Don't Crush the Crypto! Soil Crust Communities of the California Desert

Crypto in Utah with trail running through it | Photo: Jason Hollinger/Flickr/Creative Commons License

When you think of the natural side of California, you likely imagine one of California's well-known ecological communities. It might be the redwood forests of the north coast that comes to mind. Or maybe the ancient bristlecone pines in the White Mountains, the oak and grassland savannas of the central Coast Ranges, or John Muir's Great Green Wall in the Sierra Nevada conifer belt. If you've been reading the desert coverage here at KCET, perhaps the Joshua tree forests of the Mojave Desert flitter past your imagination. These natural places, along with easily a dozen more you might name, tend to define California's ecological communities in the public imagination.

There's one California community, though, that isn't often listed among its more scenic cousins, but which is every bit as crucial to maintaining the state's ecological health -- and every bit as fragile if mistreated. It's known as cryptobiotic soil crust, also sometimes called microbiotic soil crust, microphytic crust, cryptogamic crust, cryptogam, or just simply "crypto." Regardless of the name, crypto is a slow-growing community of organisms from micro- to macro- that colonizes bare soil in arid places, and it's crucial to the health of the deserts -- and to your health as well.

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Cryptobiotic soil crusts are so named because 1) they form crusts on soil and 2) they are primarily made up of cyanobacteria, green algae, fungi, lichens, and mosses that can survive long periods of drought by shutting down their metabolisms, a habit known as "cryptobiosis." ("Crypto" comes from the Greek word for hidden, and such organisms "hide their life" when it gets too dry out.)

Crypto forms when cyanobacteria start growing in bare soil, creating a web of microscopic filaments between the soil particles. Cyanobacteria, a type of bacteria once inaccurately called "blue-green algae," can create their own food through photosynthesis. Feeding on the desert sunlight and whatever water is available, the cyanobacteria send tendrils through what would have been sterile soil.

These filaments can penetrate remarkably deeply into the earth. It's not unusual for filamentous cyanobacteria to colonize soil six inches deep, though the soil crusts they form are usually much shallower. I've broken rocks in the Mojave National Preserve and found cyanobacteria growing four inches beneath the surface of the granite, thriving quite well on just the little bit of light that penetrated the quartz.

Other organisms find that web of cyanobacterial filaments a hospitable place to live. Other cyanobacteria that don't form filaments will colonize the web as well, though they tend to stay up top rather than delving the depths. Single-celled green algae -- true algae -- often join in as well, as do fungi that help break down waste products and dead cells of the other organisms.

A mature stand of crypto will often have lichens added to the mix, and you can also find mosses and liverworts, and other plants usually associated with wetter places.

Crypto, with its web of reinforcing filaments, holds down desert soils that would otherwise be liable to blow away. Its cyanobacteria take inert atmospheric nitrogen and turn it into a chemical form that plants can use as fertilizer, and most members of the crypto community also secrete organic acids that make soil phosphorus more readily available to plant roots. The photosynthesizing organisms in crypto take carbon dioxide out of the atmosphere, potentially offering some help in the climate change arena: though each square foot of crypto may not sequester much carbon, as much as 70% of the land in some parts of the desert may be covered in crypto so that even the small contributions add up.

Crypto grows anywhere in North America arid enough that other plant cover is sparse. Its form depends on local temperature and relative humidity. In California's low desert, crypto tends to form mat-like, smooth crusts less than half an inch high. The Mojave's cooler and slightly wetter, and there crypto forms bumpy crusts that can be a bit more than an inch thick, with occasional pinnacles up to a couple inches high. In the much cooler Great Basin desert and Colorado Plateau, cryptobiotic crusts can grow to truly prodigious heights, relatively speaking, with pinnacles rising to six inches in height.

Crypto in the Mojave | Photo: USGS Canyonlands Research Station

The other very important thing to know about crypto is that crypto is fragile. After all, it's an entire community of organisms based on tiny bacterial filaments holding sand and gravel together. An errant hiking boot, or cow's hoof, or set of knobbly ORV tires, can undo a century of crypto growth. As the organisms that make up the crust are cryptobiotic, meaning they shut down their metabolisms when it's dry, damaged crypto can only grow back when it's wet. Though filamentous cyanobacteria can grow fairly quickly under the right conditions, the other components of crypto crusts are usually much slower growing. And if the wind kicks up, tearing away at the newly damaged crypto more quickly than it can grow back, that one bootprint can be multiplied many times.

Which means that a little bit of damage to a cryptobiotic soil crust on sandy soil can create new sand dunes and damaged air quality where once there was intact and healthy desert. That's not good for the desert, and it poses a distinct threat to the people who live downwind.

Between the ecological services crypto provide and the similar benefits offered by its non-living colleague desert pavement, we would do well to think carefully before we go out and bulldoze the desert, lest that desert up and blow away. And if you weren't planning to bring your bulldozer, you'd still be well advised to stay on the trail where there is one. You don't want the desert to take a century or two to recover from your hike.

Chris Clarke is an environmental writer of two decades standing. Director of Desert Biodiversity, he writes from Joshua Tree regularly at his acclaimed blog Coyote Crossing and comments on desert issues on KCET weekly. Read his recent posts here.

About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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