Deserts alone cover about seventh of the land surface. We normally call deserts as “sand seas or oceans of sands”. Most of the major desert areas like as the Sahara, the Arabian, the Kalahari, and the Deserts of Australia all lie between 10 and 30 degrees north or south of the equator. Deserts are dry ecosystems comprising a substantial part of the globe. Deserts are to be fully understood in earth science studies. This report is about the Deserts as unique landforms.

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DESERT ECOLOGY
By
Prof.A. Balasubramanian
Centre for Advanced Studies in Earth Science,
University of Mysore, Mysore
Introduction:
While studying the physical features and geomorphology of landforms, a very unique nature of
landmass comes into our mind. It is very unique in various aspects. That is the dry landmass called
as the Desert. Earth has numerous land areas covered by deserts. Among all the terrestrial
ecosystems, deserts are very typical landforms due to their unique ecological conditions. Desert
and near-desert areas cover nearly one-third of the land surface of the globe .
Deserts alone covers about seventh of the land surface.
We normally call deserts as “sand seas or oceans of sands”. Most of the major desert areas like as
the Sahara, the Arabian, the Kalahari, and the Deserts of Australia all lie between 10 and 30
degrees north or south of the equator. Deserts are dry ecosystems comprising a substantial part of
the globe. Deserts are to be fully understood in earth science studies. This report is about the
Deserts as unique landforms.
Objectives:
The objectives of this report are , to provide the details about :
1. The Geomorphology of Deserts
2. The Types of Deserts
3. The Flora of deserts
4. The Fauna of deserts and
5. The Natural Resources of deserts.
Characteristics of Deserts
Deserts are characterised by the following ecological factors:
a. Sandy soils and a rocky substratum
b. Scanty rainfall and high evaporation
c. Hot and Cold weather
d. Prevailing Wind action
e. Poor Soil Moisture and water resources
Geomorphology of Deserts
Deserts are created by changes in climate and accumulation of sands and other rocky wastes. A
high proportion of the desert floor is an erosion surface of a bedrock.

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Sand covers about 10 to 20 per cent of the deserts. The rest of the land consists mostly of gravels,
boulders, mountains, and various types of soils.
A desert landscape includes various landforms created by wind erosion. In the heart of the desert
the wind has a free play. Wind erosion creates mounds of sand dunes and flat-topped hills known
as mesas and buttes. The sand bodies of deserts are always on rolling motion due to the prevailing
action of wind.
Sand drifts, Crescentic Dunes or Barchans, Loess and Longitudinal dunes and sand sheets are the
notable wind-borne geomorphic features. One of the most remarkable features of desert dunes is
their power of collecting all the sand from their neighborhood.
Sand dunes
Dunes are large piles of wind-borne sands reaching a maximum height of 250 metres above the
surface.
Dunes show many shapes and patterns that change continually due to the highly active winds.
Deserts are considered to be highly dynamic geomorphic features. Dunes are characterized by
two-sided slopes one along the windward direction and the other along the leeward side.
Soils in Deserts
Soils in desert regions are generally fertile but lacks soil moisture to encourage plant growth.
Temperature in deserts
Climatologically, deserts are the hottest places in the world because they absorb more heat from
the Sun than any other land in humid climates. Deserts are mostly under arid to semi-arid climates.
The temperature varies during day and nights.
In summer, desert temperatures often reach upto 38 °C during the day. They drop upto 25 degrees
Celsius or more at nights. During the winter, temperatures in the desert range from 10 to 21 °C.
Clouds would reflect much of the sun's intense radiation during the day, slowing the rate of heating
of the air near the surface. At night, clouds and water vapour would absorb much of the earth's
radiation--most of which consists of infrared rays--slowing the rate of cooling. Winters are much
colder in middle latitude semiarid areas and deserts.
Rainfall over Deserts
Rainfall is a determining factor of deserts. Rainfall is very scanty in all desert regions. It spite of
these deserts are not barren wastelands. Characteristics that are common to all deserts include
a) irregular rainfall of less than 250 mm per year,
b) very high evaporation rates often 20 times the annual precipitation, and
c) low relative humidity and cloud cover.
Most of the deserts receive less than 200 mm rainfall per year. However, the amount of rainfall
may vary greatly from year to year. A desert may not receive any rain for several years and in
some cases about 250mm of rain might fall within a few hours.

