Wed March 21, 2012
Earth Notes: The Desert’s Crusty Nursery
Many parts of the Colorado Plateau are covered with distinctive soil crusts. Scientists are learning more about how they aid ecosystems—especially by providing good places for plants to grow.
Soil crusts rely on tiny organisms called cyanobacteria that are good at colonizing bare soil. In cold regions, frost heaving can give a dark, pinnacled appearance to soil covered with cyanobacteria. And that complicated micro-topography is key to what comes next.
A rough, irregular soil crust traps dust that contains nutrients that would otherwise be lost in the wind. Small depressions also trap water and leaves—and seeds that can then germinate amid moisture and abundant nutrients.
A dimpled soil crust provides wind protection to small seedlings. And a dark crust traps the sun’s warmth, allowing plants to grow during cooler parts of the year when moisture is more abundant. Matthew Bowker, an ecologist with the U.S. Geological Survey, points out that cyanobacteria also help by introducing chemicals into the soil that help keep nutrients available for use by other plants.
Over time, soil crusts come to support rich colonies of mosses and lichens—and they form good seedbeds for a variety of plants. Some of those seeds rely on animals that make handy holes in the crust—such as deer prints.
But crusts are fragile, too, and it doesn’t take many boot prints or tire tracks to wear them away to nothing. So it’s best to admire their complicated architecture from the respectful viewpoint of hard slickrock, or an established trail.