Transcript HOT DESERT BIOME

HOT DESERT BIOME
OPTION 7: GEOECOLGY
WHAT IS A BIOME







Biomes are unique natural world regions which
are controlled by climate.
Examples include tropical rainforest, deciduous
forest biome, the desert and the tundra.
There are four main parts of any biome
1) climate
2) soil
3) plants
4) animals
Definition of a desert

Deserts are dry places, where the availability of water is the major factor
that determines the type of organisms that can live there.Typically
deserts have less than 250mm of precipitation 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 rain.

A desert therefore can be defined as;
“ an arid region characterised by little or no rainfall, in which
vegetation is scant or absent unless specially adapted or where
groundwater conditions are favourable,”

Contrary to popular opinion, deserts are not regions that are entirely
covered by sand. Deserts are predominately regions of boulders, gravel or
bare rock, with only about 10% of deserts worldwide being sandy.
Distribution of Hot Deserts

Hot Deserts generally occur
between latitudes 15 & 30 North
and South of the equator.They are
common on the western sides of
continents where may be called
Coastal Hot Deserts eg the
California/North Mexican in
North America, the Atacama in
South America, the Sahara in
North Africa and the Kalahari in
South Afriica.They are also found in
the heart of continents eg the
Sahara/Arabian and the Great
Australian.
Not all deserts are hot – Gobi Desert is -40
degrees in winter
 Large Diurnal range= night v day temp
 Suns rays very concentrated so hot in day
 No cloud cover so cold at night
 All deserts are dry- some 1cm a year
 Other rain in short heavy bursts
 Evaporation and run-off can lead to gullying
 Cold deserts can get snow which is no good to
plants

3 desert types

Extremely Arid – no precipitation

Arid – less than 250mm annually

Semi-Arid – 250-500mm annually
Factors causing desert climates




1) Latitude:
Located at the tropics : 15 - 30
north and south of the equator
Influence of high global pressure belts
Year round high pressure means air
sinks to the ground and warms up
Heat leads to low levels of moisture
in the atmosphere (DRY AIR)
2) Dry prevailing winds
Lie in the path of dry trade winds
 Winds become warm as they blow
towards the equator from sub tropical
(high) pressure belts
 Winds absorb moisture rather than
forming rain clouds so air remains clear
and dry

3) Cold ocean currents
Deserts on the western edges ( as seen in
distribution slide) are located beside cold ocean
currents ie. Canary currents (Sahara) Peruvian
current (Atacama)
 Currents lead to a cooling in the prevailing
winds moving across the ocean leading to heavy
rainfall
 When the winds reach the land they are dry
 Annual precipitation is less than 250mm.

4) High mountain ranges
Rain shadow effect : the reason for
the desert in the continent of
Australia,The Great Dividing Range
has caused the onshore winds from
the east to drop its moisture in the
form of relief rainfall before it
reaches the desert.
 As a result the land in the leeward
(sheltered side) receives little
rainfall as the air descends

Relief rainfall:
All of the above factors lead to highly
irregular rainfall
 Rain, when it occurs, does so in short
violent storms three to fifteen times a
year.

Desert soil
Aridsoils.
 Coarse grained aridisols found in low mt slopes have a low
water-holding capacity – they cannot retain all the water
that falls onto them, hence infertile
 Created by rock exfoliation
 Finer soils are moved to lowland areas by wind and torrential
rain – do not favour growth
Desert soil

Lack of Vegetation:
◦ poorly developed
◦ high content of mineral particles, little organic matter.
◦ low plant productivity, restricts the soil-building properties
Lack of Rainfall:
◦ Can be fertile after heavy rainfall but it doesn’t last long
Soil forming factors:
 Capillary action bring minerals to surface
 Intense evaporation of water from desert soils leaves layer of minerals which hinders
growth
 The high surface content of sodium and calcium ions can lead to extensive saltpans
where little or nothing will grow (salinisation)
 Because the calcium carbonate content is not leached through the soil because of
limited rainfall, most desert soil are alkaline with a PH level from7 to14.
 This can harden to calcite to form an impermeable hardpans

Desert flora
Hot Deserts are home to many living
things.
 Second only to the tropical rainforests in
the variety of plants and animal species
that live there.
 Many of the fascinating features of desert
plants ( xerophytes) are adaptations

