土地荒漠化是世界性的难题，全球约三分之一人口生活在荒漠化危害地区。沙尘暴困惑中国、东亚、太平洋地区，为此，全球围绕沙尘暴治理投入了大量的人力与物力，笔者课题组围绕该领域进行了7年的试验工作。最近Science以3页完整篇幅报道了我们的试验，下面是原文。文章发表时同时附5幅图片，这里没有办法显示，感兴趣的网友可以上Science 网站阅读原文，谢谢。蒋高明。

Getting at the Roots of  Killer Dust Storms

Dennis Normile   Science SCIENCE VOL 317 20 JULY 2007, pp314-316

NEWSFOCUS ECOLOGY

  East Asia’s dust storms are growing in number and ferocity. A simple experiment to wean villagers off destructive land practices suggests a way to tame the yellow blizzard.

BAYINHUSHU, CHINA—When Nasen Wuritu was a boy in this village in Inner Mongolia, “the grass grew as tall as an adult,” he says. In the 1960s, cows grazed year-round and never went hungry. After Nasen Wuritu reached
  adulthood, however, throngs of livestock had denuded the land, forcing him and other herders to spend precious cash on animal feed. Hand in hand with this crisis was a rising frequency and intensity of dust storms. “People couldn’t go outside, and we had to light candles in the middle of the afternoon,” says Nasen Wuritu, now 50.

In Bayinhushu, those hard times have passed. On a late spring day here, lush hills roll toward the horizon and the air is clear despite a steady wind. After a 5-year effort, the people of Bayinhushu—with help from officials and an army of ecologists, botanists, and economists—have restored the pastures. And dust storms here have abated.

  Bayinhushu is a rare bright spot in a bleak landscape. In the arid grasslands of northern China and Mongolia, overgrazing, over-cultivating, and squandering of scarce water resources have created a massive dust bowl
  where winds sweep topsoil away. Dust storms regularly blight eastern China, Korea, and Japan, closing schools, damaging jet engines, and triggering respiratory ailments as far away as California. A particularly nasty
  storm in May 1993 resulted in 85 deaths, the loss of 120,000 head of livestock, and the destruction of more than 4400 houses and 2.3 million hectares of crops, according to the Chinese Academy of Forestry Sciences.
  The economic toll in China alone is approximately $650 million a year, says Wang Tao, a physical geographer who heads a national project to combat desertification. Things are likely to get worse before they get better. Wang, who is based at the Cold and Arid Regions Environmental and Engineering Research Institute of the Chinese Academy of Sciences (CAS) in Lanzhou, estimates that northern China’s arid grasslands are being degraded at a rate of 3600 square kilometers—an area bigger than the U.S. state of Rhode Island—every year. Wang predicts
that as a result, dust storms, which have increased in number nearly sixfold over the past 20 years, will become more frequent, more intense, and more deadly.

  If the lessons of Bayinhushu can be applied across the vast steppes once ruled by Genghis Khan, dust storms should diminish. But there are challenges to implementing sustainable land practices in China’s northern provinces. “Ecologically, it is easy to control dust storms. Economically, it is difficult,” says Bayinhushu project leader Jiang Gaoming, a plant ecologist at the CAS Institute of Botany in Beijing. Solutions must be tailored to the needs of local residents and ecological conditions in each region. Complicating the picture, top Chinese officials still hew to discredited policies that aim to subdue dust storms by conquering the deserts. “We have a lot of convincing to do,” Jiang says.

The perfact dust storms

  The basic anatomy of East Asia’s dust storms is fairly well established. For starters, the common term “sand storms” is a misnomer. Sand particles are too heavy to get lifted high into the atmosphere. Thus, little of the dust that blights East Asia comes from deserts, where erosion over the millennia has carried away most of the smaller particles. Studies indicate that the dust originates in dry lakebeds and arid lands on desert fringes. In these regions, a crust forms on undisturbed soil, giving some resistance to wind erosion. But in springtime, that crust is broken up by plowing and livestock, which also strip the land of new growth and pound soil into dust.

