Desert and Tundra Biomes
Chapter 3
7.1 Deserts
Objectives
Describe the characteristics of a desert
Explain how desert organisms adapt to live in
their environment
Deserts are different,
but they all receive
very little rain.
Deserts continued
Desert soil
– Rich in minerals
– Poor in organic materials
– Very little leaching
Leaching a process where rainwater moving
through soil carries minerals deeper into the
soil
– Little rain -> little leaching -> upper desert soil rich
in minerals
Deserts continued
Lack of rainfall makes deserts dry
– Prevents many plants from living there
– Slows decay of organic material
– Not much topsoil
– Soil easily blown away
• Exposing the Pavement
Pavement
The lower layer of the desert soil
It is the desert floor
Made mostly of
– Hard-baked sand
– Bare rock particles
– Or both
Types of Deserts in the US
Cool Deserts - Sagebrush
– On eastern side of the mountains in western US
Hot Deserts - Cactus
– In the southwest:
• Arizona,
• New Mexico and
• western Texas
Desert Climate
Lack of precipitation is the limiting factor
Less than 25 cm per year, most less than 10
cm
– Determines the types of plants
• Determines the types of animals
Most rain during a few short storms
Most water runs off due to compacted
pavement
Desert Temperature
Varies Greatly
Moisture helps to stabilize temperature
– Acts like a blanket
– Absorbs heat in day
– Holds in warmth at night
Without this moisture, desert temperature rise
and fall dramatically within 24 hour periods
Desert Biome Video
Desert Organisms
Must be adapted to survive with
– Lack of water
– Extreme temperatures
Despite these challenges, deserts are actually
species-rich complex ecosystems
Desert Plants
They Must
– Be able to absorb scarce water from ground
– Prevent water loss form tissues
• Cactus spines (leaves) reduce water loss by reducing surface area
Succulents – have thick water filled tissue (cacti, aloe
vera)
– An attractive source of food and water for desert animals
– Spines also help protect from being eaten by animals
Desert Plants
continued
Another adaptation is the roots
Some shallow but covering a wide area
Others grow very deep
Both help to maximize the amount of water they
can get
Desert Animals
Many types
Most get water from their food
Most have adaptations to help reduce water loss
Also adaptations to survive the heat
– Many are nocturnal – active at night, sleeping during
the heat of the day
7.2 Formation of Deserts
Objective
Illustrate the processes that cause deserts to
form.
Natural Desert Formation
Two broad belts of deserts
– Northern one near Tropic of Cancer
– Southern near Tropic of Capricorn
Around the equator (tropics) very moist air
After moisture has fallen as rain air becomes dry
Then flows towards poles becoming cooler and
heavier
Sinks back to earth as dry winds forming deserts
Rainshadow Effect
Exact locations are determined by local
geographic features such as mountains
In U.S.
–
–
–
–
–
–
Winds move from west to east
Forces warm moist air over mountains
Drops moisture on mountains
Cool dry air reaches eastern side
Picks up moisture from soil
Soil becomes very dry forming desert
Life in the Desert Video
Desertification
Deserts often bordered by semiarid regions with
grasses and shrubs
Human activity (raising livestock) has caused
these semiarid regions to become deserts
The process of changing semiarid land into
desert as a result of human activity is called
desertification
Human Impact on the Desert
7.3 Tundra
Objectives
Describe why the
characteristics of the tundra
make it a fragile ecosystem
Compare the characteristics
of tundra organisms with
those of their relatives in
warmer climates
The tundra is a cold , windy, dry region.
Tundra Facts
In northern hemisphere just south of polar ice
caps in Alaska, Canada, Greenland, Iceland,
Norway and Asia
A large biome –10% of Earth’s surface
Fewer types of organisms than any other
biome
Lack of diversity makes them fragile and
unstable
Tundra Video
Tundra Climate
Like a desert little precipitation
– Less than 25cm per year
A cold climate
– Usually below 10 degrees Celsius
Most precipitation falls as ice or snow
Temperature is the limiting factor
Permafrost
Only the top layer, or active zone, of soil thaws in
summer
The active zone may be as thin as 8 cm
The frozen soil beneath the active zone is called
permafrost
A dense mat of mosses, grasses, and other plant life
keeps the ground insulated and prevents the permafrost
from melting
Any disruption of this mat affects the permafrost
Tundra Climate continued
Tundra vegetation does not recover from disruption as
quickly as in other biomes
Rain in summer cannot penetrate the permafrost
Water collects forming bogs,, marshes, ponds, and
streams
Creates a great breeding ground for mosquitoes and
black flies (an important link in the food web)
Permafrost is therefore important to the stability of a
tundra ecosystem
Tundra Organisms
Plants
– Short growing season
– Small and close to ground
– Ground warmed by radiant energy
– Roots close to surface
– Small trees (less than 1 meter)
– Lichens are very important producers
Tundra Animals
Seasonal visitors (migrate south for winter)
Safe place for breeding due to less predators
Birds feed on mosquitoes and flies
Predators feed on birds
Caribou- large migratory mammal
– Thick coat big hooves
– Feed on lichen
Fox, Bears, Wolverines don’t migrate
The
End