Ecologists find simple way of killing invasive coastal weed

Ecologists have devised a way to get rid of a pernicious weed that is invading British shores and threatening migratory birds, including at least one endangered species.

A six-year experiment to eliminate Spartina anglica – a cordgrass that turns wet mudflats into dry land – has resulted in a simple yet effective way of killing the weed while restoring the natural habitat of an estuary.

Spartina anglica is one of the most invasive weed species in Britain. Its rapid spread around the coastline has often been deliberately promoted by landowners, who plant the grass on coastal sites to prevent soil erosion.

The weed is being blamed for a catastrophic decline in many wading birds, including the dunlin and the knot, which feed off worms, crustaceans and other invertebrates living in the inter-tidal mudflats that Spartina anglica destroys.

English Nature ecologists at the Lindisfarne National Nature Reserve in Northumberland, which has suffered from the progressive encroachment of the weed for more than 70 years, have found that a form of ploughing called "rotoburying" kills it.

Phil Davey, the site manager at thereserve, said that six years after plots of the weed had been rotoburied there was still no sign of it returning.

"Even the invertebrates have come back to recolonise the land to previous levels, and we've seen birds coming back to feed for the first time in five or six years," he said. "We think it's a success story."

Spartina anglica sends out long roots that look like rat-tails, called rhizomes, which smother the delicate eel grass that grows naturally on mudflats. Its roots are particularly pernicious, causing the weed to spread by up to several yards a year.

The plant's stalks trap sand and eventually raise the level of the land, causing mudflats to dry up. Few of the smaller waders will venture into its grassy foliage because they are accustomed to feeding on an open mudflat with good all-round visibility with which to see predators, Mr Davey said.

Twenty years ago, an estimated 40,000 dunlins used the Lindisfarne mudflats as a migratory stop-off for feeding. Today, this figure has fallen to about 10,000.

"The decline in numbers is attributable largely to the encroachment of Spartina, according to some experts. Open mudflats are critical to many birds coming here during winter," Mr Davey said.

More than half of the world population of the pale- bellied Brent goose – standing at about 5,000 – stays over the winter at the Lindisfarne nature reserve. With the bar-tailed godwit and the grey plover, two important species of wading birds, the goose is dependent on the intertidal mudflats for feeding, Mr Davey said.

Spartina anglica is a hybrid of the endemic species Spartina maritima and the American species Spartina alterniflora which was introduced accidentally into Southampton Water, probably during the discharge of a ship's ballast. An infertile form of the hybrid was first recorded in 1870. In 1890 a fertile, seed-forming variety arose, and quickly spread.

Rotoburying sifts out the weed's roots and buries them in a deep trench, causing them to suffocate. It also flattens the soil surface, allowing the land to fall to a level that allows the tide to inundate it.

Mr Davey said that the rotoburying technique, unlike spraying with herbicide, restored the habitat to its mudflat state. However, it would not be suitable for all sites, he said.