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The desert gets a biocrust skin graft

Without its cover of living microorganisms, the desert is eroding.

 

Since Ancestral Puebloans made their homes in the cliffs of what is now Bandelier National Monument, soil erosion has drastically increased. Erosion threatens the integrity of these historical structures.

When Patrick Cruz’s ancestors carved honeycombed dwellings into the canyons of what’s now New Mexico’s Bandelier National Monument, the land looked very different than it does today. Biocrusts — communities of mosses, lichens and cyanobacteria — formed a living skin over the earth, anchoring it in place, storing water and carbon, and laying the foundation for ponderosa and piñon pine forests.

After drought drove the Ancestral Puebloans away from Bandelier and into nearby pueblos in the 16th century, European colonizers moved in. Their logging and livestock grazing devastated Bandelier’s biocrusts. Drought and bark beetles in the mid-20th and early-21st centuries then killed up to 90% of pines, leaving unshaded patches of dirt between juniper shrubs where little could grow. Together, these impacts now cause an astonishing 8,900 pounds of soil per acre to erode each year.

Similar erosion is on the rise across the Southwest as oil and gas drilling, recreation and new development tear up biocrusts. For Cruz, an archaeologist and tribal member of Ohkay Owingeh Pueblo, 30 miles northeast of Bandelier, one concern of this unnatural erosion is that it threatens to undercut the buildings and other sites where the ancestors of modern Indigenous people lived, prayed and are buried. Such places still hold deep significance — they “help the culture function spiritually,” Cruz says.  

The cyanboacterial filaments that make up biocrust latch onto soil particles, holding the surface together and preventing erosion.
Courtesy of Kristina Young
Eroding soil has other consequences, too. It drifts into rivers, choking aquatic life, and onto snow, causing it to absorb more sunlight and melt prematurely, thereby shrinking water supplies. Clouds of dust cause respiratory issues for thousands of people. And without nutrient-rich topsoil, plants can’t take hold, which means animals also struggle to survive. “When you start losing soil from an ecosystem, you can start to erode the whole system,” says Kristina Young, a Ph.D. student at the University of Texas at El Paso who studies biocrusts.

Now, Young and other scientists are trying to stem the loss of Southwestern soils by reintroducing biocrusts to degraded ecosystems. “We’ve gotten awesome at growing biocrusts in greenhouses and in the lab,” says Sasha Reed, a research ecologist with the U.S. Geological Survey in Moab, Utah. With a moderate temperature and extra water and light, biocrusts that take decades to grow in the wild can sprout in as little as four months indoors.

But transplanting lab-grown biocrusts into the wild is another story. In 2015, Young, Reed and several other scientists inoculated soils in Bandelier with lab-grown biocrusts. When the crusts were in a naturally occurring dormant state, they ground them up and sprinkled them on an eroding mesa, hoping some of the pieces would sprout into the kind of living skin that had once likely blanketed the area. To increase their chances, the scientists inoculated the mesa before the summer monsoon, thinking the extra moisture might help the biocrust take hold.

Waiting for these fragile environments to heal themselves isn’t necessarily an option, Young explains. When Gen. George Patton drove tanks through the Mojave Desert in a World War II training exercise, he left behind tracks that researchers later compared to undisturbed soil nearby. Based on how slowly the tracks had recovered after five decades, scientists estimated it could take biocrusts almost 2,000 years to fully rebound.

Kristina Young examines a lab-grown biocrust reintroduction plot. Biocrust can take decades to grow in the wild.
Katie Mast
Ten months after Young’s team inoculated the mesa in Bandelier, she had to concede: The inoculated areas looked no different than the control sites. Similar experiments in China and the Mojave Desert have been more successful, but just as many others have failed. Steven Warren, a U.S. Forest Service ecologist and early proponent of restoration, now thinks the time and money spent trying to artificially boost biocrusts isn’t worth the cost. In a 2018 paper, he suggested that conservationists should focus on minimizing destruction rather than reintroducing biocrusts to degraded environments. Besides, he argued, in certain Southwestern environmental niches, biocrusts have been shown to regrow on their own in less than 20 years. 

Despite Warren’s views, however, a growing group of scientists — from Iceland to Australia — hope that re-establishing wild biocrusts will soon begin to reverse decades of abuse to arid lands and “break the cycle of soil erosion,” as Young wrote in a recent paper about the Bandelier experiment.

[RELATED:https://www.hcn.org/issues/49.7/a-bizarre-biocrust-discovery]

For these researchers, even unsuccessful experiments offer insight into how seasonal timing, soil type and other factors affect biocrust establishment. Reed now hypothesizes that cultivated biocrusts may not be hardy enough to survive in the wild. She’s growing biocrusts in an outdoor nursery near Moab in hopes they’ll stand a better chance than greenhouse- or lab-grown ones. She’s also subjecting different species of lichens, mosses and cyanobacteria to extreme heat and dryness to see which respond best to the conditions expected to hit deserts in our changing climate.

Cruz supports these efforts, but remains skeptical that they’ll be more than a Band-Aid over the large-scale degradation of desert ecosystems. Still, if restoration works, he says, “it would be good for not just the archaeological sites, but for the animals, the birds and the plants and everything else.”

Krista Langlois is a correspondent with High Country News. She writes from Durango, Colorado. 

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