THE Dongtan wetland, Shanghai’s bird paradise on Chongming Island, was being slowly choked by the spread of smooth cordgrass until a program was initiated to control the noxious invasive species.

Scientifically called Spartina alterniflora Loisel, the invasive grass was introduced to China from United States in the 1970s as a tool to protect and expand tidal zones. The plant’s hardy roots readily adapt to different environments. It didn’t take long for the cordgrass to make itself at home, proliferating along coastal China from the Yalu River estuary in the north to Guangdong Province in the south. On the way, it started to crowd out indigenous plant species and harm traditional bird-feeding grounds.

“Smooth cordgrass is well adapted to coastal tidal environments, with the ability to expand in just two years,” said Tang Chendong, vice director of Shanghai Forestry Bureau and Shanghai Landscaping and City Appearance Administrative Bureau.

“At first, the species worked very well in stabilizing sand dune stabilizations and promoting silting.”

Tang is a bit of an old hand in environmental conservation. He came to work in the Dongtan wetland nature reserve after graduating from university in 1999 and later served as director of the Chongming Dongtan National Nature Reserve management station.

Before smooth cordgrass set foot in Dongtan in the mid-1990s, the tidal flats there were categorized in four sections: the reed zone, the meadow rush zone, bare flats and a subtidal zone. All abounded in food resources for birds, providing sustenance for feathered species wintering over in the area.

The cordgrass quickly spread across the wetland, first overtaking the reed and meadow bush zones and then occupying the remaining two zones. The 3,000 tundra swans (Cygnus columbianus) that used to winter over in the Dongtan wetland stopped coming.

When China compiled its first list of invasive species in 2003, smooth cordgrass ranked No 1.

Many countries have imported alien species to perform some desired task, only to find that they have unleashed a monster into the environment. One notable example is the cane toad, introduced into Australia from Hawaii to control beetles that affect sugar cane crops. The toads, which are poisonous, quickly proliferated to an estimated 200 million, destroying biodiversity without a natural predator to destroy them.

So, too, the Asian carp that is threatening the Great Lakes of the US, and Canadian pondweed has turned into a noxious nuisance in Ireland and the British Isles.

Faced with the dire consequences of the smooth cordgrass epidemic, Chinese scientific and agricultural professionals were forced to reflect on the nation’s lack of safeguards in vetting introduced species.

In addition to killing native plants, like Scirpus mariqueter, that provided food for geese, ducks and cranes, the cordgrass adversely affected coastal aquaculture. According to research in Fujian Province, when fish eggs and larvae were washed by tides into the tangled roots of smooth cordgrass, their survival rate dropped significantly.

“For example, in a normal cycle it might takes 10 years for reed field to evolve into a bare flat zone,” Tang said. “The smooth cordgrass could accomplish the same end in two or three years, causing serious disruption to the biodiversity in coastal regions and the ecosystem of the wetlands, changing its entire structure.”

Shanghai began research on controlling smooth cordgrass in 2002, under a project funded by the Municipal Agricultural Commission and later involving Fudan University, East China Normal University and the National Natural Science Foundation.

The Dongtan wetland became the Chongming Dongtan National Nature Reserve in 2005, and experts dispatched to assess the area singled out the need to control the spread of smooth cordgrass as a top priority.

“The wetland is an important ecosystem, and we need to focus on how to strengthen the stability of its ecology, protect its biodiversity and preserve its function in water conservation and purification,” explained Tang.

“In the Yangtze River estuary, wetlands play major roles in stabilizing sand dunes, providing wintering grounds for birds and other important functions. They need protection and scientific development.”

As part of the research, Tang and a team of experts travelled to San Francisco Bay to survey management options for controlling cordweed ­­— from simple manual removal to biological and herbicidal agents.

Smooth cordgrass is not indigenous to the western US. It was introduced.

In 2007, Shanghai approved a coordinated cordgrass management project. It was a six-phase plan combining physical and biological artillery. The 40-month, 103-billion (US$150 million) project officially began in September 2013.

The first step was the construction of physical barriers to prevent proliferation of the grass. Once the barriers were erected, water was allowed to flow into the sealed areas to a certain height. Above the water line, the cordgrass was cut, leaving the roots to soak underwater for half a year.

That effectively killed the cordgrass roots. When water was drained off, the soil was left to dry.

In the fifth step of the project, native species were replanted in the wetlands. They included reeds where birds could both seek shelter and feed.

The last phase of the project was adjusting water levels to the needs of different families of birds and migration seasons through hydraulic facilities.

Salinity was also adjusted to provide an environment more hostile to smooth cordgrass growth but beneficial to establishing a food chain in brackish water area.

In Dongtan, small habitats like sandbars were built up to diversify the environment in a way attractive to birds.

The project has been successful. Smooth cordgrass that previously occupied 25.3 square kilometers has largely been eradicated, with a 95 percent control rate.

“We can see many birds in Dongtan that we haven’t seen for a long time,” Tang said. “The results of the bird rehabilitation project have been excellent,” said Tang.

“The bigger challenge ahead is sustainable management to ensure that we maintain a healthy biodiversity.”

The success in Dongtan has inspired other nature reserves in China to initiate similar cordgrass control projects, including the Min River estuary in Fujian, Yancheng in Jiangsu Province and Dongying in Shandong Province.