Biological Soil Crusts Can Help Stop Deserts Spreading

Biological soil crusts are thin, living communities of organisms that form across desert ground and can be cultivated artificially to curb the expansion of deserts. They are commonly called the desert’s “living skin”.

In the wild, these crusts generally develop in three principal phases: first simple cyanobacteria establish themselves, then lichens emerge, followed by a mature moss-dominated stage.

Scientists have now created a method that can fully reverse desertification by converting sand into fertile soil.

They cultivated microbes in laboratories and used them to fasten loose desert sand into a slim, durable layer that resists being carried off by the wind.

This strengthened surface gives restoration crews an opportunity to establish shrubs and grasses before severe winds and desert temperatures destroy young vegetation.

Biological soil crust

Across straw checkerboards installed in north-west China, treated sand developed a dark surface film that remained in place following seasonal dust storms.

The Chinese Academy of Sciences (CAS) monitored these plots through periods of heat and frost, recording the rate at which the film became firm.

During experiments close to the Taklamakan Desert in Xinjiang, north-west China, CAS researchers found that crusts stabilised sand in 10 to 16 months.

Despite this rapid progress, project planners prioritised establishing the soil foundation, enabling plants introduced later to survive without repeated replanting.

Meet ancient cyanobacteria

Cyanobacteria are bacteria powered by sunlight that flourish in extreme environments, and they probably appeared around 3.5 billion years ago, long before forests existed.

By harnessing sunlight and air, many strains absorb carbon dioxide into their cells and release what remains as basic organic material.

In desert soils with little fertiliser, certain species carry out nitrogen fixation, transforming nitrogen gas into nutrients that the crust community can use for plant growth.

After becoming established, this living layer secures loose particles and provides the earliest plants with improved conditions for rooting.

Sticky sugars bind sand

Viewed under a microscope, biological soil crusts reveal a network of bacterial filaments coiled around individual sand grains.

Cells maintain this network by releasing sticky sugars into the spaces between grains; these sugars set into a thin, cohesive surface layer.

The crust works as a glue, joining sand grains and making it harder for invasive plants to establish. As footsteps, tyres and aggressive raking can damage the surface, large-scale crust development also requires lasting protection.

Carbon starts building

Throughout the first year, the treated ground started retaining nutrients in the upper 2.5 cm rather than allowing dust to carry them away.

When dead cells and released sugars combined with wind-blown mineral dust, they produced organic matter that helped capture nitrogen and phosphorus.

As these nutrients accumulated, they supported additional microbes, making the crust community more resistant to disruption.

For seedlings, this shift offered a stronger foundation, although their survival still relied on rainfall arriving at an appropriate time.

Water stays longer

Following brief rainfall, a crust-covered area retained moisture nearer the surface, whereas adjacent bare sand dried rapidly.

Its uneven pores and dark pigments limited evaporation by keeping water shaded and held beneath the delicate layer.

Retaining moisture for only a few additional days may allow grasses and shrubs to put down roots before the heat returns.

In extended dry periods, the living crust may become dormant, meaning outcomes rely on both climate and careful scheduling.

Succession adds partners

As time passed, the crust shifted from a primarily microbial layer into mixed cover containing lichens and small areas of moss.

Lichens formed a more robust surface, while their gradual growth helped the crust withstand strong winds and cold nights.

Moss added height and shade, allowing small reserves of moisture to persist while protecting newly arrived microbes.

When these later partners became established, the system grew more stable, although any damage also needed longer to recover.

A 59-year record

Today’s accelerated trials are supported by a Chinese record documenting crust development across 59 years of desert restoration.

Using crust samples of known ages, researchers compared undisturbed locations with plots treated using laboratory-grown cyanobacteria.

Nutrient improvements reflected the dominant microbes, while introducing cyanobacteria reduced a process that normally takes decades to only years.

Even under the most favourable conditions, however, a mature crust capable of resisting disturbance required two to three years to form.

Erosion drops fast

Wind is the most demanding test: when gusts strengthen, bare sand fails as grains are lifted and transported away.

Once cyanobacteria had been sprayed, the connected grains remained in place because the crust held them together, reducing the number of particles entering the air.

Controlled laboratory winds showed that a manufactured crust reduced wind-driven soil loss by more than 90%.

Reduced sand movement could result in fewer sandstorms and roads that last longer, although the crust must withstand traffic and grazing.

Limits in the field

Expanding this approach beyond individual plots requires difficult decisions about where microbes should be sprayed, as crust is not needed on every dune.

Native strains frequently cope with heat, salt and drought more effectively than introduced strains, so teams generally cultivate microbes collected from nearby deserts.

Desertification, in which land loses vegetation and becomes increasingly desert-like, arises from numerous causes; crusts therefore cannot address overgrazing or misuse of water.

If restored surfaces are not protected from vehicles and heavy pedestrian use, they can break down and may require years to recover.

What changes next

Rapid crust formation makes microbial growth a workable tool, connecting desert sand control with the slower process of restoration based on plants.

Long-term observation will determine whether the durability, benefits and side effects remain consistent across varied deserts and climates.