Tropical rainforests stretch over large areas on both sides of the equator, but do not go beyond the tropics. Here the atmosphere is always rich in water vapor. The lowest average temperature is about 18°, and the highest is usually not higher than 35-36°.
With abundant heat and moisture, everything here grows with remarkable speed. Spring and autumn are imperceptible in these forests. All year long, some trees and shrubs bloom in the forest, others fade. It is summer all year round and the vegetation is green. There is no leaf fall in our understanding of the word, when the forest is exposed by winter.
The change of leaves occurs gradually, and therefore it is not noticed. On some branches, young leaves bloom, often bright red, brown, white. On other branches of the same tree, the leaves were fully formed and turned green. A very beautiful range of colors is created.
But there are bamboos, palm trees, some types of coffee trees, which, over many square kilometers, bloom all at once in one day. This amazing phenomenon makes a stunning impression of the beauty of flowering and aromas.
Travelers say that in such a forest it is difficult to meet two neighboring trees belonging to the same species. Only in very rare cases, tropical forests of a uniform species composition.
If you look at the rainforest from above, from an airplane, it will appear surprisingly uneven, sharply broken, not at all like the flat surface of a forest of temperate latitudes.
They are not similar in color. Oak and our other forests, when viewed from above, seem to be uniformly green, only with the advent of autumn they dress up in bright and variegated colors.
The equatorial forest, when viewed from above, seems to be a mixture of all tones of green, olive, yellow, interspersed with red and white spots of flowering crowns.
Entering the rainforest is not so easy: usually it is a dense thicket of plants, where, at first glance, they all seem to be tangled, intertwined. And it is difficult to immediately figure out which plant this or that trunk belongs to - but where are its branches, fruits, flowers?
Damp twilight reigns in the forest. The rays of the sun weakly penetrate into the thicket, so trees, shrubs, all plants stretch upward with amazing force. They branch a little, only in three - four orders. One involuntarily recalls our oaks, pines, birches, which give five to eight orders of branches and widely spread their crowns in the air.
In the equatorial forests, trees stand in thin, slender columns and somewhere at a height, often 50-60 meters, they carry small crowns to the Sun.
The lowest branches begin twenty to thirty meters from the ground. To see the leaves, flowers, fruits, you need good binoculars.
Palm trees, tree ferns do not give branches at all, throwing out only huge leaves.
Giant columns need good foundations, like buttresses (slopes) of ancient buildings. And nature took care of them. In the African equatorial forests, ficuses grow, from the lower parts of the trunks of which additional - plank - roots develop up to a meter or more in height. They hold the tree firmly against the wind. Many trees have such roots. On the island of Java, residents make table covers or cart wheels from plank roots.
Trees of smaller height, four or five tiers densely grow between giant trees, bushes even lower. Fallen trunks and leaves rot on the ground. The trunks are twined with vines.
Hooks, spikes, mustaches, roots - by all means, creepers cling to tall neighbors, twist around them, crawl along them, use devices known to the people as "devil's hooks", "cat's claws". They intertwine with each other, sometimes merging into one plant, then separating again in an unstoppable desire for light.
These thorny barriers terrify the traveler, who is forced to take every step among them only with the help of an ax.
In America, along the valleys of the Amazon, in the virgin rain forests, creepers, like ropes, are thrown from one tree to another, climb the trunk to the very top and comfortably settle in the crown.
Fight for the world! In a tropical rainforest, there are usually few grasses on the soil, and shrubs are also few in number. Everything that lives must receive some share of the light. And many plants succeed in this because the leaves on the trees are almost always located vertically or at a significant angle, and the surface of the leaves is smooth, shiny and perfectly reflects light. This arrangement of leaves is also good because it softens the force of the impacts of rain showers. Yes, and prevents stagnation of water on the leaves. It is easy to imagine how quickly the leaves would fail if water lingered on them: lichens, mosses, fungi would populate them immediately.
But for the full development of plants on the soil, there is not enough light. How then to explain their diversity and splendor?
Many tropical plants have nothing to do with the soil at all. These are epiphyte plants - lodgers. They don't need soil. Trunks, branches, even tree leaves give them an excellent shelter, and everyone has enough heat and moisture. In the axils of the leaves, in the crevices of the bark, a little humus forms between the branches. Wind, animals will bring seeds, and they germinate and develop perfectly.
The very common bird's nest fern produces leaves up to three meters long, forming a rather deep rosette. Leaves, bark flakes, fruits, animal remains fall into it from trees, and in a humid warm climate they quickly form humus: the “soil” is ready for the roots of the epiphyte.
AT botanical garden in Calcutta they show such a huge fig tree that they mistake it for a whole grove. Its branches have grown above the ground in the form of a green roof, which is supported on pillars - these are adventitious roots growing from the branches. The crown of the fig tree is spread over more than half a hectare, its number aerial roots about five hundred. And this fig tree began its life as a freeloader on a date palm. Then she entwined her with her roots and strangled her.
The position of epiphytes is very advantageous compared to the "host" tree, which they use, making their way higher and higher towards the light.
Often they carry their leaves above the top of the "host" trunk and take away the sun's rays from it. The "owner" dies, and the "tenant" becomes independent.
Tropical forests are best described by the words of Charles Darwin: "The greatest sum of life is carried out with the greatest variety of structure."
Some epiphytes have thick fleshy leaves, some swellings on the leaves. They have a supply of water - in case it is not enough.
In others, the leaves are leathery, hard, as if varnished, as if they lack moisture. The way it is. In the hot time of the day, and even with a strong wind, in a highly raised crown, the evaporation of water increases sharply.
Another thing is the leaves of shrubs: they are tender, large, without any adaptations to reduce evaporation - in the depths of the forest it is small. Herbs are soft, thin, with weak roots. There are many spore plants, especially ferns. They spread their sheets on the edges of the forest and in rare lighted clearings. Here are brightly flowering shrubs, large yellow and red cannes, orchids with their intricately arranged flowers. But grasses are much less diverse than trees.