  Meanwhile, the temperature difference between a chilly atmosphere and a surface warmed by intensifying spring sunlight creates updrafts that lift dust into the air. As air streams south and east from Siberia, the
  winds bump up against the mountain ranges that ring northern China and Mongolia, forming low-pressure pockets that suck airborne dust into the upper atmosphere. Easterly winds sweep the particulate matter to
Beijing, Seoul, Tokyo, and sometimes across the Pacific Ocean to North America.

  There are good years and bad years. Heavy snows add moisture to the soil, dampening dust in early spring. Conversely, without snow cover, soil dries out during winter and is more prone to wind erosion.

This dynamic has persisted for centuries, as have dust storms. But the storms have been worsening. Seoul, which bears the brunt of East Asia’s dust storms, suffered “dust events” on 23 days during the 1970s,
41 days in the 1980s, 70 days in the 1990s, and 96 days so far this decade, according to the Korea Meteorological Administration.

The primary reason for this onslaught, most scientists believe, is degradation of fragile ecosystems. The population of Xilingol League, the district that includes Bayinhushu, increased from about 200,000 in the late
  1940s to more than 950,000 in 2000, Jiang says. Over that period, herds of grazing animals skyrocketed from around 1 million head to more than 24 million, while the grazing area shrank from 5 hectares per animal to about one-tenth of a hectare.

  Staggering growth such as this occurred all across northern China. The national government encouraged nomadic herders to settle in villages and multiply herds to boost incomes, says Jiang. Livestock created an ever-widening ring of denuded land around settlements. The government also encouraged Han Chinese farmers to migrate to northern regions to “tame the deserts” with artificial oases and irrigation. The migrants
cleared land for farms and cut brush for fuel. Irrigation gradually dried up many lakes and rivers. The result, Jiang says, is that 90% of China’s grasslands, an area encompassing 4 million square kilometers, are degraded.

  Authorities have long recognized the problem, but attempted fixes have been futile if not counterproductive. Since 1978, China has spent at least $1 billion planting trees in arid and semiarid regions to combat desertification, says Luo Yiqi, an ecologist at the University of Oklahoma in Norman, who with colleagues at the Cold and Arid Regions Institute has studied such afforestation efforts. Afforestation is misguided, Luo asserts. “People proposed the idea without considering ecological principles,” he says. “They set out to create forests in regions where forests naturally do not grow due to limited precipitation.” The tree of choice has been the poplar.
  If watered, poplars grow rapidly, but without intensive care, they die. Sticks protruding from barren earth—dead poplar saplings— line roads in Inner Mongolia. Where poplar groves become established, Luo says, the deeply rooted trees hemorrhage water through transpiration, lowering the water table and making it harder for native grasses and shrubs to survive.

  China’s tree-planting campaign has successfully reforested areas with ample rain, says Luo. But planting poplars in arid regions, he says, “does not help combat desertification.” The government continues
to pour money into afforestation, regardless of water resources, through a bureaucracy whose mission is to plant trees. “It is time for the Chinese government … to scientifically evaluate long-term policies,” Luo says.

Sustainable living

  In 2000, CAS applied a scientific approach to dust storms by funding five grassland-restoration pilot projects, including Jiang’s. Jiang headed for Zhenglan County, a subdivision of Xilingol League, partly because the Institute of Botany has a research station there that had documented the loss of 12 centimeters of topsoil to wind erosion in the past 24 years. Another reason: Beijing is only 180 kilometers south. “If [the land] is degraded here, the dust will affect Beijing,” Jiang says.

  Realizing that the key to solving the dust problem is involving the people who live on the land—a big task given, Jiang says, “their poverty and their level of education”—he invited onto his team social scientists and economists as well as ecologists and animal husbandry specialists. The goal was to improve the lives of villagers while reducing environmental degradation. At the start of the 5-year, $600,000 project, Bayinhushu consisted of 72 households with 316 people and 11,560 head of livestock—75% sheep and goats, the rest cattle. The village manages 7330 hectares of land, much of it communal pasture.

