The wilderness is not so lifeless a place where it appears. At least, sandy desert, which to us and seems when we hear this word. After short rains, the desert is literally transformed before our eyes - both flora and fauna are activated in order to have time to enjoy the life-giving moisture and absorb its strength. However, among the deserts there are also truly lifeless.
Interesting facts about deserts.
- Deserts occupy about one-fifth of the land surface on Earth, and half of this area falls on the dry deserts of Antarctica (see the facts about Antarctica).
- In the Sahara desert, the air temperature was once recorded at +58 degrees.
- In the sandy desert it is very hot during the day and cold at night, sometimes even frost falls.
- In the hot sand in the desert during the day it is possible to bake a chicken egg.
- In the deserts dust storms are born. Especially from these natural disasters gets Australia (see the facts about sandstorms).
- Deserts are constantly moving, the dunes move at an average speed of 7-10 meters per year.
- Some dunes in sandy deserts reach a height of two hundred or three hundred meters.
- The world's largest desert is the Sahara located in Africa, its area exceeds 9 million square kilometers, which is only slightly smaller than the US (see facts about Africa). By the way, scientists say that the territory where the Sahara is now located was once very fertile.
DESERT AND HALF
In the southeast of the European part of Russia there are semi-deserts and deserts. The border separating the steppes and semi-deserts passes just south of Volgograd. From the left bank of the Volga it goes northeast towards Kazakhstan, and from the right bank turns sharply to the south and, reaching the foothills of the Caucasus, coincides with the valley of the Terek.
The word "desert" suggests that the territory is practically devoid of any kind of life.
However, in reality it is not. Scientists did not immediately agree on whether or not to consider the desert space of the Pre-Caspian Sea in the lower reaches of the Volga and Kuma, or not. Probably at the end of XX century. the dispute would have been resolved more quickly: due to unclear human activity, the large spaces in these areas turned out to be bare.
But the semi-desert in Russia is real, with all the signs of this landscape: climate, soils, and fau! yu and flora. The climate is dry and harsh: the summer is hot and the winter is frosty. Evaporation is several times higher than the amount of precipitation, which falls mainly in spring and early summer (about 250 mm in semi-desert and less than 200 mm in the desert).
So the heyday of life is short-lived - from April to June. In winter, frosts are often accompanied by strong winds that blow snow from the soil. Extensive bare spaces - “black lands” really look black and are called so not only because there is no snow on them: in deserts and semi-deserts there is a lot of black wormwood - plants with dark twigs and almost imperceptible leaves.
This sparse vegetation still helps the animals during the winter starvation. A significant part of the territory is set aside for the reserve, which is called Black Earth.
Most of the semi-deserts and deserts are located on the former seabed - Caspian lowland. The word "plain" weakly reflects exceptional local relief. A pedestrian traveler feels like a bug, sandwiched between a flat sky and flat earth, and wherever you look - everywhere is absolutely flat horizon.
Only in the west, the bleak landscape is enlivened by the contour of the steep slopes of Ergeny (the elevation between the Caspian lowlands and the valley of the Don), and small rounded hills are occasionally found on the marine plain.
These unusual natural formations are called salt shchpolami. At the base of them lies rock salt, which, under the pressure of surrounding rock layers, slowly flows upwards in the form of a huge drop. Where it rises, a hill swells, sometimes several tens of meters high. There are a lot of salt in the Caspian desert. Together with the fine dust, the summer dry winds carry them over great distances - to the steppe and forest zones.
Vegetation in the semi-desert is special - wormwood and ephemeroids dominate here - perennial grasses that quickly fade, but keep their organs in the ground (tubers, bulbs, etc.)
d.). There are plants and ephemera, the whole development cycle from birth to death, they manage to pass in two to three months. Such, for example, is a tiny grass.
In ordinary years, the plant is inconspicuous - it barely has time to collect two or three “onions” in its ear (in fact, these are germinated seeds). But in especially wet years, the whole plain is covered with green cover from edge to edge. Despite the seemingly dull monotony of semi-desert landscapes, its vegetative and soil cover is a kind of mosaic. On a flat, seemingly ground land there are usually numerous rises and falls.
They barely reach several centimeters in height and depth, but this is enough for noticeable differences in moisture. During rains or melting snow, water quickly drains into depressions. The soil in them is not only soaked to a greater depth and stores moisture, but also freed from salts. Here, as well as in the steppe, the perennial grass of fescue, many grasses grows. The soil in the depressions is also in many respects similar to the steppe: it is dark from humus and very fertile.
And on elevations, the soil is moistened a little, the water evaporates quickly, and salt solutions are pulled from the depth to the surface. In such areas, even black wormwood feels bad. Most often, they are covered with a specific layer of soil - the cortical saline, saline land is located here already at the depth of the spade bayonet.
