What is a desert?

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llltkl | College Teacher | (Level 3) Valedictorian

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Deserts, arid lands, are one of the most extensive environments on the planet, comprising up to 40% of the terrestrial surface. They are mainly found around the Tropics of Cancer and Capricorn.

Typically, a desert is defined as an area that is characterized by having little and unpredictable rainfall; less than 250 mm per year. But a more important factor is that deserts have a strong tendency to lose water by evaporation, and this potential for water loss exceeds the annual rainfall. These areas may be the result of various factors such as high pressure zones, continentality, cold ocean currents, and/or rain shadows.

So, deserts are characterised by having sparse vegetation, and the organisms that live in deserts are specially adapted to withstand or avoid water stress.

Deserts are natural laboratories in which to study the interactions of wind and sometimes water on the arid surfaces of planets. They contain valuable mineral deposits that were formed in the arid environment or that were exposed by erosion. Because deserts are dry, they are ideal places for human artifacts and fossils to be preserved. Deserts are also fragile environments. The misuse of these lands is a serious and growing problem in parts of our world.

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ssarfraz | Student, Professional | (Level 2) Honors

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Deserts are large dry areas that contains different plants and animals that are adaptive to harsh environments.

According to some definitions, any environment that is almost completely free of plants is considered desert, including regions too cold to support vegetation—i.e., “frigid deserts.” Other definitions use the term to apply only to hot and temperate deserts, a restriction followed in this account.

Origin

late Middle English: from Old French deserter, from late Latin desertare, from Latin desertus 'left waste' (see desert2).

Basic Facts of Deserts

Deserts are found across our planet along two fringes parallel to the equator at 25–35° latitude in both the northern and southern hemispheres. Deserts are arid or dry regions and receive less than 10 inches of rain per year. Biologically, they contain plants and animals adapted for survival in arid environments. Physically they are large areas with a lot of bare soil and low vegetation cover. The world’s deserts occupy almost one-quarter of the earth’s land surface, which is approximately 20.9 million square miles.

Deserts receive little rainfall, however, when rain does fall, the desert experiences a short period of great abundance. Plants and animals have developed very specific adaptations to make use of these infrequent short periods of great abundance.

Types of Desert

  • Hot and dry deserts

The hottest type of desert, with parched terrain and rapid evaporation. In the hot and dry desert soils are course-textured, shallow, rocky or gravely with good drainage and have no subsurface water. They are coarse because there is less chemical weathering. The finer dust and sand particles are blown elsewhere, leaving heavier pieces behind.

  • Cool coastal deserts

These deserts are located within the same latitudes as subtropical deserts, yet the average temperature is much cooler because of frigid offshore ocean current. In the coastal desert the soil is fine-textured with a moderate salt content. It is fairly porous with good drainage.

  • Semi arid deserts

These deserts are located within the same latitudes as subtropical deserts, yet the average temperature is much cooler because of frigid offshore ocean current. In the coastal desert the soil is fine-textured with a moderate salt content. It is fairly porous with good drainage.

Desert Formation

Deserts landscapes are more diverse than many expect. Some are found on a flat shield of ancient crystalline rocks hardened over many millions of years, yielding flat deserts of rock and sand such as the Sahara. Others are the folded product of more recent tectonic movements, and have evolved into crumpled landscapes of rocky mountains emerging from lowland sedimentary plains, as in Central Asia or North America .

Characteristics of Deserts

  1. Different types; i.e. Hot, Cold and Dry
  2. Different types of deserts contains different types of plants and animals.
  3. Deserts receive little rain throughout the year
  4. Deserts will often be extremely hot during the day and less hot at night. Because of the reason that there is little evaporation in the atmosphere to block sunlight during the day and at night allows heat to escape easily.
  5. Some deserts are made of very fine, red sand, others consist of sand mixed with pebbles and rocks.
  6. In deserts, mostly minerals, and sometimes oil can be found hidden deep within the rocks.

A few of worlds famous deserts are as follows:

  • Sahara Desert
  • Sonoran desert
  • Atacama desert

The deserts of the world occur in six global bio-geographical realms:

  1. Afrotropic deserts, found in the sub-Saharan part of Africa, and in the southern fringe of the Arabian Peninsula. Pressures on the ecosystem from humans are relatively high, especially in the Horn of Africa and Madagascar.
  2. The Australasian deserts comprise a series of lowland arid ecoregions in the Australian heartland. Hardly inhabited, their mean population density is less than 1 person per square kilometer. They have by far, the lowest human footprint among the global deserts.

  3. The Indo-Malay region has two hot lowland deserts: the Indus Valley and the Thar. These are the deserts with the most intense human use in the world.

  4. The Nearctic deserts cover 1.04 million square miles in North America. Because of the growth of large urban conglomerates such as Phoenix in the United States, their mean population density is high.

