Desert and Tundra Biomes

Chapter 7

7.1 Deserts

ObjectivesDescribe the characteristics of a desertExplain 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 soilIt is the desert floorMade 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 factorLess 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 stormsMost water runs off due to compacted pavement

Desert Temperature

Varies GreatlyMoisture 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 rootsSome shallow but covering a wide areaOthers grow very deepBoth help to maximize the amount of water they can get

Desert Animals

Many typesMost get water from their foodMost have adaptations to help reduce water lossAlso adaptations to survive the heat– Many are nocturnal – active at night, sleeping during

the heat of the day

7.2 Formation of Deserts

ObjectiveIllustrate 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 airAfter moisture has fallen as rain air becomes dryThen flows towards poles becoming cooler and heavierSinks back to earth as dry winds forming deserts

Rainshadow Effect

Exact locations are determined by local geographic features such as mountainsIn 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 shrubsHuman activity (raising livestock) has caused these semiarid regions to become desertsThe process of changing semiarid land into desert as a result of human activity is called desertification

Human Impact on the Desert

7.3 Tundra

ObjectivesDescribe why the characteristics of the tundra make it a fragile ecosystemCompare 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 AsiaA large biome –10% of Earth’s surfaceFewer types of organisms than any other biomeLack 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 snowTemperature is the limiting factor

Permafrost

Only the top layer, or active zone, of soil thaws in summerThe active zone may be as thin as 8 cmThe frozen soil beneath the active zone is called permafrostA dense mat of mosses, grasses, and other plant life keeps the ground insulated and prevents the permafrost from meltingAny disruption of this mat affects the permafrost

Tundra Climate continued

Tundra vegetation does not recover from disruption as quickly as in other biomesRain in summer cannot penetrate the permafrostWater collects forming bogs,, marshes, ponds, and streamsCreates 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 OrganismsPlants–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 AnimalsSeasonal visitors (migrate south for winter)Safe place for breeding due to less predatorsBirds feed on mosquitoes and fliesPredators feed on birdsCaribou- large migratory mammal– Thick coat big hooves– Feed on lichen

Fox, Bears, Wolverines don’t migrate

The End