Hmm, I wonder what a desert is?
Funny you ask that!
Deserts cover 30 percent of earth's surface, yet not many
people know alot about this biome.
To be sophisticated, a desert is:
"An area where evaporation exceeds precipitation"
Where do deserts exist?
General Biodiversity- Producers
• Make food through photosynthesis
• Survive as spores and come to life during rain
• Obtain nutrients from dead matter
• Parasitic form that leeches onto green plants or help them
• Reproduce as spores
Algae and fungi living together
• Fungi surround algae cells
• Live on desert rocks
• Only available nutrients: nitrogen, phosphorus, potassium
• Require hard trunks to keep upright, even with loss of
• Waxy leaves to keep in moisture
• Smaller leaves so less direct sun
Soft spongy interior to hold water
Photosynthesis happens in trunk
2. Woody Shrubs and Trees
Spines to protect from animals
Wide root system
Sage brush, salt brush, cresote,
mesquite, joshua trees
Produce dates which support a lot of
Can grow in soil with high salt content
• Long grasses
• Appear after seasonal rains
General Biodiversity- Consumers
• lack backbones
• termites, locus,spiders
• primary consumers
• frogs and toads
• eat tadpoles during rainy season
• snakes and lizards
• cold-blooded so can survive
• sticky tongue for catching insects
• migrate to the desert
• ground birds- eat plants and insects
• birds of prey- eat small mammals
• rabbits- herbivores
• kangaroos- herbivores
• camels- herbivores
• hyenas- carnivores
Different Types of Deserts
Known as the "hot" desert
• Soils are course-textured, shallow, or gravely
o Coarse b/c of chemical weathering
o Fine dust and sand are blown away- leaving heavier
o good drainage and have no subsurface water.
• Plants are mainly ground-hugging shrubs and short woody
Temperate Desert Biodiversity
Plants (Prickly Pear and Saguaro Cactus)
• Reduction of leaves
• Photosynthesis in stem
• Store mass amounts of water
• Waxy coating
Animals (Bactrian Camel and Zebratail Lizard)
• Nocturnal lifestyle
• Live in burrows
• Slender bodies and long limbs
• Waxy body coating
• Protective eyelids from sun
• Efficient kidneys
• Known as the most extreme of the deserts
• Rainfall is sporadic, sometimes years without a
• Found in the subtropics
o found within 25-40 latitude
• Have the highest annual average temperature on
• Skies remain cloud free
o causes insolation- lets warm air escape at
• Consists of sand dunes and minimal biodiversity
Tropical Desert Biodiversity
Plants (Acacia trees and Palms)
• Low to the ground
o less wind= less water loss
• Store water trunk
• Root spread horizontal
• Small leaves
Animal (Dromedary Camel and Cheetah)
• Light colored
• Live near plants for shade
More aquatic animals
• Nearly all moisture in the air is in the form of ice
• Mostly bedrock or gravel plains
• Snow dunes are in areas where precipitation is more
• Water continually freezes and thaws and creates texture
on the ground
• Most common during ice ages
• During the warmest month the mean temperature is 10 C
Polar Desert Biodiversity
Plants (Saxaul Tree and Tamarix)
• Small shrubs and grass
• Store water in trunk
• Survive high salt content
Animals (Snow Leopard and Golden Eagle)
• Dark fur
• Store water
• Fur for insulation
Tropical vs. Temperate vs. Polar
• Hot and dry most of • Hot in day & cold • Cold
the year at night • Icy
• The sky is cloud • Gravely Soil • Summers are
free • Ground-hugging warm
• Hard surface shrubs
o Rocks and some
• The two main factors that determine
climate are both the temperature and
• The elements of secondary
importance to defining climate are
winds, humidity, air pressure, and
sunshine versus cloud cover.
• Different climates lead to different communities of organisms, especially
• Each biome contains many ecosystems whose communities have adapted to
differences in climate, soil, and other environmental factors.
• Climates change over the earth’s history.
• Temperature, precipitation, and soil type are the most important factors in
producing the type of biome.
• Deserts are the world's
• These climates receive less
than 10 inches of rainfall a
• Often, precipitation over
lands take streamers of
water that evaporate into
the dry air before they even
reach the ground.
• The daily temperature in deserts
• The reason for this fluctuation is
that little humidity is available to
absorb incoming sunlight during
the day and there is virtually no
cloud cover to trap the heat
escaping from the surface at night.
• Deserts come in hot and cool
Hot Deserts: Temperature
• Hot deserts, are the hottest places on
• Hot deserts, daytime temperatures
reach between 105 and 115°F and
occasionally exceed 120°F.
• At night it cools off to around 75°F.
Occasionally, during the winter the
temperature at night drops below
• The world's hot deserts are located in
the subtropics between 15° and 30°
latitude north and south.
Cool Deserts: Temperature
• Cool deserts, afternoon
temperatures in summer reach
• However, it is not uncommon for
nighttime temperatures in winter
to dip below 30°F.
• Cool deserts, on the other hand,
have an annual mean temperature
below 65°F and, for at least one
month out of the year, a mean
temperature below 45°F.
• Humidity is the average amount
of water vapor in the air.
• Lack of humidity is particularly
because hot areas can hold so
• Deserts have long periods of little to no rain before
receiving short bursts of precipitation, but the amount
of humidity that enters the air is rare.
• The desert air is so dry that the rate of evaporation
exceeds the rainfall rate, and the rainfall may
evaporate before it hits the ground.
• Average humidity within deserts: 10% - 40%
Global air circulation is
affected by the rotation of
the earth on its axis.
Atmospheric regions called
cells are made from belts
of major winds
continuously blowing) that
distribute heat and
Coriolis effect ------->
Sunshine vs. Cloud Cover
• Except during dust storms, the atmosphere of a desert is
very clear with a rare occurrence of clouds.
• Because of the lack of cloud cover the incoming solar
energy reaches a maximum.
• Throughout the night, air temperature decreases rapidly,
because there is little counter radiation from clouds.
• Another consequence of sparse cloud cover is that after rain
water in the soil surface evaporates quickly.
Human Effect On Deserts
Deserts of North America
-populated desert in north america
-Tuscon and Phoenix
-use canals and underground irrigation
systems that have destroyed or
degraded an estimated 90 percent of
desert raparian areas like the Gila
Great Basin Desert
-around 1900, humans introduced a
new "cheat grass" that allowed for the
sagebrush to be ignited on fire, and
thus destroyed, helping agriculture
without killing the grass roots.
Human Effect on Deserts
Deserts in South America
-Initial human occupation coincided
with a change from very dry
environments to humid
- associated with drying of the
-through the process of
desertification, the Sahara has been
slowly claiming the arable land in
- Modern technology, such as the
building of the Aswan Dam, has
attempted to halt this process, and
has met with some success
Human Effect On Deserts
- Extreme heat prevails all throughout the day,
while nights are freezing cold in this desert.
-unsuitable for human habitation.
-acted as a barrier to both invasion and cultural
- forced most of China's people to live in the
more fertile east, as no good farmland exists
- fantastic resource of fossils
Human Effect On Deserts
-significant human settlement
-extensive sheep and cattle grazing
-there has not been a process of desertification (i.e. spread of the
-most obvious signs of recent human impacts on Australian deserts
have been the extinction of native plants and animals, the invasion of
introduced species, and changes in the timing and extent of natural
processes such as fire.
This is a quick overview of the material we went over in class.
Click on link below:
"Living in the Environment" Chapter 5 powerpoint and resources
"Climate" Science in Context 2008
"Desert" Science in Context July 1, 2009
Video Biomes: Our Earth's Major Life Zones