  Jiang’s team calculated that villagers could boost incomes if they reduced sheep and goat numbers and introduced an improved breed of dairy cattle, while curtailing open grazing. It was not easy to convince them, however. Mongols consider the size of the herd a measure of wealth. To help overcome doubts, local authorities chipped in additional incentives: They dug wells and extended the power grid to Bayinhushu to run pumps and electrify houses. The county also improved the dirt track connecting the village to a paved road.

  The villagers agreed to ban grazing on 2670 hectares of communal rangeland to allow vegetation to recover. Harvesting hay from this land in autumn provided enough forage for a smaller number of livestock during a typical winter, eliminating the expense of commercial feed. To tide the villagers over while the land recovered, Jiang’s team planted corn on several dozen hectares.

  Jiang’s team made some mistakes along the way. More than half of the initial budget went to aerial grass seeding and planting trees to form windbreaks. Both proved “a waste of money,” Jiang says. The trees died, and sown plots fared no better than those left to recover naturally. By and large, however, the simple plan worked. The villagers grew enough corn to feed animals without grazing in the common pasture. Herds were reduced to 5783 head, a little over half of which were sheep and goats. Milk production doubled per head. By the end of the third summer, the grass had recovered to provide more than enough hay for the village’s needs.

  Five years later, Jiang says, the land looks much as it probably did a century ago. Annual incomes have increased 46%, from $315 to $460 per capita. In Nasen Wuritu’s living room, a framed ceramic relief of Genghis Khan hangs on the wall. A large-screen TV and a satellite dish in the front yard pipe in previously unimagined entertainment. “We used to joke that there was nothing for Mongols to do at night but sleep and make babies,” Nasen Wuritu says. And the dust storms, which used to drive people indoors once or twice a month, are now occasional nuisances.

  Bayinhushu is a “good example” of grassland restoration, Wang says. In an encouraging sign, herders in nearby villages are restricting grazing on communal pastures. Still, the Bayinhushu experience may not be easy to replicate in places with less favorable ecological conditions. Jiang notes that Bayinhushu had sufficient topsoil replete with seeds, and groundwater levels had not been affected by excessive irrigation.

  Severe degradation may require “human facilitation of the restoration process,” says Lu Qi, a desertification specialist at the Institute of Forestry in Beijing. After studying restoration projects on the Tibetan Plateau, where extreme degradation has created shifting sand dunes, Lu found that a hands-off approach led to a slow and spotty revegetation and little stabilization of the dunes. In contrast, erecting sand barriers and planting soil-stabilizing shrubs promoted the healthy recovery of native plants. Because shifting dunes smother new vegetation before it can take root, Lu argues that active intervention is needed to reverse desertification.

  The toughest task may be to undo the harm wrought by artificially expanding oases, like one at Minqin, between the Tengger Desert and the Badain Jaran Desert in Gansu Province, west of Inner Mongolia. Beginning in the 1950s, irrigation on a massive scale helped establish thousands of farms but eventually dried up natural rivers and depleted groundwater, fueling the expansion of the two deserts. Earlier this year, provincial authorities ordered 10,500 people to vacate farms in a 1000-km2 area surrounding Minqin within 3 1/2 years.

  Wang says that resettling the farmers elsewhere “may relieve some problems in this area but cause new problems in another area.” It would be better, he argues, to introduce water-conservation techniques, such as those pioneered in Israel, which might allow sustainable farming in the area.

  At Bayinhushu, Jiang continues to measure the experiment’s results and explore ways to further raise village
incomes. The project is leaving an unexpected legacy. Before the project began, Nasen Wuritu says, village youngsters typically dropped out of school after the compulsory 9 years. But the scientists who spent time in the village exposed the youngsters to the Internet and text messaging. “Many young people realized the importance of an education,” he says. Exhibit A is Nasen Wuritu’s eldest son, now studying to be a veterinarian at Inner Mongolia University in Hohhot. “He wants to stay in the city to pursue a better life,” Nasen Wuritu says. That would mean one less person eking out a living on the grasslands—and a greater chance of enjoying an environment increasingly liberated from dust.