1. Introduction to desert environments
Arid desert land occupies as much as 33% of the global terrestrial
surface, much of which surrounds the equator. The Sahara desert
alone occupies the same square acreage as the United States. Arid
climates are defined by the significant absence of rainfall. Within
this climate zone are three generally accepted subcategories:
hyper-arid regions, which receive less than 100mmannual rainfall,
arid regions, which receive 100e300 mm annual rainfall and subarid
regions, which can receive up to 800 mm annual rainfall. Of
these three subcategories, arid is the most common, occupying
14.6% of the world’s land area (FOA Forest, 1989).
While rainfall averages are useful in generalizing the arid
climate, there are also vast exceptions in drought/rainfall cycles.
The Atacama Desert in Chile suffered a 400-year drought, interrupted
in 1971 by a torrential downpour. The Atacama, one of the
driest deserts in the world, is considered the physiological dryness
limit for life (Davila et al., 2008). What little precipitation does
occur in such harsh environments is not always available to thespecies. After dusk, near or below freezing temperatures can freeze
and lyse plant cells. Hot deserts typically experience diel temperature
ranges from 0 C to 37 C, while cold deserts such as those in
Greenland, can fluctuate from as little as 0 C to 4 C. The Hopq
Desert in China experiences minimum temperatures below 30 C
and high temperatures above 40 C