asia, belonging to the genus Macaranga.

The second group includes species whose representatives also grow rapidly in the early stages of development, but their growth in height lasts longer, and after it is over, they are able to live for a very long time, probably more than one century. These are the most characteristic trees of the upper tier, the crowns of which are usually not shaded. These include many economically important trees, the wood of which is commonly called "mahogany", for example, species belonging to the genus Swietenia(tropical America), Khaya and Entandrophragma(tropical Africa).

Finally, the third group includes representatives of shade-tolerant species growing slowly and long-lived. Their wood is usually very heavy and hard, it is difficult to work it, and therefore it does not find such widespread use as wood of the second group of trees. Nevertheless, the third group includes species that give noble wood, in particular Tieghemella heckelii or Aucoumea klainiana, whose wood is used as a substitute for mahogany.

Most trees are characterized by straight, columnar trunks, which often rise to more than 30 meters without branching. Only there at the freestanding giant trees a spreading crown develops, while in the lower tiers, as already mentioned, trees, due to their close arrangement, form only narrow crowns.

In some tree species, near the base of the trunks, board-like roots are formed (see figure), sometimes reaching heights of up to 8 m. They give the trees greater stability, since the root systems, which develop shallowly, do not provide a sufficiently strong anchorage for these huge plants. The formation of board-like roots is genetically determined. In representatives of some families, for example, Moraceae (mulberries), Mimosaceae (mimosa), Sterculiaceae, Bombacaceae, Meliaceae, Bignoniaceae, Combretaceae, they are quite common, while others, for example Sapindaceae, Apocynaceae, Sapotaceae, do not have them at all.

Trees with board-like roots are most often found in moist soils. It is possible that the development of plank-like roots is associated with poor aeration, which is characteristic of such soils, which prevents secondary growth of wood on the inner sides of lateral roots (it is formed only on their outer sides). In any case, trees growing on moisture-permeable and well-aerated soils of mountain rainforests do not have board-like roots.

Stilted roots are characteristic of trees of other species; they are formed above the base of the trunk as adventitious and are especially common in trees of the lower layer, which also grow mainly in damp habitats.

Differences in the microclimate inherent in different layers of the tropical rainforest are reflected in the structure of the leaves. While the upper tier trees are usually elliptical or lanceolate in outline, smooth and dense leathery leaves such as laurel leaves (see illustration on page 112), capable of withstanding dry and wet alternations throughout the day, the lower tier leaves show signs indicating intense transpiration and rapid removal of moisture from their surface. They are usually larger; their plates have special cusps, on which water collects, and then drops from them, so there is no water film on the surface of the leaf that would impede transpiration.

The change of foliage in tropical rainforest trees is not affected by external factors, in particular drought or cold, although here it is possible to replace the well-known periodicity that varies in different species. In addition, some independence of individual shoots or branches is manifested, therefore, not the whole tree is leafless at once, but only a part of it.

The peculiarities of the tropical rainforest climate also affect the development of foliage. Since there is no need to protect the growing points from cold or drought, as in areas with a temperate climate, the buds are relatively weak and not surrounded by kidney scales. With the development of new shoots, many tropical rainforest trees exhibit leaf drooping, which is caused by an extremely rapid increase in their surface. Because of mechanical fabrics do not form as quickly, young petioles first, as if withered, hang down, the foliage seems to droop. The formation of the green pigment - chlorophyll - can also be slowed down, and young leaves turn out to be whitish or - due to the content of the anthocyanin pigment - reddish (see picture above).

The "drooping" of young leaves of the chocolate tree (Theobroma cacao)

The next feature of some trees of tropical rainforests is caulifloria, that is, the formation of flowers on the trunks and leafless areas of the branches. Since this phenomenon is observed primarily in trees of the lower layer of the forest, scientists interpret it as an adaptation to pollination, which is often found in these habitats, with the help of bats (chiropterophilia): for pollinating animals - bats and flying dogs - when approaching a tree it is more convenient to grasp the flowers ...

Birds also play a significant role in the transfer of pollen from flower to flower (this phenomenon is called "ornithophilia"). Ornithophilous plants are noticeable due to the bright color of their flowers (red, orange, yellow), while in chiropherophilous plants, flowers are usually inconspicuous, greenish or brownish.

There is practically no clear distinction between the layers of shrubs and grasses, as is, for example, typical for the forests of our latitudes, in humid tropical forests. We can only note the upper tier, which, along with tall large-leaved representatives of the banana, arrowroot, ginger and aroid families, includes shrubs and young undergrowth of trees, as well as the lower tier, represented by undersized, extremely shade-tolerant grasses. By the number of species herbaceous plants give way to trees in a humid rainforest; but there are also such lowland humid forests that have not experienced human impact, in which only one layer of grasses, poor in species, is generally developed.

