Deserts are getting hotter and bigger. Protecting the 'biocrust' can prevent them spreading 

When you think about climate action, you probably think about saving the rainforests or protecting island nations from rising sea levels. But spare a thought for deserts, which may yet prove the most vulnerable of all ecosystems.

The rising temperatures that drive climate change are most keenly felt in the world’s deserts. Scientists predict that “super and ultra-extreme” heat events with temperatures above 56°C will become frequent in the Middle East and North Africa in the second half of this century.

Now new research has shown just how extreme heat could destroy life in the world’s deserts.

Plants and animals that live in deserts depend on the landscape’s surface protective layer, known as biocrust, because it is rich in microorganisms. Fungi, lichens, mosses, blue-green algae and other microbes play a vital role in deserts’ natural ecosystems by retaining water and producing nutrients used by other organisms, from plants to small mammals.

Scientists had assumed that because these tiny life forms have evolved to live with extreme temperatures, they would survive climate change. But a study of desert areas in the south-western United States shows they are more vulnerable than previously thought.

“Biological soil crusts (biocrusts), comprised of mosses, lichens and cyanobacteria are key components to many dryland communities,” wrote the team from the US Geological Survey (USGS) when presenting their findings, which are based on twice-yearly sampling of desert crusts.

Combining their own work with earlier studies, the team were able to use 53 years’ worth of data. They conclude that the desert biocrust is reaching a tipping point from which it may not recover. Already, they’ve found a sharp decline in the number of lichens living in desert soil.

The areas they studied have been protected from grazing to preserve the pristine desert environment. But now the scientists say that rising temperatures “may partially negate decades of protection from disturbance”.

If the biocrust dies, so will the plants and the animals that depend on them. This will lead to deserts eventually spreading and engulfing productive agricultural land. The United Nations estimates that 12 million hectares of productive land are already lost each year, much of it to encroaching deserts.

Scientists say that biocrusts cover 12% of the Earth’s surface. USGS ecologist Rebecca Finger-Higgens, who led the latest research, told Science.org that a type of lichen that fixes nitrogen in the soil has declined from 19% of the biocrust in 1996 to just 5% today.

“Climate mitigation strategies on a large scale” – including reductions in fossil fuels and emissions of CO2 – will be needed to save the biocrust, she said in the interview. “Otherwise, there’s not much we can do.”

Other studies have warned that 25-40% of the world’s biocrusts will be lost by 2070 without urgent climate action. “If we lose the biocrust, we see major impacts on the soil stability, vegetation and wildlife,” says Sue Bellagamba, of the Nature Conservancy in the US state of Utah.

Her organisation is part of a project to re-grow biocrust on a biocrust farm. They will then use this to perform a “skin graft for the desert” to restore areas of Utah’s Canyonlands National Park, where the natural biocrust has been lost.

Biocrust has been removed from areas of deserts in Arizona and California where roads and pipelines were being constructed. It was then taken to Utah, and within three years they had grown about 0.7 hectares of new biocrust.

Mats of new biocrust were taken out and unrolled in the desert to create islands of growth that the scientists hope will regenerate a much larger area. Dr Sasha Reed of the USGS has hailed the project as “an outrageous success”.