  5. The Neotropic deserts in South America cover 684,000 million square miles, of which only 6 per cent receives legal protection..

  6. The Paleartic realm concentrates the largest set of deserts in the world, covering a remarkable 9.9 million square miles that total 63 per cent of all deserts on the planet and are known for their sheer inaccessibility and extreme aridity. The Sahara occupies 9 million square miles, or 10 per cent of the African continent. In contrast, the deserts of Central Asia have folded mountains with high landscape heterogeneity and enclosed basins.

Where deserts form

Dry areas created by global circulation patterns contain most of the deserts on the Earth. The deserts of our world are not restricted by latitude, longitude, or elevation. They occur from areas close to the poles down to areas near the Equator. The People's Republic of China has both the highest desert, the Qaidam Depression that is 2,600 meters above sea level, and one of the lowest deserts, the Turpan Depression that is 150 meters below sea level. Deserts are not confined to Earth. The atmospheric circulation patterns of other terrestrial planets with gaseous envelopes also depend on the rotation of those planets, the tilts of their axes, their distances from the Sun, and the composition and density of their atmospheres. Except for the poles, the entire surface of Mars is a desert. Venus also may support deserts.

Classification of Deserts

Deserts are classified by their geographical location and dominant weather pattern.

  • Trade wind Deserts
  • Mid Latitude Deserts
  • Rain Shadow Deserts
  • Coastal Deserts
  • Monsoon Deserts
  • Polar Deserts
  • Paleodeserts
  • Extraterrestrial deserts

Desert Plants

Most desert species have found remarkable ways to survive by evading drought. Desert succulents, such as cacti or rock plants (Lithops) for example, survive dry spells by accumulating moisture in their fleshy tissues. They have an extensive system of shallow roots to capture soil water only a few hours after it has rained. Additionally, many cacti and other stem-succulent plants of hot deserts present columnar growth, with leafless, vertically-erect, green trunks that maximize light interception during the early and late hours of the day, but avoid the midday sun, when excessive heat may damage plant tissues.

One of the most effective drought-survival adaptations for many species is the evolution of an ephemeral life-cycle. An ephemeral life cycle is characterized by a short life and the capacity to leave behind very hardy forms of propagation. This ability is found not only in plants but also in many invertebrates. Desert ephemerals are amazingly rapid growers capable of reproducing at a remarkably high rate during good seasons.

Desert Animals

Birds and large mammals can escape critical dry spells by migrating along the desert plains or up into the mountains. Smaller animals cannot migrate but regulate their environment by seeking out cool or shady places. In addition to flying to other habitats during the dry season, birds can reduce heat by soaring. Many rodents, invertebrates, and snakes avoid heat by spending the day in caves and burrows searching out food during the night. Animals active in the day reduce their activities by resting in the shade during the hotter hours.

Mineral Resources found in Deserts:-

  • Gypsum
  • Salt
  • Borates
  • Sodium Nitrate
  • sodium Chloride
  • Boron
  • Borax
  • Copper
  • Iron
  • Chromite
  • Uranium Deposits

Structure and Function:

The different components of a desert ecosystem are:

(A) Abiotic Component:

The abiotic component includes the nutrients present in the soil and the aerial environment. The characteristic feature of the abiotic component is lack of or­ganic matter in the soil and scarcity of water.

(B) Biotic Component: The various biotic components representing three functional groups are:

1.  Producer organisms:

The producers are mainly shrubs or bushes, some grasses and a few trees. Surprisingly, there are many species of plants that survive in the desert. Most of them are succulents, which mean they store water. Others have seeds that lay dormant until a rain awakens them. Regardless, these plants find a way to get water and protect themselves from the heat.

The most famous desert plant is the cactus. There are many species of cacti. The saguaro cactus is the tall, pole shaped cactus. The saguaro can grow up to 40 feet tall. It can hold several tons of water inside its soft tissue. Like all cacti, the saguaro has a thick, waxy layer that protects it from the Sun.

Other succulents include the desert rose and the living rock. This strange plant looks like a spiny rock. It’s disguise protects it from predators. The welwitschia is a weird looking plant. It has two long leaves and a big root. This plant is actually a type of tree and it can live for thousands of years.

There are many other kinds of desert plants. Some of them have thorns others have beautiful flowers and deadly poisons. Even in the worst conditions, these plants continue to thrive.

2.  Consumers:

These include animals such as insects and reptiles. Besides them, some rodents, birds and some mammalian vertebrates are also found.

  • Desert Insects and Arachnids:

There are plenty of insects in the desert. One of the most common and destruc­tive pests is the locust. A locust is a special type of grasshopper. They travel from place to place, eating all the vegetation they find. Locusts can destroy many crops in a single day.

Not all desert insects are bad, though. The yucca moth is very important to the yucca plant, because it carries pollen from the flower to the stigma. The darkling beetle has a hard, white, wing case that reflects the Sun’s energy. This allows the bug to look for food during the day.