From the height of bird flight, semi-desert looks like a carpet with an intricate speckled pattern.
Light stripes and spots correspond to cortical solonetz, and dark ones to areas of rather abundant vegetation.
Closer to the Caspian Sea, the land becomes more scarce, and the semi-desert gradually passes into the desert.
The gaze covers even more bare and dull spaces with clay soils on which rare wormwood bushes grow. There are areas of the present sandy desert in these places - the market is a sandpit (this is the name of an array of sands in the Caspian lowlands, and nowhere else).
Sandy waves stretch from horizon to horizon under the scorching sun. Most of the sands are fixed by plant roots. The fact is that in the sandy desert there is much more water than in the clay: the sand perfectly passes snow and rain water and keeps it from evaporation at depth. Therefore, plants with long roots easily coexist here, for example, elimus, or hair-nets - powerful, human-sized, grass. The hairy lush on the sandy slope from afar can be mistaken for a bush.
The brown soils of the deserts are extremely poor: from above — a thin, almost imperceptible layer of humus, below — a slight compaction connected with solonets — that is all.
Paradoxically, however, it is because of the harsh climate and poor vegetation that the animal world in semi-deserts and deserts is richer than in the steppes. The man did not have time to truly master these lands, they are used at best as pastures for sheep.
Of the permanent inhabitants here are the most rodents: gophers and jerboas, field mice, hamsters.
Here then there you can see a watchful gopher standing like a column. Seeing a man, he lets out a whistle, and at once all his neighbors hide, literally falling through the ground - into holes. Rodents feed mainly on herbs and their seeds, so the majority of these animals are not agricultural pests, as is commonly believed.
In winter, almost all rodents hibernate, some of them fall asleep for a long time and in the summer heat. Previously, steppe marmots (baibaki) lived here, but they turned out to be too good targets for hunters and were completely exterminated.
Rodents serve food to many predators, among which is the local chanterelle - korsak, and polecats, and various birds, and snakes. The abundance of the latter unpleasantly affects the novice - you must be very careful not to step on the viper or the snake.
Of the large animals, saiga are wonderful. At the beginning of the century, these northernmost antelopes were almost completely exterminated and survived only in remote areas of Kazakhstan.
But thanks to conservation measures, the number of saigas rapidly increased, and at the end of the 20th century. they again became inhabitants of the Caspian deserts and semi-deserts. The speed with which flocks of graceful animals jump, if disturbed, is amazing - up to 80 km / h!
In spring and early summer, many birds appear in the semi-desert, arranging nests right on the ground.
The only defense of many birds at this time is camouflage coloring. The very rapid development of chicks also avoids unnecessary risk.
By the end of June, the hubbub of a bird subsides, the grass burns out, and the dull colors of the semi-desert fade.
Life freezes for the time of unbearable summer heat.
Semi-deserts and deserts of Russia
Steppes are spaces with a vegetation cover of more or less xerophilic herbaceous plants. Steppe vegetation is found in those areas of the temperate zone, where summer is relatively hot and dry, and winter is more or less cold. The climate is characterized by continental and aridity.
The amount of precipitation is less than evaporation, therefore, throughout the entire summer period, the plants experience a lack of moisture.
Steppe soils, various types of black soil and chestnut soils are distinguished by high fertility.
The basis of vegetation cover is usually made up of turf grasses, a significant role is played by herbs. There are some shrubs, but in small quantities. Often there are ephemera and ephemeroids that develop in springtime, when there is enough moisture in the soil. A characteristic feature of the steppes is the absence of trees that cannot grow here due to unfavorable water supply conditions.
The steppe zone is located to the south of the forest zone in the middle of the continents and nowhere goes to the shores of the ocean.
In Russia, it forms a fairly wide band in the European part and in Western Siberia. In Eastern Siberia, the steppes have only island distribution.
As we move from north to south, the climate of the steppe zone becomes more and more arid, and as a result, the vegetation cover also changes. The northernmost part of the steppe zone forms a subzone of meadow steppes, or forest-steppe.
It is characterized by the fact that in it the herbaceous phytocenoses are combined with small forest areas, formed to the west of the Urals by oak, and in Western Siberia - by birch.
Forest-steppe represents a transitional zone in which forests and steppes occupy relatively equal positions.
Meadow steppes have a fairly high and dense grass cover, in which the grasses prevail. In appearance they resemble meadows. Typical plants of meadow steppes are: meadowsweet (Filipendulavulgaris , sage meadow (Salviapratensis ), coastal rump (Bromopsisriparia ), ovaceous pubescent (Helictotrichonpubescens ) and etc.
Further to the south is a subzone of these steppes.
