Desert biomes exist when the annual rainfall is less than 50 centimeters annually and they cover about one fifth of the Earth’s surface. Because warm air has the capacity to hold more moisture than average, rainfall is less likely to occur in areas that are classified as desert. Many of the Earth’s deserts are situated either 30 degrees north or 30 degrees south of the equator, but there are major deserts in other latitudes.
The most common classifications for deserts are: Hot and Dry, Semi Arid, Coastal and Cold.
The Hot and Dry deserts are at very low altitude, where heat is at its highest levels. These are generally hot and dry deserts, and the term hot and dry is one type of classification for deserts. This type of desert exists in North America: Chihuahua, Sonora, Mojave and Great Basin. Other hot and dry deserts are in Asia, Latin America, Ethiopia and Australia.
The daily temperatures are extreme, with very hot days due to the lack of moisture in the atmosphere to block the suns rays. As a result, they get more of the heat, but also lose the heat very quickly. By some estimates, about twice the heat of more moisture laden areas builds up in the day and about twice the heat is lost at night. Annual rainfall is about 1.5 cm/.6 inch annually. Temperatures can reach highs of 120 F/49C. Low temperatures can reach freezing levels.
The soil is coarsely grained, as there is less chemical action from water and less breakdown from water movement. In addition, finer particles have blown away over time. Plants tend to be short or water retentive with thick cuticles, and there is a decided lack of a plant canopy. Animals tend to be nocturnal burrowers or scavengers, insects and arachnids. There is, however, plenty of life in hot and dry deserts.
The Semi Arid deserts are hot and dry in the Summers, with some low amounts of rainfall in the Winter. There are more concentrations of dew which might bring more moisture than the annual rainfall in Hot and Dry deserts. The American Great Basin Sagebrush deserts of Utah, and Montana, plus Russian, European, Greenland and North Asian Semi Arid Deserts are examples.
Temperatures in the Semi Arid Deserts average in the 70-80F/21-27C range, with some visits to the low 100s F/ 39C range. Nights are cool, in the 50 F/ 10 C region, which allows more moisture retention in plants and animals. The soil is more finely textured, with loose rocks, gravel and sand.
Semi Arid plants have spiny, hairy or glossy leaves and can have bad odors in order to ward off predators. Sagebrush, Creosote, thorn bushes, sage and mesquite grow in semi arid deserts. Animals are burrowing animals and insects as well as rabbits that follow the shadows of the brush, burrowing owls, and kangaroo rats.
The Coastal deserts have the Atacama of Chile as an example. These deserts hug the edges of continents where cold coastal currents exist. They are generally near the tropics of Capricorn and Cancer. These are referred to as “unstable” deserts, as local winds may overwhelm the trade winds, and they are at the junction of ocean, terrestrial and atmospheric conditions. With upsurges of cold coastal air, fog forms, blocking sunlight but producing moisture laden fog.
Soil has a higher salt content than in Semi Arid or Hot and Dry deserts. Plants have thick leaves and well established root systems. Salt Bush, Buckwheat Bush, Rice Bush and Black Sage are some of the plants. With the presence and absence of water, the animals and insects include those which can go dormant. Fairy Shrimp, toads, horned owls and bald and golden eagles, along with coyotes, lizards and snakes live in the costal deserts.
The Cold Deserts are located in the Antarctic,Greenland and the Nearctic regions. Annual temperatures average freezing in the winter to highs around 70F/20C in the Summer. There is high snow and rainfall in the Winter, with rains that may go through the Summers. Soil is alluvial fan, pourous, and with good drainage and salt leaching due to the high moisture.
Cold deserts host widely spaced deciduous, low profile plant life, only about 10 percent coverage, except for areas of sagebrush that may approach 80 percent coverage. Widely spaced burrowing animals include jackrabbits, rats and mice and some ground squirrels, along with carnivores, such as badgers, coyote and kit fox. Lizards are the reptiles, and some deer are around during Winter.
CITATIONS:
Coastal Deserts