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Wind movement in deserts
Wind movements in deserts are capable of eroding, transporting and depositing the sand masses.
The following are the processes expected:
Deflation is a kind of Wind Erosion. It is a process by which loose sediments are removed by the
wind.
The sediments must be dry. The sand and silt sized material will be moved first. The larger sized
material are generally left behind. Deflation creates its own types of landforms. The deflation
landforms are:
a) Blowouts – these are shallow depressions formed by removal of sediment. Their diameters
range from a few meters to 1000 meters.
b) Desert Pavement – these are fine material removed from the surface leaving a cover of pebbles,
cobbles
and boulders. The coarser material protect the fine material beneath the surface from further
erosion.
Abrasion
Another kind of erosional mechanism in desert by the wind is abrasion. Abrasion is a kind of "sand
blasting". In this process, the impact of windblown particles on exposed surfaces will remove
material from that surface. Abrasion will also reduce the size of the particles that are being moved.
It is generally limited to heights of 1 meter (2 meters max.) Abrasion creates its own kind of
landforms. The notable ones are ventifacts and yardangs.
Ventifacts are land surfaces containing pebbles, cobbles or boulders that have been eroded on one
or more
sides by wind abrasion. Yardangs are ridges which run parallel to dominant wind direction,
believed to be
formed by abrasion. They also create a pillar-like structure which are undercut by abrasion.
Dust Storms in deserts
Deserts experience severe dust storms regularly. Dust storms are heavy concentration of dust (silt-
sized particles) in a turbulent air mass. The dust can be carried hundreds or thousands of meters
into the air. The large dust storms can carry as much as 100 million metric tons of material for
several kilometers distance.
Sand Storms
Sand storms are low moving blankets of wind-driven sands. In this, the sand reaches heights of 1-2
meters above surface. The sand storms often contain dust and sand.
Water availability in Deserts

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Another controlling factor of desert is the presence of water. Due to very scanty rainfall and sandy
soil, deserts have no or very little possibility of holding water. Only in some depressions very little
water may exists. Soil moisture is a rare feature in deserts. Even if little soil moisture is present,
due to hot climate and prevailing winds, it will be evaporated quickly. The drainage system is made
up of dried streams called arroyos. After a rainfall, water fills the arroyos. They run down the
mountains and cut away the land, carrying deposits of gravel, rock, and sand to the bottom. Oasis is
a wet and fertile zone in a desert with vegetation. Underground water comes nearer to the ground
surface. Open wells and springs do exist in such spots. Water that occurs within an oasis has been
drawn through groundwater base flow from distant catchments like mountains or hills. Because
oases have some water, farming and settlement are expected to be more. Some oases may be small
and can support only a few people, but others are large enough to support millions of people.
Desert Topography
The typical desert topography includes playas, alluvial plains, Pediments, inselbergs, mesas, buttes
and badlands. Playa are dry lake beds formed by evaporation from temporary (few hours to
several months), shallow accumulations of excess water (playa lake) following infrequent and
intense rainstorms. Playas are characterized by mudcracks and precipitated salt crystals, forming
salt pans.
Alluvial fans are sediments deposited downslope of the land, typically as aprons at the mouth of
canyons or as a piedmont plain. Alluvial fans coalesce to form a bajada, a broad alluvial apron
with an undulating surface. Pediments are the sloping low-relief surfaces adjacent to mountains
resulting from erosion and retreat of the mountain front. Most covered by thin veneer of debris,
alluvial fans, or bajadas.
Inselbergs
Inselbergs are isolated, steep-sided erosional remnants of bedrock (characterized by greater
resistance to weathering than surrounding mountains) that rise above flat desert plains.
Inselberg is a German word meaning "island mountain".
Mesas and buttes
Mesas are broad, flat-topped erosional remnants bounded on all sides by steep slopes. Mesas
consist of relatively easily weathered sedimentary rocks capped by nearly horizontal and more
resistant rock layer.
Buttes are isolated pillar-like structures resulting from continued eathering and erosion of mesas
Badlands are areas of closely spaced ravines with little or no vegetation.
Major kinds of Deserts
The distribution of arid regions or deserts is determined by the climate and topography. Based
these two factors, arid terrains are subdivided into
a) tropical deserts and