Here the role of narrow-leaved turf cereals sharply increases. Tipchak prevails (Festucavalesiaca ) and various cobbles (Stipasalesskii, S. capillata ). Among the grasses, more drought-resistant species also prevail - Veronica Belovoylochnaya (Veronicaincana ), zopnik prickly (Phlomispungens ), some wormwood (Artemisiaglauca, A.
In the present steppes, seasonality is expressed in the growing season, during summer drought the plants become dormant, the steppe “burns out”, acquiring a yellow-brown color, and in early spring ephemera and ephemeroids bloom.
The southernmost is the subzone of deserted feather-fescue steppes.
Here narrow-leaved turf cereals absolutely dominate: fescue and cobbles. Herbs are very few. Grass cover is thin and low. Half-shrub wormwood begins to play an increasingly prominent role (Artemisiafrigida, A.
incana ), signifying the approach of a semi-desert.
The steppes of the European part of Russia and Western Siberia have much in common. The vegetation of the island steppes of Eastern Siberia, by contrast, is very peculiar.
Here there is, for example, a very special type — the nytelistnik steppes, in which the basis of the vegetation cover is not cereals, but the semi-shrub — the Siberian filament (Filifoliumsibiricum ). Mongolian elements are widespread in the flora of the steppes of Eastern Siberia.
Currently, most of the steppes are plowed and used as agricultural land.
Many medicinal plants grow in the steppe zone, for example, adonis spring (Adonisvernalis ), thermopsis lanceolate (Thermopsislanceolata ), pharmaceutical camomile (Chamomillarecutita ) and etc.
Semi-desert andthe desert common in areas with extremely dry, sharply continental climate.
The amount of precipitation is 3-4 times less than evaporation. The summer is exceptionally hot, and the winter is more or less frosty. Very large differences between low winter and high summer temperatures, as well as temperature fluctuations during the day in the summer. With a strong evaporation of soil solutions, salts accumulate in the upper soil horizons.
Soil salinization occurs.
A characteristic feature of the vegetation cover of the desert is its strong sparseness. Plants are located at a more or less significant distance from each other and are not closed by their above-ground parts.
In Russia, semi-deserts and deserts are located in the Caspian and Eastern Ciscaucasia.
Semi-deserts are located in the north of the zone and are characterized by transitional features from steppes to deserts.
Sparse wormwood-grass vegetation is widespread here. Soils contain less humus and are less fertile. For vegetation cover is characterized by pronounced spotting. On sandy soils, vegetation resembles a steppe (cereals dominate), on loamy and clayey soils - desert.
Towards the south, the climate is becoming more and more arid, the steppe grasses disappear from the vegetation cover, the semi-deserts give way to real deserts. Usually there are two subzones - the northern and southern deserts.
The northern deserts are characterized by more or less uniform moistening throughout the year, low winter temperatures, and the presence of snow cover in the winter, albeit thin and unstable.
The total amount of precipitation is small - 160-250 mm per year, the plants are almost always lacking moisture.
The zonal here is the vegetation that develops on clay soils - wormwood and wormwood and solyanka desert communities.
In the desert of this type dominate shrubs: various kinds of wormwood (Artemisiaterrae — albae, A. incana ) and leafless and almost leafless members of the haze family — biyurgun (Anabasissalsa ), cockpit (Atriplexcana ), teresken (Krascheninnikovia ) and others. The appearance of the northern clay desert is peculiar: separate rounded squat “bushes” of plants of grayish-green and green color are scattered on a yellowish-brown background.
Solyanka communities are formed on saline soils, where the types of saltvines dominate (Salsola ), anabasis (Anabasis ) and other halophytes.
For the northern deserts is characterized by the absence or slight participation in the vegetation cover of ephemera and ephemeroids.
On strongly saline, moist soils, edaphic-conditioned saline deserts are formed.
Succulent halophytes from the haze family dominate here: Sarsazan (Halocnemumstrobilaceum ), Soleros (Salicorniaeuropaea ), types of intelligence (Suaeda black saxaul (Haloxylonaphyllum ) - leafless large shrub or small tree up to 6-8 m high.
The subzone of the southern deserts is located outside Russia, in the territory of Central Asia.
The climate here is warmer, winter is relatively mild, sunny, mostly snowless. There is little precipitation (60-200 mm), with about half of their annual amount falling in spring. Summer is very hot and dry, drought lasts 3-4 months.
Zonal here are ephemeral deserts, whose vegetation is formed almost exclusively by herbaceous perennials - ephemeroids.
The appearance of such a desert varies dramatically in the seasons. Весной, когда в почве много влаги, пустыня представляет собой сплошной зеленый газон с густым, но низким травяным покровом.
К лету надземная часть растений полностью отмирает, остается только голая поверхность глинистой почвы, твердая и сухая.
