Moab • The sandstone towers near Castle Valley glowed as a few rays of evening light cut through the clouds, but Sasha Reed’s eyes were turned to the ground.
A mottled crust covered the deeply furrowed hillside, and Reed, a Moab-based biogeochemist with the United States Geological Survey (USGS), was explaining the complex community of organisms that grow atop soils on the Colorado Plateau.
“We have yellows, blacks, pinks, toothpaste greens,” Reed said of the fungi, lichens, cyanobacteria and mosses blanketing the ground. “Each color is a different species.”
In desert environments, biological soil crusts — or biocrusts — play a key role in slowing erosion, supporting plant growth, controlling dust and holding moisture.
Many visitors to desert environments are familiar with the fragility of living soil crusts, which can be destroyed by overgrazing, off-road vehicle use or even a single human footprint. The slogan “Don’t bust the crust” is found in educational campaigns across Utah.
The biocrusts, which can take decades to form, may seem unexciting, but Reed pointed to signs of a frenzy of life on the soil.
“Here the mosses that are wet, see how green they are?” Reed said. “When they get wet, they unfurl their little leaves and open themselves up to the sky.”
She pointed out species of cyanobacteria, photosynthetic organisms sometimes called blue-green algae, that are capable of burrowing in the soil or moving to the surface depending on weather conditions.
“Our biocrusts on the Colorado Plateau are so beautiful,” she said. “They’re so diverse and topographically extreme.”
When soil experts from 30 countries met in Moab for a conference in 2016, Reed recalls several people weeping at the sight of healthy Utah biocrusts.
A single square inch of ground may contain over a dozen species that work together to store carbon, a complex, tiny, web of interactions that scientists are just beginning to understand.
What’s clear is that biocrusts play a key ecological role and support surrounding plant and animal communities. They are common in the dryland ecosystems that cover 40% of the earth’s land surface, including much of the southwestern U.S.
As the climate warms and deserts grow worldwide, that number could increase to 57% by 2100, Reed said. But relatively little is known about how biocrusts will respond to hotter temperatures.
At a small research station outside of Castle Valley, scientists like Reed have been working since 2005 to answer questions about how biocrust systems function and to better understand the impacts of climate change on biocrust and plant communities.
“In the world, this is the only climate manipulation experiment in any dryland that I know of,” Reed said. The facility uses infrared lamps to actively heat plots to two or four degrees Celsius above the ambient temperature, simulating the potential impacts of climate change.
While other experiments use greenhouses to warm biocrusts, the heat lamps are thought to be a better, if still imperfect, mimic of global warming.
Even to the untrained eye, the difference between the warmed and unwarmed plots is staggering. The research plots not subjected to warming feature the richly textured mounds of soil supporting clumps of native ricegrass and saltbush.
The warmed plots, by contrast, are red squares of flat, cracked dirt with a few dead sprigs of invasive cheatgrass. While the heated plots were not devoid of native plant species or biocrust organisms — cyanobacteria, for example, often live under the soil and are not readily visible — the warmer plots have seen sharp declines in biodiversity.
The impacts of warming were not apparent early in the experiment, said Armin Howell, a USGS biologist who conducts research at the facility.
“It took seven or eight years before we saw the effects of the warming on biocrusts,” he said. “Desert species are adapted to be able to handle that sort of heat. But repeat exposure to elevated temperatures takes effect almost a decade down the road.”
Research conducted at the federally funded facility has generated international interest, appearing in a recent Intergovernmental Panel on Climate Change report as well as being presented at COP27, the 2022 United Nations Climate Change Conference in Egypt last month.
Biocrusts and water supply
Howell explained that the research has contained nuggets of good news for biocrusts, demonstrating how lichens and mosses have begun to recover in areas that were disturbed when the facility was constructed in 2005.
It was initially thought it would take decades or centuries for some biocrust species to return to disturbed crusts, Howell said, “but lichens have managed to come back, along with the mosses, in fairly short order.”
Reed co-authored a paper published in the journal Nature Climate Change last year that included similar findings.
The researchers also found, however, that biocrust recovery was greatly limited under warmer conditions, which could have significant implications for not just the ecological health of drylands but also possibly for the Southwest’s water supply.
Howell believes the most crucial function of biocrusts is soil stabilization.
“Losing them is going to have cascading effects on everything around them,” he said, “even translating to increased snowmelt once the dust gets blown into the atmosphere and lands on snowpacks.”
A 2010 study showed that in the Colorado River basin, dust storms that land on mountain snowfields can decrease runoff into streams and rivers by as much as 5%, adding to the effects of a megadrought that has depleted reservoirs in Utah and surrounding states since the year 2000. Other studies have shown that dust can be a more significant driver of when and how quickly snow melts than the air temperature.
Unusually dry soils have also decimated water runoff in recent years. Last year, for example, snowpack in the upper Colorado River basin was around 90% of average, but the soils were so dry that only 30% of the average runoff found its way to the river.
It’s possible that the loss of biocrusts could make that trend worse since soils with healthy biocrusts can increase soil moisture by 14%.
“If you have an intact layer of biocrust, you can maintain soil moisture longer,” Howell said. “They do also act like a sponge. So I think it takes a little bit more for the water to infiltrate into the deeper layers. But once it’s down there, I imagine it sticks around a little bit longer.
Reed said there are many questions related to dryland soils that still need to be explored, including their role in global carbon sequestration.
And if biocrusts are critical to dryland ecosystems and are highly susceptible to disturbance, can they be actively restored by land managers?
Just down the road from the climate manipulation experiment, USGS scientists partnered with the Moab-based nonprofit Rim to Rim Restoration to find out.
Reed said earlier attempts to grow biocrusts in a greenhouse at first seemed shockingly successful. In a matter of months, researchers were able to grow organisms that take decades to form in the wild. But when the biocrusts were moved outdoors, they quickly died.
“One of the hypotheses we had was that the greenhouse in the lab made life too easy for the biocrusts,” Reed said. “It bulked them up successfully, but it didn’t give them the biochemistry and the pigments and the kind of life experience to prepare them for the real world.”
In 2018, two acres of Rim to Rim’s native plant propagation center along the Colorado River were planted with biocrust species and watered for over a year. That attempt to farm biocrusts outdoors was far more promising.
The biocrust was grown atop biodegradable weed mats, and after it was allowed to dry, the mats were rolled up like sod.
“I thought it would never work to roll them up,” Reed said. “I was like, ‘This is not a good idea.’ But they worked beautifully; it was really, really surprising. They stayed intact and they were able to be transported and rolled out on the landscape.”
The transplanted crusts are being monitored to track their longtime viability.
“We’re the largest biocrust farm in the world,” said Kara Dohrenwend, director of Rim to Rim Restoration. “It’s easy to be the largest when you’re the only biocrust farm in the world.”
The experiment at Rim to Rim’s farm proved that growing and replanting biocrusts was possible, but Dohrenwend said the next question is how the project can be scaled.
Rolling up the mats took a huge amount of labor, including from teams of volunteers, and Dohrenwend would like to explore whether the process can be done with a tractor.
Landowners who are planning to disturb biocrusts with new construction projects have successfully transplanted the organisms into biocrust gardens. Reed recommends scraping large chunks of soil from the ground in areas that are going to be destroyed, keeping them upright and intact, and initially watering them when they’re moved to a new location.
“Once you get into biocrust, you just start to love it,” Reed said.
For visitors to southern Utah, the standard rule is still the best: stay on trails and don’t bust the crust.