Attention is drawn to the fact of variegation, which has not yet found an explanation, as well as the presence of metallic-shiny or dull-velvety surface areas in the leaves of plants living in the subsoil layer of grasses of a humid tropical forest. Obviously, these phenomena are to some extent related to the optimal use of the minimum of sunlight that reaches such habitats. Many "variegated" plants of the lower tier of tropical rainforest grasses have become favorite indoor ornamental plants, for example, species of genera Zebrina, Tradescantia, Setcreasea, Maranta, Calathea, Coleus, Fittonia, Sanchezia, Begonia, Pilea and others (picture on page 101). In deep shade, various ferns, plunks dominate ( Selaginella) and mosses; the number of their species is especially great here. So, most of the species of plunks (and there are about 700 of them) are found in tropical rainforests.

Also noteworthy are the saprophytic (that is, using decaying organic matter) fungi of the Clathraceae and Phallaceae families living on the soil of tropical rainforests. They have peculiar fruiting bodies - "flower mushrooms" (see figure on page 102).

Lianas. If you swim through the tropical rainforest along the river, you will notice the abundance of lianas (plants climbing trees with woody stems) - they, like a dense curtain, cover the trees growing along the banks. Lianas are one of the most amazing components of tropical vegetation: over 90% of all species are found only in the tropics. Most grow in moist forests, although they require good lighting for their development. That is why they are not found everywhere with the same frequency. First of all, they can be seen along forest edges, in naturally formed lightened areas of the forest and - along at least sometimes - in layers of woody plants that are permeable to sunlight (see figure on page 106). They are especially abundant on plantations established in the area of ​​tropical rainforests, and in secondary forests that appear in clearings. In lowland humid forests, which have not experienced the influence of humans, where dense, well-developed tree crowns are tightly closed, lianas are relatively rare.

According to the method of fixing on the plants that serve as their support, vines can be divided into different groups. For example, leaning vines can be held on other plants with the help of supporting (clinging) shoots or leaves, thorns, thorns or special outgrowths such as hooks. Typical examples of such plants are rattan palms of the genus Calamus, 340 species of which are common in the tropics of Asia and America (see figure on page 103).

Vines that are fixed with roots are held on to the support with the help of many small adventitious roots or cover it with longer and thicker roots. These are many shade-tolerant vines from the aroid family, for example, species of the genera Philodendron, Monstera, Raphidophora, Syngonium, Pothos, Scindapsus as well as vanilla ( Vanilla) is a genus from the orchid family.

Curly vines cover the support with internodes that grow strongly in length. Usually, as a result of the subsequent thickening and lignification, such shoots are fixed tightly. The group of climbing trees includes most tropical vines, for example, representatives of the mimosa family and the related family of cesalpiniaceae, which are rich in species and widespread throughout the tropics, in particular the climbing entad ( Entada scandens); the beans of the latter reach 2 m in length (see picture on page 104). The so-called monkey ladder, or bauginia sassaparelevidnaya ( Bauhinia smilacina), forming thick woody shoots, as well as vines with bizarre flowers (species of Kirkazon, Aristolochia; Kirkazon family) (see figure on page 103).

Finally, the lianas attached to the antennae form lignified antennae - with them they cling to the plants that serve as their support. These include representatives of the genus common throughout the tropics Cissus from the Vinogradov family, different types legumes, in particular (see figure), as well as types of passion flower ( Passiflora; family of passion flowers).

Epiphytes. Adaptations to the conditions of existence in humid tropical forests in the so-called epiphytes - plants living on trees - are extremely interesting. The number of their types is very large. They abundantly cover the trunks and branches of trees, due to which they are sufficiently well lit. Growing high in trees, they lose the ability to get moisture from the soil, so water supply becomes a vital factor for them. It is not surprising that there are especially many types of epiphytes where precipitation is abundant and the air is humid, but for their optimal development, it is not the absolute amount of moisture falling out, but the number of rainy and foggy days that is decisive. The unequal microclimate of the upper and lower arboreal layers is also the reason that the communities of epiphytic plants living there are very different in species composition. In the outer parts of the crowns, light-loving epiphytes dominate, while shade-tolerant ones dominate inside, in constantly humid habitats. Light-loving epiphytes are well adapted to the alternation of dry and wet periods of time during the day. As the examples below show, they do this in different ways (picture on page 105).

In orchids, represented by a huge number of species (and most of the 20,000-25,000 orchid species are epiphytes), the organs that store water and nutrients are thickened shoots (the so-called bulbs), leaf blades or roots. This lifestyle is also facilitated by the formation of aerial roots, which are covered from the outside with layers of cells that quickly absorb water (velamen).