The general green tone of herbaceous plants is pleasantly interspersed with white, red, gold, silver leaf spots. Whimsically patterned, they are not inferior in beauty to the flowers themselves.
It may seem at first glance that the tropical forest is poor in flowers. In fact, they are not so few
they are simply lost in the green mass of foliage.
Many trees have self- or wind-pollinated flowers. Large bright and fragrant flowers are pollinated by animals.
In the rainforests of America, tiny hummingbirds in brilliant plumage hover over flowers for a long time, licking honey from them with a long tongue folded in the form of a tube. In Java, birds often act as pollinators. There are honey birds, small, similar in color to hummingbirds. They pollinate flowers, but at the same time they often “steal” honey without even touching the stamens and pistils. In Java, there are bats that pollinate vines with brightly colored flowers.
In a cocoa tree, breadfruit, persimmon, ficus, flowers appear directly on the trunks, which then turn out to be completely hung with fruits.
In the equatorial humid forests, swamps are often found, flowing lakes come across. The animal world here is very diverse. Most animals live on trees, eating fruits.
Tropical forests of different continents have many common features, and at the same time, each of them is different from the others.
In Asian forests there are many trees with valuable wood, plants that give spices (pepper, cloves, cinnamon). Monkeys climb in the crowns of trees. An elephant roams on the outskirts of the tropical thicket. Rhinos, tigers, buffaloes, poisonous snakes live in the forests.
The humid equatorial forests of Africa are famous for their impenetrable thickets. Without an ax or a knife, it is impossible to make your way here. And there are many tree species with valuable timber. The oil palm tree is often found, from the fruits of which oil, coffee tree and cocoa are extracted. In places in narrow hollows, where fogs accumulate and mountains do not let them go, tree-like ferns form whole groves. Heavy dense fogs slowly creep up and, cooling down, pour heavy rains. In such natural greenhouses, spores feel the best: ferns, horsetails, club mosses, curtains of delicate green mosses descend from the trees.
Gorillas and chimpanzees live in African forests. Monkeys tumble in the branches; baboons bark in the air. There are elephants, buffaloes. Crocodiles prey on all kinds of animals in the rivers. Frequent encounters with a hippopotamus.
And everywhere mosquitoes, mosquitoes fly in clouds, hordes of ants crawl. Perhaps even this "little thing" is more noticeable than large animals. It disturbs the traveler at every turn, stuffing itself into the mouth, nose and ears.
The relationship of tropical plants with ants is very interesting. On the island of Java, in one epiphyte, the stem below is a tuber. Ants lodge in it and leave their excrement on the plant, which serve as fertilizer for it.
In the rain forests of Brazil, there are real ant gardens. At a height of 20-30 meters above the ground, ants arrange their nests, dragging seeds, leaves, berries and seeds onto branches and trunks along with earth. Of these, young plants sprout, fastening the earth in the nest with roots and immediately receiving soil and fertilizers.
But ants are not always harmless to plants. Leaf cutter ants are a real scourge. They attack coffee and orange trees and other plants in droves. Having cut pieces from the leaves, they put them on their backs and move in continuous green streams to the nests, baring the branches,
Fortunately, other types of ants can settle on plants, which destroy these robbers.
The tropical forests of America along the banks of the Amazon River and its tributaries are considered the most luxurious in the world.
Vast flat expanses, regularly flooded with water during the flood of rivers, are covered with coastal forests. Above the flood line stretch huge virgin forests. And the drier regions are occupied by forests, although less dense and lower.
There are especially many in the coastal forests of palm trees, which form entire groves, running in long alleys along the banks of the rivers. Some of the palms scatter their leaves in a fan, others stretch pinnate leaves 9-12 meters long. Their trunks are straight, thin. In the undergrowth are small palm trees with clusters of black and red fruits.
Palm trees give a lot to people: the fruits are used for food, the locals get fibers from the stems and leaves, and the trunks are used as building material.
As soon as the rivers enter their course, grasses develop with extraordinary speed in the forests, and not only on the soil. Hanging from trees and bushes are green garlands of climbing and climbing herbaceous plants, adorned with bright flowers. Passion flowers, begonias, "beauties of the day" and many other flowering plants form draperies on the trees, as if laid out by the artist's hand.
Beautiful myrtle, brazil nuts, flowering ginger, cannes. Ferns and graceful feathery mimosas support the overall green tone.
In the forests above the flood line, trees, perhaps the tallest of all tropical representatives, stand in a dense close formation on props. Notable among these are the Brazil nut and the mulberry cotton plant, with its enormous plank poles. Laurels are considered the most beautiful trees in the Amazon. There are a lot of acacias from legumes, a lot of aroids. Philodendron and monstera are especially good with fantastic cuts and cuts on the leaves. There is often no undergrowth in this forest.
In less tall, unflooded forests, lower tree tiers of palms, shrubs and low trees appear, sometimes very dense and almost impassable.
The grassy cover cannot be called luxurious: a few ferns, sedges. In some places, there is not a single blade of grass in a large area.
Almost the entire Amazonian lowland and part of the northern and eastern coasts of the mainland are occupied by humid forests.
Even high temperatures and an abundance of rainfall make all days look like one another.
Early in the morning the temperature is 22-23°, the sky is cloudless. The leaves are dewy and fresh, but the heat is rising rapidly. By noon and a little later, it is already unbearable. Plants drop leaves and flowers and seem to be completely wilted. No air movement, the animals hid. But now the sky is covered with clouds, lightning flashes, thunder is deafening.
Crowns are shaken by sharp gusts of wind. And the blessed downpour enlivens all nature. It floats strongly in the air. A sultry, hot, and damp night sets in. Leaves and flowers plucked by the wind fly.
