The Great Wall of China, which used to be much larger, is now only a fraction of its former self due to erosion over time. However, it has been observed that sections of the remaining walls are being protected by a thin layer of bacteria, moss, lichen, and other organisms known as biocrusts. These “living skins” have likely shielded the Great Wall from corrosive forces such as wind and rain. With advancements in technology and research, scientists may eventually be able to cultivate new biocrusts to further preserve the wall.
The protective effects of biocrusts are not surprising, as they are known to stabilize dryland ecosystems and prevent soil erosion. While many sections of the Great Wall are made of stone or brick, other parts are constructed from compacted soil, which can break down over time. However, this soil can also host biocrusts, which cover approximately 12% of the Earth’s land surface and are concentrated in drier regions like northern China. Biocrusts come in different forms, ranging from thin bacteria networks to thicker layers of moss and lichen.
To investigate the role of biocrusts in stabilizing the Great Wall, scientists collected samples from biocrust-covered sections and compared them to bare sections of rammed earth. The results showed that the biocrust-covered soil was less porous and had higher shear strength and compressive strength, indicating greater stability. These properties help protect the wall from degradation by reducing wind erosion, preventing water and salt from seeping in, and enhancing overall stability. Thicker biocrusts dominated by moss were found to be more protective than thinner ones dominated by cyanobacteria.
This study challenges the prevailing notion that plant growth can damage heritage sites, as biocrusts do not have penetrative root systems. However, biocrusts themselves are under threat due to climate change and intensive land use, which could result in their disappearance and the loss of their protective benefits for the Great Wall. Efforts are being made to restore damaged biocrusts, but research is still ongoing to understand their growth rates in different climates and levels of disturbance.
Growing biocrusts intentionally along the Great Wall, which is a relatively small feature, would be easier than restoring them over a larger area. Given the cultural significance of the Great Wall to China, it is crucial to find effective ways to preserve this site for future generations.