Plants of tropical rainforest, developing in the subsoil layer

The family of bromeliads, or pineapple (Bromeliaceae), whose representatives are widespread, with one exception, in North and South America, consists almost exclusively of epiphytes, whose rosettes of leaves, similar to funnels, serve as drainage reservoirs; of these, water and nutrients dissolved in it can be absorbed by the scales located at the base of the leaves. The roots only serve as organs that attach the plants.

Even cacti (for example, species of genera Epiphyllum, Rhipsalis, Hylocereus and Deamia) grow in mountain humid tropical forests as epiphytes. Except for a few species of the genus Rhipsalis, also found in Africa, Madagascar and Sri Lanka, they all grow only in America.

Some ferns, for example, bird's nest fern, or nesting asplenium ( Aspleniumnidus), and antler fern, or deer-horned platycerium ( Platycerium), due to the fact that the first leaves form a funnel-shaped rosette, and the second has special leaves adjacent to the trunk of the supporting tree, like patch pockets (picture on page 105), are even able to create a soil-like, constantly moist substrate in which their roots grow.

Epiphytes developing in shaded habitats are represented primarily by the so-called hygromorphic ferns and mosses, which have adapted to existence in a humid atmosphere. The most characteristic components of such communities of epiphytic plants, especially pronounced in mountain humid forests, are hymenophyllous, or fine-leaved, ferns (Hymenophyllaceae), for example, representatives of the genera Hymenophyllum and Trichomanes... As for lichens, because of their slow growth, they do not play such a big role. From flowering plants in these communities there are species of the genera Peperomia and Begonia.

Even the leaves, and above all the leaves of the trees of the lower tiers of the tropical rainforest, where the air humidity is constantly high, can be inhabited by various lower plants. This phenomenon is called epiphyllia. Lichens, liver mosses and algae, which form characteristic communities, mainly settle on the leaves.

Hemiepiphytes are a kind of intermediate stage between epiphytes and lianas. They either grow at first as epiphytes on tree branches, and as aerial roots are formed, reaching the soil, they become plants self-consolidating in the soil, or in the early stages they develop as vines, but then lose their connection with the soil and thus turn into epiphytes. The first group includes the so-called strangler trees; their aerial roots, like a net, cover the trunk of the supporting tree and, growing, prevent it from thickening so much that the tree eventually dies off. And the aggregate of aerial roots then becomes, as it were, a system of "trunks" of an independent tree, in the early stages of development that was an epiphyte. The most typical examples of strangler trees in Asia are species of the genus Ficus(mulberry family), and in America - representatives of the genus Clusia(family of St. John's wort). The second group includes species of the aroid family.

Evergreen lowland rainforests. Although the floristic composition of tropical rainforests varies widely in different regions of the world, and the three main areas of such forests show only slight similarities in this respect, nevertheless, similar modifications of the basic type can be found in the nature of their vegetation cover everywhere.

The prototype of the tropical rainforest is considered to be an evergreen tropical rainforest of non-flooded lowlands that are not damp for a long time. This is, so to speak, a normal type of forest, the structure and features of which we have already spoken about. The forest communities of river floodplains and flooded lowlands, as well as swamps, differ from it usually in a less rich species composition and the presence of plants that have adapted to existence in such habitats.

Floodplain rainforest occur in close proximity to rivers in regularly flooded areas. They develop in habitats formed as a result of the annual deposition of nutrient-rich river sediments - carried by the river, suspended in the water and then settled by the smallest particles. This muddy water the so-called "whitewater" rivers bring mainly from the treeless regions of their basins *. The optimal content of nutrients in the soil and the relative supply of oxygen in running water determine high productivity plant communities developing in such habitats. Floodplain tropical forests are difficult to reach for their development by humans, so they have largely retained their original state to this day.

* (The rivers, called by the authors of this book "white water", in Brazil it is customary to call white (rios blancos), and "black water" - black (rios negros). White rivers carry muddy water, rich in suspended particles, but the color of the water in them can be not only white, but also gray, yellow, etc. In general, the rivers of the Amazon basin are characterized by an amazing variety of water colors. Black rivers are usually deep; they have transparent waters - they appear dark only because they do not contain suspended particles that reflect light. Humic substances dissolved in water only enhance this effect and, apparently, affect the color shade.)

Rainforest vines

Moving from the very bank of the river across the floodplain to its edge, it is possible to reveal a characteristic sequence of plant communities due to a gradual decrease in the level of the soil surface from high river-bed banks to the edge of the floodplain. On sparsely flooded river-bed ramparts, a river-bed forest rich in lianas grows, further from the river turning into a real flooded forest. At the edge of the floodplain far from the coast, there are lakes surrounded by reed or grass bogs.

