Crust vegetation

Biological soil crusts, often abbreviated as biocrusts, are communities of living organisms inhabiting the surface of soils in arid and semi-arid ecosystems, which form stable aggregates of soil particles in a thin layer millimeters to centimeters thick. They are found throughout the world with varying species composition and cover depending on topography, soil characteristics, climate, plant community, microhabitats, and disturbance regimes. An estimated 12% of Earth's surface is covered by biocrusts. Biological soil crusts perform important ecological roles including carbon fixation, nitrogen fixation and soil stabilization; they alter soil albedo and water relations and affect germination and nutrient levels in vascular plants. They can be damaged by fire, recreational activity, grazing and other disturbances and can require long time periods to recover composition and function. Other names for biological soil crusts include cryptogamic, microbiotic, microphytic, or cryptobiotic soils.