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b) topographic deserts.
Tropical Deserts:
The Tropical deserts have a big diurnal temperature range and very high daytime temperatures,
whereas mid-latitude deserts have a wide annual range and much lower winter temperatures (in
the Mongolian desert the mean temperature is below freezing point for half the year). Heat
enhances evaporation over deserts.
Topographic Deserts:
Topographic controls on desert formation also reflect a deficiency in rainfall. Topographic deserts
are located near the center of continents, where climates are hot in summer and cold and dry in
winter. These regions are typically far from ocean moisture sources, and most often are cut off
from rain-bearing winds by high mountains.
Steppes
Steppes are Deserts and adjacent semi-arid regions. These regions may get rainfall between 10
and 20 inches per year. They are characterized by a non-continuous vegetation cover. The
tropical desert lie within latitudes from 5º to 30º. The rainfall are mainly caused by the descent of
air. This is responsible for the warmness of land and loss of moisture.
Types of Deserts
Based on their surface forms and soil composition, deserts are classified into the following four
types:
a) Rocky Deserts
b) Stony Deserts
c) Sandy Deserts
d) Clayey Deserts.
Rocky deserts
Rocky deserts have uneven topography between mountain ridges and groups of small hills.
Mountain ridges have rugged summits and crests, steep slopes with outcrops of rocks. Talus and
scree debris are numerous on hill sides. They are not completely devoid of vegetation. Isolated
small and large shrubs can be located on the lower parts of the slopes., in valleys and depressions.
Some water springs appear on valley floors.
Stony deserts
Stony deserts are completely flat or gently undulated areas with stones of rocky wastes comprising
sharp edged rock fragments or pebbles. There may not be any vegetation and water. Sahara and
Arabian Deserts are stony deserts.

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Sandy deserts
Sandy deserts are areas of loose sand which forms hillocks in the shape of barchans and dunes.
These are characterised by uneven surfaces of undulating chains of dunes with isolated short
valleys or hollows with little vegetation. They resemble like sea-waves. Barchans reach a height of
200m. It is difficult to walk straight across on these zones. One has to clim the crets and descend
into the hollows. It is easier to walk aided by wind. Sand storms are common creating an
atmospheric haze.
Clayey Deserts
Clayey Deserts are not extensive. The clayey floors are crackd into polygonal sections. Soil is of fine
silt in composition with sparse vegetation. Soils of Clayey deserts are mostly saturated with salts.
Geographical classification of deserts
Deserts are also classified based the geographic conditions.
The geographical classification of deserts also include:
a) Continental deserts- eg. Gobi desert
b) Rain-shadow deserts- due to tall mountain ranges- eg. Judean desert in Israel
c) Coastal deserts- Eg. Atacama Desert in S. America, Namib Desert of Africa.
d) Trade wind deserts- Eg. Sahara desert- temperature goes upto 57deg.C
e) Monsoon deserts- eg. Thar Desert in India, Cholistan Desert of Pakistan
f) Polar deserts- Eg. The Dry Valleys of Antarctica – are ice free for thousands of years.
g) Extra-terrestrial deserts- deserts of other planets, Eg. Mars have shown eolian features.
h) Montane deserts.
Hot and Cold Deserts
From an ecological point of view, deserts are also classified into two major kinds as
a) Hot deserts and
b) cold deserts.
Flora of deserts
Desert plants cannot use so much water at once, and the desert soil cannot absorb all of it. Most of
the water runs off, carrying away the soil particles.
Most deserts plants are drought or salt tolerant, such as Xerophytes. Some store water in their
leaves, roots and stems. Other desert plants have long tap roots that penetrate the water table,
anchor the soil, and control erosion. The stemps and leaves of some plants can lower the velocity of
sand-carrying winds and protect the ground from erosion.
Life forms of Plants
The following three life forms of plants that are adapted to deserts:
a) The annuals, which avoid drought by growing only when there is adequate moisture

