Chinese border policemen patrol in the northern Badain Jaran Desert in Alxa League (File photo)

For years, experts have warned of the giant dust bowl that is forming in northwestern China. Overgrazing, overuse of land, and drought have created what some agronomists say is the world's biggest transformation of productive land into desert. Official estimates say the deserts, advancing by thousands of square kilometers a year, now make up between 18 and 27 percent of China's surface. Experts in China's rural communities say the phenomenon is contributing to massive migration and possibly threatening food production. 

Zhang, a 70-year-old farmer, stands in a cornfield, sifting a handful of powdery sand through his fingers.

It is this light brown colored sand, Zhang says, that blew with the wind a few years ago and nearly buried his house here in Langtougou village, less than 200 kilometers from the capital, Beijing.

Zhang says the government came and ordered villagers to plant trees that he says have held the ground in place and prevented dust from burying houses any further.

Villager in Langtougou holding clump of sand, says conditions are much better after tree-planting campaign and ban on grazing

A fellow villager, 55-year-old farmer Li Bingcheng, gazes at the green hillsides and smiles as he says corn is once again growing on his field. But his grin fades as he says he has taken a loss after the authorities ordered him to stop raising goats.

"The government told us to raise dairy cows instead of goats because cows do not eat the grass on the hillsides," he said. "It is not easy for us to buy cows on our own, so it was up to the government to help us buy them. I was used to earning more in the past when I had many more goats that I could sell for as much as about $1,200 a year."

Scene in Gansu province shows farmland stretching far up the hillsides; Experts say overuse of land in China is one of the key causes of desertification

Despite the drawbacks for farmers, measures forcing farmers to raise cows in pens and plant trees have made Langtougou, by most accounts, a success story in China's war on advancing deserts.

However, government officials have little reason to claim an overall victory. At a recent briefing in Beijing, Liu Tuo, an official in charge of sand control at China's State Forestry Administration, said the rate has, in the best of cases, merely slowed.

"Five years ago, sandy areas were expanding at an annual rate of 3,436 square kilometers, but now that rate of expansion is decreasing by 1,283 square kilometers [a year] and this has laid a solid foundation for the sanded areas," he noted.

Some environmentalists are not so optimistic and say the drop in the rate of expansion makes little difference when the desert is spreading so fast.

Uigher child looks back as he climbs a sand dune which is burying structures of village in Xinjiang (File photo)

Lester Brown is head of the Earth Policy Institute, a research organization in the United States. He says making Chinese farmers change their ways is proving to be a tough challenge in impoverished areas such as Gansu province and Inner Mongolia, where people are more dependent on livestock for their living.

On a visit to Beijing recently, Brown said overgrazing has been the leading cause of desertification in China since the country began its transition from socialist-style collective farming toward a free-market economy.

"What has happened is that, after the economic reforms in 1978 when agriculture shifted away from production teams into families, the government lost control of livestock numbers," explained Brown. "And so we have a classic sort of tragedy of the commons, where each family wants to keep expanding the number of sheep and goats but with no one looking at the entire effect of this."

Farmers plant trees on a slope near Yudushan in Yanqing County to control desertification (File photo)

That effect is that, once the vegetation has been removed by overgrazing, strong winds that blow in from Siberia and Mongolia dry the land and kick up dust at first, and when the small particles are gone, the sand blows.

2006 has seen a number of unusually strong sandstorms in northern China, which some meteorologists say is a result - in part of - desertification. Cities such as Beijing have days in which sand fills the air, blocking the sun and creating long-lasting health hazards.

Experts also warn about the social consequences of the spreading deserts in China, including mass migration and falling food production. The United Nations estimates that 400 million Chinese people live in areas threatened by expanding deserts, which could force many into cities in search of jobs. The Asian Development Bank says at least 4,000 villages have already been buried by sand and their occupants forced to move to greener areas.

And there are concerns that the loss of arable land ultimately may cut grain production.

In Langtougou village, Li Bingcheng says he begins to see the benefits of changing his farming habits - even if it means a shorter-term financial loss.

"Now that I have no more goats, I do not earn as much money as I did before," he said. "It takes more time to make money from cows. The returns are slow. But, to tell you the truth, we have enough to eat. We need to look to the future. We need to consider the generations to come."

Tree-planting has helped keep soil in place, but environmentalists say efforts like these are not keeping up with pace of expanding deserts

Li's attitude is the result of one of several pilot programs that have been carried out by the central government - programs that the Communist Party leadership likes to point to as examples of how it is working to stabilize the situation and reverse it.

However, environmentalists warn that Langtougou is only a small example and that nothing the government has done has come close to stopping the advance of the deserts across China's vast landscape.