Sandy deserts are most prevalent in the southern desert subzone. They are most favorable for plant life. High bushes and small trees dominate here: juzgun (Calligonum ), sand acacia (Ammodendronconollyi ), Circassian (Salsolarichteri ), white saxaul (Haloxylonpersicum ) and etc.
Deserts and semi-deserts serve as natural pastures for many species of domestic animals.
From medicinal plants there is harvested licorice smooth (Glycyrrhizaglabra , citrus wormwood (Artemisiacina ), leafless anabasis (Anabasisaphylla ), garmalu (Peganumharmala ) and etc.
In addition to zonal vegetation, intrazonal plant communities — meadows and marshes — are widespread in Russia.
Deserts are called extremely dry areas of the globe, poor in water and plant life.
According to UNESCO, deserts make up 23% of the area of all continents.
In Africa, almost all of the northern part of the continent belongs to deserts, from 12–15 ° N. to the shores of the Mediterranean. The largest desert of South Africa Namib stretches from the Atlantic coast to the south-east along the valley of the Orange River. In the central part of the continent there is a rocky semi-desert Kalahari.
The size of the desert is quite different.
So, for example, the Sahara occupies 7-8 million sq. Km, almost 25% of the total area of the African continent. The desert climate is characterized by high air temperatures. The average temperature of the shade in summer exceeds 25 °, often reaching 50 °. The maximum temperature (+ 58 °) was recorded in Az-Zawiya (in Libya).
Extremely high intensity of direct solar radiation, due to the high transparency of the air and low clouds. The annual total radiation in North Africa is 200–220 kcal / sq. cm (in the middle lane, near St. Petersburg, - 80 kcal / sq. cm).
Under sunlight, the soil heats up to 70-80 °. Metal objects are so hot that touching them can cause a burn.
In the deserts of the tropical belt (Sahara) there is no clearly defined seasons, but still the winter period is more favorable for the existence of man.
In October-March, the average temperature does not rise above 10–12 °. The minimum night temperature rarely drops to 0 °, but in December — February, at elevated places, frost often occurs with a decrease in temperature to minus 14 °. In the afternoon with the rising sun the temperature quickly rises, reaching 25–30 °.
The most important feature of the desert is extreme poverty. During the year, they fall no more than 100-200mm.
In a number of areas of the Libyan and Nubian deserts, their number approaches zero. Rainfall is a rarity. But sometimes these rare rains fall in the form of stormy rains, accompanied by thunderstorms.
This is how the English traveler A. Buchanan describes such a “flood” in the Sahara: “The view of the whole area instantly changed, boiling streams appeared everywhere, merging, they gradually grew to alarming proportions.
Behind us, from the hills, came the faint murmur that was coming nearer, and we watched in the course of time, like a rage, tipping everything in its path, little river. She rushed like a tidal wave to the sandy coast, however, having reached it, did not break, and under pressure the water behind us swept past our camp to the south, leaving a riverbed filled with water ... We looked at the flooded area and remembered that several hours ago we unsuccessfully searched for drinking water here. ”
Desert air is extremely dry, and this is one of the most important features.
Daytime relative humidity varies from 5 to 20%, rising to 20 to 60% at night. More favorable are the climatic conditions of deserts located in the coastal zone of the Atlantic Ocean and the Persian Gulf, where the climate is somewhat mitigated by their influence.
Here there is a higher air humidity (up to 80 - 90%), the daily temperature sweeps are less, dew and fogs periodically fall out.
The climatic characteristics of the desert would be incomplete if not to mention the wind, which is called the great host of the desert.
As the Arab proverb says, “in the Sahara the wind rises and falls together with the sun”. It was not by chance that the locals called the desert windy names. Such are the Sahara Sirocco, the Gebli, the Khamsin of the Libyan Desert. But as if they were called, they are all hot, dry, dusty, differing in a certain constancy of direction, duration, frequency of appearance.
Cirocco, for example (he is a shekhili, ifri), in Africa blows several times a month from May to October.
Winds often turn into a dust storm. In one day, a veterinarian can carry a million tons of dust from the Sahara.
If it was loaded in railway cars, the train would be 400 km long. The air temperature this time rises to 48-50 ° C, accompanied by a sharp drop in humidity.
In the ordinary view of people, the desert is a vast ocean of sand.
These are endless chains of sandy hills, sometimes like yellow-brown waves, sometimes resembling multi-rayed stars, sober-like, like a scimitar, dunes, or round oghurds. Sometimes sand deposits are only slightly elevated above the surface, like a sea swell, sometimes rising to a height of tens or even hundreds of meters.
Sand dunes may be parallel ridges separated by broad valleys (ridge sands), or
They are countless flat hills with uneven slopes, called hilly.
And the latticed dunes scattered in all directions create such confusion that even an experienced desert connoisseur may lose orientation and wander aimlessly in the maze of sands for many hours.