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b) The succulents- such as the cacti, which store water and survive
c) The desert shrubs- which have numerous branches with small but thick leaves to store water.
Adaptation to desert environment and arid climate involves the ability to avoid wilting and remain
dormant for long periods rather than an increase in transpiration efficiency. Desert soils are
infertile, lacking in humus and generally grey or red in colour. Deserts cannot support the
abundant plant and animal life as found in humid climates. But many kinds of plants and animals
thrive in deserts. The few plants capable of surviving such conditions are widely spaced, scrubby
and often thorny. Long-rooted plants (phreatophytes) such as the date palm and musquite
commonly grow along dry stream channels. Salt-loving plants ( halophytes) such as saltbushes
grow in areas of highly saline soils and near the edges of playas (dry saline lakes).
Xerophytes
Xerophytes are drought-resistant and survive by remaining leafless during the dry season or by
reducing water losses with small waxy leaves. They frequently have shallow and widely branching
root systems and store water during the wet season (for example, succulents and cacti with pulpy
stems).
Desert plants survive compete with small amount of water available. Some desert plants obtain
water from deep beneath the surface of the earth. For example, the American mesquite tree has
roots that extend as deep as 12 metres. Other plants store large amounts of water in their leaves,
roots, or stems. The stem of the barrel cactus bulges with water after a rainfall and shrinks as the
plant uses the water.
All desert vegetation has a highly characteristic spatial distribution plants. Individual plants are
scattered. This spacing reduces competition.
Some of the typical flora of deserts are:
a) Creosote bush- (Larrea) – North America, hot deserts
b) Sagebrush –( Artemisia) Great basin- Cool Deserts
c) Bur sage( Franseria)- high altitude plants
d) Giant cactus- ( Sahuaro)-
In addition to these little grass also grows on deserts but are grazed by the animals. Greesewood(
sarcobatus) is a typical vegetation in cool deserts.
The extensive sand bar grounds of deserts is not necessarily free from plants.
Mosses, algae, and lichens may be present. Blue green algae are the nitrogen fixers in these regions
also.
After every rainfall, colourful flowers and lush vegetation cover parts of deserts. This dramatic
change occurs because many desert plants do not grow during a drought. Due to rain, plants
sprout, flower, scatter their seeds, and die. The entire process usually takes only a few weeks. The

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seeds of annuals can survive even the longest dry periods. The seeds lie buried until the rains
return. They then sprout, and the plants complete their life cycle within a few weeks.
In the deserts of Australia, the dominant plants are
tussock grasses, such as porcupine grass or spinifex, and
succulent herbs, such as parakeelya.
After the rains, the deserts come alive with beautiful flowers, such as the purple mulla-mullas.
In the deserts of North and Central America, cactuses are prominent. Cactuses are protected from
grazing animals by their sharp spines. Many cactuses have beautiful flowers.
In Africa, the most abundant desert plants are the euphorbias, which have a poisonous milky sap.
The Sonoran Desert of the American Southwest has the most complex desert vegetation on earth.
The giant “saguato cacti” provide nests for desert birds and serve as “trees”of the desert. Saguaro
grow slowly but may live upto 200 years. Its branches develop after 75 years. When fully grown it
is 15 m tall and weigh 10 tons.
In addition to these, other types of plants belonging to pea family and sunflower family are seen in
deserts.
Fauna of deserts
Animals of the deserts have developed special body structure and ways of life that enable them to
survive under the extreme heat.
Centipedes, gerbils, kangaroo rats, snakes, and
scorpions spend the day in burrows.
They come out to search for food only when temperatures drop at night.
Many insects,
lizards, and
tortoises can tolerate high desert temperatures and are active in the daytime.
Many of them retreat underground or find the shade of a tree, during the hottest part of the day.
Some snails, insects, frogs, lizards, mice, and
ground squirrels aestivate in deserts, i.e they sleep through the summer.
Elf owls, roadrunners, snakes, spiders, bees and butterflies are the other fauna of deserts.
Many desert dwellers have light-coloured skin, which helps keep them cool by reflecting sunlight.
Desert animals include many kinds of insects, spiders, reptiles, birds, and mammals. Deer, foxes,
wolves, and other animals may visit a desert after a rainfall.

