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South western USA
Managing hot deserts…read more

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The Sonoran desert- Location
· Located on the borders of Southern California, Sothern
Arizona and Northern Mexico.
· Area is made up of mountain ranges, plains and basins
underlain by igneous or metamorphic sediments
· The most arid part is the Salton trough, which is the lowest
part at 71m below sea level.
· From the Gulf of California the relief rises through the Sonora
uplands towards the Sierra Madre Occidental Mountains.…read more

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· Sonoran is a arid desert created by its position in a subtropical
high pressure zone (air subsides and is warmed up stopping
clouds from forming, also prevents air rising off the ground
and forming clouds)
· The peninsular ranges cause aridity by preventing winter
westerly's spreading in from the pacific creating the rain
shadow effect.
· The cold Californian Ocean current reduces humility along the
· Temperatures range from 11 degrees C in January to 30
degrees C in July. Temperatures can be 40 degrees C in the
Salton trough.
· Rain is bi-seasonal.…read more

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Plant and Animal adaptations
· Plant adaptations
· Saguaro cactus
· Can be 15m tall and can live for 175 years
· Accordion like stem which can expand and fill with water during periods of rainfall (succulent)
· Ribbed stem reduces wind currents, which would reduce evaporation losses.
· Shallow roots catch water that falls from storms before it evaporates.
· Mesquite bush
· Phreatophytes grow beside streams and on edges of salt pans
· Are able to survive in soils of high salinity (halophytes)
· Prickly pear
· Fleshy stems store lots of water (succulents)
· Waxy skin less water loss via transpiration (cuticle)
· Spines instead of leaves- reduce water loss as spines have a smaller surface area and they help to protect the plant
from predators.
· Animal adaptations
· Ring tail lemur
· Nocturnal- to avoid the heat at daytime and to avoid predators.
· Gets a lot of water from seeds
· Desert tortoise
· Burrows underground to escape heat on the surface
· Stores water in its bladder
· Harris squirrel
· Thick tail used for protection from the high insolation from the sun
· Kangaroo rat
· Drinks no water so instead gets water from the seeds it eats…read more

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Disturbances of land use and agriculture
· Cities such as Phoenix have replaced deserts containing cacti and creosote bushes
· Water is taken from rivers and ground water to support cities with a growing population.
This has affected Phreatophytes such as mesquite bushes that grow along river banks by
reducing the amount of water available to them.
· Roads being constructed and gas and water pipelines have displaced natural habitats.
Fenced highways restrict the migration of animals such as the pronghorn antelope as they
migrate in drought seasons in search of water. A drought in 2001-2 caused numbers to fall
as the fences prevented them from reaching the water.
· The increasing amount of vehicles off road from tourism and the military bases in the
Mojave Desert have damaged soil and plants as tank tracks and car tyres crush stems and
leaves and compact the soil, reducing the soil's ability to hold air and water.
· Overgrazing by cattle has compacted soils and destroyed Cryptobiotic soil crusts, these
prevent erosion, absorb water and fix nitrogen, which provides other plants with an ideal
habitat to germinate, and cattle have also destroyed lizard and tortoise habitats.
· Domesticated animals such as Donkeys have escaped and multiplied in the wild, which
caused a decline in native species like the bighorn sheep.
· Non-native species like tamarisk introduced as a windbreak displacing cotton woods, and
desert willows. Baffle grass was introduced to improve pasture; by occupying gaps in the
vegetation it has increased the fire risk. In 1994 a fire affected 1150 acres of Saguaro
national park, which destroyed 340 acres of desert scrub and killed many tortoises. The
saguaro cactus was not fire resistant so 20% died.…read more

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