Hot deserts (p.65, Understanding GCSE Geography)

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Hot deserts(p.65, Understanding GCSE Geography)

• Learning objective.
• To be able to recognise the characteristics of
  the vegetation, climate and soils of hot deserts.
  
• To be able to describe the main adaptations of
  vegetation to soil and climate in hot deserts.

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Starter.Imagine that you travel along the 20o
longitude line North from the Equator to the
Arctic Ocean.Write the biomes you would pass
through in the correct order.(Mediterranean,
Tropical rainforest, Coniferous forest, Deciduous
forest, Tundra, Hot desert, Savanna
grassland)Use the Biomes map to help you.
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Exam technique exercise.1 . Figure 1 shows the
location of areas of tropical forest. It also
shows changes in the area covered by forest
between the year 2005 and 2010.
(a) Study Figure 1. Describe the distribution of
forests shown in Figure 1.
(b) Suggest two reasons for this distribution.
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• Now compare your answers to these model answers.
• (a) Tropical rainforests are distributed mainly
  along the equator, between the Tropics. For
  example, the Amazon basin in South America, the
  Congo basin in Africa and parts of South East
  Asia

(b) They are distributed in this way because
these areas have a tropical climate with high
temperatures (27o ) and high precipitation
(2,000mm). These areas do not have very
different seasons, because in the Tropics the day
length does not vary very much so there is always
the same amount of insolation
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Hot deserts are examples of extreme environments
caused by great daytime heat under a baking sun
and absence of rainfall. Although surface
vegetation is sparse, small and separated by
large areas of bare ground, it does exist, even
in the driest place on Earth, the Atacama desert.
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Task. Make a copy of the table
below.As we go through the next 6
slides fill in the table.
Plant Adaptation to the climate.
Cacti 1. 2. 3.
Thorn bush 1. 2. 3.
Desert flowering herb 1. 2.
Date palm
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Plants need to grow far apart so that they are
not competing for scarce resources, principally
water. Vegetation with adaptations for living in
a dry environment is called xerophytic.
One type is a succulent - a plant that stores
water in its stem for use during the long periods
of drought. Cactus is the
best-known example.
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The other type of desert plant has very deep
roots to enable it to tap underground water
supplies
It has shallow roots to trap water from
infrequent rains. Thorns help reduce water loss,
as well as protecting the plant from desert
animals.
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Only a small part of the plant is above the
surface, where it is exposed to the scorching
heat. Plants like this are woody and often thorny
to reduce water loss to a minimum. Any leaves
they have are tough and leathery, reducing
transpiration further by means of dense hairs
that cover their surfaces.
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Plants have adapted to survive in hot deserts in
other ways as well. Some have incredibly strong
seeds, which lie dormant for years, until it
rains. Then the desert blooms. The appearance of
bare rock and sand surfaces is transformed by the
abundance of flowering plants.
The Mojave desert, California after a rare heavy
rainfall
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These can only bloom for as long as water is
available they are annual plants with no
xerophytic adaptations of their own. It is their
seeds that are adapted to the dry desert climate.
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Most desert soils have no organic content they
are made up of pieces of rock and sand. In
low-lying areas, where water is closer to the
surface, desert soils re often saline (salty).
One of the few plants that has the ability to
grow in saline groundwater is the date palm.
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Task.HigherComplete the Hot desert ecosystem
summary sheet. Higher using Understanding GCSE
Geography to help you. FoundationComplete the
Hot desert ecosystem summary sheet.
Foundation using Understanding GCSE Geography to
help you. Start by drawing a sketch of a
climate graph for the hot desert climate in the
box on the sheet.
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Task.Do activity 2, page 65.
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• Key points for you to know for revision.
• The hot desert biome has a rainfall lt 250mm per
  year.
• The plants in deserts are xerophytes (adapted to
  living in dry conditions).
• Many plants are succulents (like cacti) and store
  water in their stems.
• Other adaptations include deep tap roots,
  leathery leaves, dense hairs, and thorns.
• Ephemeral plants survive as seeds and grow fast
  when the infrequent rain does come. They then
  die and survive as dormant seed in the ground.
• The soil is made up of rock and sand with no
  humus (organic content).