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Most desert animals avoid the extreme midday heat by feeding at night after the temperature has
dropped. Many small animals dig burrows underground and stay there during the day. Some of
these animals are dormant (inactive) throughout the summer.
Desert foxes and hares have long ears.
When overheated, these animals move to a cool cave or burrow where they can get rid of excess
body heat through their ears.
The Cape ground squirrel makes its own shade by using its fluffy tail like a parasol.
Fairy shrimp and spadefoot toads may spend months or years underground waiting for rain to
create ponds. Then they quickly feed and reproduce before the ponds dry again.
Larger desert animals try to remain in shady areas during the day. The evaporation of water from
their bodies lowers their body temperature, but this water must be replaced. Such animals obtain
water from the food they eat and from the few water holes that exist in a desert.
Desert animals also use water that is produced in their bodies during digestion. This source of
water is particularly important to camels, which can go for long periods without food and water.
Large amounts of fat are stored in the humps of camels. A camel can live for months on the water
produced when its body breaks down this fat for use as energy.
Most deserts lie near the edges of the tropics. Food and water are often scarce in deserts, and
temperatures in the summer can be scorching. Despite these conditions, many kinds of animals
live there.
Whenever deserts are discussed no one can forget anout the “Ship of the Deserts” ie. The Camels.
These are unique creatures which can not only survive, but also help the human beings across hot,
dry deserts with little food or water. They walk easily on soft sand where even trucks would get
stuck, and carry people and heavy loads to places that have no roads. Camels also serve the people
of the desert in many other ways. A Camel carries its own built-in food supply on its back in the
form of a hump. The hump is a large lump of fat that provides energy if food is hard to find.
There are two chief kinds of camels:
(1) the Arabian camel, also called dromedary, which has one hump, and
(2) the Bactrian camel, which has two humps.
Hybrids (crossbreeds) of the two species were used widely in Asia. These hybrid camels had one
extra-long hump and were larger and stronger than either of their parents.
Camels have been the domestic animals to support humans for thousands of years. There are
several million Arabian camels, and most of them live with the desert people of Africa and Asia.
This desert ship can go for long distances without water for days or even months. The amount of
water a camel drinks varies with the time of year and with the weather. The camels that graze in
the Sahara can go all winter without water and may refuse to drink if water is offered to them. But

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a large, thirsty camel can drink as much as 200 litres a day. This water is not stored in the camel's
body but replaces water previously used up.
Most animals sweat when hot, and the evaporation of the water from their skin keeps them cool.
But camels do not sweat much. Instead, their body temperature rises by as much as 6 degree
Celsius during the hot summer day and then cools down during night.
On extremely hot days, a camel keeps as cool as possible by resting rather than feeding.
Adaptation to the topography, landforms and climate is a unique feature of desert animals. They
live with very scanty food resources.
Human population in deserts
Human population in deserts are also equally facing the same issues. Deserts do not support a large
number of people as in humid regions. People living in desert regions must adjust to the local and
prevailing hot or dry climate. Air-conditioning and irrigation projects have made life more
comfortable for other desert dwellers.
Natural Resources of deserts
Deserts have enormous sands and soil resources. The soil of deserts are mineral soils often called
as aridisols with low organic content.
Most desert soil is too dry to support widespread vegetation, but much of it is rich in salt, uranium,
and other minerals. Playas are sources of mineral deposits formed by evaporation.
Gypsum, sodium nitrate, sodium chloride salts and Borates are the major precipitates.
Minerals formed by evaporation are often referred to as evaporites. Many of them are used in the
manufacture of glass, ceramics, enamel, agricultural chemicals, water softeners and
pharmaceuticals. Sodium nitrites are used for explosives and fertilizers. Many metallic and non-
metallic mineral resources also are obtained from the desert zones.
Annual production of dry matter
The primary production in deserts depend on the little amount of available water and also the
consumption strategy adopted by the plants. It is very low as 30-200 gm/ sq.m in arid zones, above
the ground. The herbivores have a pronounced impact on primary producers. The detrital food
chain seems to be less important in the desert than any other ecosystems. Because of the limited
production and decomposition, nutrients are limited in the deserts.
Walter in 1954 has measured the net productivity of a series of deserts and semi-arid communities.
The annual production of dry matter was a linear function of rainfall upto 600cms. This has also
shown that the overall limiting factor of deserts in productivity is the moisture. It has been found