However, most of the deserts can not be called the kingdom of sand, as pure sand often takes up no more than 10-15% of their surface.
The “sandy sea” of the Sahara is only 10% of its surface, and more than 70 — these are the endless rocky plateaus of the “hamad” ... separated by shallow valleys — depressions. Their surface is dotted with silicon gravel, calcined by the sun. Sometimes it is covered with a black glossy shell, “desert varnish”, the Kli “desert tan.” - a precipitate of iron and manganese salts precipitated from the groundwater that has risen to the surface.
And among these debris ringing under the traveler's notes, dusty, stunted stalks of wormwood and bluegrass make their way. The central euryons are low mountains lacking in vegetation. From time to time the dead silence of mountain gorges is announced by sharp sounds like shots, sounds. Rocks under the influence of temperature drop are filled with rock fragments forming shallow debris in places.
Another type of desert topography is the “serir” -sandy plain, covered with fine gravel, or flat endless surfacesfrom destroyed rocks.
A person who finds himself in a “series” feels as if in the center of a flat disk, which has not a single reference point.
For deserts, the so-called takyrs are very characteristic - huge, stretching for many kilometers, lifeless areas, covered with a table-like solid clay layer, cracked on innumerable 4-6-faced tiles.
The clay layer does not let in water, which soon dries up, and the clay hardens again and cracks.
But more often, deserts represent a complex, diverse mosaic of stony and clayey plateaus, hilly sands, closed drainage basins, isolated mountain elevations, salt marshes and takyrs.
The large waterways of the desert, such as the Nile, the Niger in Africa, originate far from the desert areas and, crossing them, enliven only a narrow strip of land along its bed, having almost no effect on the rest of the vast desert territory.
The hydrographic network of deserts is mainly represented by drying channels, in which water flows only during the rainy period, disappearing after a few days or weeks.
All water forming a more or less long-term drain is rainwater. True, in the mountainous regions there is a small amount of flow of streams, but almost all of them are quickly lost in the sands, or, at best, flow into an indoor pool, which is a dry-saline lake.
Heavy rainfalls occurring once every 3-4 years sometimes form powerful, destructive streams breaking through short, but deep, steep valleys, subsequently drying out, called “wadi”.
A dense network of vadipok 200-250-kilometer strip along the entire coast of the Red Sea, spreading to the west of it, to the valley of the Nile. During the rain, mills walk through such a valley, sweeping away all life on the way. Therefore, the locals at the first sign of a threat rush to climb as high as possible so that they can wait out the weather in a safe place.
At the same time, showers give life to numerous small natural wells. They are located at a shallow depth due to water seeping into the ground.
Lakes often contain salt or bitter-salt water, unfit for drinking. The main source of fresh water in the desert zone is groundwater and condensation water. Condensation waters of shallow depth are formed due to the penetration of rare rain and water into the sand mass, which condenses out of the atmosphere during a sharp decrease in air temperature at night.
The horizons of fresh water in the Sahara are located at a depth of 3-5 to 20-30 m. Often fresh water forms a kind of lens that floats on top of heavily mineralized, heavier water. As water is being dispersed, as a result of diffusion processes, salinization occurs more gradually.
The Foggars of the Western Sahara represent a peculiar water supply system.
This is a chain of wells, starting near the reservoir or the old river bed, interconnected by tunnels.
In the mountainous regions and foothills, water can be found in the indentations and crevasses, where, after rain, it persists for several weeks and even months.
Most caravan roads, motorways, paths, as a rule, go through water sources. The distances between them are usually great, sometimes 100 km or more.
One of the features of the desert and the consequence of its climatic conditions is the poverty of the plant world.
Some areas of the desert, especially stony, rubble, clay and isolonak, are almost completely devoid of vegetation ./>
Only areas of permanent water sources - oases - are truly rich in vegetation.
Bright green crowns of date palms. In the dense foliage of olive trees, birds chirping, cicadas ringing. A traveler after a grueling trip through the sands can relax in the cool shade of orange groves. Here you can see peaches and lemons, figs and quinces.
But how insignificantly small islands of life in the vast ocean of the desert! Of the millions of square kilometers of Saharyn, the share of oases is only 350 square meters.
When moving from the zone of steppes, semi-desert and savannahs to the desert as the plant world diminishes, the fauna also becomes poor. Living creatures on salt marshes and takyrs are rarely found.
However, their complete disappearance should be considered an exceptional phenomenon.
Where there is at least some vegetation, you can always meet living creatures. Many of them, avoiding the damaging effects of sunlight, are nocturnal, climbing into the holes in the daytime. At 30–40 cm from the surface, the sand is more humid and cool, and at a depth of 1–1.5 m, the temperature for a year round is between 10–170 at any time of day.
