Throughout the ages and across dynasties China has been known as a builder of defensive walls. Its most famous defense is its protection of Beijing from invading Moguls - the Great Wall of China.

Now, with only 2% of its forests left in tact, there is a new foe: desertification. Extensive logging and rampant overgrazing have sped the degradation of its land and soil; over a quarter of Chinese territory is now covered in sand. So, against this new dusty enemy, China is building a Great Green Wall.

Since 1978, 66 billion trees have already been planted by Chinese citizens, which makes the Three North Shelterbelt Project by far the world’s largest tree-planting project.

The scale of Chinese projects never ceases to astound me. By the end of this ambitious project, planned for 2050, 2800 miles of new trees will have been planted along the threshold of China’s northern deserts. 2800 miles of newly planted forests will increase the world’s forest cover by one tenth!

"Vegetation has improved and dust storms have decreased significantly in the Great Green Wall region, compared with other areas," says Minghong Tan of the Institute of Geographical Sciences and Natural Resource Research in Beijing.

Planting 100 billion trees by 2050 to stop desert encroachment is surely is one of the most aggressive environment-altering projects ever attempted. King Canute thought his command could hold back the tide. Communist China is commanding that the deserts be held back.

But is such an aggressive attitude towards managing natural resources as short-sighted as King Canute’s folly? Hong Jiang of the University of Hawaii at Manoa, says planting trees where they do not grow naturally, will not ultimately work. "Instead of controlling nature, we need to follow nature," she says. Sometimes that means "allowing sand the freedom to roll".

David Shankman of the University of Alabama says it is not clear how permanent the Green Wall would be. "What is the mortality rate of planted trees? What happens when they die? And how do these trees affect grass and shrubs, which in general are more resistant to drought and more effective at erosion control?"

If this forest defense does work could parts of the Sahara be afforested so that the Sahel, South of it, could thrive again?