Geography Reference
In-Depth Information
produce
rain shadows
(leeward slopes that lack rain) create dry, desert conditions. These causative
factors occur over a wide latitudinal range, which explains why deserts are rather widely distributed.
Hollywood movies have a penchant for depicting deserts as seemingly never-ending seas of
sanddunes.Peoplewholiveindesertareasorwhohavetraveled throughthemknowdifferent,
however. Most deserts are covered mainly by gravel, with enough sand and soil mixed in to
support plant life. The descriptive term for this is
reg,
a word that English-speaking students
of desert environments have borrowed from Arabic, a language which was born in desert sur-
roundings and therefore has a much richer desert-related vocabulary than does English. Con-
trary towhat Hollywood might have youbelieve, about 65percent ofthe Sahara is
reg.
Anoth-
er 30 percent is
erg,
the classic sand dune landscape. The remaining 5 percent is
hammada,
or
rock-covered.
The natural vegetation of deserts consists of
xerophytes
(“dry-loving” species), which are plants that
have adapted to dry conditions. To help conserve internal moisture, and thus live in lands where they
would otherwise transpire to death, most xerophytes have defense mechanisms. These may include
tough (even waxy) exteriors often complemented by thorns that ward off birds and other animals that
might peck away at their exteriors and expose fleshy innards to the hot dry air. Because it takes a
rather specialized plant to thrive in desert conditions and usually a very long time to grow to maturity
in these regions of low-moisture availability, some xerophytes of the American Southwest (such as
the giant saguaro cactus) are now protected by law.
Semi-desert (steppe)
Areas with semi-desert climate receive between 10 and 20 inches of precipitation per year. They nor-
mally are located between deserts and humid climate-types of either the tropical or middle latitudes.
Semi-desert owns the record for the greatest latitudinal range. Instances of it are found on the equator
in East Africa and in Western Canada at about Latitude 52° North. The same climatic determinants
that explain the rather broad distribution of deserts also generally explain the geography of semi-
desert. The natural vegetation of this climate is
steppe
— short grasses that grow in clumps with bare
earth in between. Steppe is Russian in origin and describes what one sees in the vast, treeless, semi-
arid plains of south-central Eurasia.
Crop-growing without irrigation in semi-desert areas is an iffy proposition. During those years
when precipitation is average to above average, some production is possible. Below-average years,
