Just as our skin is the key to our well-being, the “skin” that covers desert soils is essential to life in dry places. Made up of fungi, lichens, algae, blue-green algae, and other microbes, this “biodust” retains water and produces nutrients that can be used by other organisms. Now, new research shows that climate change is destroying the integrity of this skin.
Such “bioforests” cover 12% of all land on Earth, so keeping them healthy is essential to the health of the planet. Deserts may expand as they disappear, says Bettina Weber, an ecologist at the University of Graz, who was not involved in this work.
Until the 1980s, few scientists cared about grinding underfoot while walking through grasslands, deserts, and other drylands. It turns out that crackling comes from centuries-old clumps of life that help retain a little water and produce life-sustaining nutrients like nitrogen and carbon. “Microorganisms play an important role in arid ecosystems,” says Trent Northen, a biochemist who studies microbial communities at Lawrence Berkeley National Laboratory.
The researchers hypothesized that anything in biodynamic agriculture could withstand heat, since they thrive where it is hot and dry. But in 2013, scientists discovered that climate change is altering the microbial composition of biodust. A new survey of these organisms in the pristine grasslands of Canyonlands National Park in Utah has revealed a hidden vulnerability of some lichens in these lichens.
Twice a year since 1996, researchers from the United States Geological Survey (USGS) have gone to 12 football-field-sized plots in the park’s grasslands to assess the types and amounts of lichens, algae, fungi, microbes and surrounding plants. The original goal was to monitor the spread of a non-native plant called cheatgrass and its effects on bioxit and other life. The researchers were able to compare their results with the results of a study conducted in the park in the late 1960s. “It’s really impressive that the authors have these records over such a long period of time,” Weber says.
The southwestern United States is warming rapidly, and the Canyonlands is no exception, says USGS ecologist Rebecca Finger-Higgins, who led the analysis. Weather measurements over the past 50 years have revealed that temperatures in that park have increased by 0.27 degrees Celsius each decade, and recent summers have been particularly warm.
At the same time, nearly all lichens were waning, especially species that help convert nitrogen in the air into a form that organisms can use, Finger-Higgens and her team report today in Proceedings of the National Academy of Sciences. In 1967 and 1996, that nitrogen-fixing lichen made up 19% of biodust, although the proportion fluctuates from year to year. Since then, that percentage has only shrunk to 5%, and it shows no sign of increasing again.
The researchers also found that prior to 2003, lichens would sometimes temporarily drop and bounce back; Lately, however, they always seem to be on the decline. The biodust may have reached a tipping point, says Finger-Higgens, where there is a permanent shift in the composition of organisms, which could lead to more bare ground. “The apparent decline in lichens is impressive and worrisome,” says Christina Young, a dryland ecologist at the Utah State University Extension, Grand County, who helped collect the survey data.
When bio-dust species disappear, the soil dries up and the potential for volatilization increases. Suspended bio-dust but with fewer lichens will produce less nitrogen fertilizer, so fewer plants may be able to survive, leaving more bare ground. Because animals depend on plants that depend on nutrients from biodust, the loss of biodust can have a cascading effect on an entire ecosystem, says Finger-Higgens.
The danger extends beyond the Canyonlands. From her own team’s studies, Weber estimates that by 2070, 25% to 40% of bio-dust will be gone. Finger-Higgens says there will be more dust, less settled and drier soil, and likely a change in what can survive in these dry places.
Efforts are underway to grow vital plants and plant them in disturbed places, but even these may not produce enough nutrients to sustain life in dry land. “Good results have been obtained for growth [blue-green algae] Monica Ladron de Guevara, a dryland ecologist at the Arid Zones Experimental Station in Almeria, Spain, says,
According to Finger-Higgens, what is needed are “large-scale climate change mitigation strategies”. This could include reductions in fossil fuel use and carbon dioxide emissions and other recommendations made recently by the United Nations’ Intergovernmental Panel on Climate Change. Otherwise, she adds, “there’s not much we can do.”