Another climate victim: Cryptobiotic crust
The stuff that "holds the place in place" is imperiled by warming
When I was a youngster and my family went to Canyon Country in southeastern Utah, which we did quite often, we had a few immutable rules: Don’t pocket potshards or other artifacts, don’t throw rocks off the cliff if you don’t know who or what’s down below, and do whatever you can to avoid trampling the cryptobiotic crust.
We followed the first and third rules religiously. We’d pick up and admire the remnants of an ancient bowl, the way hands had worn the intricately painted surface smooth, and then put it back exactly as we’d found it. And I know that I must be a curious sight for the pinyon jays and coyotes as I do my cryptobiotic crust dance: zigzagging through the trees, tiptoeing along narrow game trails, ungainly jetéing from slickrock patch to slickrock patch.
The crust is alive, it’s a critical component of the desert ecosystem, and when crushed by a cow- or person-hoof it can take years or even decades to recover. A new study1 finds that it’s not just cattle and people imperiling the crust, but also climate change.
At first glance the crust looks just like, well, dirt, only with a dark-brown-to-black hue that resembles desert varnish. Bend down and look more closely, however, and you’ll see a miniature, living world—a symbiotic mingling of lichens, mosses, soil heterotrophs, and cyanobacteria—which is particularly noticeable when the crust is wet. Filaments reach out and web their way into the soil, binding them together to form a sort of soil-cap that, as renowned cryptobiotic crust researcher Jayne Belnap puts it, “holds the place in place.”
And when the crust is destroyed, it leaves the fine red desert earth vulnerable to erosion and to the harsh winds that scrape across the region every spring. This “can result in the restructuring of ecosystems, which can ultimately push a system across a critical tipping point,” the authors of the recent study note. “Such tipping points or nonlinear changes make it extremely difficult or even impossible for an ecosystem to return to its original state.”
White settlers’ cattle, sheep, and horses trampled vast swaths of the stuff beginning in the mid- to late-1800s. Approximately 90% of the Colorado Plateau has been grazed by livestock since, according to the study. Hikers, OHVs, oil and gas development, bulldozers, and invasive species have also taken a toll.
That makes it tough for researchers to find a patch of never-grazed grasslands to study. Luckily one such place exists: Virginia Park in the Needles District of Canyonlands National Park. Ringed by cliffs, it was inaccessible even to Al “Mormon Cowboy” Scorup and his rugged livestock, and after the park was established land managers put it off limits to people, too, with the exception of permitted researchers (so don’t try to go there).
Biocrusts in Virginia Park have been studied and observed since 1967, and in the 1990s, after an invasion of cheatgrass—which outcompete native grasses and can hamper photosynthesis in the crust— researchers set up long-term monitoring sites. This natural lab, paired with diligently recorded weather observations, allowed the authors of the recent study to isolate climate drivers from other impacts.
They found, unsurprisingly, that it’s getting warmer out there, with mean annual temperatures increasing at a rate of .27 degrees Celsius between 1967 to 2019. From 1996 to 2019, mean annual temperatures were above the 52-year mean for 17 of the 23 years. There have not been similar “systemic patterns or directional changes” in annual precipitation across the same period (which is not to say we aren’t in the midst of a once-in-a-millennium megadrought).
As temperatures have warmed, the lichens in the crust have declined in both richness and the amount of ground covered. “Nitrogen-fixing lichen cover declined from 19% mean cover in 1967 and 1996, to 5% mean cover in 2019.” At the same time, mosses have increased in cover.
More concerning, still, is that the lichens may not bounce back, even in the unlikely event that the climate starts cooling, the authors say: “Additionally, for N-fixing lichens (there was) an apparent tipping point around 2003, after which the population was unable to recover back to previously recorded levels, despite cooler June temperatures.”
Warming temperatures have thus reduced the lichen cover in Virginia Park to about 5% of total ground cover, making it similar to that of nearby areas that have been grazed historically and been trampled by hikers, “potentially marking a shift in the ecosystem that may persist after the current drought abates.”
It’s yet another reason to stop burning fossil fuels, to reduce carbon emissions, and to slow or halt the warming trend. And it also makes the cryptobiotic crust avoidance dance more important than ever.
Speaking of dust, here’s a great Twitter thread about a huge plume of the stuff.
And, yes, the New Mexico fires continue to rage. Ooof …
Compact sans Context
These are from Water Power and Flood Control of the Colorado River Below Green River, Utah, by E.C. La Rue. USGS. 1925. The diagrams are La Rue’s proposed locations for Glen Canyon Dam, one just above Lee’s Ferry, the other in Horseshoe Bend. Note how the spillways and penstocks go through the cliff to the other side of the oxbow rather than through or around the dam. The text is an account of the 1884 flood.
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Decline in biological soil crust N-fixing lichens linked to increasing summertime temperatures Rebecca Finger-Higgens; Michael C. Duniway; Stephen Fick, Erika L. Geiger, David L. Hoover, Alix A. Pfennigwerth, Matthew W. Van Scoyoc, and Jayne Belnap. Proceedings of the National Academy of Sciences Vol. 119 | No. 16; April 19, 2022.