The Great Wall of China at Simatai (Photo contributed by Bill Price ’09)

Dear Readers, New Scientist had a most fascinating article this week about how a ‘biocrust’ (a mixture of moss, lichen  and cyanobacteria) are helping to protect the Great Wall of China from erosion. This extraordinary structure was started in about 200 BC, and rebuilt many times. Today, less than 6 percent of the original wall is well-preserved, and much of it has vanished altogether.

Much of the wall was built with a mixture of soil and gravel, compacted together to create ‘rammed earth’. Scientist Bo Xiao and his team at the China Agricultural University in Beijing sampled a 600 kilometre section of the remaining wall, and found that more than two-thirds of it was covered in biocrust. Traditionally, such layers are removed (not just in China but in most sites of archaeological/historical interest), but the scientists found that the biocrust actually strengthened the wall, in addition to forming an insulator which helped to reduce the temperature extremes that the structure experiences.

The areas covered in biocrust were also less porous so there was less water-penetration, erosion and salinity. Interestingly, these sections of the Wall also showed increased resistance to mechanical assault. It seems that in some places this mixture of algae, moss and lichen is literally holding the wall together. What a shame that this protective vegetation is so often removed to improve the aesthetic value of a monument!

You can read the whole article here, and very interesting it is too.

Plus, I went for a walk in St Pancras and Islington Cemetery yesterday, and found lots of biocrusts – some kinds of headstones and memorials definitely attract more moss and algae than others, but I was particularly taken  by this little bit of retaining wall. There is clearly a whole mini-community going on here, and I’m very glad that no one has yet found the time to ‘tidy it up’.

There is a lot of scientific study into biocrusts going on at the moment, and many seem to indicate that they improve the drought-resistance of soil, and can help with bioremediation of ex-mining sites and other contaminated areas, and even in Arctic tundra areas where the biological community has been damaged by trampling. I expect we’ll hear a lot more about biocrusts in the future. Watch this space!