5 May 2017 - DESERTS




DESERTS

G'day folks,

Australia is supposedly the driest continent on earth, but what is a desert? A desert is a barren area of land where little precipitation occurs and consequently living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation. Here are some more detailed facts.

Basic Facts About 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 .

 

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.



Cool 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.

Semi arid deserts
 


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



 Desert Plants

Most desert species have found remarkable ways to survive by evading drought. Desert succulents, such as cacti or rock plants (Lithops) for example, survive dry spells by accumulating moisture in their fleshy tissues. They have an extensive system of shallow roots to capture soil water only a few hours after it has rained. Additionally, many cacti and other stem-succulent plants of hot deserts present columnar growth, with leafless, vertically-erect, green trunks that maximize light interception during the early and late hours of the day, but avoid the midday sun, when excessive heat may damage plant tissues.

One of the most effective drought-survival adaptations for many species is the evolution of an ephemeral life-cycle. An ephemeral life cycle is characterized by a short life and the capacity to leave behind very hardy forms of propagation. This ability is found not only in plants but also in many invertebrates. Desert ephemerals are amazingly rapid growers capable of reproducing at a remarkably high rate during good seasons.


 
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.



 
  


 Clancy's comment: It amazes me how animals and plants survive in such places. Certainly not a place to be lost.

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