Have you ever been on a long road trip, running on empty, only to find the rest stop you were counting on closed? Some birds that migrate along China's coast face something like that. According to a 2021 study in the Journal of Environmental Management by Micha Jackson and colleagues, smooth cordgrass was introduced to China in 1979 to turn tidal flats into dry land. It has spread rapidly since then. The study says the grass reduces the feeding and resting space that shorebirds depend on. Why China brought the grass inSmooth cordgrass (Spartina alterniflora) is a marsh plant that is native to the Atlantic coast of North America.

Jackson says the species has been introduced into China deliberately to promote the development of tidal flats into dry land. A preliminary survey reported by the Chinese government in 2023 found that the plant covered about 68,000 hectares. Smooth cordgrass is widely grown in the provinces of Jiangsu, Zhejiang, Fujian, Shandong, and in Shanghai. The Chinese government now recognizes it as the most damaging invasive plant on the country's coastal mudflats.

How fast it spreadSmooth cordgrass was introduced to Jiangsu Province in 1979, according to a 2016 review of the species in the journal Emu by David Melville, Ying Chen and Zhijun Ma. It said the plant had spread along more than 400 kilometers of coast. By the early 2000s, it had developed into bands up to 4 kilometers wide. The Jackson study notes that it grows mainly on bare tidal flats, and can gradually replace open mud with dense grass. What this means for the shorebirdsShorebirds rely on tidal flats for food.

The Jackson study says the grass reduces feeding and resting space, and may be most destructive where tidal flats have already been lost.

The Emu review makes a similar point, saying the spread has removed roosting sites and smothered feeding grounds. In China, the Jackson team surveyed 53 sites on the coastal mainland where internationally important numbers of shorebirds have been recorded. In 2015, grass was present at 28 of these sites. At 22 of the 28 sites, the tidal flat area also declined from 2000 to 2015.

Over the entire 53 sites, tidal flats shrank by a net 15% over this time period. The combined pressures were most severe in eastern coastal China. Species that rely heavily on this region, including the Critically Endangered Spoon-billed Sandpiper, could be particularly impacted, the authors say.

Not the only threat, and what comes nextThe grass is not the only problem. The Jackson study says several species have declined because of tidal flat loss from land reclamation and other processes. The threats listed in the Emu review along China’s Yellow Sea coast include aquaculture, harvesting and pollution. So cordgrass is one part of a bigger puzzle.

China has also launched a special campaign to control the plant. The National Forestry and Grassland Administration said in February 2023 it aimed to bring the plant under effective control nationwide by 2025 and clear more than 90% in various provinces. Officials said they would strengthen monitoring, boost scientific and technological support and improve relevant laws. The administration has since reported that its national clearing task of 1.46 million mu (about 97,000 hectares) was completed in 2025, and in 2026 it set a new goal of keeping the plant cleared nationwide through 2030.

The 2021 study authors say there is an urgent need to stop further tidal flat declines and build a full control program for the plant.

This story shows how a solution can end up creating problems nobody planned.

The Emu review says China's Yellow Sea wetlands are a major staging area for shorebirds on the East Asian–Australasian Flyway, so what happens there affects a wider migration route.