Swampy rain forest. Boggy tropical rain forests grow in habitats where soils are almost constantly covered with stagnant or slowly flowing water. They can be found mainly near the so-called "black water" rivers, the sources of which are in forested areas. Therefore, their waters do not carry suspended particles and are colored from olive to black-brown due to the content of humic substances in them. The most famous "black-water" river is the Rio Negru, one of the most important tributaries of the Amazon; it collects water from a huge area with podzolic soils.

Unlike floodplain rainforest, swampy forest tends to cover the entire river valley. It is not the deposition of pumps that occurs here, but, on the contrary, only uniform leaching, therefore the surface of the valley of such a river is flat.

Due to the lack of nutrients in habitats, swampy rain forests are not as lush as floodplains, and due to the lack of air in the soil, plants with aerial and stilted roots are often found here. For the same reason, the decomposition of organic matter occurs slowly, which contributes to the formation of thick peat-like layers, most often consisting of more or less decomposed wood.

Semi-evergreen lowland humid forests. Some areas of rainforest rainforests are characterized by short dry periods, causing foliage changes in trees in the upper tier of the forest. At the same time, the lower tree layers remain evergreen. Such a transitional step to the dry forests leafed during the rainy season (see p. 120) is called "semi-evergreen, or semi-deciduous, humid lowland forests." In dry periods, moisture can move in the soil from the bottom up, therefore, such forests receive enough nutrients and turn out to be very productive.

Epiphytes of the tropical rainforest

Above Asplenium nesting Asplenium nidus and below Cattleya citrina

Mountain tropical rainforests. The forests described above, the existence of which is determined by the presence of water, can be contrasted with such variants of tropical rainforest, the formation of which is associated with a decrease in temperature; they are mainly found in humid habitats located in different altitudinal zones of mountainous regions of tropical regions. In the foothill zone, at an altitude of about 400-1000 m above sea level, the tropical rainforest is almost indistinguishable from the lowland forest. It has only two tiers of trees, and the trees in the upper tier are not so tall.

But the tropical humid forest of the mountain belt, or, as they say, the mountain humid forest growing at an altitude of 1000-2500 m, reveals more significant differences. It also has two tree tiers, but they are often difficult to identify, and their upper limit often does not exceed 20 m.In addition, there are fewer tree species than in humid lowland forests, and some characteristics trees of such forests, in particular and stilted roots, as well as caulifloria. The leaves of trees are usually smaller and do not have any sharp edges to remove water droplets.

The layers of shrubs and grasses are often dominated by ferns and bamboo species. Epiphytes are very abundant, while large vines are rare.

At even higher altitudes of the constantly humid tropics (2500-4000 m), mountain humid forests are replaced by subalpine mountain forests developing at the cloud level (see vol. 2).

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Rainforests- biomes, located approximately 10 degrees north and south of the equator. A biome is biotic environment with homogeneous characteristics, with its own special species of plants, animals and climate. Rainforests are divided into tropical rainforests and dry deciduous tropical forests (subtropics). They are widespread in Asia, Australia, Africa, South and Central America, Mexico and many Pacific islands. Temperatures in these forests range from 20 ° C to 35 ° C with no hot or cold seasons. And the average humidity reaches 77% - 80%. The Amazon rainforest is the most famous of the various rainforests in the world. Wet and warm rainforests are home to 80% of all animal and plant species on the planet. These forests in the world are called "the largest pharmacy in the world" because more than a quarter of modern medicines are made from the plants growing in these forests. Undergrowth in the humid tropics is limited in many areas due to the lack of sunlight at ground level. This fact makes rainforests passable for humans and animals.

If the crowns of trees are destroyed or broken for some reason, then it reaches the ground and then everything very quickly becomes overgrown with vines, shrubs and small trees - this is how the jungle appears. They are also called "the lungs of the Earth", since a humid climate promotes effective air filtration, due to the condensation of moisture on microparticles of pollution, which generally has a beneficial effect on the atmosphere.

The struggle for existence in these forests led the vegetation to the fact that the forest began to divide into separate layers. These include:

Emerging or new layer: it is formed from tree crowns reaching 30 - 70 meters. They have the shape of a dome - an umbrella, which receive maximum amount sunlight when the high levels of the rainforest are reached. The trees of this layer are home to a large number of animals and birds such as eagles, monkeys, the bats and .

Upper tier: forms a dense "ceiling" of evergreen trees with wide leaves that grow close to each other. It is because of this layer that sunlight cannot penetrate into the lower levels and to the ground. The growth of trees in this region is from 20 to 40 meters. This layer is the main life support of the rainforest and is home to most tropical animals - leopards, jaguars and exotic birds.

