Biological Soil Crusts: A Crucial Component of Arid Ecosystems

Biological soil crusts are a complex community of primitive organisms that thrive worldwide in harsh, arid and semiarid regions where other vegetation such as trees, shrubs, and grasses is sparse. These crusts play a key role in stabilizing bare soil, stemming erosion from wind and rain, trapping moisture, fixing carbon and nitrogen in the soil, and providing shelter for the seeds of vascular plants. Together, the species that make up soil crusts—cyanobacteria or blue green algae, green algae, fungi, lichens, and mosses—have developed synergistic communities critical to these dry ecosystems. In the semi-arid Great Basin, juniper has encroached into areas once dominated by soil crusts, sagebrush, and native grasses. The lack of fire has led to dense juniper stands and even-aged stands of older sagebrush more prone to carry intense wildfire than mixed-aged stands. Researchers are exploring the use of fire to reverse juniper encroachment and foster a healthier mix of sagebrush stands. There is little information, however, on the effects of fire on fragile soil crusts. A recent study explored the effects of a controlled burn on crusts at a site in the foothills of the Onaqui Mountains in Utah. The results indicate that low-intensity fire has few long-term adverse effects. The study also documented the baseline condition of biological soil crusts in a fairly healthy system. This information may help guide restoration of soil crusts in other, more impaired, ecosystems