Desert Lichens Can't Deal with Increasing Heat

Biocrust at the Birds of Prey National
Conservation Area, Idaho / public domain

 One of the points Alisha and I make in our book, Funky Fungi, is that fungi help hold the earth together. The fungi living in and on the soil are so small – many of them microscopic – that we don’t see them. And too often we don’t pay attention to those we do see, such as lichen crusts.

But those lichens and tiny fungi, along with other soil organisms, play a critical role in some of Earth’s ecosystems. And climate change is killing them off. In particular, increased heat is harming the biocrusts that protect desert soils in the arid western United States.

The biocrusts are made up of fungi, lichens, mosses, blue-green algae, and other microbes. They act as a skin on desert soils, retaining water and producing nutrients (such as nitrogen and carbon) that other organisms can use. But new research shows that the warming climate is destroying the integrity of the desert soil “skin” in Canyonlands National Park in Utah.

The study, started back in 1996, was originally meant to monitor the spread of a nonnative plant called cheatgrass, as well as look at how it affected the biocrust in the grasslands and the other plants. Researchers surveyed a dozen soccer field–sized plots, counting the  numbers and kinds of  lichens, mosses, fungi – and the surrounding plants. They were able to compare their data with results of an earlier study done in the 1960s.

Here's what they have noticed in the intervening years:

Repeat photos of biocrusts from the same area in 2004, 2009, 

2014, and 2019 / USGS photo by Rebecca Finger-Higgins

• Over the past 50 years, weather data show that temperatures in that park have increased 0.27°C each decade (nearly half a degree F). In addition, recent summers have been particularly warm.
• Nitrogen-fixing lichens have declined significantly. In 1967 and in 1996, those lichens made up 19% of the biocrust (the percentage fluctuated slightly from year to year). Since then, the percentage of nitrogen-fixing lichen has shrunk to just 5%, with no sign of increasing again.
• Before 2003, lichens sometimes declined temporarily and bounced back. Recently, they have showed a steady decline.

USGS ecologist Rebecca Finger-Higgens says the biocrust may have reached a tipping point, where a permanent shift in the community of biocrust organisms could lead to more bare ground. If the biocrusts disappear, the desert soils will dry out and blow away in strong winds. If the biocrust hangs on with fewer lichens, the loss of soil nitrogen will mean reduced survival of the grassland plants. That would have a disastrous effect on the animals that rely on the plants – and lead to a cascading effect on the entire ecosystem.