Lower tier- undergrowth. It is located just below the upper tier and consists of tropical plants that grow up to 20 meters. There is little air movement in this layer and the humidity is constantly high. Due to the lack of sunlight, this layer is constantly in the shade, and grasses, shrubs, trees and woody vines grow here.

And the last one - forest litter. She barely receives sunlight. Hardly any vegetation can be found in this layer, but it is rich in microorganisms. This layer is rich in animals and insects. Giant anteaters, beetles, frogs, snakes, lizards and many insects inhabit the forest floor.

How animals and plants survive in such a warm and humid climate typical of these forests. Here are some examples of adaptation:

• Rainforest trees should not have thick bark to prevent moisture loss. Thus, they have a thin and smooth bark.
• These forests are characterized by big amount rainfall and tree leaves, have developed a "drip run" so that rainwater drains off quickly. These are the grooves of the wax coating on the leaves.
• The leaves of the trees are wide at lower levels, and narrow at higher levels, in order to allow sunlight to pass to lower levels.
• There are creepers that climb tree trunks and reach the uppermost layers in search of.
• There are plants like that that grow directly on trees.
• Plants in the lower layers of tropical rainforest have spectacular blooms and attract insects for pollination, as there is not much wind at these levels.
• Carnivorous Plants: Many of the tropical plants get their food by eating animals and insects.

Other commercially important plants: cashews, cardamom, cinnamon, cloves, coffee, cocoa, mango, bananas, papaya, peanuts, pineapple, nutmeg, sesame seeds, sugarcane, tamarind, turmeric, vanilla are just a few of the many plants with which we have to face in everyday life and which grow precisely in tropical rainforests.

Of the often found with us indoor plants grow here: monstera, spathiphyllum, stromanta, ferns, (dendrobium, cattleya, vanda, oncidium, phalaenopsis, papiopedilum, etc.), anthurium, medinilla, akalifa, selaginella, pineapple, banana, baraneliconia, vriesia, maresia , gloriosa, gusmania, diplodendia, dieffenbachia, jacaranda, philodendron, zebrina, ixora, calathea, caladium, ktenanta, clerodendrum, episode, coleria, codiaum, coconut, columnea, costus, crossandra, neoregelia, neoplastic, pachisectu , saintpaulia, sinningia, scindapsus, Robelen date, eschinanthus. All of them need high air humidity in room conditions.

Rainforests located in the tropical, equatorial and subequatorial belts between 25 ° N. and 30 ° S, as if "surrounding" the Earth's surface along the equator. Rainforests are torn apart only by oceans and mountains.

The general circulation of the atmosphere occurs from a zone of high atmospheric pressure in the tropics to a zone of low pressure in the equator, and evaporated moisture is transported in the same direction. This leads to the existence of a humid equatorial belt and a dry tropical one. Between them is the subequatorial belt, in which moisture depends on the direction of the monsoons, depending on the season.

The vegetation of tropical forests is very diverse, depending mainly on the amount of precipitation and its distribution over the seasons. When abundant (more than 2000 mm), and relatively uniform distribution develop humid tropical evergreen forests.

Further from the equator, the rainy period gives way to dry, and the forests are replaced with leaves falling off during the drought, and then these forests are replaced by savanna forests. At the same time, there is a pattern in Africa and South America: monsoon and equatorial forests replaced by savannah forests.

Rainforest classification

Tropical rainforest, tropical rain forest these are forests with specific biomes located in equatorial (humid equatorial forest), subequatorial and humid tropical areas with a very humid climate (2000-7000 mm of precipitation per year).

The rainforests are characterized by tremendous biodiversity. This is the most vibrant natural area. It is home to a large number of its own, including endemic species of animals and plants, as well as migratory animals. Two-thirds of all animal and plant species on the planet live in tropical rainforests. It is estimated that millions of animal and plant species have not yet been described.

These forests are sometimes called " jewels of the earth" and " the largest pharmacy in the world", Because a large number of natural remedies have been found here. They are also called “ lungs of the earth", However, this statement is controversial, since it does not have scientific justification, since these forests either do not produce oxygen at all, or they produce very little of it.

But it should be borne in mind that a humid climate promotes effective air filtration, due to the condensation of moisture on microparticles of pollution, which generally has a beneficial effect on the atmosphere.

Undergrowth formation in tropical rainforests is severely limited in many places due to the lack of sunlight in the lower tier. This allows humans and animals to move through the forest. If, for any reason, deciduous canopy is missing or weakened, the lower tier is quickly covered with a dense thicket of vines, shrubs and small trees - this formation is called a jungle.