A special type of forest covers in tropical countries the sea coasts, protected from waves and winds. These are mangrove forests - dense thickets of evergreen shrubs and low trees on flat banks near river mouths, in lagoons, bays. The soil here is a swamp with black, foul-smelling silt; it undergoes rapid decomposition with the participation of bacteria organic matter. At high tide, such thickets appear to emerge from the water.
With the ebb, their so-called roots are exposed - stilts, which stretch far along the silt. From the branches in the silt there are still roots-props.
Such a system of roots well establishes the trees in silty soil, and they are not carried away by the tide.
Mangroves push the coast to the sea, because plant residues accumulate between the roots and trunks and, mixing with silt, gradually form land. Trees have special respiratory roots, which are very important in the life of these plants, since the silt contains almost no oxygen. Sometimes they are serpentine in shape, at other times they resemble a bent pipe or stick out of the silt like young stems.
The method of reproduction found in mangroves is curious. The fruit is still hanging on the tree, and the embryo is already sprouting in the form of a long, up to 50-70 centimeters, pin. Only then does it break away from the fruit, fall into the silt, burrowing into it with its end, and it is not carried away by water into the sea.
These plants have leathery, shiny, often fleshy leaves covered with silvery hairs. The leaves are arranged vertically, the stomata are reduced. All these are signs of plants of arid places.
It turns out a paradox: the roots are immersed in silt, they are constantly under water, and the plant lacks moisture. It is assumed that sea water, with its saturation with salt, cannot be easily absorbed by the roots of trees and shrubs - and therefore they must evaporate sparingly.
Together with sea water, plants receive a lot of table salt. The leaves are sometimes almost completely covered with its crystals, isolated by special glands.
The richness of species in tropical forests is exceptionally great, and it is achieved primarily by the fact that the use of space by plants has been brought here by natural selection to the extreme limits.
Rainforests located in the tropical, equatorial and subequatorial belts between 25 ° N.L. and 30 ° S, as if "surrounding" the surface of the Earth along the equator. Tropical forests are only torn apart 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 time of year.
The vegetation of tropical forests is very diverse, depending mainly on the amount of precipitation and its distribution over the seasons. With abundant (more than 2000 mm), and relatively uniform distribution develop humid tropical evergreen forests.
Further from the equator, the rainy period is replaced by a dry one, and the forests are replaced with leaves falling during the drought, and then these forests are replaced by savannah forests. At the same time, in Africa and South America, there is a pattern: from west to east, monsoon and equatorial forests are replaced by savannah forests.
Tropical forest classification
tropical rainforest, tropical rain forest these are forests with specific biomes located in equatorial (moist equatorial forest), subequatorial and humid tropical areas with a very humid climate (2000-7000 mm of precipitation per year).
Tropical rainforests are rich in biodiversity. This is the most livable natural area. It is home to a large number of its own, including endemic species of animals and plants, as well as migratory animals. Tropical rainforests are home to two-thirds of all animal and plant species on the planet. It is assumed that millions of species of animals and plants have not yet been described.
These forests are sometimes referred to as " jewels of the earth" and " the largest pharmacy in the world”, as a large number of natural medicinal remedies have been found here. They are also called " lungs of the earth”, however, this statement is debatable because it has no scientific justification, since these forests either do not produce oxygen at all, or produce very little of it.
But it should be borne in mind that a humid climate contributes to effective air filtration, due to the condensation of moisture on the microparticles of pollution, which has a generally beneficial effect on the atmosphere.
Understorey formation in tropical forests is severely limited in many places due to lack of sunlight in the lower layer. This allows man and animals to move through the forest. If for any reason the leafy 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 the jungle.
The largest areas of tropical rainforests are found in the Amazon basin (“Amazonian rainforests”), in Nicaragua, in the southern part of the Yucatan Peninsula (Guatemala, Belize), in most of Central America (where they are called “selva”), in 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 rainforests characteristic:
- variety of flora
- the presence of 4-5 tree tiers, the absence of shrubs, a large number of vines
- the predominance of evergreen trees with large evergreen leaves, poorly developed bark, buds, not protected kidney scales, deciduous trees in monsoon forests;
- the formation of flowers and then fruits 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 ledges. Previously it was assumed that these ledges help the tree to maintain balance, but now it is believed that water with dissolved nutrients flows down these ledges to the roots of the tree. Wide leaves of trees, shrubs and grasses of the lower tiers of the forest are characteristic. The wide leaves help the plants absorb sunlight better under the tree edges of the forest, and they are protected from the wind from above.
Tall young trees that have not yet reached the topstory also have broader foliage, which then decreases with height. The leaves of the upper tier, forming a canopy, usually smaller size and heavily indented to reduce wind pressure. On the lower floors the leaves are often tapered at the ends so that it allows water to run off quickly and prevents microbes and moss from growing on them that destroy the leaves.
The tops of the trees are often very well interconnected with creeper or epiphytic plants attached to them.
The trees of the humid tropical forest are characterized by unusually thin (1-2 mm) tree bark, sometimes covered with sharp thorns or thorns, the presence of flowers and fruits growing directly on tree trunks, a wide variety of juicy fruits that attract birds and mammals.
Insects are very abundant in tropical rainforests, especially butterflies (one of the richest fauna in the world) and beetles, and fish are abundant in rivers (about 2000 species, approximately one third of the world's freshwater fauna).
Despite the stormy vegetation, the soil in tropical rainforests is thin and with a small humus horizon.
Rapid decay caused by bacteria prevents the accumulation of the humus layer. The concentration of iron and aluminum oxides due to laterization soil (the process of reducing the silica content of the soil with a simultaneous increase in iron and aluminum oxides) turns 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.
Tropical rainforest levels (tiers)
The rainforest is divided into four main levels, each of which has its own characteristics, has a different flora and fauna.
