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Desert Ecosystems

Case Study by Kim Kerr

What is a desert like?
Deserts cover approximately one-third of the world's land surface. There are two main types of deserts
hot deserts and cold deserts. The main feature of deserts is their lack of moisture. Deserts receive
less than 250 mm of precipitation each year. Other features of deserts include:

Long dry periods between rainfall

Scattered vegetation
Almost all the annual increase in population occurs in the developing world
Plants and animals that are especially adapted to the harsh environment
Very few people

Where are deserts located?

Deserts are located on all continents. Hot deserts are usually caused by a combination of the following
factors:

On most continents, they are located on the west coast due to cold ocean currents. The cool air
above these ocean currents is less able to hold moisture, than warm air. Winds blowing
onshore over cold oceans are drier than they would be if they blew over warm ocean currents.

Mountain ranges act as barriers, particularly to moist, onshore winds blowing on the eastern
sides of continents. These mountain barriers block rain-bearing winds, causing orographic
rain to fall on the windward side of the mountain, creating deserts on leeward side of the
mountain, in a rain shadow.
High pressure systems made up of dry, heavy air are the main pressure system found over
deserts. The air in these systems is relatively stable, resulting in little precipitation.
Distance from the sea (or continentality), results in easterly winds depositing most of their
moisture on the east coast, before they reach the interior or west coasts of the continents.

Simplified cross section from east to west across a continent

The Biophysical Environment of Deserts

The Biosphere
Due to the extreme temperatures, lack of water and apparently infertile soils, deserts are probably the
most intimidating environments on earth. Despite these conditions, they are able to support a surprising
amount and variety of both plants and animals that have special adaptations, which allow them to
survive in this harsh environment.
Desert plants are called xerophytes. They have adapted to the harsh climatic conditions of low and
irregular rainfall, extreme temperatures and high evaporation by being able to store water or reduce
moisture loss through transpiration so that they can survive.

1
Even in totally arid places animals cannot survive without moisture. Some of them are expert at
conserving the moisture within their bodies. Some don't drink at all, instead they obtain moisture from
the bodies of their prey. Others have ingenious ways of trapping atmospheric moisture, such as the fog
beetle found in the Namib desert.

2
The camel originally came from Asia where it was domesticated and then introduced into Africa. It has
been used there by nomadic tribes such as the Tuareg in their camel caravans, carrying goods such as
dates, salt and millet. Camels have a large number of adaptations allowing them to survive in the
desert. Many of these adaptations can be seen in these photographs.

Wide spreading feet to prevent the camel from sinking into the sand
Tough patches of skin on their knees for kneeling
Thick fur to insulate them from the sun
The hump, used for storing fatty tissue (not water), to provide energy

Tough lips for eating hard, thorny plants

Long eyelashes, hairy ears and nostrils that close to keep sand and dust out

Camels can also go for days without drinking water.

They can smell water, which can be quite a number of kilometres away
They can drink salty water
They can drink up to 100 litres (or 13 of their body weight) in 10 minutes and then travel for
100 kilometres on this supply.

The Lithosphere
As there is little vegetation cover, sand and soil can be easily eroded by both wind and running water,
producing spectacular desert landforms.

In dry periods, winds blow loose sandy material away, leaving behind heavier rock and stones. These
stony deserts are known as gibber deserts in Australia and hamada in Saudi Arabia. Sand dunes are the
result of the deposition of this finer material. Sand dunes occur in a variety of shapes and sizes.

3
When rain does occur, it is usually in the form of sudden, heavy downpours, which cause flash floods.
The power of these storms removes all loose surface material, causing a number of different erosional
landforms (such as arroyos, mesas, buttes, wadis and badlands) and depositional landforms (such as
alluvial fans, bolsons and playa lakes).

Desert landforms produced by wind and running water.

Climate (Atmosphere and Hydrosphere)

The desert temperature is not always hot. During the night, desert temperatures are quite cold, even
below freezing point.
The daytime temperatures are hot because there is very little cloud cover. This means that that
maximum radiation from the sun reaches the surface of the earth. In summer the temperature can reach
as high as 40C, while in winter, the temperature can reach 24C.