Desert flora
Desert plants have a number of adaptations;
1. Well spread out to conserve the available water. Leading to
large open spaces between the plants
2. Short life cycle - Many of the scrub like plants have the ability
to lie dormant for years and to burst into life with the advent
of rain, only to die away shortly after the rain stops –
(ephemerals)
3. Succulents – Ability to store water, fleshy sponge like interior,
groves in skin to allow it to expand and act as funnel to bring
water to roots, and Skins tend to be waxy, leaves small &
spiky to prevent loss of moisture through evapotranspiration.
4 Roots are radial or tap in nature.
Radial root are shallow and spread out over large
area near the surface e.g. cacti
Tap roots have one long root up to 50m long that
reaches the water table below e.g. mesquite bush
5. Defensive:
Spiky leaves or unpleasant smell to deter animals
Desert flora: Cactus plants




drought resistant plants
due to their absence of
leaves
ability to store water in
their stems (Succulents)
waxy skin seal in
moisture.
extensive shallow root
system radiates out from
the base, allowing for the
quick acquisition of water
when it rains.



Adaptaion of the rose
family (short thorny
leaves)
roots can survive years of
drought on the water
collected from a single
rainfall.
they store water both in
the core and stems
Desert flora: Creosote Bush
one of the most successful of all desert species
 Instead of thorns, it relies for protection on a smell
and taste wildlife find unpleasant.
 It has tiny leaves that close their stomata (pores)
during the day to avoid water loss and open them
at night to absorb moisture.
 extensive double root system- both radial and deep
– to accumulate water from both surface and
ground water.

Creosote bush and soils

The Creosote bush has a
very shallow root system
that spreads out near
the surface to avail of
any moisture that is
available near the
surface and so it is again
not dependant on water
in the soil.
Desert flora: Creosote Bush
Desert flora and soils
Desert plants have adapted
to their environment in a
number of ways
 The Saguaro Cactus due to
the hardpan has a shallow
root system and does not
depend on the arid soil for
water. Instead the plant
itself absorbs up to one
ton of water through its
roots when it rains.
Desert holly

The Desert Holly
absorbs salt from
the saline soil and
coats its leaves. The
white colour reflects
the direct rays of the
sun during the day
and so reduces
evapotranspiration
Flora and soils

Other plants have very long roots that penetrate through the dry
soil to the water table to soak up sufficient moisture for life.
Desert fauna
Many desert animals have evolved mechanisms to
solve the heat and water problems the desert
environment creates. Among the thousands of
desert animal species, there are almost as many
remarkable behavioural and structural adaptations
developed for avoiding excessive heat. Equally
ingenious are the diverse mechanisms various
animal species have developed to acquire, conserve,
recycle, and actually manufacture water.
Desert fauna: how they adapt to
climate
1.
2.
3.
4.
5.
Few large animals life in desert climates
Many animals ( especially mammals and reptiles) are only
active at dawn and dusk
Others like bats, many snakes, and mammals like foxes
are nocturnal, sleeping in a cool den, cave or burrow by
day.
Some smaller animals (insects & reptiles) burrow below
the surface of the soil or sand.
Some like Desert Toads, remain dormant deep in the
ground until the rain arrives.Then they emerge ,breed lay
eggs and replenish their body reserves of food and water
for another long period.
6.
7.
8.
Many mammals have large ears to dissipate heat.These
large ears have many blood vessels which release heat
when the animal is resting.
Reptiles and birds excrete body waste in the form of uric
acid, wasting very little water in the process.
Adaptations can be made to absorb water ie. Camels and
kangaroo rats.
Desert fauna: the camel





Found in Sahara and Middle –
East deserts
Excellent example of adaptation.
Don’t pant and perspire very
little = conserving body fluids
&avoiding unnecessary water
loss.
Ears lined with fur to filter out
sand and dust.
eyes are protected by a double
row of long curly eyelashes that
helps to keep out sand and dust.



Thick bushy eyebrows shield the
eyes from the desert sun.
Broad, flat, leathery pads with
two toes on each foot.When the
camel places its foot on the
ground the pads spread,
preventing the foot from sinking
into the sand.
They can go 5 – 7 days with
little food or water, and can lose
a quarter of body weight
without impairing its normal
functions.
Desert fauna: camel
Desert fauna and soils