The fauna of the desert is not diverse, although some individuals are quite numerous.
Nevertheless, the desert biomass (the amount of living matter per unit area) is very small. Thus, for ungulates, the Sahara's biomass is 0.003–1.9 g / ha, while in the Central African and East African savannas it is up to 235 g / ha.
In African deserts mammals are represented by several species of antelope, jackals, hyenas.
Typical representatives of ungulates for the Central Asian deserts are gazelles, saigas. Of rodents in the deserts can be found taraboganov, gophers, jerboas, marmots, gerbils. Reptiles are represented by numerous lizards, various species of snakes, of which many are poisonous (cobra, gyurza, ef, sand viper, etc.). In the spring, many different birds nest near the reservoirs.
For example, 74 species of birds are found only in the Sahara. The world of insects has more than 500 species of beetles, grasshoppers, ants, praying mantis, representatives of Diptera and hymenoptera.
High air temperature, intense solar radiation, strong winds, lack of water sources create extremely unpleasant conditions for autonomous human existence in the desert. It is known that in the desert the human body receives an enormous amount of heat from the outside — more than 300 kcal / hour.
It comes from all sides: with a stream of sunlight, from the glowing heat of the sand and sultry wind.
To reduce the flow of exogenous heat and heat production of the organism, to increase the heat transfer - this is the task that confronts people in the desert. It can be solved in three ways: the construction of a sun cover by limiting physical activity, rational use of available water reserves.
Since the bulk of the heat (up to 72%) comes from solar radiation, the simplest sun canopy can reduce its influx by 72–114 kcal / hour. In addition, an awning saves a person from receiving 100kkal / hour, which he would receive by holding heat from a heating sand.
To take off all your clothes - the first desire of a person when it becomes hot.
But in the desert this should not be done. Clothing not only protects the skin from direct sunlight, but also significantly prevents the drying and overheating effects of hot air.
Finding water in the desert is difficult, but not as hopeless as it may seem at first glance.
But where to look for water, if there seemed to be no sign of it: Niderevtsa, not a bush, only endless chains of yellow-brown sand dunes? However, sometimes it is worthwhile to dig deeper into the lowland of the old dried bed or in a hollow at the foot of the dune on the leeward side - and good luck will come. First, dark, damp sand will appear at a depth of one to two meters, and after a while the excavated hole will gradually fill the ground water.
And it is not by chance that the Kazakhs — experts of the desert nature say: “Kum bar - sous bar!” This means: where sand is water there! />
Desert connoisseurs believe that the higher and bare the barchan chains, the deeper the hollows between them, the greater the chances of success.
In the mountain-desert terrain, the source can be found at the foot of the mountain plateaus, on steep slopes. The water leaks out of the beds, covering the rock with thick drops, or is hidden by subtle breaking of the soil.
Often, after the last rains, the water accumulates in the depressions at the base of the rocks, along the edges of the pebble scree.
The proximity of groundwater is sometimes indicated by the swarming of midges and mosquitoes, observed after sunset, bright green patches of vegetation among vast expanses of bare sand.
In search of water often help some plants. In the African deserts, the date palm serves as such an indicator of the subsoil source.
In addition to natural water sources in the waste there are artificial reservoirs - wells. It is they who support the power of izhi people during the many days of grueling crossings over the sandy ocean. The well is usually located not far from the caravan road, but it is tactfully sheltered from the sun that an inexperienced person can walk two steps away, not suspecting its existence.
Meanwhile, the water in the desert can be obtained directly ... from the sand, with the help of the so-called solar capacitors.
The fact is that sand is never completely dry. Its capillary forces firmly hold a small amount of moisture, which, paradoxically, does not evaporate into the sun-baked, sun-dried desert air. The basis of the design of the solar capacitor is a thin film of transparent, water-repellent plastic. For a day, one capacitor can give up to 1.5 liters of water.
Semi-desert - a landscape that combines areas of steppes and deserts, found in temperate, subtropical and tropical zones of the Earth and forms a natural zone located between the steppe zone in the north and the desert zone in the south.
The strongly rarefied vegetation cover of the semi-desert often appears in the form of a mosaic consisting of perennial xerophytic grasses, turfy cereals, saltworms and wormwood, as well as ephemera and ephemeroids.
Succulents are common in America, mainly cacti. In Africa and Australia, thickets of xerophytic shrubs and sparsely low-growing trees (acacia, doom palm, baobab, etc.) are typical.
Semi-deserts, also called desert steppes, serve as a transitional zone between steppes and deserts: they contain steppe vegetation consisting of xerophytic herbs mixed with mesophilic, and plants of the desert type (wormwood, solyanka).