4
At nighttime, the lack of cloud cover allows the heat of the day to escape quickly, resulting in cold,
even freezing, temperatures. The difference between the daily minimum and maximum temperatures is
known as the diurnal range.
Seasonal temperature changes are distinct, but annual temperature range is moderate. The diurnal
temperature range is often great. Precipitation does occur in desert regions, although the amount that
falls is low and irregular. There is a very high evaporation rate due to the constantly high daytime
temperatures.
The Namib Desert (on the west coast of Namibia, Africa) is one of the world's oldest deserts, with an
average annual rainfall of less than 100mm. The Namib desert is a result of the cold ocean current that
flows northwards, parallel to the coast.
Although called a desert, parts of the Kalahari Desert (mainly located in Botswana, Africa) are in fact
semi-desert areas as they receive an annual average rainfall of more than 250 mm. Up to 660 mm per
year falls in the north, 400-450 mm per year in the east, but less than 200 mm per year in the
southwest. The number of species of plants decreases with the rainfall, and eventually plants are only
found in the ephemeral river valleys.

page 121

The Bushmen of the Kalahari

The indigenous people living in the Kalahari Desert are known as the San or the Bushmen. There is
evidence that they have been living there continuously as nomadic hunter-gatherers for at least twenty
thousand years. Currently, there are over 95,000 Bushmen in southern Africa.

5
Despite the fact that they have adapted to the harsh Kalahari environment, today there are only a small
number of the San still following their traditional way of life in the Kalahari.
The Bushmen live as nomads because of the harsh desert environment, which provides little food and
few animals. Villages consist of 10-30 people. Their dwellings are simple structures made from grass
and branches, with one door opening onto a central communal area. They have few possessions. When
their water source dries up, the villagers move to a new location where a reliable source of water can be
found.
They are a hunter-gatherer society. The women gather food. They look for roots, berries, fruits, nuts
and bulbs and dig them out with pointed sticks. Some plants, such as the tsama, also contain water.

The men hunt animals with spears, bows and arrows, which have been tipped with poison made from
the juices of various plants and animals (snakes, spiders and scorpions). The mixture is boiled until it
becomes a gummy paste, which is fixed to the arrow tips just before use. The poison-tipped arrows do
not kill instantaneously. Animals may take between two hours and two days to die, depending on their
size. The animals they hunt include wildebeest, gemsbok, antelopes, zebras, ostriches and giraffes.
They also kill various reptiles and birds, and collect honey when it is available. Women might
occasionally kill small mammals.
Apart from getting water from plants, the Bushmen also find it under the ground. They dig a hole, then
use a long hollow reed to suck up the water. To ensure they have a supply of water, they store it in
ostrich shells, which they bury to drink later.
To keep cool, the Bushmen wear little clothing and do not move around much during the hottest part of
the day. At night, when the temperatures are much cooler, they build a small fire outside their hut for
warmth. They might wrap an animal skin or a blanket around themselves.

What problems do the Bushmen face?

Today, only a small number of Bushmen follow their traditional way of life as modern civilization is
threatening the natural resources of the Kalahari. Mineral companies have discovered large coal,
copper, and nickel deposits in the region, and one of the world's largest diamond mines is located in the
north-eastern Kalahari.
Around 1500 years ago, cattle herding Bantu tribes invaded the hunter-gatherer's homelands. The
invasion was continued by white colonists over the last few hundred years. These invasions reduced
their numbers from several million to 100,000. A few thousand were relocated to the Central Kalahari
Game Reserve, which was created in 1961. Here they were meant to be able to continue their nomadic
lifestyle, due to the large number of game living in the Reserve.
In 1997, the Botswana government forced the Bushmen to move to large settlements, outside the
Reserve, which provided education and health-care facilities. Some Bushmen refused to go and in early
2002, the government banned hunting and gathering and also destroyed the Bushmen's water supply.
Hunger and thirst then forced the Bushmen to move. They were 'resettled' into fixed camps.
Some people and organisations have accused the Botswana government of 'ethnic cleansing' so that the
Reserve could be 'opened up' for mining and tourism. Diamonds are known to exist in the Reserve.
Prior to the removal of the Bushmen from the Reserve, tourism could only be conducted under
government licence. Now, private safaris are possible.
The government has used nature conservation as one justification for their actions. They have also said
that it was too costly to continue to supply water to the Bushmen; and that it would be better for the
Bushmen if they became 'settled and civilised'. The Ditshwanelo (the Botswanan Centre for Human
Rights), claim that the Government's motives are legitimate, but ill-advised.

