DESERTS

DESERTS 

Deserts are found across our planet along two fringes parallel to the equator at 25–35° latitude in both the northern and southern hemispheres. Deserts are arid or dry regions and receive less than 10 inches of rain per year. Biologically, they contain plants and animals adapted for survival in arid environments. Physically they are large areas with a lot of bare soil and low vegetation cover. The world’s deserts occupy almost one-quarter of the earth’s land surface, which is approximately 20.9 million square miles.

The Mojave Desert is so diverse that it is subdivided into five regions: northern, south-western, central, south-central, and eastern. Elevations range from below sea level at Death Valley National Park to 2.26 miles on Mt. Charleston in the Spring Range of Nevada.

Deserts receive little rainfall, however, when rain does fall, the desert experiences a short period of great abundance. Plants and animals have developed very specific adaptations to make use of these infrequent short periods of great abundance.

Desert Formation

Deserts landscapes are more diverse than many expect. Some are found on a flat shield of ancient crystalline rocks hardened over many millions of years, yielding flat deserts of rock and sand such as the Sahara. Others are the folded product of more recent tectonic movements, and have evolved into crumpled landscapes of rocky mountains emerging from lowland sedimentary plains, as in Central Asia or North America .

Types of Habitat

Hot and dry deserts
The hottest type of desert, with parched terrain and rapid evaporation. In the hot and dry desert soils are course-textured, shallow, rocky or gravely with good drainage and have no subsurface water. They are coarse because there is less chemical weathering. The finer dust and sand particles are blown elsewhere, leaving heavier pieces behind.

Semi arid desertsCool coastal deserts
These deserts are located within the same latitudes as subtropical deserts, yet the average temperature is much cooler because of frigid offshore ocean current. In the coastal desert the soil is fine-textured with a moderate salt content. It is fairly porous with good drainage.

Deserts that are marked by stark temperature differences from season to season, ranging from 100° F in the summer to 10° F in the winter. In the semi-arid deserts the soil can range from sandy and fine-textured to loose rock fragments, gravel or sand.

Polar regions are also considered to be deserts because nearly all moisture in these areas is locked up in the form of ice.

Desert Locations

Most large deserts are found away from the coasts, in areas where moisture from the oceans rarely reaches. Some deserts, however, are located on the west coasts of continents, such as the Namib in Africa, or the Atacama in Chile, forming coastal fog-deserts whose aridity is the result of cold oceanic currents.

The deserts of the world occur in six global bio-geographical realms:

§      Afrotropic deserts are found in the sub-Saharan part of Africa, and in the southern fringe of the Arabian Peninsula. Pressures on the ecosystem from humans are relatively high, especially in the Horn of Africa and Madagascar.

§      The Australasian deserts comprise a series of lowland arid ecoregions in the Australian heartland. Hardly inhabited, their mean population density is less than 1 person per square kilometer. They have by far, the lowest human footprint among the global deserts.

§      The Indo-Malay region has two hot lowland deserts: the Indus Valley and the Thar. These are the deserts with the most intense human use in the world.

§      The Nearctic deserts cover 1.04 million square miles in North America. Because of the growth of large urban conglomerates such as Phoenix in the United States, their mean population density is high.

§      The Neotropic deserts in South America cover 684,000 million square miles, of which only 6 per cent receives legal protection..

§      By far, the Paleartic realm concentrates the largest set of deserts in the world, covering a remarkable 9.9 million square miles that total 63 per cent of all deserts on the planet and are known for their sheer inaccessibility and extreme aridity. The Sahara occupies 9 million square miles, or 10 per cent of the African continent. In contrast, the deserts of Central Asia have folded mountains with high landscape heterogeneity and enclosed basins.

§      Desert Animals

Birds and large mammals can escape critical dry spells by migrating along the desert plains or up into the mountains. Smaller animals cannot migrate but regulate their environment by seeking out cool or shady places. In addition to flying to other habitats during the dry season, birds can reduce heat by soaring. Many rodents, invertebrates, and snakes avoid heat by spending the day in caves and burrows searching out food during the night. Animals active in the day reduce their activities by resting in the shade during the hotter hours.

Threats

§        Military activities and off-road vehicles do cause extensive, lasting damage to the fragile desert cover.

§        Although mining activities affect small areas directly, they have significant impacts on surrounding areas.

§        Grazing pressure on the desert, and especially on the desert margin, is the most extensive agent of land degradation

§        The impacts of changes in precipitation and temperature patterns due to global climate change will be highly variable from one region to the next, but they are likely to be felt the hardest in desert margins and in desert montane areas, as these are where the principal arid rangelands are located.