Stretching from West Texas to Durango, Mexico, the Chihuahuan Desert doesn’t lack for superlatives. It’s the continent’s largest desert, and the most diverse desert in the Americas. In terms of distinctive species, it may be the most biologically diverse desert in the world.
It also stands out for a particular type of terrain. Gypsum landscapes occur globally, but they abound in the Chihuahuan Desert, from Coahuila and Durango to the Guadalupe Mountains in Texas and New Mexico’s White Sands. These white-sand outcrops are certainly harsh. But they’re also hotspots of biodiversity.
That includes the complex, fragile ecosystems known as “biocrusts.”
That’s Katelyn Gobbie, a “biocrust technician” at the University of Nevada-Las Vegas.
“I'll go off of gypsum and study biocrusts,” Gobbie said, “and then I come back to gypsum and I’m amazed every single time. I'm like, ‘Wow, this is incredible.’ They're just everywhere. They look amazing. They're beautiful.”
Gobbie is passionate about gypsum landscapes.
Those landscapes are uniquely inhospitable for life. Gypsum soils are high in sulphur and calcium, and nearly devoid of nutrients – like phosphorus – plants typically require. But those constraints have driven evolutionary innovation. In the Chihuahuan Desert, there are more than 200 known “gypsophiles,” plants that grow only on gypsum. Many occur on just a single gypsum outcrop.
Then there are the biocrusts. Known as the “living skin of the desert,” biocrusts appear nondescript, dark and rough-textured, like “dirty dirt.” But they’re rich ecosystems, composed of ancient lifeforms – mosses and lichens, cyanobacterias and “micro-animals” like rotifers, roundworms and tardigrades.
Biocrusts are conspicuous on gypsum soils. But they haven’t been studied like larger plant life has.
“In our U.S. deserts, such as the Chihuahuan and Mojave deserts,” Gobbie said, “where gypsum is most abundant, we don't know a lot about our biocrust communities on gypsum. So that was sort of the train of thought for my master's thesis work: Can we characterize these biocrusts? Can we learn more about their nonvascular plant species?”
Gobbie selected 10 gypsum sites in the Chihuahuan and Mojave deserts, and 10 adjacent non-gypsum locales. In our region, her sites included White Sands National Park and the Yeso Hills, east of the Guadalupes. Gobbie’s Mojave research centered on Lake Mead, along the Nevada-Arizona line.
Gobbie’s findings confirmed some of her expectations. Biocrusts do appear to thrive especially on gypsum, and there do seem to be moss species that favor gypsum soils.
“I think for the U.S. portions of the Chihuahuan Desert and the Mojave Desert,” Gobbie said, “we can say that the biocrust communities are more abundant on gypsum and that the moss diversity is greater on gypsum.”
But there were also surprises. While the Chihuahuan Desert boasts the greatest number of gypsophilic vascular plants, the Mojave Desert seems to have a greater richness of biocrust mosses.
That could be due to precipitation patterns. The Mojave gets most of its moisture in winter. A cooler growing season may give mosses there a better chance of survival. In our region, rain comes in the heat of the summer.
“These biocrust mosses are almost getting steamed, potentially,” Gobbie said. “So I think that could be one of the reasons why there was less species richness in the Chihuahuan Desert.”
What specific adaptations allow biocrusts, and other “gypsophilic” life, to survive in harsh gypsum soils is a mystery. Indeed, Gobbie said that biocrusts remain a terra incognita. It’s a reminder that the Chihuahuan Desert contains worlds within worlds.
