China battles alien marsh grass at unprecedented scale | Science –
Along its 18,000 kilometers of coastline, China has been taken over by a green invader. Smooth cordgrass (Spartina alterniflora) grows tall and thick across tidal mudflats, depriving endangered migratory birds of habitat, clogging shipping channels, and ruining clam farms. Now, China aims to beat back 90% of the weed by 2025. “This is a mammoth undertaking,” says Steven Pennings, a coastal ecologist at the University of Houston. “It’s audacious.”
The nationwide effort, launched last month, “is by far the largest action plan for wetland invasive species control in China and even in the world,” says Bo Li, an invasion ecologist at Fudan and Yunnan universities who was not involved in creating the plan. It won’t be simple or cheap, costing hundreds of millions of dollars, Li estimates. And schemes to dig up, drown, or poison the weed all have side effects. “It’s going to be really difficult,” says Sam Reynolds, a biologist at the University of Cambridge.
Spartina, native to eastern North America, was brought to China starting in 1979 to stabilize tidal mudflats and turn them into land for agriculture or development. The plan worked, but the Spartina kept spreading and now covers about 68,000 hectares, about the area of New York City. The government has realized, says Yihui Zhang, a wetland ecologist at Xiamen University, that “the harm of Spartina alterniflora outweighs its benefits.” It dominates native salt marshes, outcompeting native plants that provide food for indigenous species such as the reed parrotbill, which has declined as a result.
Also at risk are birds migrating along the East Asian–Australasian Flyway, “the most important flyway in the world for coastal water birds,” says Nicola Crockford, principal policy officer at the Royal Society for the Protection of Birds. Spartina is the biggest threat to habitat for migratory birds in China because it prevents them from gathering food, Crockford says.
China has already launched smaller scale Spartina control projects. Li was involved in a well-known success at the Chongming Dongtan National Nature Reserve. After Spartina was planted there in 2001, it ruined habitat for dozens of fish species and migratory birds. To remove the weed, engineers built a seawall and flooded the wetland to drown the grass. By 2018, the project had eliminated 95% of the Spartina in 2400 hectares, and native plants and bird populations began to recover. But the price tag was steep: about $150 million, largely for erecting the seawall. A smaller project in Jiangsu had similar success at lower cost by covering Spartina with silt dredged from a shipping channel. In both cases, follow-up weeding was necessary to remove survivors.
But local control efforts aren’t enough, because the weed spreads so readily. Under the national plan, provinces will map the distribution of Spartina and work together. Officials in the 11 coastal provinces submitted control plans last week to the National Forestry and Grassland Administration, which is overseeing the effort. Funds will come from the national and local governments.
Li says scientists and policymakers have yet to solve a key challenge: identifying the combination of eradication methods that would work best in the variety of habitats Spartina has invaded. None of the possible methods is a sure thing. Releasing insects that eat weeds, a technique called biocontrol, has worked against other plants, but so far researchers have not found anything that can be used against Spartina in China. Other techniques have limitations. Flooding, for instance, can starve the sediment of oxygen, which can kill worms and other animals that live in it. Baoshan Cui, an expert in wetland protection and restoration at Beijing Normal University, says waterlogging causes more problems than other strategies, so it should be avoided. But backhoes and other construction equipment, which can drive onto firm mudflats to dig up and bury Spartina, compact the mudflats, disturbing the habitat of sediment-dwelling creatures. And herbicides have rarely been used against Spartina in China.
Researchers who reviewed 116 studies of Spartina control—all of them much smaller than China’s plan—found that physical controls such as digging and burying are highly effective in the short term, but the weed grows back. Herbicides worked very well at controlling Spartina, but only when applied year after year. Overall, combined methods worked best, Reynolds and other researchers conclude in a preprint. Shengyu Wang of Fudan University, a co-author, hopes to see large-scale tests of herbicides.
Donald Strong, an ecologist at the University of California, Davis, who studied Spartina eradication in Washington state, says China’s plan is feasible. He and others emphasize the need to eliminate survivors and prevent regrowth. “You have to hunt them down one at a time,” Pennings says. In New Zealand, land managers have used drones and trained dogs to find remaining patches and even lone plants.
If China succeeds in eliminating Spartina from vast areas, it would be an inspiration to other countries as they face their own invaders, Pennings says. “Maybe we’ll look again at all the other problematic invasives and say, ‘Well, if it could be done with Spartina, why not?’”