China Battles Alien Swamp Grass on an Unprecedented Scale | Science

On a long coastline of 18,000 kilometers, China has been taken over by a green invader. smooth grass (Spartina alterniflora) grows tall and thick along tidal flats, depriving endangered migratory birds of their habitat, clogging shipping channels and destroying clam farms. Now, China aims to defeat 90% of the weed by 2025. “This is a mammoth undertaking,” says Steven Pennings, a coastal ecologist at the University of Houston. “It’s bold.”

The nationwide effort, which began last month, “is by far the largest action plan to control wetland invasive species in China and even the world,” says Bo Li, an invasive 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 plans to dig up, smother, or poison the weed all have side effects. “It’s going to be very difficult,” says Sam Reynolds, a biologist at the University of Cambridge.

Spartina, native to eastern North America, has been transported to China since 1979 to stabilize tidal muds and convert them into land for agriculture or development. The plan worked, but the Spartina it continued to spread and now covers about 68,000 hectares, about the size of New York. The government has realized, says Yihui Zhang, a wetland ecologist at Xiamen University, that “the damage of Spartina alterniflora outweighs its benefits.” It dominates native salt marshes, outgrowing native plants that provide food for native species such as the reed parrot, which has declined as a result.

Also at risk are birds migrating along the East Asia-Australasia, “the world’s most important corridor for coastal seabirds,” says Nicola Crockford, principal policy officer at the Royal Society for the Protection of Birds. Spartina is the biggest threat to the habitat of migratory birds in China because it prevents them from foraging, Crockford says.

China has already started on a smaller scale Spartina control projects. Li participated in a well-known success in the Chongming Dongtan National Nature Reserve. After Spartina planted there in 2001, destroyed habitat for dozens of fish species and migratory birds. To remove the weed, engineers built a sea wall and flooded the wetland to smother the grass. By 2018, the project had eliminated 95% of the Spartina on 2400 hectares, and native plant and bird populations began to recover. But the price was steep: about $150 million, mostly for building the sea wall. A smaller project in Jiangsu had similar success at a lower cost than coverage Spartina by dredging mud from shipping channel. In both cases, it was necessary to eradicate the herbs to remove the survivors.

But local control efforts are not enough, because the weed spreads so easily. According to the national plan, the provinces will map its distribution Spartina and cooperate. Officials in the 11 coastal provinces submitted control plans last week to the National Forest and Range Administration, which is overseeing the effort. The funds will come from 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 are certain. Releasing weed-eating insects, a technique called biocontrol, has worked against other plants, but so far researchers haven’t found anything that can be used against Spartina in China. Other techniques have limitations. Flooding, for example, can strip sediment of oxygen, which can kill worms and other animals that live in it. Baoshan Cui, an expert on wetland protection and restoration at Peking Normal University, says flooding causes more problems than other strategies, so it should be avoided. But excavators and other construction equipment, which can lead to fixed mudslides to dig and bury Spartina, condense mudflats, disrupting 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 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 in control Spartina, but only when applied year after year. Overall, the combined methods worked best, Reynolds and other researchers concluded in a preprint. Shengyu Wang of Fudan University, one of the authors, hopes to see large-scale trials 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 stress the need to eliminate survivors and prevent regrowth. “You have to go after them one at a time,” says Pennings. In New Zealand, land managers have used drones and trained dogs to find remaining patches, even single plants.

If China manages to eliminate Spartina from vast areas, would be an inspiration to other countries as they deal with their own invaders, Pennings says. “Maybe we’ll look back at all the other problematic hackers and say, ‘Well, if it could be done with Spartinawhy not?'”

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