Frost heaving can leave mounds bound by crust organisms. Crust cover is inversely related to vascular plant cover. In other words, crusts do not compete well with higher plants, so they are more common where there are fewer plants. However, relative lichen and moss cover increases with elevation and effective precipitation until vascular plant cover precludes their growth. Shallow soils often support a wide variety of cyanobacteria, lichens, and mosses regardless of soil texture.
Soil texture does influence species composition.
Severely, newly, or frequently disturbed soils are generally dominated by low successional, large filamentous cyanobacteria. When disturbance is less severe, less frequent, or some time has elapsed since disturbance, crusts are generally in a mid-successional state with some mosses or lichens present. Predominant crusts for the Great Basin are mosses and lichens. Predominant crusts for the Columbia Basin are tall mosses and green algae. Functions Crusts contribute to a number of environmental functions, primarily at the soil surface.