Technically, any area that averages less than 10 inches (25 cm) of rain per year qualifies as a desert. The desert biome mostly lies in subtropical latitudes, stretching across parts of Asia, Africa, and North America. To survive here, flora and fauna must compete for water and withstand harsh sunlight, high temperatures, and strong winds.
The desert biome can be subdivided into dry, cold, shrub, and coastal desert. In general, sandy, rocky soil is rich in mineral nutrients but poor in organic matter. Temperatures vary greatly, especially for high elevation deserts, from a blazing 111º F (44º C) to a frigid 0º F (-18º C). Deserts are often formed in the shadow of great mountain ranges that block storms and bring winds that don't carry much moisture. In fact, more moisture evaporates into the atmosphere than falls as precipitation in most deserts.
Some semi-arid areas support shrubs and cactus, but deserts have very little plant cover. Plants stay spread out, in order to access enough moisture in the ground. These drought-resistant plants are known as xerophytes. Some have adapted stomata, pores that can open and absorb water during a storm, but close during the heat of the day. Unlike most of the world, leaves don't have to compete for sunlight, but protect themselves from its searing power.
With so little plant cover, erosion poses a serious problem. Some areas with dunes shift significant amounts of soil in a process called deflation. Strong wind moves light grains of sand to form and reform dunes. There, hardly any plant or animal can live on the constantly shifting surface.
In more hospitable areas, nocturnal animals take advantage of the cool of dawn, dusk, and night. Kangaroo rats, owls, snakes, and bobcats all hunt or forage under cover of darkness. During daylight, they burrow deep underground, or stay in the shade of cacti. In the milder coastal or shrub deserts, there are plentiful quantities of diverse reptiles, amphibians, insects, birds, and rodents.
