A survey showed more than a quarter of China's land remained either degraded or lost to sand and gravel due to a combination of a naturally dry climate, centuries of over-cultivation and decades of excessive demand on water and soil from the world's biggest population and fastest growing economy.

Despite the world's biggest tree-planting campaign, the relocation of millions of "eco-migrants" and restrictions on herding and farming, the report noted the "desertification trend has not fundamentally reversed".

There were small signs of improvement. In the five years to 2010, the authors estimated the area of desert had shrunk by an annual average of 1,717 square kilometres. This was 40% better than the results from 2000-05, the first in China's history to ever show a gain.

The report said desertification continued to pose a "serious hidden danger" to China's security and its capacity for economic development.

"We've made progress, but we face a daunting challenge," said Liu Tuo, head of the desertification control office in the state forestry administration. "It may take China 300 years."

Zhu Lieke, deputy head of the state forestry administration, said climate change was another growing concern.

"The frequent occurrence of extreme meteorological disasters, such as prolonged drought, has increased the vulnerability of the land to desertification," said Zhu Lieke, citing climate simulations that project a 17% increase in desert areas with each 1 degree rise in temperature.

Tibet, Qinghai, Xinjiang and Inner Mongolia remain badly affected, partly because they are at a high elevation and more vulnerable to rising global temperatures, glacier melt, retreating snowlines and water shortages.

The government has controversially moved hundreds of thousands of nomadic herders off degraded grasslands in the past 10 years. Tibetan critics are suspicious that this is being done to clear land for development or resource extraction. Many environmentalists also question whether it is a mistake to put too much of the blame on overgrazing.

Liu Tuo said China has the world's worst desertification problem because it has to meet the demands of such a huge population. Finding a balance is the government's stated goal, but it remains elusive.

(Source: China makes gain in battle against desertification but has long fight ahead [Guardian])