The topmost level
This layer consists of a small number of very tall trees rising 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 the majority of tall trees, usually 30-45 meters high. This is the densest layer known in all terrestrial biodiversity, with neighboring 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 varied. 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 developed practical methods research. It wasn't until 1917 that the American naturalist William Bead stated that "another continent of life remains unexplored, not on Earth, but 200 feet above its surface, spreading over thousands of square miles."
True exploration of this layer only began in 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 at an early stage. Other research methods include balloon or aircraft travel. The science of access to the tops of trees is called dendronautics.
Middle level
Between the forest canopy and the forest floor there is another level called the undergrowth. It is home to a number of birds, snakes and lizards. Insect life at this level is also very extensive. The leaves in this tier are much wider than at crown level.
forest floor
In 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 area of Santarem (Brazil) 0.5-1%. In the north of the island of Sumatra, in the dipterocarp forest, the illumination is about 0.1%.
Away from river banks, swamps, and open spaces where dense, low-growing vegetation grows, the forest floor is relatively free of plants. On this level, rotting plants and animal remains can be seen, which quickly disappear due to the warm, humid climate that promotes rapid decomposition.
Selva(Spanish " selva" from lat. " silva"- forest) is humid equatorial forests in South America. It is located on the territory of countries such as Brazil, Peru, Suriname, Venezuela, Guyana, Paraguay, Colombia, etc.
Selva is formed on vast lowland areas of land in conditions of constant freshwater moisture, as a result of which the soil of the selva is extremely poor. minerals washed away by tropical rains. The selva is often swampy.
The flora and fauna of the selva is a riot of colors and a variety of species of plants, birds and mammals.
The largest selva in terms of area is located in the Amazon basin in Brazil).
In the Atlantic Selva, the level of precipitation reaches two thousand millimeters per year, and the humidity fluctuates at the level of 75-90 percent.
The selva is divided into three levels. The soil is covered with leaves, branches, fallen tree trunks, lichens, fungus and moss. The soil itself has a reddish color. The first level of the forest consists 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 tidal strip of sea coasts in tropical and equatorial latitudes, as well as in temperate zones, where warm currents favor this. They occupy the strip between the most low level water at low tide and highest at high tide. These are trees or shrubs that grow in mangroves, or mangrove swamps.
Mangrove plants live in coastal sedimentary environments where fine sediments, 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 established, the roots of mangrove plants create a habitat for oysters and help slow down the flow of water, thereby increasing sediment deposition in areas where it is already occurring.
As a rule, finely dispersed, oxygen-poor sediments under 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 areas of the world where mangroves have been destroyed during development, the disruption of these sedimentary rocks creates the problem of heavy metal contamination of seawater and local flora and fauna.
It is often claimed that mangroves are of significant value in the coastal zone, acting as a buffer against erosion, the onslaught of storms and tsunamis. While there is some reduction in wave height and energy as seawater passes through mangroves, it must be recognized that mangroves usually grow in those areas of the coastline where low wave energy is the norm. Therefore, their ability to withstand the powerful onslaught of storms and tsunamis is limited. Their long-term impact on erosion rates is also likely to be limited.
The many river channels meandering through the mangroves actively erode the mangroves on the outside of all the bends in the river, just as new mangroves appear on the inside of the same bends where the deposition takes place.
Mangroves are a habitat for wildlife, including a number of commercial fish and crustaceans, and in at least some cases the export of mangrove carbon is important in the coastal food web.
In Vietnam, Thailand, the Philippines and India, mangroves are grown in coastal areas for coastal fisheries.
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 mangrove forests of the eastern formation (the shores of the Malay Peninsula, etc.) are considered.
Foggy forest (moss forest, nephelogilea) – humid tropical montane evergreen forest. It is located in the tropics on the slopes of mountains in the fog condensation zone.
The foggy forest is located in the tropics on the slopes of mountains in the fog condensation zone, usually starts from an altitude of 500-600 m and reaches a height of up to 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 it is even more humid here, up to six cubic meters of water falls per square meter per year. And if it doesn't rain, then the moss-covered trees stand shrouded in fog caused by intense evaporation.
Foggy forest formed by trees with abundant vines, with a dense cover of epiphytic mosses.
Tree-like ferns, magnolias, camellias are characteristic, the forest may also include non-tropical vegetation: evergreen oaks, podocarpus, which distinguishes this type of forest from flat hyla
Variable rainforests- forests common in tropical and equatorial zones, in a climate with a short dry season. They are located south and north of the humid equatorial forests. Variably humid forests are found in Africa (CAR, DR Congo, Cameroon, northern Angola, extreme south of Sudan), South America, India, Sri Lanka, and Indochina.
Variable rainforests are partially deciduous dense rainforests. They differ from tropical rainforests in lower species diversity, a decrease in the number of epiphytes and lianas.
Dry tropical evergreen forest. They are located in areas with an arid climate, while remaining dense and evergreen, becoming 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.
However, these forests play a significant role in the turnover of carbon dioxide, since they are its established basins, and the cutting down of such forests leads to an increase in the carbon dioxide content in the Earth's atmosphere. Tropical rainforests also play a role in cooling the air that passes through them. So tropical rainforests - one of the most important ecosystems of the planet, the destruction of forests leads to soil erosion, reduction of flora and fauna species, shifts in the ecological balance by large territories and on the planet as a whole.
Tropical rainforests often reduced to plantations of cinchona and coffee trees, coconut palms, and rubber plants. In South America, tropical rainforests are also seriously threatened by unsustainable mining.
A.A. Kazdym
List of used literature
- M. B. Gornung. Constantly humid tropics. M.:, "Thought", 1984.
- Hogarth, P. J. The Biology of Mangroves. Oxford University Press, 1999.
- Thanikaimoni, G., Mangrove Palynology, 1986
- Tomlinson, P. B. The Botany of Mangroves, Cambridge University Press. 1986:
- 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.
- http://www.glossary.ru/cgi-bin/gl_sch2.cgi?RSwuvo,lxqol!rlxg
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In the rainforest, high humidity and fever. How did plants and animals adapt to its bathing conditions?