The largest areas of tropical rainforest are found in the Amazon Basin ("Amazon rainforests"), Nicaragua, southern Yucatan Peninsula (Guatemala, Belize), much of Central America (where they are called "selva"), equatorial Africa from Cameroon to the Democratic Republic of the Congo, in many parts of Southeast Asia from Myanmar to Indonesia and New Guinea, in the Australian state of Queensland.

For tropical rainforest are characteristic:

• variety of flora,
• the presence of 4-5 tree layers, the absence of shrubs, a large number of vines
• predominance evergreen trees with large evergreen leaves, poorly developed bark, buds, not protected by kidney scales, in monsoon forests- deciduous trees;
• the formation of flowers, and then fruit directly on the trunks and thick branches

Trees in tropical rainforests have several general characteristics which are not observed in plants of less humid climates.

The base of the trunk in many species has wide, woody ridges. Previously, it was assumed that these protrusions help the tree to maintain balance, but now it is believed that water with dissolved nutrients flows down these protrusions to the roots of the tree. Wide leaves of trees, shrubs and grasses of the lower layers of the forest are characteristic. Wide leaves help plants to better absorb sunlight under the forest's tree edges, and they are protected from the wind from above.

Tall young trees that have not yet reached the upper tier also have wider foliage, which then decreases with height. Leaves of the upper tier, forming a canopy, usually smaller and heavily cut to reduce wind pressure. On the lower floors, the leaves are often tapered at the ends so that this facilitates the rapid drainage of water and prevents the growth of microbes and moss on them, which destroy the leaves.

The tops of the trees are often very well connected with each other by lianas or epiphytic plants fixing on them.

Trees of tropical rainforest are characterized by an unusually thin (1-2 mm) tree bark, sometimes covered with sharp thorns or thorns, the presence of flowers and fruits growing right on the trunks of trees, a wide variety of juicy fruits that attract birds and mammals.

In humid tropical forests there are a lot of insects, especially butterflies (one of the richest faunas in the world) and beetles, and in the rivers there are many fish (about 2000 species, approximately one third of all freshwater fauna in the world).

Despite the lush vegetation, the soil in tropical rainforests is thin and with a small humus horizon.

Rapid rotting caused by bacteria interferes with the accumulation of the humus layer. The concentration of iron and aluminum oxides due to laterization soil (the process of decreasing silica content in the soil with a simultaneous increase in iron and aluminum oxides) stains the soil bright red and sometimes forms deposits of minerals (for example, bauxite). But on rocks of volcanic origin, tropical soils can be quite fertile.

Levels (tiers) of tropical rainforest

The rainforest is divided into four main levels, each of which has its own characteristics, has a different flora and fauna.

Topmost level

This layer consists of a small number of very tall trees towering above the forest canopy, reaching a height of 45-55 meters ( rare species reach 60-70 meters). Most often, the trees are evergreen, but some shed their foliage during the dry season. Such trees must withstand harsh temperatures and strong winds... This level is inhabited by eagles, bats, some species of monkeys and butterflies.

Crown level (forest canopy)

The crown level is formed by most of the tall trees, usually 30-45 meters high. It is the densest layer known in all terrestrial biodiversity, with adjacent trees forming a more or less continuous layer of foliage.

According to some estimates, the plants of this tier make up about 40 percent of the species of all plants on the planet - perhaps half of the entire flora of the Earth can be found here. The fauna is similar to the upper level, but more diverse. It is believed that a quarter of all insect species live here.

Scientists have long suspected the diversity of life at this level, but only recently have developed practical research methods. It was only in 1917 that the American naturalist William Beed declared that "another continent of life remains unexplored, not on Earth, but 200 feet above its surface, spreading over thousands of square miles."

Real research into this longline did not begin until the 1980s, when scientists developed methods to reach the forest canopy, such as shooting ropes at the treetops with crossbows. The study of the forest canopy is still on early stage... Other research methods include traveling on balloons or aircraft. The science of treetop access is called dendronautics.

Average level

There is another level between the forest canopy and the forest floor, called the undergrowth. It is home to a number of birds, snakes and lizards. The life of insects at this level is also very extensive. The leaves in this layer are much wider than at the crown level.

Forest litter

V Central Africa in the tropical primary forest of Mount Virunga, the illumination at ground level is 0.5%; in the forests of southern Nigeria and in the Santarema region (Brazil) 0.5-1%. In the north of Sumatra, in the dipterocarp forest, the illumination is about 0.1%.

Far from river banks, swamps and open spaces where dense, low-growing vegetation grows, the forest floor is relatively free of plants. At this level, rotting plants and animal remains can be seen, which quickly disappear thanks to the warm, humid climate that promotes rapid decay.

