Though winter’s chilly grasp has forced most plants around Flagstaff into dormancy, inside one Northern Arizona University greenhouse, mosses, lichens and cyanobacteria are growing like it’s springtime.
They don’t make much of an initial impression, looking more like piles of loamy soil scattered on top of a sandy base. But these tiny species play an outsized role in ecosystems across the Colorado Plateau, weaving themselves into a biological soil crust, or biocrust, that prevents erosion, cycles nutrients, improves plant fertility and catches water, said Matthew Bowker, a soil ecologist at Northern Arizona University.
In some places, they can be more important than plants in stitching soil together, Bowker said.
The NAU professor's biocrust experiments are among just a few efforts worldwide to grow the darker-colored, textured crust in a lab setting, then transplant it back into nature and get it to establish and survive on its own. The ultimate goal of the process is to help restore areas where preexisting crust has been disturbed or destroyed.
Degradation of biocrust across the globe is extensive and studies have shown that loss of these soil-shielding organisms leads to decreases in soil fertility, an increase in invasive plants and wind and soil erosion that strip ecosystems of their soil, Bowker said.
In many places the biocrust get destroyed by human activities such as off-roading or livestock grazing. Frequent desert hikers will recall signs that discourage people from going off trail with images of a wide-eyed biocrust looking up fearfully at a hiking boot about to trample it.
On top of that, warmer temperatures and shifts in precipitation regimes caused by climate change further threaten biocrusts’ ability to survive, Bowker said. Because they grow during cool, moist parts of the year, any rise in temperatures or changes in when or how much precipitation falls have detrimental impacts to the organisms, he said.
Growing Earth's living skin
Many of Bowker's greenhouse experiments tweak variables like water, shade and soil type to figure out the best conditions for growing various types of biocrust.
So far, his team has been able to speed up biocrust growth significantly compared to the years, decades and even centuries it takes crusts to grow back in natural settings. In the best case, they were able to, in eight weeks, get a spoonful of collected biocrust to grow enough to cover the surface of a circular container about 8 inches in diameter, Bowker said.
His team then transplants the crust to four different field sites in New Mexico, Montana, and Utah in hopes that they will take hold and keep growing naturally. The results have been variable, with the Utah experiments showing at least partial success, but no promising results coming from New Mexico yet. It’s too early to tell in Montana, Bowker said.
The next step will be to scale up. Biocrust restoration could play a role in fixing some of the more challenging land use-driven erosion problems, Bowker said.
“But it’s only going to be super useful if you can do it big,” Bowker said.
Climate change adapters?
Also growing in the NAU greenhouse are biocrust samples collected from across the arid west for a project spearheaded by U.S. Geological Survey ecologists Colin Tucker and Sasha Reed. Eventually, the two will transplant those samples to different field sites in Utah that reflect the area’s current conditions and conditions that are warmer than today’s normal. The goal is to determine how different species will survive now and in a future made hotter and drier by climate change.
The Colorado Plateau has a lot of ecosystems where biocrust plays a huge role in soil stability, fertility and hydrology so restoration of those crusts on a shorter timescale is of high interest for resource managers, Reed said.
Advances in satellite imagery have scientists hopeful that in the future they will be able to map biocrust and biocrust degradation occurring around the world, which will help those managers as well, she said.
While current land use patterns do pose a major threat to biocrust, Bowker said he doesn’t see removing them completely as the only viable solution. Instead, he would like to see more serious thought given to withdrawing some areas from grazing that aren’t highly productive for forage but are seeing significant damage from livestock.
“There’s probably a middle ground that nobody really talks about enough,” he said.