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Fact Sheet 065–01

Biological Soil Crusts: Webs of Life in the Desert

By Jayne Belnap

Thumbnail of and link to report PDF (922 KB)What and Where Are Biological Soil Crusts?

Although the soil surface may look like dirt to you, it is full of living organisms that are a vital part of desert ecosystems. This veneer of life is called a biological soil crust. These crusts are found throughout the world, from hot deserts to polar regions. Crusts generally cover all soil spaces not occupied by green plants. In many areas, they comprise over 70% of the living ground cover and are key in reducing erosion, increasing water retention, and increasing soil fertility. In most dry regions, these crusts are dominated by cyanobacteria (previously called blue-green algae), which are one of the oldest known life forms. Communities of soil crusts also include lichens, mosses, microfungi, bacteria, and green algae. These living organisms and their by-products create a continuous crust on the soil surface. The general color, surface appearance, and amount of coverage of these crusts vary depending on climate and disturbance patterns.

Immature crusts are generally flat and the color of the soil, which makes them difficult to distinguish from bare ground. Mature crusts, in contrast, are usually bumpy and dark-colored due to the presence of lichens, mosses, and high densities of cyanobacteria and other organisms.

For additional information contact:
Director, USGS Southwest Biological Science Center
Canyonlands Field Station
2290 S West Resource Blvd
Moab, UT 84532

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Suggested citation:

Belnap, Jayne, 2001, Biological soil crusts—Webs of life in the desert: U.S. Geological Survey Fact Sheet 065-01, 2 p.


What and Where Are Biological Soil Crusts?

Erosion Control

Water Retention

Soil Health

Human Impacts


What Can You Do to Preserve a Healthy Desert Ecosystem?

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