Great Green Wall

CHINA is good at building defensive walls. But the record of its most celebrated one is mixed. In 1211 Mongol armies rode round the fortification in Zhangjiakou, the northern gateway to Beijing. Today the city lies on one of two routes that bring another relentless foe to the capital: sand. Blown from northern deserts and degraded drylands, it coats roads, clogs railways and desiccates pastures. According to Greenpeace, just 2% of China’s original forests are intact. Decades of rampant logging and overgrazing have speeded the degradation of its land and soil; over a quarter of its territory is now covered in sand.

Against this new foe, China is building another Great Wall, this time a green one. The Three North Shelterbelt Project is by far the world’s largest tree-planting project. Since 1978, 66 billion trees have been planted by Chinese citizens. By the project’s end, planned for 2050, it is intended to stretch 4,500km (2,800 miles) along the edges of China’s northern deserts, cover 405m hectares (42% of its territory) and increase the world’s forest cover by more than a tenth.