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that he annual net productivity of true deserts is less than 2000 kg per hectare. When this is
overcome due to rain, then the soil becomes a limiting factor.
Other produces
Date palm tree produces date fruits. They thrive in hot, dry climates. They grow along oases
throughout northern Africa and the Middle East. The date palm is one of the oldest crop plants
known to have been used for at least 5,000 years. Even today, dates form an important part of the
diet in many desert countries. Dates are also supplied to other places from these lands.
In addition to these, large deposits of oil and natural gas lie under many desert lands. Some of the
more productive petroleum areas on Earth are found in arid and semi-arid regions of Africa and
the Middle east although oil fields were originally formed in shallow marine environments. Recent
climate change, in geological time scale, has placed these reservoirs in an arid environment. The
hydrocarbon reservoirs of the North Sea is associated with extensive evaporite deposits. Many of
the major U.S. hydrocarbon resources may come from eolian sands.
Location of Oases
The location of Oases has been of critical importance for trade and transportation routes in desert
areas. Caravans must travel through these places that supplies water and food.
The natural factors creating deserts have not changed much for thousands of years. It is observed
over the world that various human activities have caused expansion of desert regions. This has
happened due to continuous loss of fertile land on the outskirts of such regions. Planting shelter
belts of trees will be one of the solutions.
The role of human beings in reconstructing the desert landscapes on their outskirts will certainly
stop their expansion over the other regions.
Desert Regions of the World
Desert Region is a geographic zone experiencing a mean annual precipitation of 10 inches or less,
and relatively devoid of vegetation. There are Four types of desert regions which can be classified
as:
- Subtropical Deserts
- Rainshadow Deserts
- Continental Deserts
- Polar Deserts
The Subtropical Deserts exist between 25°-30° Latitude.
These deserts form in response to dry descending air mass in Hadley Cell circulation. Examples are,
Sahara Desert, Arabian Peninsula, Kalahari Desert, and the Great Sandy Desert.

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The Rainshadow Deserts exist over the mountain ranges which block the passage of moist air. The
leeward side of the ranges are normally arid. Examples are, Atacama Desert, Patagonia, Death
Valley, eastern Washington and eastern Oregon.
The Continental Deserts are centralized locations of deserts with in the continental interiors. There
may be no nearby, large sources of water. Examples are many including the Gobi Desert.
The Polar Deserts are located around polar regions. Cold air is unable to hold much moisture. This
kind of Polar areas are arid having very little precipitation. The polar Deserts are not defined by
temperature. Examples are- Greenland; Antarctica.
Conclusion
Deserts are dry landforms comprising of sand and sediments. They are the cradles of centrifugal
eolian forces. Deserts sometimes contain valuable mineral deposits that were formed in the arid
environment or that were exposed by erosion. Evaporation in arid regions enriches the mineral
accumulation in their lakes. Playas may be sources of mineral deposits formed by evaporation.
Water evaporating in closed basins precipitates minerals such as gypsum, salts (including sodium
nitrate and sodium chloride), and borates. The minerals formed in these evaporite deposits depend
on the composition and temperature of the saline waters at the time of deposition. The natural
forces that create deserts have not changed much for thousands of years. However, various human
activities have caused desert regions to expand considerably. The major causes of desert
expansion include mining, improper farming methods, and destruction of trees.