There are also several species of ants in the desert. The harvester ants gather seeds and store them for use during the dry season. And the honey pot ants have a very weird habit. Some members of the colony eat large amounts of sugar, so much that their abdomens get too large for them to move. The rest of the colony feeds off this sugar.

There are also arachnids in the desert. Spiders are the most notable arachnids, but scorpions also belong in this group. Some species of scorpions have poison in their sharp tails. They sting their predators and their prey with the piercing tip.

  • Desert Reptiles:

Reptiles are some of the most interesting creatures of the desert. Reptiles can withstand the extreme temperatures because they can control their body tem­peratures very easily. You can put most of the desert reptiles into one of two categories: snakes and lizards.

Many species of rattlesnakes can be found in the desert. Rattlesnakes have a noisy rattle they use to warn enemies to stay away. If the predator isn’t careful, the rattlesnake will strike, injecting venom with its sharp fangs. Other desert snakes include the cobra, king snake and the hognose.

Lizards make up the second category of desert reptiles. They are probably the most bizarre looking animals in the desert. While some change colors and have sharp scales for defense, others change their appearance to look more threaten­ing.

One such creature is the frilled hazard. When enemies are near, the lizard opens its mouth, unveiling a wide frill. This makes the hazard look bigger and scarier. The shingle back has a tail with the same shape as its head. When a predator bites at the tail, the shingle back turns around and bites back. There are only two venomous lizards in the world, and one of them is the gila monster. It has a very painful bite.

  • Desert Birds:

Like the other inhabitants of the desert, birds come up with interesting ways to survive in the harsh climate. The sand grouse has special feathers that soak up water. It can then carry the water to its young trapped in the nest.

Other birds, like the gila woodpecker, depend on the giant saguaro as its home. This woodpecker hollows out a hole in the cactus for a nest. The cool, damp inside is safe for the babies.

The roadrunner is probably the most well known desert bird. Roadrunners are so named because they prefer to run rather than fly. Ostriches also prefer to use their feet. Even the young depend on walking to find food and water. The galah is one of the prettiest desert birds. It is one of the few species that return to the same nest year after year.

Galahs are interesting birds, in that the number of eggs they lay depends on the climate. If the desert is in a drought, they don’t lay any. However, during more tolerable years, the galah may lay as many as five eggs.

  • Desert Mammals:

There are several species of mammals in the desert. They range in size from a few inches to several feet in length. Like other desert wildlife, mammals have to find ways to stay cool and drink plenty of water. Many desert mammals are burrowers.

They dig holes in the ground and stay there during the hot days. They return to the surface at night to feed. Ham­sters, rats and their relatives are all burrowers. Not only do the burrows keep the animals cool, they are also a great place to store food.

Of course, not all animals have in holes in the ground. The kangaroo and spiny anteater both live in the Australian desert region. Spiny anteaters are unusual mammals because they lay eggs.

The desert is also full of wild horses, foxes and jackals, which are part of the canine family. And we can’t forget the cats. Lions are found all over the deserts of southern Africa. They get their water from the blood of their prey.

  • Camels – The Cars of the Desert:

Camels could be included in the mammal section. Camels are the cars of the desert. Without them, people would have great difficulty crossing the hot ter­rain. There are two types of camels: Bactrian and dromedary. The main differ­ence between the two is the number of humps. Dromedaries have one hump, and Bactrian have two. Both kinds are used by people, but only Bactrian’s are found in the wild.

Camels are great for transportation because they use very little water. Camels can withstand very high temperatures without sweating. They also store fat in their humps for food. If a Bactrian camel travels a long distance without eating, its hump will actually get smaller.

3.  Decomposers:

Due to poor vegetation the amount of dead organic matter is very less. As a result the decomposers are very few. The common decomposers are some bacte­ria and fungi, most of which are thermophile.

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amysor | Student, Grade 10 | (Level 1) Valedictorian

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A desert is a type of biome. It has dry land, and very little water. Although, most deserts have sand, but not all, as Antartica is a desert as well. Most animals or plants that grow in the desert, only exist in the desert because they are accustomed to the dry land and little water. I have also attached a pdf, that describes major biomes, including the characteristics of a desert in more detail. 

Sources:
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parama9000 | Student, Grade 11 | (Level 1) Valedictorian

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A desert is a dry region with no body of water nearby. This means that Antarctica is a desert!

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nyteacher1212 | Elementary School Teacher | eNotes Newbie

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A desert is a dry region of land which has no body of water nearby. They usually are large, such as a Sahara Desert in Africa. Few animals and plant life exist in this tough, dry terrain. One great example is a cactus which can survive in this region because it's capable of storing water from the few rains that it's environment gives it. Some small creatures such as mice can survive in deserts as well due to their ability to burrow underground where temperatures are cooler.

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