Eighty-five miles from the small town of Moab, Utah, located on the Colorado Plateau in the southwest of the US, soil ecologist Rebecca Finger-Higgens is hopscotching on copper-toned sandstone to avoid stepping on the desert’s black, burnt-looking crust of soil. “Don’t bust the crust,” the saying here goes. “Don’t tiptoe on the crypto.”
Cryptobiotic soil—or biocrust—forms the top layer of the desert, a “skin” squirming with living organisms. Just as microscopic organisms are vital to our health (think gut bacteria for digestion and disease prevention), the desert’s skin hosts a whole community of organisms that are vital to the ecosystem. Without the desert’s skin, much less life would exist in these lands; flowers would wilt and sparse pockets of shrubs would struggle to survive.
The plateau’s biocrust is easily identifiable under a bright yolk sun: a dark, bumpy surface that stretches between shrubs, like snakeweed and yucca, and the towering buttes and mesas that make up the Colorado Plateau’s iconic landscape. It’s here that Finger-Higgens pricks metal pin flags into square grids that crisscross 12 football-field-sized plots of land.
She’s part of an ongoing study that has tracked the health of biocrusts since 1996, with some records reaching back as far as 1967. Until the past few decades, biocrusts have been largely overlooked; the desert’s scruffy top layer was seen as a static feature of the ecosystem. It’s only relatively recently that the importance of biocrusts in sustaining the life and integrity of the desert has been understood—and that damage to them has been recorded.
“I think the study is awesome,” says Matthew Bowker, a soil ecologist and associate professor at Northern Arizona University who was not involved in the research. “It’s pretty much the only data set of biocrusts that I know of that goes back that far.”
Finger-Higgen calls the plots of land here “pristine.” By this, she means no cattle have grazed on the land, and bikers and hikers are prohibited. Pristine is an important distinction. If you’ve been to Moab and the surrounding canyonlands, you’ll know that all-terrain vehicles roar out of town and through the landscape, usually on designated roads but sometimes swerving off-piste and into unpaved desert. Cattle graze through the land, and enthusiastic hikers tromp the soil in boots. And yet the desert’s harsh reputation belies the fragility of a landscape where life lives on the edge.
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Scientists colloquially refer to biocrusts as “living skin” because the first organisms to take up residence are cyanobacteria, which under a microscope look like little worms that glide through the soil, leaving a trail of sticky fibers in their wake. Soil particles stick to these fibers and create a spongelike structure that absorbs water when it rains. Soon moss, algae, fungi, and lichens move in as tenants. It can take years to decades—and in extreme cases up to a century—for this community to form a thick, knobby crust.
The microbial filaments in the crust can resist strong winds due to their “tensile strength”—how much they can be pulled before breaking. However, they are vulnerable to compressional forces, such as a human foot punching through the crust, which can leave sun-loving cyanobacteria, lichens, and mosses buried with no light.
“When you trample it, you’re resetting a clock that’s been going for a long time back to zero,” says Finger-Higgens, whose latest findings on biocrust degradation were published last month in PNAS. “And so now the system has to repair itself.”
To keep her plots devoid of damage, Finger-Higgins prefers to keep quiet about the exact location of her research site. But what should be immaculate desert crust with white fungi peeping through, she says, is not as healthy as expected. Something is amiss—and not just on the Colorado Plateau (which bleeds into four US states: Utah, Colorado, Arizona, and New Mexico), but elsewhere too.
Deserts are, in some ways, the forgotten landscapes of climate change. This is all the more incredible considering drylands cover around 40 percent of Earth’s land surface and support some 2 billion people, with biocrusts covering 12 percent of our planet’s surface. And yet Finger-Higgins’s study suggests that even without human interference, “warming may partially negate decades of protection from disturbance, with biocrust communities reaching a vital tipping point.” A “tipping point” refers to the moment when ecosystems can only take so much more stress before they fundamentally change.
Rising temperatures and drought mean we may be “circling the drain on that,” says Finger-Higgens. Nitrogen-fixing lichens seemingly held steady from 1967 to 1996 at 19 percent of the biocrust’s cover, but then they dropped from this constant down to 5 percent in 2019. “Our study corroborates a lot of experimental work that is done globally. It shows that there are upper heat limits to biocrust that we didn’t fully know until recently.”
Bala Chaudhary, a soil ecologist and assistant professor at Dartmouth College who was not involved in the study, agrees. Even if humans are proactive about how their physical presence affects the landscape, “biocrusts are being impacted by global climate change,” she says.
Of course, it’s tough for even long-term observational studies to whittle away all the possible confounding factors, which is why scientists have also taken experimental steps to simulate biocrusts in a warming world.
For example, between 2005 and 2014 a team used infrared heat lamps to warm a plot of crust on the Colorado Plateau by 2–4 degrees Celsius. They too found that warming led to a decline in mosses and lichen compared to an unaltered plot of land.
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Then there was a 2018 study that analyzed data from more than 500 publications and estimated that biocrusts “will decrease by about 25–40 percent within 65 years, due to anthropogenically caused climate change and land-use intensification.”
Finger-Higgens’s “paper offers a little more realism” than these experimental studies, says Bowker. It shows “something that unfolded over an extended period of time in a natural ecosystem.”
So is stripping the desert of its crusty skin really a big deal? If you have spent time in the southwest of the US, you know it’s extremely windy and that storm systems can whip through the land. The biocrust acts as a protective layer—a kind of glue that holds the soil together. Biocrusts are sometimes referred to as ecosystem engineers, says Chaudhary, who compares them to beavers in their ability to alter a landscape.
“Without the biocrust, we’d have no soil. The soil would have been blown off into the river. We’d be inhaling it. We wouldn’t be able to grow crops,” says Finger-Higgens. The biocrust prevents the “horrible dust storms and dust bowls like we saw in the 1930s.”
“You do not want to be breathing in that dust,” she adds. “That can have really bad problems for respiratory illness.” We would also lose the desert’s seed bank. The sponge-like biocrust not only absorbs water, it provides a stable place for plants to grow, increases soil fertility, aids in carbon storage, reduces mudslides, and impacts the hydrological cycle in the region.
“If the surface becomes a hard surface that water can’t infiltrate, you’re not going to get groundwater recharge. It’s all just going to be surface runoff and then fill rivers and have these flash systems,” says Finger-Higgens. “So you’re losing the groundwater sources. You’re losing clean municipal water sources. And you’re silting up your rivers that you do have.”
The other unforeseen problem with erosion is that the dust can settle onto glaciers. It then lowers the surface albedo of the snowpack—how much sunlight it reflects—causing the glacier to absorb more energy and melt faster, says Chaudhary. “It feeds into this climate change positive feedback cycle.”
Hearing all this, it’s easy to fall into climate grief, the feeling that nothing can be done, but Chaudhary says that’s far from the truth. “In the last five years, there has been an explosion of research dedicated to restoring biocrusts through different culturing techniques, technologies, and nutrient additions,” she says.
For example, scientists are testing whether adding doses of bacteria to the soil can help biocrusts rebound faster. There is also discussion of salvaging soil crusts from sites that are slated for road construction and relocating them to degraded lands. Then there are researchers performing desert “skin grafts” by transplanting lab-grown biocrusts into the wild.
But ecologists like Steven Warren contend that while there is some success to be had with these methods, large-scale solutions are few and far between. Instead, he suggests we tend to “passive restoration,” where a swathe of land is protected so the biocrust can heal itself.
Everyone can help with this, Finger-Higgens says. “If you are traveling off-trail or in the backcountry, think about where you’re stepping. Try to minimize your impact.” In other words: Don’t bust the crust.