Desert ecosystems are slow-growing, starved of nutrients and water. Trampled desert plants take much longer to recover than forest vegetation. Desert soil may look sandy, dry, and uninhabitable—a lifeless rock dust. But a large part of it is covered by a living layer, called a biological soil crust, made up of some combination of cyanobacteria, fungi, algae, and mosses. “It’s a consortium of different organisms—together they make a living skin on top of the soil,” says Matthew Bowker, soil ecologist at Northern Arizona University’s school of forestry. (They are also sometimes called cryptogamic crusts, referring to the “secret marriage” of the crust organisms).