ABSTRACT
The lack of water in semiarid and desert regions restricts the development of vascular plant cover. As a result, most of the surface of the ground is exposed to full sunlight and the elements, in response to which a heterogeneous mix of microbiological and cryptogamic communities often occurs. Biological surface communities in semiarid lands and hot and cold deserts show a superficial similarity around the globe. Among factors most influential in determining the kinds of biological surface features and their activities are parent materials (mineral substrates), soil texture, light, source and availability of water, temperature regime, topography, history of use, and time.
