Cryptobiotic crusts comprised of algae, lichens, mosses, microfungi, and bacteria are also important components of many of the plant communities. They are often seen as a black crust or covering on the soils beneath the plants. These small organisms play an integral role in binding and protecting the soils from erosion, in fixing nitrogen for the plants to use, in storing water, and in the nutrient cycling process that further develops the soils. - NPS