Scientists see trouble for desert biocrusts due to climate change.

More severe summertime heat is hurting many types of lichen

With data going back to 1967, scientists were able to discern, over a 53 year period, the effects of climate change on mosses and lichens in a portion of the Colorado Desert. They found that increasing temperatures have reduced lichens, mosses have increased, and all this complicated by invasive cheat grass.

It might be easy to think of deserts as dry, rocky places with the occasional saguaro cactus or ocotillo. Yet much of desert landscapes can be blanketed with communities of what are called biocrusts. Comprising lichen, moss, and cyanobacteria, they make a “living skin” of the desert surface that retains water, brings nutrients to the soil through nitrogen fixation, and protects the soil against erosion. In some desert or drylands biocrusts can cover more than 70 percent of the landscape.

If you’ve ever spent time in the desert, and someone points out biocrust, you’ll think, “Oh yeah, I’ve seen this all over the desert.” Photo: KNAU Arizona Public Radio knau.org

The scientists found a steep decline, both in number and cover, in the nitrogen fixing lichen from 1996 to 2002, which coincided with an extended drought, and some types of lichen have never been able to recover from this period. They attribute this decline to increasing summertime temperatures due to climate change. Litter from invasive cheatgrass also hampered the lichens, although moss wasn’t as badly affected by the invasive European grass. The scientists published their findings earlier this month in the Proceedings of the National Academy of Sciences, the official journal of the National Academy of Sciences.

These biocrusts are easily disturbed by human foot traffic, and disturbed more so by cattle grazing and the trampling done by the cattle. As glorified in the old television show Rawhide and scores of cowboy westerns, starting in the mid to late 1800s, European settlers grazed cattle throughout the newly expanded territories of the United States. Over 90 percent of the Colorado Plateau was grazed, leading to soil depletion and erosion.

Jake and Elwood singing the praises of cattle driving with their rendition of Rawhide. They probably don’t know it, but they are also singing about soil depletion and erosion.