Recent research has unveiled a fascinating aspect of the Great Wall of China’s longevity: a biological community, known as biocrusts, playing a pivotal role in protecting this UNESCO World Heritage Site. The findings, published in the journal Science Advances, reveal how these biocrusts – comprising photosynthetic bacteria, mosses, and lichens – contribute significantly to the structural integrity of the ancient fortifications, countering erosion caused by environmental factors.
Spanning over 21,000 kilometers, the Great Wall, with segments dating back 2,000 years, represents a colossal feat of ancient engineering. Its most prominent sections, erected during the Ming Dynasty (1368-1644), traverse diverse landscapes, including arid regions where many segments were constructed using rammed earth – a technique involving the compaction of soil and gravel into dense structures.
For long, there has been a debate among heritage conservationists regarding the impact of natural vegetation on the wall. Some believed that it might hasten the weathering process. However, this new study offers a contrasting perspective, demonstrating the protective role of biocrusts.
A team of researchers from the Chinese Academy of Sciences and China Agricultural University conducted thorough analyses on samples collected from eight sections of the Ming-era Great Wall made from rammed earth. Their investigation revealed that biocrusts enveloped approximately 67 percent of these sections. Interestingly, the composition of these biocrusts varied with the climate: cyanobacteria, known for their blue photosynthetic pigment, were predominant in arid areas, while Pottiaceae mosses flourished in more humid, semi-arid regions.
The study’s findings are striking in terms of the protective benefits these biocrusts offer. According to Xiao Bo, the corresponding author, the presence of biocrusts, particularly those dominated by moss, was found to enhance the mechanical strength and soil stability of the wall by a remarkable 37 percent to 178 percent compared to areas without such biological cover.
These biocrusts serve multiple protective functions simultaneously. They act as stabilizers, forming a sacrificial layer that takes the brunt of environmental impacts like wind and rain. Furthermore, they function as a sort of ‘drainage roof,’ mitigating the effects of temperature fluctuations. This multifaceted protective role aligns with several conventional conservation approaches, yet it does so in a naturally eco-friendly manner.
This discovery not only sheds light on the resilience of the Great Wall but also underscores the importance of the symbiotic relationship between natural processes and cultural heritage preservation. The insights gained from this study could pave the way for innovative, nature-based solutions in the conservation of other historical structures and sites worldwide, blending the realms of environmental science and heritage conservation.
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