| China’s move to contain its northern deserts with a Great Green Wall has resulted in more than 30 million hectares of forest planted in 40 years. But while this has cut down on dust storms, it has also caused serious allergy problems. The forestation program used a variety of hardy, drought-tolerant and fast-growing plants, many of which are wind-pollinated. Willows and poplar trees, both widely planted in the north, have high pollen output that sweeps across northern Chinese cities every spring, causing allergic reactions among residents. Wormwood grass, or Sha Hao in Chinese, was also commonly used in the greenification push and is a major hay fever trigger. As a result, people living in the Great Green Wall area are more likely to suffer from hay fever. While its overall prevalence among adults in China is about 18%, in Yulin, a city in the region where the forestation project is carried out, 27% suffer from hay fever. In Inner Mongolia, the rate is 32%. Environmental experts said China didn’t have a better choice of plants when it started the forestation campaign. The northern regions are very hot in summer, cold in winter and are arid. Plants like poplar, willow and wormwood were good choices because they are tough and easier to scale up. China’s goal was to “get green first, and then to consider other things,” Gu Lei, an associate professor of botany at Capital Normal University told local news outlets. The health toll has spurred some cities to replace heavily pollinating plants. Yulin’s government has been using other plants like pine trees to replace Sha Hao in residential areas. Beijing, where snow-like catkins from poplar and willow cover its streets every spring, has also been replacing those trees with gingko, plum and a new breed of poplar that doesn’t produce catkins. Yet this process has been slow, in part because it’s expensive. In a recent five-year forestation project, Beijing spent 6 billion yuan ($830 million), or about 450,000 yuan ($62,000) per hectare. This helps explain why most of the original plants in rural areas have remained. “Pollens can spread tens and hundreds of kilometers away with just a gust of wind,” Yin Jia, a physician at Peking Union Medical College Hospital, told Chinese media. “If you just remove the ones in the urban neighborhood, can it really solve the problem?” So to deal with the pollen that plagues cities for weeks every spring, authorities are hosing down sidewalks in densely populated areas and spraying plant hormones on female trees to suppress growth of flower buds. And Beijing issues alerts to let hay fever sufferers know how long the peak pollen is expected to last and what times of day the levels are particularly high. But the calendar offers the ultimate relief: Beijing’s spring pollen season is over at the end of this month. — Karoline Kan | 
