Deserts have an annual rainfall of less than 25 cm. Typically highly variable.

Deserts cover about 12% of the continents.

Temperature also variable:

Hot deserts

Cool deserts

Cold deserts

Conditions that contribute to desert formation:

Prevailing high pressure

Rain shadows

Cold coastal waters

Substrate conditions are a key factor

May find a concrete-like caliche at depth, formed by leached carbonates.

Desert landscapes not subjected to human activity may actually be very stable.

May develop sand dune systems.

Desert washes may vary in pattern, but typically maintain a stable position on the landscape.

Desert soils typically have a relatively stable surface layer. Sometimes, the removal of fine soil has resulted in a “desert pavement”.

Desert soils may develop a soil crust.

Algae, fungi, and lichens can form a cryptobiotic crust.

If disturbed, such crusts may require 200 years to reestablish.

the root- CWNP articles

DESERT CRUSTS

Arid and semiarid are particularly vulnerable to human impact.

Impacts include:

Overgrazing

Cutting of fuel-wood

Physical disturbance of the surface.

Bromus forms a continuous ground layer. When it dies, it promotes fires. Many desert shrubs cannot resprout after a fire.