Some animals/ insects e.g. scorpions bury themselves in the
sand to escape the intense heat of the day.
The Sidewinder snake uses muscles along its body to move
quickly sideways over the sand and so reduces friction with
the hot surface sand and so does not get burned.
The Marsupial Mole lives a subterranean life, rarely
emerging on the surface.They are totally blind and are fast
burrowers, using their hard nose pad and front feet to
excavate sand, while their luxuriant fur helps reduce the
friction of the sand.
Desert toads after birth bury themselves in the still moist soil
and hibernate for a number of years until the rains appear.
Then they emerge, mate and breed in the temporary ponds
that appear and the cycle begins again.
Slide winder snake
Human interaction in the desert biome
very fragile environment because of a
shortage of water and plants.
 Plants bind the soil in the desert
 If plants destroyed so is the soil
 The soil will quickly erode away in the
strong winds.
 Positive and negetive effects

(1) Recreational Use;
Recreational use of off road vehicles eg
dune buggies and motorcycles destroys
vegetation and compact the soil.
 reduces the soils ability to absorb water.
 landscape more susceptible to wind and
water erosion, resulting in dust storms,
sand storms and muddy flash floods

(1) Recreational Use;
Tourism: This results in the building of
Interpretive Centres, restaurants, rest rooms
etc.
 demand for water rises. Many desert
streams, rivers, and lakes once used by
animals have been drained
 exhaust fumes from vehicles also damage
and destroy fauna and flora.

2) Global warming
Man made emissions of CO2 resulting in
global warming has affected both rainfall
levels and temperatures
 last 25 yrs overall temperatures in Hot
Desert areas has risen between 0.5 and
2.0ºC, (Global average of 0.45ºC)
 Precipitation: deserts of the Middle East
has seen a drop 16%, the Kalahari of
South Africa a 12% decrease.

2) Global warming
As plant species die out so too will the
animals that depend on them.
 Ultimately local soils will be eroded by wind
and water further damaging this fragile
environment.

3) Collection of plants and animals
People who collect rare species of cacti
have completely wiped out entire
populations
 As the cacti become extinct so also does
the natural habitat for certain insects,
birds etc and can lead to their extinction.
 species of lizards have also been targeted
to be sold in the pet trade

3) Collection of plants and animals
vehicles used by the collectors also damage
and destroy fauna and flora and can lead to
soil erosion.
 invasion of non-native plants

4) Development
Deserts are also being destroyed by
development
 buildings plus access roads etc leads to
the clearing away of the natural vegetation
 increase in tourism eg in the Nile Valley,
pressure on water resources
 The development of agriculture in these
arid areas necessitates irrigation

4) Development
valuable natural water supplies reduces the
amount available for local fauna and flora.
 The clearing of the land for crops also
destroys native species.
 Mining and ranching have also decreased
many plant species

5) Hunting
Laws have also been passed against plant
and animal collecting.
 Illegal trade of restricted plants and
animals still occur, but it is not as
common as it used to be.

6) Agriculture
Irrigation has developed farming with in
these areas.
 Countries such as Saudi Arabia, the USA,
Israel and Egypt have benefited greatly
from the use of irrigation.
 Crops grown include cotton, rice, nuts,
olives, peaches and fruit etc

6) Agriculture
impacts are as follows:
 damage to soil due to increased salinity
 pollution of groundwater and oasis
 land subsidence
 destruction of natural habitat
Thar desert (India)
3162 square km
 April, May and June hottest
 Avg temp in this time between 24°C and 41°C
 Dec-Feb temp avg 28°C to 9°C
 Temp affected by lattitude, altitude and distance from
the sea
 Rainfall is 100mm-500mm – mainly july-sept
 Water gathers in small ponds (tobas) / only source of
water in Thar Desert

Soil
Arid, sandy
 10% is shifting sand dunes
 90% fixed dunes, rock outcrops and salt
pans
 Hard pan exists
 Salination – ph 7- 9.5
 Lack of organic matter due to lack of
plants leads to lack of humus
 Soil light grey colour

Flora
Classed as Northen Desert Thorn forest
 Vegetation increases from west to east
due to rainfall
 Drought resistant
 700 plant species with 107 being grass
 Deep rooted and tenacious

Fauna
23 species of lizard
 25 species of snake
 Indian gazelle and wild ass
 Smaller than similar animals in other
climates
 Indian Desert Eagles are the largest flying
predator

Human
Most populated desert, 84 per km2
 Depends on agriculture and animal husbandry
 Pop increase has led to damaging of fragile soil
 Low living standards
 Nomadic people move from one tobas to another
 Livestock are sheep, goats, camels etc
 Irrigation projects – Indira Gandhi Nahar Canal Project
 Desert increasing by ½ km per year