Selva(Spanish " selva " from lat. " silva "- forest) is humid equatorial forests in South America... Located in countries such as Brazil, Peru, Suriname, Venezuela, Guyana, Paraguay, Colombia, etc.

Selva is formed on vast low-lying areas of land under conditions of constant freshwater moisture, as a result of which the soil of the selva is extremely poor in minerals washed out by tropical rains. Selva is often boggy.

Vegetable and animal world jungle is a riot of colors and a variety of species of plants, birds and mammals.

The largest selva by area is located in the Amazon basin in Brazil).

In the Atlantic jungle, the level of precipitation reaches two thousand millimeters per year, and the humidity fluctuates at the level of 75-90 percent.

Selva is divided into three levels. The soil is covered with leaves, branches, trunks of fallen trees, lichens, fungus and moss. The soil itself is reddish in color. The first level of the forest is made up of low plants, ferns and grass. The second level is represented by shrubs, reeds and young trees. On the third level, there are trees from twelve to forty meters high.

Mangroves - evergreen deciduous forests common in the intertidal zone sea ​​coasts in tropical and equatorial latitudes, as well as in areas with a temperate climate, where warm currents favor it. They occupy a strip between the lowest water level at low tide and the highest at high tide. These are trees or shrubs growing in mangroves, or mangrove swamps.

Mangrove plants inhabit the sedimentary coastal environment, where fine sedimentary deposits, often with a high organic content, accumulate in places protected from wave energy.

Mangroves have an exceptional ability to exist and develop in a salty environment on soils deprived of oxygen.

Once rooted, the roots of mangrove plants create a habitat for oysters and help slow the flow of water, thereby increasing sediment deposition in areas where it is already occurring.

Typically, the fine, oxygen-poor sediments under the mangroves act as reservoirs for a wide variety of heavy metals (traces of metals) that are captured from sea ​​water colloidal particles in sediments. In those parts of the world where mangroves were destroyed during the development of the territory, the violation of the integrity of these sedimentary rocks gives rise to the problem of pollution of seawater with heavy metals and local flora and fauna.

It is often argued that mangroves are of significant value in the coastal zone, acting as a buffer against erosion, storms and tsunamis. While there is a certain decrease in wave height and energy as seawater passes through mangroves, it must be recognized that mangroves tend to grow in areas of the coastline where low wave energy is the norm. Therefore, their ability to contain the powerful onslaught of storms and tsunamis is limited. Most likely, their long-term impact on the rate of erosion is also limited.

Many river channels, winding through mangrove areas, actively erode thickets of mangroves on outside all the bends in the river, just as new thickets of mangroves appear on the inside of the same bends where precipitation takes place.

Mangroves are a habitat for wildlife, including a range of commercially available fish and crustaceans, and, at least in some cases, the export of mangrove accumulated carbon has essential in the coastal food web.

In Vietnam, Thailand, the Philippines and India, mangroves are grown in coastal areas for coastal fishing.

Despite ongoing mangrove breeding programs, more than half of the world's mangroves have already been lost.

The floristic composition of mangrove forests is relatively uniform. The most complex, high and multi-species are considered to be the mangrove forests of the eastern formation (the coast of the Malacca Peninsula, etc.).

Foggy forest (moss forest, nephelogyleum) – humid tropical mountain evergreen forest. Located in the tropics on the slopes of the mountains in the fog condensation zone.

The foggy forest is located in the tropics on the slopes of the mountains in a zone of fog condensation, usually starts from an altitude of 500-600 m and reaches an altitude of 3500 meters above sea level. It is much cooler here than in the jungle, located in low-lying places, at night the temperature can drop to almost 0 degrees. But here it is even more humid, up to six cubic meters of water falls per year per square meter. And if it doesn't rain, the moss-covered trees are shrouded in fog caused by intense evaporation.

Foggy forest formed by trees with abundant lianas, with a dense cover of epiphytic mosses.

Tree ferns, magnolia, camellia are characteristic, the forest can also include non-tropical vegetation: evergreen oaks, podocarpus, which distinguishes given type forests from lowland giles

Variable rainforest- forests common in tropical and equatorial belts, in climates with a short dry season. Are located south and north of the humid equatorial forests... Variable wet forests are found in Africa (CAR, DR Congo, Cameroon, northern Angola, extreme south of Sudan), South America, India, Sri Lanka, Indochina.

Variable-humid rainforest - Partially deciduous dense rainforest. They differ from humid tropical forests in less species diversity, a decrease in the number of epiphytes and lianas.

Suhotropic evergreen forest. Located in areas with an arid climate, while remaining dense and evergreen, they become stunted and xeromorphic.

HUMAN IMPACT ON TROPICAL FORESTS

Contrary to popular belief, tropical rainforests are not large consumers carbon dioxide and, like other established forests, are neutral to carbon dioxide.