Photo: Udo Schmidt
Vegetation of semi-deserts in the same climatic conditions is determined by the nature of the soil. On this basis, it is reduced to the following three basic formations:
а) растительность на суглинистых и глинистых почвах, представляющих пятнистую комплексную полупустыню, в которой наряду с ксерофитными разнотравно-злаковыми растениями большое место занимают прутняково-чернополынные ассоциации на солонцах,
б) растительность на песках и песчаных массивах (Черные земли, Прикумские песчаные массивы и т.
c) vegetation on flood meadows-limans, located mainly in the lower reaches of semi-desert rivers.
On loamy and clayey soils, slightly saline and poorly moistened, grow a fescue, Lessing wadding, white wormwood and chamomile.
Also characteristic here are kohiya creeping, grazing grass and a few annuals. Herbage is very rarefied, the development of ground mass is insufficient.
In the solonetz vegetation is represented mainly by black polynya, white polynya, prutnyakom.
In addition, camphor, kohia, wheatgrass, spring annuals and lower plants - algae, lichens and mosses are found in large numbers on these soils.
In basins with dark-colored soils, a more moisture-loving type of vegetation develops - grass steppe.
The vegetation in the grassy steppe is more dense, a significant proportion in the herbage is occupied by a fescue, a cobblestones, a keleria, and a harp; sometimes a large number of steppe grasses are mixed in.
The composition of plants developing on sand and sand massifs depends on the nature of the sand.
Vegetation on moving sand dunes consisting of individual hills 4–20 m or more or from a ridge of these hills is poor, on the tops most often there are no plants, on the slopes of the dunes and in depressions between them (blowing depressions) there are individual bushes or small Kumarchik and kiyak thickets, which are mixed with swollen sedge, Colchian sedge, sand wormwood, dzhuzgun, solyanka and other plants.
In the semi-deserts, an even sharpening of the grass stand is observed than in the steppes.
The dominant associations are grass-wormwood. The microrelief determines the diversity of soil and vegetation cover, determines its microcomplexity.
In the northern part of semi-deserts, where moisture conditions are somewhat better, cereals dominate, wormwood plays a subordinate role.
In the southern part of wormwood dominate, here are abundantly represented solyans. The short stature of plants helps to reduce evaporation, and a developed root system ensures maximum use of soil moisture.
White wormwood is common on slightly saline soils, black wormwood is more common on more saline soils. In black wormwood, the leaves open after the rain, in the driest season, the plant drops them, the root system of wormwood is distributed to a depth of more than 1 m. Black wormwood is ethereal. Perennials are characteristic of grasses, especially a lot of fescue, pinnose hairs dominate from curls. The squat shrub is characteristic.
In the spring in semi-desert ephemeroids bloom: tulips, buttercups, viviparous bluegrass, goose onions, green ephemera.
Black wormwood, camphor, prutniak, ebelek or weary-field, biyurgun grow on solonetz. On salt marshes typical solyanka.
On free-flowing sands, grassy hairs of up to 1.5 m height grow well-consolidating them, on poorly wavy sandy areas - Siberian grass-stock, chiy, in the hollows of shrubs - willow, goof. When fresh groundwater is near, white poplar, willow, and wild rose grow in the river valleys. On sandy soils closer to the deserts occurs rubber - chondrillum.
Farming in semi-deserts is possible under the condition of artificial irrigation.
Due to the abundance of the sun, valuable industrial crops are grown here, especially cotton. Semidesert vegetation mainly in springtime is used for cattle grazing.
Vegetation in the semi-desert is special - wormwood and ephemeroids dominate here - perennial grasses that quickly fade, but keep their organs in the ground (tubers, bulbs, etc.). There are plants and ephemera, the whole development cycle from birth to death, they manage to pass in two to three months.
Such, for example, is a tiny grass. In ordinary years, the plant is inconspicuous - it barely has time to collect two or three “onions” in its ear (in fact, these are germinated seeds). But in especially wet years, the whole plain is covered with green cover from edge to edge.
Despite the seemingly dull monotony of semi-desert landscapes, its vegetative and soil cover is a kind of mosaic. On a flat, seemingly ground land there are usually numerous rises and falls. They barely reach several centimeters in height and depth, but this is enough for noticeable differences in moisture.
During rains or melting snow, water quickly drains into depressions. The soil in them is not only soaked to a greater depth and stores moisture, but also freed from salts. Here, as well as in the steppe, the perennial grass of fescue, many grasses grows. The soil in the depressions is also in many respects similar to the steppe: it is dark from humus and very fertile. And on elevations, the soil is moistened a little, the water evaporates quickly, and salt solutions are pulled from the depth to the surface.
In such areas, even black wormwood feels bad. Most often, they are covered with a specific layer of soil - the cortical saline, saline land is located here already at the depth of the spade bayonet.
How do deserts and semi-deserts arise?
