The Living Land: Biotic Soil Crusts in the Arid West

photo by Gardner Dee

photo by Gardner Dee

Dispatch by Maya Aurichio

On Pace Hill outside of Castle Valley, Utah, life teems across the sunbaked earth, forming a patchwork pattern of overlaid bacteria, mosses, fungi, and lichens.  Collectively, these communities are called “biologic soil crusts.” In the arid west, soil crusts play numerous roles in the maintenance of healthy desert ecology.   Like any other plant community, biotic crusts form in an expected progression. Cyanobacteria form a thin veneer across the soil, creating a substrate for lichens and mosses to grow. Like a leaf spread across the land, biotic crusts harness sunlight via photosynthesis and return organic matter and nitrogen to desert soil.  Cyanobacteria, the earliest colonizers, excrete a sticky substance that binds surface soil, while mosses and lichens send out tiny hair-like roots, called rhizomes that further knit together the developing crust.  The resulting community is highly resistant to erosion by wind or water action. 

Today, biotic crusts are both more important and more threatened than ever. Global climate change is leading to a hotter, less predictable climate in the arid west, increasing soil erosion that can bury biotic crust and prevent it from photosynthesizing properly.  During rain events, which are becoming more erratic and intense, the biotic crust acts as a sponge, slowing the flow of rainwater, giving it time to infiltrate into the ground.  This water is then retained and released slowly, prolonging the presence of soil moisture.  Furthermore, eroded soil blown into alpine areas darkens snow, attracting sunlight and speeding spring melting cycles.

Many desert ecosystems in the western United States fall under the “public land” classification, meaning that the land is managed by the federal government, but owned collectively by all Americans.  Soil crusts across public land often suffer compressional destruction by grazing livestock, hikers, and off road-vehicles.  Once crushed, soil crusts become highly susceptible to wind and water erosion.  Damaged areas can take up to 250 years to recover to a mature state.  The health of our public lands, particularly in the face of a changing climate, is contingent upon collective stewardship of the soil itself.  Maintaining livestock allotment fences, reminding hikers and motorists to stay on trail, and increasing education can help prevent further damage to the delicate biotic communities that sustain our land.