Chapter 7Desert and Tundra
DESERTS
RECEIVE LITTLE RAIN – 10-25 cm per year
SOIL IS RICH IN MINERALS – but poor in organic material (nutrients) because there is NO LEACHING – rain that carries minerals deeper into the soil
SOIL is loose and dry and blows away easily in the wind
PAVEMENT – hard desert floor is exposed (hard-baked sand and rock)
DESERT TYPES
TWO TYPES IN NORTH AMERICA
COOL DESERTS –to the east of mountain ranges in the north western U.S. Ex: Sierra Nevada, Rocky Mountains
HOT DESERTS – in the southern U.S. (Ex: Arizona, New Mexico, western Texas, Mexico)
Anza-Borrego Desert State Park, Texas
Badlands National Park, South Dakota
DESERT CLIMATE
Very Low Rainfall – 10-25 cm in any single year
Most deserts receive less than 10 cm
Few short thunderstorms with long dry periods
Temperature Variation – great variation due to lack of moisture in the air Ex: freezing cold at night and searing hot during the day
DESERT PLANTS
Must be able to Absorb and Hold Water in thick spongy tissues (Ex: Cacti or Aloe vera which are succulents)
Adapt to Prevent Water Loss (spines on cactus are modified leaves)
Have broad shallow roots (cacti) or very deep tap roots (mesquite and Joshua tree)
DESERT ANIMALS
Many types of animals: insects reptiles, birds and mammals.
Insects and reptiles have thick outer shells (scorpion, tarantula) or scales (gila monster) to protect them from the harsh climate and retain water
Mammals either stay underground during the day (kangaroo rat) or have adaptations like the long ears of the fennec which help to release heat from their bodies
DESERT FORMATION
Deserts are on every continent except Antarctica
Desert belts form on either side of the equator
Sun rays heat the air at the equator causing rapid evaporation followed by repeated rainfall
The dry air that’s left after the rain moves towards the poles
This causes deserts to form
DESERT FORMATION
RAINSHADOW EFFECT – In the U.S. winds move
from the west coast toward the east coast
Moist air from the Pacific passes over the Sierra Nevada mountains - the cold air forces the water out and leaves cool dry air to continue towards the east.
The cool dry air takes any moisture from the soil east of the mountains and causes deserts to form
DESERTIFICATION Regions near deserts that are not
as dry are called SEMIARID (partially dry).
HUMAN ACIVITY such as overgrazing, deforestation, bad farming practices all cause vegetation loss. Climate change and drought also cause desertification.
Lack of vegetation causes soil erosion, leaving hard packed dirt and rocks exposed.
This changes weather patterns, heats the air and land and starts desert formation.
Spreading deserts are found in Africa, China, Europe (Spain), South America, the Caribbean and the U.S. Results in between 6 and 12 million square kilometers of soil loss.
TUNDRA
COLD, WINDY DRY REGION
LOCATED JUST BELOW THE NORTH POLE
ALASKA, CANADA, GREENLAND, ICELAND, NORWAY, SIBERIA, ASIA
LARGEST BIOME IN AREA – 10% OF THE EARTH’S SURFACE
LIMITED BIODIVERSITY – FRAGILE AND UNSTABLE ECOSYSTEM
TUNDRA FACTS
Less than 25 cm precipitation (mostly snow and ice) per year
Air temperature rarely rises above 10oC (50o F) which is the limiting factor for this biome
PERMAFROST – only the top layer (~ 8 cm) of soil ever defrosts - the rest stays frozen
Rainfall can’t soak into the ground forms marshes and bogs instead
Plants stay low to the ground and do not recover quickly
TUNDRA PLANTS
Short growing season (60 days)
Mosses, lichens, low shrubs and grasses – few trees (willows and birch) are very small
Roots are shallow, because of PERMAFROST
Have to be able to survive long cold winters with no light for 6 months
TUNDRA ANIMALS
Many tundra animals migrate (long-distance seasonal travel) with the weather and the food sources like migrating birds.
Arctic hare, lemmings, ground squirrel, caribou, musk oxen, puffin, snow goose, arctic loon
Few predators: Arctic fox, polar bears, snowy owl, wolverines, wolves,
CHAPTER 7 VOCABULARY
LEACHING
PAVEMENT
SUCCULENT
NOCTURNAL
RAINSHADOW EFFECT
DESERTIFICATION
PREMAFROST
MIGRATION
CLIMATOGRAM