There are many reasons why deserts arise. For example, there is little rainfall in the Atacama Desert because it is located at the foot of the mountains, which with its crests cover it from the rain.
Ice deserts were formed for other reasons. In Antarctica and the Arctic, the main mass of snow falls on the coast, to the inner regions of the snow clouds almost do not reach. Rainfall mainly varies greatly, for one snowfall, for example, the annual norm can fall. Such snow deposits are formed over hundreds of years.
Hot deserts are distinguished by the most diverse relief. Only some of them are completely covered with sand. The surface of the majority is dotted with pebbles, stones and other various rocks. Deserts are almost completely open to weathering. Strong gusts of wind pick up fragments of small stones and hit them on the rocks.
In sandy deserts, the wind carries sand across the territory, creating undulating sediments called dunes. The most common type of dunes - dunes. Sometimes their height can reach 30 meters. The ridge dunes can have a height of up to 100 meters and extend for 100 km.
The climate of deserts and semi-deserts is quite diverse. In some regions, daytime temperatures can reach up to 52 o C. This phenomenon is due to the absence of clouds in the atmosphere, thus, nothing saves the surface from direct sunlight. At night, the temperature is greatly reduced, which again is explained by the absence of clouds that are able to trap the heat emitted by the surface.
In hot deserts, rain is a rare phenomenon, but sometimes there is heavy rainfall. After the rain, the water is not absorbed into the soil, but rapidly drains from the surface, washing away particles of soil and pebbles into dry channels, which are called wadis.
Location of deserts and semi-deserts
On the continents, which are located in northern latitudes, there are deserts and semi-deserts of the subtropical and temperate zones. Sometimes there are also tropical - in the Indo-Gangetic lowland, in Arabia, in Mexico, in the south-west of the United States. In Eurasia, the extratropical desert regions are located in the Caspian lowland, on the Central Asian and South Kazakh Plain, in the basin of Central Asia and in the Near Eastern highlands. The Central Asian desert formations have a sharply continental climate.
In the southern hemisphere, deserts and semi-deserts are less common. There are such desert and semi-desert formations as Namib, Atacama, desert formations on the coast of Peru and Venezuela, Victoria, Kalahari, Gibson Desert, Simpson, Gran Chaco, Patagonia, the Great Sandy Desert and the Karoo semi-desert in southwestern Africa.
The polar deserts are located on the mainland islands of the glacier regions of Eurasia, on the islands of the Canadian Archipelago, in northern Greenland.
For many years, the animals of the deserts and semi-deserts in such areas have been able to adapt to the harsh climatic conditions. From cold and heat, they hide in underground burrows and feed mainly on underground parts of plants. Among the representatives of the fauna there are many species of carnivores: Fenek fox, reed cats, cougars, coyotes and even tigers. The climate of deserts and semi-deserts has contributed to the fact that many animals have developed an excellent thermoregulation system. Some desert dwellers can tolerate fluid loss up to a third of their weight (for example, geckos, a camel), and among invertebrates there are species that can lose water up to two-thirds of their weight.
In North America and Asia, there is a mass of reptiles, especially many lizards. Snakes are also quite common: efy, various poisonous snakes, strangers. Of the large animals, there are saiga, kulans, camels, pronghorn, the Przewalski horse has just disappeared (you can still see it in captivity).
The animals of the desert and semi-deserts of Russia are a wide variety of unique representatives of the fauna. In the desert regions of the country there are hares, sandstones, hedgehogs, kulan, jaiman, poisonous snakes. In the deserts that are located on the territory of Russia, you can also find 2 types of spiders - karakurt and tarantula.
Polar deserts are inhabited by polar bears, musk oxen, arctic fox and some species of birds.
Deserts and semi-deserts: soil
The soil is, as a rule, poorly developed, in its composition water-soluble salts predominate. Among the soil-forming rocks, ancient alluvial and loess-like sediments predominate, which are processed by winds. Gray-brown soil is inherent to elevated plain areas. Deserts are also characterized by salt marshes, that is, soils that contain about 1% of readily soluble salts. In addition to deserts, salt marshes are also found in steppes and semi-deserts. Groundwater, which contains salt, when it reaches the surface of the soil is deposited in its upper layer, resulting in salinization of the soil.
Completely different soil types are characteristic of such climatic zones as subtropical deserts and semi-deserts. The soil in these regions has a specific orange and brick red color. Due to its shades, it received the appropriate name - red and yellow. In the subtropical zone in northern Africa and in South and North America there are deserts where serozems have formed. Red-yellow soils have formed in some tropical desert formations.
Natural areas of the desert and semi-desert - a huge variety of landscapes, climatic conditions, flora and fauna. Despite the harsh and cruel temper of the desert, these regions have become home to many species of plants and animals.