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.
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.
I'm ...
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