Compared with the bare sections, biocrust-covered rammed earth was less porous and had higher shear strength and compressive strength, the team reports today.

The researchers suggest these properties and others linked to biocrusts protect the Great Wall from degradation in a few ways, including by reducing wind erosion, preventing water and salt from seeping in, and increasing the overall stability of the rammed earth. Perhaps unsurprisingly, thicker, moss-dominated biocrusts were generally more protective than thinner ones dominated by cyanobacteria.