How have the leaves adapted?
Throughout life, the leaves of some tropical plants change shape. In young trees, while they are still covered by the crowns of the trees of the upper tier, the leaves are wide and soft. They are adapted to capture the slightest rays of light breaking through the upper canopy. They are yellowish or reddish in color. So they try to save themselves from being devoured by animals. Red or yellow color may seem inedible to them.
When the tree grows to the first tier, then its leaves decrease in size and seem to be covered with wax. Now there is a lot of light and the leaves have a different task. Water should drain completely from them, without attracting small animals.
The leaves of some plants can regulate the flow of sunlight. In order not to overheat in bright light, they stand parallel to the sun's rays. When the sun is shading the cloud, the leaves turn horizontally to take more of the sun's energy for photosynthesis.
Pollination of flowers
For pollination, flowers must attract insects, birds, or bats. They attract with their bright color, smell and delicious nectar. To attract their pollinators, even the plants of the upper tier decorate themselves with beautiful flowers. Moreover, at the time of flowering, they even shed some of their leaves so that their flowers stand out more noticeably.
abstract
by geography
on the topic
"Rainforests".
Completed: student 6 "A" class Ts.O. No. 1430
Kotlova Sveta
- Introduction……………………3p.
- The main part…………….4-6p.
- Conclusion…………………7p.
- References………..8p.
- Application…………………9-10p.
Introduction.
I was interested in tropical forests. Therefore, I decided to write this essay. In it, I will talk about animals living in the tropics. I will also talk about tropical plants. Of course, there will be pictures in my essay, because pictures are visual material. animals that are not found elsewhere. But my essay will tell you more about them. And I hope that he will explain clearly. So, let's start:
Rainforests.
Tropical forests (from the Greek tropikos (kyklos) turning, circle), parallels with latitudes 23 ° 07 "- the common name for forests common in the equatorial, subequatorial and tropical zones of the Earth. Depending on the degree and rhythms of moisture, tropical forests are very diverse. In The constantly humid equatorial zone is dominated by dense forests with a variety of plant species.These are hylaean forests in the Amazon basin in South America, the Congo in Africa and on the islands of Indonesia.In the subequatorial and tropical zones with a dry season, hylaean forests monsoonal areas and dry tropical forests at the transition to savannahs.In the coastal strip of the tropics with a monsoonal climate - mangrove vegetation.On the slopes of the Andes, where condensation fogs are common, hylaean forests turn into a kind of mixed: evergreen, broad-leaved and deciduous foggy forests.
Among dry forests, the most interesting are eucalyptus forests, which are found only in eastern Australia. Eucalyptus trees are usually very tall trees with sparse, almost shadeless crowns. Every year, eucalyptus trees shed their bark so that it does not interfere with their growth. The great height of trees is not connected with the pursuit of light - in this way they are saved from forest fires. The undergrowth often burns out, but eucalyptus trees, as a rule, survive: after all, their crown is high, and their dense bark burns poorly. Precipitation in eucalyptus forests falls up to 1000 mm per year, but because of the heat, a lot of moisture evaporates, so there is not enough water for active growth. You have to save it and at the same time: overheat. It is for this reason that the leaves of eucalyptus trees are turned towards the sun. Lower trees - acacias - have their own ways: some of their species grow wide pinnate leaves in the wet season, change them to long and thin ones in the dry season, others simply shed their leaves. The Kazarina tree generally does without leaves, their role is played by green shoots. Lianas are also found in the eucalyptus forest. One of them, cissus, has become common houseplant. There are many grasses in the eucalyptus forest, it is burning. All vegetation has a grayish tint. It is given by a wax coating or covers of the smallest bristles, which make it difficult to evaporate. The roots of plants in search of water grow both deep and wide, and the most powerful roots penetrate far beyond the soil for tens of meters into the rock. Despite the dryness, eucalyptus forests can feed a lot of animals, birds and insects. Of the animals, the most famous is the koala - a marsupial bear that lives in the branches of the eucalyptus and feeds on its foliage. Outwardly, the koala resembles a teddy bear. Australian rainforests and woodlands are very sensitive to interference in their lives.
Dry tropical forests in South America are much lower - there are no trees as tall as eucalyptus trees, but there are many types of cacti. But these forests are also light, especially in the dry season, when some of the trees shed their foliage.
Deserts in the tropics are formed where there is a catastrophic lack of water even for those plants and animals that can literally get by with drops. The living creatures of the Earth have a limit of endurance, after which it is no longer possible to adapt. Therefore, the vegetation here is sparse, sometimes it does not exist at all. The most terrible deserts are clay and rocky. They are lifeless, their landscapes are almost unchanged throughout the year. The stones do not withstand sudden changes in temperature and burst, crumbling and falling asleep at the foot of the rocks sticking out like broken teeth. Sandy deserts cover, like waves, moving hills - dunes. Wind-driven sand rolls, flies and spills from place to place, burying roads and rare oases under it. However, sand has one very important property: passing water through itself, it retains it at a certain depth. If there is water, then life becomes possible. In some places, rare bushes of thorns cling to the slopes of the dunes. When there are a lot of them, they stop the winding of sand.
Klima t: In the tropics, at least twice a year the sun is directly overhead in the sky. And on other days it rises higher than in more northern latitudes. Therefore, the sun in the tropics bakes very strongly and hot air rises. As a result, an area with reduced air pressure is formed above the equator, and in order for the pressure to equalize, constant winds called trade winds blow from the northwest and southwest from higher latitudes. They carry air that contains a lot of moisture. When air rises, its temperature drops. As the air cools, the water vapor it contains condenses into droplets and large clouds form. Some of them are carried away by the winds, and they fall as rain, sometimes far from their place of origin. Of those that remain, heavy rains hit the forests almost every day, close to noon, in some places as regularly as if right on schedule.
