Mature biological, cryptobiotic crust on desert soil surface, Coconino National forest, Arizona

Biological soil crusts are important components of desert ecosystems. They are a mix of organisms and their metabollic byproducts, including cyanobacteria, bacteri, liverworts, algaes, lichens and fungi. They help plants by stabilizing sand and dirt, preventing erosion, retaining moisture, and fixing nitrogen. Cryptobiotic soils are extremely fragile - a footprint or tire track can disturb the crust and harm the organisms. In arid regions recovery can take a century or more.