How are the Bushmen resolving their problems?

In January 1996, 'Intu Africa', with the aid of two South African anthropologists, invited 40 Bushmen
to re-establish a self-sustainable community on the company's Kalahari Game Reserve, rather than
continue living on government handouts.
These families now are working successfully in a variety of income generating projects such as game
guiding, camp site supervision and the making and selling of traditional handicrafts. Although the
Bushmen have built a typical village where visitors come to learn about their traditions, they actually
live in the privacy of their own village.
This ecotourist development gives visitors a rare opportunity to learn from the Bushmen themselves
about their hunter-gatherer traditions and the ecosystem of the Kalahari Desert. The highlights of the

program are an early morning desert walk, where the Bushmen demonstrate tracking skills and share
their desert survival secrets and an afternoon visit to the village.

Conclusion
Due to the extreme temperatures, lack of water and apparently infertile soils, deserts are perhaps one of
the harshest environments on earth. Despite these conditions indigenous people, such as the Bushmen
of the Kalahari, are able to survive in this environment. The threat to their existence, and that of other
indigenous groups, comes from exploitation by modern civilisation and governments for the mineral
resources found in desert ecosystems.
Without appropriate actions by responsible citizens and sound management policies these indigenous
groups will not survive. It is not just the responsibility of the governments to protect the desert
ecosystems, their people and their resources. Each of us can contribute to the survival of indigenous
people by respecting them and their traditional way of life.

When you finish reading the Case Study, click to start Activities.

Desert EcosystemsFact File 1

In some areas of the Atacama Desert, in Chile, virtually no rain (0.08 mm) has ever been recorded in
the 59 years that statistics have been recorded. The lowest rainfall recorded (in 39 years) at Wadi Halfa,
Sudan is less than 0.3 mm.

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Desert EcosystemsFact File 2

The fog beetle, found in the Namib Desert in Africa, collects the water by standing on sand dunes and
facing the wind. It collects the water from fog and drinks up to 40% of its body weight in the span of
one day by letting the water trickle down its back and into its mouth. This is called fog basking.

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Desert EcosystemsFact File 3

The Sahara Desert is the largest hot desert in the world. It is so large that the continent of Australia
would fit into it.

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Desert EcosystemsFact File 4

The highest temperatures ever recorded in the desert have been 58C in El Azizia, Libya, 57C in Death
Valley, USA and 53C in Cloncurry, Queensland.

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Desert EcosystemsFact File 5

A number of different terms are used to identify the inhabitants of the Kalahari Desert, including San,
Basarwa and Bushmen. According to some sources, the inhabitants prefer to be called 'Bushmen',
which was a term first used by early Europeans, while other sources state that 'Bushmen' is a insulting
term and that they prefer to be known as 'San'.

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Case Study

Web Destinations

Activities
1. If you have not done so yet, read the Case Study and describe where deserts are located.

Desert Ecosystems

2. Answer the following questions using the link below.

a.
b.
c.

Examine the graph at 'What is a desert like?' and rank the ecosystems / biomes according to
the amount of precipitation they receive each year (in inches.)
Which countries surround Venezuela?
Convert the precipitation for each biome to mm. (Note: 10 inches equals approximately
250 mm.)

Desert Topics

3. Use the link below to answer the following questions.

a.
b.
c.
d.
e.
f.
g.

Examine the table at 'Types of deserts: hot deserts' and locate each of the hot deserts (in red or
orange) mentioned in the table, on a world map.
Rank the deserts in order of size. Where does the Kalahari desert rank?
List some of the physical features of these deserts.
What similarities do you notice about the indigenous people who inhabit these deserts
(mentioned in the special facts column)?
Examine the table at 'Types of deserts: cold deserts' and on the same world map, locate each of
the cold deserts (in blue) mentioned in the table.
Rank the deserts in order of size. Where does the Namib desert rank?
List some of the physical features of these deserts.

Desert Topics
4. Answer the following questions using the link below.
a.
b.

Briefly explain the different types of deserts (Do not explain monsoon or paleo deserts).
Where is the extraterrestrial desert located?

Types of Deserts
Where are deserts located?
5. Copy and complete the following passage by referring to the world map on pages 144145, 148 and
149.