So along the equator a belt with a damp warm climate is formed. It is under these conditions that a tropical rainforest can exist. It grows wherever the temperature ranges from 20 to 28 C and a lot of precipitation falls annually - 2000 - 4000, and in some places even 10,000 mm per year per 1 sq.m (for comparison: in the Moscow region - 700 mm). It is also important when these showers are poured: precipitation should be distributed evenly throughout the year. So, where tropical forests grow, there are no sharp warming or cooling, so here the seasons do not change.
Age: These forests have existed on Earth for 60 million years, although they did not always grow where they are now. After the Ice Age, a green belt formed along the equator. In recent centuries, the area of rainforests has been declining more and more rapidly. This happens not because the climate is changing, but solely because of the destructive activities of people. Now on Earth there are from 4 to 8 million square kilometers of tropical forest.
There are more than 40 types of tropical forests. I will cover three important ones:
1. Plain tropical rainforest or evergreen tropical rainforest - the most characteristic of all tropical rainforests. The air temperature fluctuates here from 25 to 27 C, at least 1800 mm of precipitation falls annually, most often in the form of heavy showers that occur in the afternoon. Humidity is constantly high - 80%. These forests occupy the largest area. There are virgin, or primary, and secondary (grown after the destruction of the virgin) tropical rainforests.
2. The mountain rain forest grows in the tropics at an altitude of 1800 to 3500 m. The air here is also always humid, and thick fogs often lie. During the day it is always warm, but at night the temperature drops, occasionally even to zero.
3. Variable wet or summer green, rainforests are located further from the equator in the Northern and Southern Hemispheres than tropical rainforests, in places where the seasons already differ. There comes a short winter every year and some trees drop some of their leaves. Evergreens in such forests include only undergrowth shrubs and herbaceous plants.
A variety of animals live in the wilds of the rainforest. From gigantic elephants, rhinos, hippos to barely noticeable insects - everyone finds shelter and food here.
Representatives of some animal groups in tropical forests are numerous. It is here that most monkeys live, including anthropoids. Of the birds alone
There are more than 150 species of parrots in South America. The Amazon parrot is easy to teach to speak. The parrot does not understand the meaning of the spoken words - it simply imitates the combination of sounds. There are a lot of insects in the rainforest: over 700 species of butterflies are known in Brazil, which is almost five times more than in Europe. Some of them are giants, such as the tizania butterfly: its wingspan is up to 30 cm.
Structure and structure. It is almost impossible to give a generalized description of the structure of the tropical rainforest: this most complex plant community exhibits such a variety of types that even the most detailed descriptions. A few decades ago, it was believed that a wet forest is always an impenetrable thicket of trees, shrubs, ground grasses, lianas and epiphytes, since it was mainly judged by descriptions of mountain rainforests. Only relatively recently it became known that in some humid tropical forests, due to the dense closure of the crowns of tall trees, sunlight almost does not reach the soil, so the undergrowth here is sparse, and one can pass through such forests almost unhindered.
It is customary to emphasize the species diversity of the tropical rainforest. It is often noted that it is unlikely to find 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 species-poor, "monotonous" moist forests. These include, for example, special forests, consisting mainly of trees of the dipterocarpaceae family, growing in areas of Indonesia that are very rich in precipitation. Their existence indicates that in these areas the stage of optimal development of tropical rainforests has already been passed. The extreme abundance of precipitation makes it difficult to aerate the soil, as a result, there was a selection of plants that have adapted to living in such places. Similar conditions of existence can also be found in some damp regions of South America and the Congo basin.
The dominant component of the tropical rainforest is trees of various appearance and different heights they make up about 70% of all species of higher plants 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 located below the tiers. The crowns of such trees do not close, in many cases these trees are scattered in the form of individual specimens that seem to be overgrown. On the contrary, the crowns of trees of the middle tier, having 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 lianas and epiphytes found in different tiers of the forest (pp. 100-101).
Often there is also a tier of shrubs and one or two tiers 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 in danger of wilting. Thus, they constantly assimilate.
According to the intensity and nature of growth, the trees of the tropical rainforest can be divided into three groups. The first are 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, clarified 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), an African species Musanga cecropioides and representatives of the Euphorbiaceae family growing 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 at the end of it 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 genera Swietenia(tropical America), Khaya and Entandrophragma(tropical Africa).
Finally, the third group includes representatives of shade-tolerant species that grow slowly and are long-lived. Their wood is usually very heavy and hard, it is difficult to process it, and therefore it does not find such a wide application as the wood of trees of the second group. Nevertheless, the third group includes species that give noble wood, in particular Tieghemella heckelii or Aucomea klainiana, the wood of which is used as a substitute for mahogany.
Most of the trees are characterized by straight, columnar trunks, which often, without branching, rise to more than 30 meters in height. Only there, in isolated giant trees, a spreading crown develops, while in the lower tiers, as already mentioned, the trees, due to their close arrangement, form only narrow crowns.
In some species of trees near the bases of the trunks, board-like roots are formed (see figure), sometimes reaching a height of up to 8 m. They give the trees greater stability, since the root systems that develop shallowly do not provide a strong enough fixation for these huge plants. The formation of plank roots is genetically determined. Representatives of some families, such as Moraceae (mulberry), Mimosaceae (mimosa), Sterculiaceae, Bombacaceae, Meliaceae, Bignoniaceae, Combretaceae, have them quite often, while others, such as Sapindaceae, Apocynaceae, Sapotaceae, do not have them at all.
Trees with plank roots most often grow in damp soils. It is possible that the development of plank-like roots is associated with poor aeration characteristic of such soils, which prevents the secondary growth of wood on the inner sides of the lateral roots (it is formed only on their outer sides). In any case, trees growing on permeable and well-aerated soils of mountain rainforests do not have plank roots.
