Desert Biome

Deserts cover about one fifth of the Earth’s surface and occur where rainfall is less than 50 cm/year.

Although most deserts, such as the Sahara of North Africa and the deserts of the southwestern U.S., Mexico, and Australia, occur at low latitudes, another kind of desert, cold deserts, occur in the basin and range area of Utah and Nevada and in parts Asia.

Soils often have abundant nutrients because they need only water to become very productive and have little or no organic matter.

Disturbances are common in the form of occasional fires or cold weather, and sudden, infrequent, but intense rains that cause flooding.

There are relatively few large mammals in deserts because most are not capable of storing sufficient water and
withstanding the heat. Deserts often provide little shelter from the sun for large animals. The dominant animals of
warm deserts are nonmammalian vertebrates, such as reptiles. Mammals are usually small, like the kangaroo mice of
North American deserts.

Desert biomes can be classified according to several characteristics. There are four major types of deserts:

Hot and Dry Desert

• The seasons are generally warm throughout the year and very hot in the summer. Temperatures exhibit daily extremes because the atmosphere contains little humidity to block the Sun’s rays. Desert surfaces receive a little more than twice the solar radiation received by humid regions and lose almost twice as much heat at night. Many mean annual temperatures range from 20-25° C.
• Rainfall is usually very low and/or concentrated in short bursts between long rainless periods. Sometimes rain starts falling and evaporates before reaching the ground. Rainfall varies in depending on the location from 1.5 cm. 28 cm a year and some years may even be rainless.
• Soils are course-textured, shallow, rocky or gravely with good drainage and have no subsurface water.
• Plants are mainly ground-hugging shrubs and short woody trees. In the cacti, the leaves are much-reduced (to spines) and photosynthetic activity is restricted to the stems. Some plants open their stomates only at night when evaporation rates are lowest. These plants include: yuccas, ocotillo, turpentine bush, prickly pears, false mesquite, sotol, ephedras, agaves and brittlebush.
• The animals include small nocturnal (active at night) carnivores. The dominant animals are burrowers and kangaroo rats. There are also insects, arachnids, reptiles and birds. The animals stay inactive in protected hideaways during the hot day and come out to forage at dusk, dawn or at night, when the desert is cooler.

Semiarid Desert

• The summers are moderately long and dry, and like hot deserts, the winters normally bring low concentrations of rainfall. Summer temperatures usually average between 21-27° C.
• As in the hot desert, rainfall is often very low and/or concentrated. The average rainfall ranges from 2-4 cm annually.
• The soil can range from sandy and fine-textured to loose rock fragments, gravel or sand. There is no subsurface water.
• The large numbers of spines shade the surface enough to significantly reduce transpiration. The same may be true of the hairs on the woolly desert plants. Many plants have silvery or glossy leaves, allowing them to reflect more radiant energy. Semiarid plants include: Creosote bush, bur sage, white thorn, cat claw, mesquite, brittle bushes, lyciums, and jujube.
• Many animals find protection in underground burrows where they are insulated from heat. These animals include mammals such as the kangaroo rats, rabbits, and skunks; insects like grasshoppers and ants; reptiles are represented by lizards and snakes; and birds such as burrowing owls and the California thrasher.

Coastal Desert

• These deserts occur in moderately cool to warm areas. The average temperature ranges from 5¾- 24° C.
• The average rainfall measures 8-13 cm in most areas.
• The soil is fine-textured with a moderate salt content. It is fairly porous with good drainage.
• Some plants have extensive root systems close to the surface where they can take advantage of any rain showers. All of the plants with thick and fleshy leaves or stems can take in large quantities of water. The plants living in this type of desert include the salt bush, buckwheat bush, black bush, rice grass, little leaf horsebrush, black sage, and chrysothamnus.
• Some animals have specialized adaptations for dealing with the desert heat and lack of water. Some toads seal themselves in burrows with gelatinous secretions and remain inactive for eight or nine months until a heavy rain occurs. Amphibians that pass through larval stages have accelerated life cycles, which improves their chances of reaching maturity before the waters evaporate. Some insects lay eggs that remain dormant until the environmental conditions are suitable for hatching. The fairy shrimps also lay dormant eggs. Other animals include: insects, mammals (coyote and badger), amphibians (toads), birds (great horned owl, golden eagle and the bald eagle), and reptiles.

Cold Desert

• These deserts are characterized by cold winters with snowfall and high overall rainfall throughout the winter and occasionally over the summer.. The temperature range is between -2¾ to 26° C .
• The winters receive snow. The mean annual precipitation ranges from 15-26 cm. The heaviest rainfall is usually in April or May.
• The soil is heavy, silty, and salty.
• The plants are widely scattered. Plant heights vary between 15 cm and 122 cm. The main plants are deciduous, most having spiny leaves.
• Widely distributed animals are jack rabbits, kangaroo rats, kangaroo mice, pocket mice, grasshopper mice, badger, kit fox, and coyote, ground squirrels, and several lizards. Deer are found only in the winter.

edited from information on UCMP The World's Biomes website