Recent studies show that most rainforests, on the contrary, are intensively produce carbon dioxide, and swamps produce methane.

Nevertheless, these forests play a significant role in the circulation of carbon dioxide, since they are its established pools, and the deforestation of such forests leads to an increase in the carbon dioxide content in the Earth's atmosphere. Rainforests also play a role in cooling the air that passes through them. That's why tropical rainforest Is one of the most important ecosystems of the planet, the destruction of forests leads to soil erosion, a reduction in flora and fauna species, and a shift in the ecological balance by large territories and on the planet as a whole.

Tropical rainforest are often reduced to plantations of cinchona and coffee trees, coconut trees, and rubber plants. In South America, rainforests are also seriously threatened by unsustainable mining.

A.A. Kazdym

List of used literature

1. M. B. Gornung. Constantly humid tropics. M .:, "Thought", 1984.
2. Hogarth, P. J. The Biology of Mangroves. Oxford University Press, 1999.
3. Thanikaimoni, G., Mangrove Palynology, 1986
4. Tomlinson, P. B. The Botany of Mangroves, Cambridge University Press. 1986:
5. Jayatissa, L. P., Dahdouh-Guebas, F. & Koedam, N. A review of the floral composition and distribution of mangroves in Sri Lanka. Botanical Journal of the Linnean Society, 138, 2002, 29-43.
6. http://www.glossary.ru/cgi-bin/gl_sch2.cgi?RSwuvo,lxqol!rlxg

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The rainforest is composed of many layers of varied evergreens. In the upper tier, trees reach 100 meters in height. Here you can also find palms - lianas, which are the most long plants on Earth they grow by 300 or even 400 meters.

some types of animals are the most common. For example, it is in the rainforest that greatest number species of monkeys, and among them there are apes.
Among the birds, parrots alone, there are about 150 species. A lot in
tropical forest of butterflies and some of them are truly gigantic in size, such as tizania (the largest moth), whose wings reach 30 cm.
The rainforest is rich in water and, as a consequence, a variety of reptiles. Among them are crocodiles, snakes, lizards, turtles. These animals are truly gigantic in size. For example, tropical crocodiles are found in lengths up to ten meters, and the anaconda (South American boa constrictor) reaches a length of nine meters.

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Our presentation will introduce students to geographic location tropics, with a tropical climate, will tell you about the natural zones included in tropical belt... Children will look at the amazing plants growing in tropical forests, learn about the fauna of this belt through the example of its most interesting representatives.

Equatorial humid forests (or rainforests) are a geographic natural area that runs along the equator, moving southward.

Diversity of flora and fauna.

Complex multi-tiered forest structure. There are four main tiers of tropical rainforest, which differ not only in flora, but also in fauna.

The presence of a humid climate with a large amount of precipitation and high temperature air.

The flora is predominantly represented by evergreen tree-like plants with poorly developed bark, as well as flowers and fruits that form on tree trunks and branches.

The conditions in which tropical rainforests grow are due to low air pressure, abundant tropical rainfall and heat. Various tropical crops such as coconut, banana, cocoa and pineapple are also well cultivated under these conditions. These forests are called the "lungs" of the planet, but such a statement is controversial in the opinion of scientists who claim that the vegetation of tropical forests emits enough oxygen into the atmosphere.

Climate

Rainforests are characterized by a humid and hot equatorial climate. There are slight temperature fluctuations throughout the year (from 24 ° C to 28 ° C), intense and uniform precipitation (from 2000 to 10000 mm per year) and high air humidity due to the high content of water vapor and reaching 80% and above ... Seasons in this natural area followed by a dry season and a season of tropical showers.

In such a climate, vegetation develops rapidly in humid equatorial forests. The trees here are weakly branching, have a dense evergreen crown, and the height of the trunks reaches several tens of meters.

The upper tier is represented mainly by palms and ficuses, and the lower tier is represented by tree ferns, lianas and large plants. At the foot of the trees, twilight always reigns, created by lush crowns, which is why, due to the lack of sunlight in the rainforests, there is practically no undergrowth.

The soil

Despite the growth of lush vegetation, the soil of tropical rainforests, due to the hot climate, is poorly fertile and very rich in aluminum and iron oxides. The great content of these chemical compounds gives it a red or red-yellow color, and the rapid decomposition of plants under the influence of bacteria prevents the accumulation of the humus (fertile) layer of the earth.

Geographical position

Wet equatorial forests are widespread in tropical regions with an equatorial climate, such as Central and South America (Amazon basin), equatorial Africa, Southeast Asia (Malaysia, Indonesia, Philippines), northeastern Australia, and the Pacific Islands ...