Trees of other species are characterized by stilted roots; they are formed above the base of the trunk as adnexal and are especially common in trees of the lower tier, also growing mainly in damp habitats.
Differences in the microclimate characteristic of different tiers of the tropical rainforest are also reflected in the structure of the leaves. While upper-story trees typically have elliptical or lanceolate outlines, smooth and dense leathery laurel-like leaves (see figure on page 112) that can tolerate alternating dry and wet periods throughout the day, the leaves of lower-story trees exhibit signs indicating intensive transpiration and rapid removal of moisture from their surface. They are usually larger; their plates have special points on which water collects and then drops from them, so there is no water film on the leaf surface that would prevent transpiration.
The change of foliage in trees of humid tropical forests is not affected by external factors, in particular drought or cold, although here, too, a certain periodicity, which varies in different species, can be replaced. In addition, some independence of individual shoots or branches is manifested, so not the whole tree is leafless at once, but only part of it.
Features of the climate of the humid tropical forest also affect the development of foliage. Since there is no need to protect the points of growth from cold or drought, as in temperate regions, the buds are relatively weakly expressed and are not surrounded by bud scales. With the development of new shoots, many trees of the tropical rainforest experience "drooping" of the leaves, which is caused exclusively by the rapid increase in their surface. Due to the fact that mechanical tissues do not form as quickly, young petioles at 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 whitish or - due to the content of the anthocyanin pigment - reddish (see figure above).
"drooping" of the young leaves of the chocolate tree (Theobroma cacao)
The next feature of some tropical rain forest trees is caulifloria, that is, the formation of flowers on the trunks and leafless parts of the branches. Since this phenomenon is observed primarily in the trees of the lower tier of the forest, scientists interpret it as an adaptation to pollination with the help of bats (chiropterophilia), which is often found in these habitats: bats and flying dogs - when approaching a tree, it is more convenient to grab onto 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 conspicuous by the bright colors of their flowers (red, orange, yellow), while chiropterophilous plants usually have inconspicuous, greenish or brownish flowers.
A clear distinction between the tiers of shrubs and grasses, as, for example, is typical for the forests of our latitudes, practically does not exist in tropical rainforests. One 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 herbs. In terms of the number of species, herbaceous plants in the tropical rainforest are inferior to trees; but there are also such lowland moist forests that have not experienced human influence, in which only one tier 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 matte-velvety surface areas on 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 amount of sunlight that reaches such habitats. Many "variegated" plants of the lower tier of grasses of the humid tropical forest have become a favorite indoor ornamental plants, for example, types of genera Zebrina, Tradescantia, Setcreasea, Maranta, Calathea, Coleus, Fittonia, Sanchezia, Begonia, Pilea and others (figure on page 101). The deep shade is dominated by various ferns, mosquitoes ( Selaginella) and mosses; the number of their species is especially great here. So, most species of mosquitoes (and there are about 700 of them) are found in tropical rainforests.
Also noteworthy are 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 - "mushroom-flowers" (see the picture on page 102).
Lianas. If you swim through the tropical rain forest along the river, the abundance of lianas (plants with woody stems climbing trees) is striking - they, like a dense curtain, cover the trees growing along the banks. Lianas are one of the most amazing components of the vegetation cover of tropical regions: over 90% of all their species are found only in the tropics. Most grow in moist forests, although they require good lighting to thrive. That is why they do not occur everywhere with the same frequency. First of all, they can be seen along the forest edges, in naturally formed lightened areas of the forest and - at least sometimes - in the layers of woody plants that are permeable to the sun's rays (see the figure on page 106). They are especially abundant on plantations established in areas of tropical rainforests, and in secondary forests that appear in clearings. In the lowland moist forests, which have not experienced the influence of man, where the dense, well-developed crowns of trees are tightly closed, creepers are relatively rare.
According to the method of fixing on the plants that serve as their support, creepers can be divided into different groups. For example, leaning creepers 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 distributed in the tropics of Asia and America (see the figure on page 103).
Rooted creepers are held on a 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 subsequent thickening and lignification, such shoots are fixed tightly. Most tropical vines belong to the climbing group, for example, representatives of the mimosa family and the related Caesalpinia family, rich in species and common throughout the tropics, in particular climbing entada ( Entada scandens); the beans of the latter reach 2 m in length (see drawing on page 104). To the same group belong the so-called monkey ladder, or sarsaparilla bauginia ( Bauhinia smilacina), forming thick woody shoots, as well as creepers with bizarre flowers (species of kirkazon, Aristolochia; kirkazon family) (see figure on page 103).
Finally, the vines attached with tendrils form lignified tendrils - with which they cling to the plants that serve as their support. These include representatives of the genus distributed throughout the tropics. Cissus from the Vinogradov family, different types legumes, in particular (see figure), as well as types of passionflower ( Passiflora; family of passionflowers).
Epiphytes. Extremely interesting are the adaptations to the conditions of existence in tropical rainforests in the so-called epiphytes - plants that live on trees. The number of their species is very large. They abundantly cover the trunks and branches of trees, due to which they are quite well lit. Developing high on trees, they lose the ability to get moisture from the soil, so the supply of water becomes a vital factor for them. It is not surprising that there are especially many types of epiphytes where precipitation is plentiful and the air is humid, but for their optimal development, it is not the absolute amount of precipitation that is decisive, but the number of rainy and foggy days. The unequal microclimate of the upper and lower tree layers is also the reason why 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 wet habitats. Light-loving epiphytes are well adapted to the change of dry and wet periods of time that occurs during the day. As the examples below show, they use different possibilities to do this (picture on page 105).
In orchids, represented huge number species (and most of the 20,000-25,000 orchid species are epiphytes), the organs that store water and nutrients are thickened areas of shoots (the so-called bulbs), leaf blades or roots. This lifestyle is also facilitated by the formation of aerial roots, which are covered on the outside with layers of cells that quickly absorb water (velamen).
