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World Biomes
Deserts
Global Air Circulation
Climate
• Dry desert climates are formed by highpressure zones in which cold air descends.
Then the descending air becomes warm but,
instead of releasing rain, the heat from the
ground evaporates the water before it can
come down as rain. The ground is super hot
because the sun's rays beat down on it directly
overhead. Not a lot of atmosphere to protect it
from radiant energy.
• Approximately 0.25 cm of rain falls in dry
deserts per year. The average annual
temperature of these miles of hot sand is 18°
C.
Distribution of biome
• The latitude range is 15-28° north and south of
the equator. Their global range covers about
1/5 of the earth, including the world's great
deserts: Sahara, Sonora, Thar, Kalahari and
the Great Australian.
Distribution
Soil
• There is poor
development of
horizons, with
accumulation of calcium
carbonate at or near the
surface. Sparse
vegetative cover and
tiny leaves results in
little humus and soils
typically have a light
gray colour.
Plants I
• Plants of the Dry Desert have adapted to the
lack of water by using dew for moisture and
taking in water through their leaves and stems.
• Shrubs are the dominant growth form of
deserts. They may be evergreen or deciduous;
typically have small leaves; and frequently
have spines or thorns and/or aromatic oils.
Shallow but extensive root systems procure
rainwater from well beyond the canopy of the
shrub whenever it does rain.
Plants II (growthforms)
• Some plants have long taproots that may
extend downward 20 to 30 feet to tap ground
water supplies. Especially along intermittent
streams or under dunes, underground water
may be readily available.
• Succulents store water accumulated during
rains for use during the intervening dry spells.
Different species store water in different parts
of the plant.
Plants III (growthforms)
• Another growthform adapted to desert
conditions is the ephemeral. This is an
especially short-lived annual plant that
completes its life cycle in two-three weeks.
The seeds are encased in a waterproof
coating that prevents desiccation for years if
necessary.
• Perennial plants with underground bulbs
store nutrients and water in underground
tissues and also remain dormant most of the
year. They can sprout rapidly after sufficient
rains and replenish their underground stores.
Saguaro Cactus
Brittle Bush
Welwitschia
Animals I
• Behavioral adaptations such as being active
during night and staying the shade during the
heat of day are common.
• Morphological adaptations. The better to
radiate body heat to the environment from
warm-blooded animals, body sizes are small.
Bodies are light coloured to reflect sunlight
and help prevent the absorption of heat form
the environment.
Animals II
• Rarer, but important, are physiological
adaptations such as dormancy during
summer, the absence of sweat glands, the
concentration of urine, localized deposits of fat
in tails or humps; and salt glands to secrete
salt without loosing fluids.
• Reptiles with their waterproof skin, production
of uric acid instead of urine, hard-shelled eggs,
and ability to gain body heat directly from the
sun and to retreat to shade or underground to
avoid heat are exceptionally well adapted to
drylands.
Jerboa
Horned lizard
Gila Monster
Scarabeus
Cactus Wren
Scorpion
People I
Bushmen
People II
Bedouins
Oasis
People III
Oil drilling