Biological Soil Crust

The fascinating community that holds the Utah desert in place

If you’ve spent much time hiking the Arizona desert, you’ve probably come across a sign that says, “Don’t bust the crust!” These signs refer to a biological soil crust that is actually a living and complicated community of cyanobacteria, green algae, lichens, mosses and fungi.

Biological soil crusts are not uncommon. The topsoil of most semiarid and arid ecosystems in the world is held together by such biologic communities. However, the crust is very easy to damage and it is essential to our Utah and Arizona desert ecosystem.

The crust swells when it rains like a sponge covering the ground, and this increases the soil’s absorption, making more water available to plants. The crust also binds grains of soil together and stabilizes the soil, reducing erosion. In addition, it makes nutrients such as nitrogen more readily available to plants. Most plants on the Colorado Plateau are not nitrogen fixing and they rely on bacteria and lichen to pull nitrogen from the air and make it available in the soil.

Also, seeds that land in a healthy biological crust have a better chance of gaining a roothold because the ground is more likely to hold moisture. It supplies nutrients and even helps block the wind. Isn’t nature remarkable?

Unfortunately, this essential component of desert life is very fragile. Simply stepping on a biological crust can compact the complex community and severely limit its function. The footsteps from several people, bike tires or ATVs can create a path in which water will flow until soil erodes and gullies form. Scientists say it can take between 5-250 years for a biological soil crust to recover. Factors that affect recovery include weather and the extent of the original damage. Do your best to stay on established trails and roads. If there isn’t a people trail, follow an animal trail, a wash or gully, walk on rock or at the very least, step directly into the footprints of the person in front of you. The goal is to reduce contact with the fragile soil as much as possible. Hiking to the Wave? Stay in the Wire Pass wash instead of taking shortcuts.

The crust varies in thickness, biologic makeup and color depending on where it is found. Crusts in the Arizona and Utah desert may appear as a black or dark gray bumpy texture that covers the ground. If you want to get a good look at the crust, it is probably most apparent on our tours to Toroweap or on our Photographer’s Dream Tour through the Grand Staircase-Escalante National Monument.

Information sources include “A Naturalist’s Guide to Canyon Country” by David B. Williams and Wikipedia.