Tropical rainforest plants growing in the ground layer
The family of bromeliads, or pineapples (Bromeliaceae), whose representatives are distributed, with one exception, in North and South America, consists almost only of epiphytes, whose rosettes of leaves, like funnels, serve as catchment reservoirs; of these, water and nutrients dissolved in it can be absorbed by scales located at the base of the leaves. Roots serve only as organs that attach plants.
Even cacti (for example, species of genera Epiphyllum, Rhipsalis, Hylocereus and Deamia) grow as epiphytes in mountain rainforests. With the exception of a few species of the genus Rhipsalis, also found in Africa, Madagascar and Sri Lanka, they all grow only in America.
Some ferns, such as the bird's nest fern, or nesting asplenium ( Aspleniumnidus), and deer-antler fern, or deer-horned platicerium ( 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 support tree, like patch pockets (picture on page 105), they are even able to create a soil-like, constantly moist substrate in which their roots grow.
Epiphytes that develop in shaded habitats are primarily represented 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, which are especially pronounced in mountain moist forests, are hymenophyllous, or thin-leaved, ferns (Hymenophyllaceae), for example, representatives of the genera Hymenophyllum and Trichomanes. As for lichens, they do not play such a big role because of their slow growth. Of the 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 humid tropical forest, where the humidity of the air is constantly high, can be inhabited by various lower plants. This phenomenon is called epiphylly. Lichens, hepatic mosses and algae mostly settle on the leaves, forming characteristic communities.
A kind of intermediate step between epiphytes and vines are hemiepiphytes. They either grow first as epiphytes on tree branches, and as aerial roots form, reaching the soil, they become plants that strengthen themselves in the soil, or in the early stages they develop as lianas, but then lose contact 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 its thickening to such an extent that the tree eventually dies off. And the totality of aerial roots then becomes, as it were, a system of "trunks" of an independent tree, in the early stages of development of the former epiphyte. The most characteristic examples of strangler trees in Asia are species of the genus Ficus(mulberry family), and in America - representatives of the genus Clusia(St. John's wort family). The second group includes species of the aroid family.
Lowland evergreen tropical rainforests. Although the floristic composition of tropical rain forests in different parts of the globe is very different, and the three main areas of such forests show only a slight similarity in this respect, nevertheless, similar modifications of the main type can be found everywhere in the nature of their vegetation.
The prototype of the tropical rainforest is considered to be an evergreen tropical rainforest of unflooded 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. Forest communities of river floodplains and flooded lowlands, as well as swamps, differ from it in usually less rich species composition and the presence of plants that have adapted to existence in such habitats.
Floodplain rainforests found 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 sediment - tiny particles brought by the river suspended in water and then settled. The so-called "white-water" rivers bring this muddy water mainly from the treeless regions of their basins *. The optimal content of nutrients in the soil and the relative supply of running water with oxygen determine the high productivity of plant communities developing in such habitats. Floodplain rainforests are difficult to access for human development, so they have largely retained their originality to this day.
* (Rivers, called "white water" by the authors of this book, in Brazil are usually called 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; the waters in them are transparent - they seem dark only because there are no suspended particles in them that reflect light. Humic substances dissolved in water only enhance this effect and, apparently, affect the color shade.)
Tropical rainforest vines
Moving from the very bank of the river across the floodplain to its edge, one can identify a characteristic succession of plant communities due to the gradual lowering of the soil surface level from high riverbeds to the edge of the floodplain. Riverside forests rich in lianas grow on seldom flooded riverbanks, further from the river turning into a real flooded forest. At the farthest edge of the floodplain, there are lakes surrounded by reed or grass marshes.
Swampy rain forest. In habitats whose soils are almost constantly covered with stagnant or slowly flowing water, marshy tropical rainforests grow. They can be found mainly near the so-called "black-water" rivers, the sources of which are located in forested areas. Therefore, their waters do not carry suspended particles and have a color from olive to black-brown due to the content of humic substances in them. The most famous "black-water" river is the Rio Negro, one of the most important tributaries of the Amazon; it collects water from a vast area with podzolic soils.
In contrast to the floodplain rainforest, swampy forest usually covers the entire river valley. Here there is no deposition of pumps, but, on the contrary, only uniform washing out, therefore the surface of the valley of such a river is even.
Due to the insecurity of habitats, marshy rain forests are not as lush as floodplain forests, 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 moist forests. Some areas of tropical rain forests experience short dry spells that cause leaf changes in the upper forest layer trees. At the same time, the lower tree tiers remain evergreen. Such a transitional stage to dry forests leafed during the rainy season (see p. 120) has been called "semi-evergreen or semi-deciduous lowland moist forests". During dry periods, there can be movement of moisture in the soil from the bottom up, so these forests receive enough nutrients and are very productive.
Epiphytes of the tropical rainforest
Above Asplenium nest Asplenium nidus and below Cattleya citrina
Montane tropical rainforests. The forests described above, whose existence is determined by the presence of water, can be contrasted with those variants of the 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 the mountainous regions of tropical regions. In the foothill zone, at an altitude of about 400-1000 m above sea level, the tropical rainforest almost does not differ from the lowland forest. It has only two tiers of trees, and the top tier trees are not as tall.
On the other hand, the tropical rain forest of the mountain belt, or, as they say, the mountain rain forest, growing at an altitude of 1000-2500 m, reveals more significant differences. It also has two tree layers, but they are often difficult to identify, and their upper limit often does not exceed 20 m. In addition, there are fewer tree species here than in lowland moist forests, and some characteristics trees of such forests, in particular stilted roots, as well as caulifloria. Tree leaves are usually smaller and do not have points to remove water droplets.
The shrub and grass layers are often dominated by ferns and bamboo species. Epiphytes are very abundant, while large creepers are rare.
At even higher altitudes in the permanently humid tropics (2500-4000 m), mountain rainforests give way to subalpine mountain forests that develop at cloud level (see t. 2).