Hot deserts are mainly found between 30 ___________ and ___ south of the ___________. The cold
deserts are found at latitudes greater than ___ in the _____________________ and _____________
hemispheres.
Deserts are found in most areas of Australia, with the exception of the _______________ and
_____________ coasts. Deserts also cover Antarctica, ____________ and _______________ Africa,
south-western and central _______ and the _____________ coasts of __________ and __________
America.
The _____________ is the largest ______ desert and is located in ___________.

pages 144145, 148 and 149

6. Refer to the maps on page 121 and 123 to describe the location of the Namib, Kalahari and Karoo
Deserts. Use latitude and longitude, as well as naming the countries in which they are located.

pages 121 and 123

The Biophysical Environment of Deserts
7. Explain why animals and plants are able to survive in the desert using the links below.

Desert Animals

Desert Plants
8. Use the link below to describe the lithosphere of the Kalahari Desert.

The Kalahari Desert

9. Study the climate maps of Africa on page 122 to answer the following questions.
a.
b.
c.

Estimate the temperature range experienced in the Kalahari and Namib Deserts in summer and
winter.
In which direction has the low pressure system moved in July?
c) Estimate the average annual rainfall experienced in the Kalahari and Namib Deserts.

10. Study the climatic graphs for Station 13 (Darwin) and Station 14 (Alice Springs). Describe the
differences in temperature and precipitation experienced by these two stations.

pages 148 and 149

11. Using the climatic statistics below, construct a climatic graph for both stations. Which station is
located in the desert and which station is located in a semi-desert region?

Location: Maun, Botswana (19S 23E)

Altitude: 940 m

Temp (C)
Precip (mm)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sep

Oct

Nov

Dec

Total

25.3
108.1

25.1
98.5

24.0
71.9

22.4
24.7

18.4
5.6

15.4
0.8

15.2
0.1

18.0
0.2

22.8
2.9

26.1
17.0

26.4
48.5

25.7
83.0

465.2

Location: Luderitz, Namibia (26S 15E)

Altitude: 23 m

Temp (C)
Precip (mm)

Jan

Feb

Mar

Apr

May

June

July

Aug

Sep

Oct

Nov

Dec

Total

17.8
0.8

17.8
1.8

17.3
2.4

16.2
3.7

15.7
2.4

15.1
3.0

14.4
2.1

13.8
2.1

14.0
1.6

14.7
0.5

15.8
0.5

17.0
1.1

22.4

The Bushmen of the Kalahari

12. Use the link below to describe how the Bushmen have survived in the Kalahari Desert.

Survival of the Kung San People in the Kalahari Desert

13. Use the following website to outline how Bushmen communities have participated in political
activities.

Current Trends Among the San of Southern Africa

14. Select one 'Kalahari Desert Project' from the following website and explain how the Bushmen will
benefit from this project.

Pilgrim Relief Society

Quizzes
15. Complete the desert landforms quiz using the link below.

Understanding Desert Landforms

16. Complete the desert landforms multiple-choice quiz using the link below.

Desert Landforms Multiple Choice Quiz

See these links for further research.

Case Study

Activities

Desert EcosystemsWeb Destinations

Useful websites for further research include:
Blue Planet Biomes
http://www.blueplanetbiomes.org/desert.htm
This site has information about all of the world's biomes, with specific examples related to each biome.
The example for deserts is the Mojave Desert, USA.
Desert Landforms
http://ruby.colorado.edu/~smyth/G1010/14Deserts.PDF
The explanations and photographs of wind eroded desert landforms at this site are very good.
The Discovery Channel
http://school.discovery.com/lessonplans/programs/deserts/
The Discovery Channel site includes lesson plans on a variety of geographical and ecological topics.
This lesson plan relates to desert animals and their adaptations.
Enchanted Learning
http://www.enchantedlearning.com/biomes/desert/desert.shtml
This interactive site has information and graphics for all biomes. The reproducible resources are
excellent. There are many links to other topics.
Missouri Botanical Gardens
http://mbgnet.mobot.org/sets/desert/
As well as information about terrestrial biomes, this website also has information about freshwater and
marine ecosystems. The information presented is very easy to read and includes links to other useful
sites.
Survival International
http://www.survival-international.org/welcome.htm
This site has a wealth of information about a variety of indigenous groups and the problems they face.
The section on the Bushmen of the Kalahari is outstanding.

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