Biological Soil Crusts
Biological soil crusts, a specialized community of cyanobacteria, algae, microfungi, lichens, and bryophytes, typically cover the open spaces in arid and semiarid regions. They provide key ecosystem services, such as increasing erosion resistance, generally increasing infiltration, contributing organic matter, and fixing atmospheric nitrogen. Cyanobacteria weave through the top few millimeters of soil, providing stability and fixed nitrogen. Lichens (a composite, symbiotic organism comprised of a fungus and either a cyanobacteria or a green algae) and bryophytes (small, non-vascular plants, including mosses and liverworts) occur on the surfaces of soil. While biological soil crusts can be found on almost all soil types, their distribution is influenced by soil chemistry, elevation, timing of precipitation, vascular plant community structure, and disturbance. Recovery of a disturbed biological soil crust community depends on several factors, including the type of disturbance and the climatic regime. Disturbed crusts recover slowly in areas with high annual temperature and low annual precipitation.