Invasive plants thriving in Britain include the Himalayan balsam
At dawn today a television gardener and a junior government minister will wade into the River Wandle in southwest London to scoop up armfuls of an inoffensive looking plant.Charlie Dimmock and Huw Irranca-Davies, the Minister for Marine and Natural Environment, will help to clear the river of a choking weed known as floating pennywort. It grows at the rate of 20cm (8in) a day and can clog a waterway in days. The Be Plantwise campaign to urge gardeners to help to keep the foreigners under control is the first of two offensives beginning this year.
In June the trust will recruit a volunteer army to clear invasive plants from 77 properties — from skunk cabbage spreading across Grasmere, Cumbria, to holm oak on Lighthouse Down above the white cliffs of Dover.
The best known and most difficult to eradicate is Japanese knotweed, the botanical equivalent of the cockroach, which can force its way through concrete and has roots that grow so deep they could survive a nuclear war. It has a foothold on the site of the London Olympics, forcing contractors to remove soil to a depth of 5m (16ft).
But other less well-known invaders have been taking over rock pools, carpeting sand dunes and squeezing out native plants and wildlife. Among them is jap weed, a seaweed that has been gradually clogging rock pools along the Channel coastline and is now doing the same on the Gower Peninsula in South Wales.
Simon Ford, the trust’s nature conservation adviser who is co-ordinating its campaign, said: “Jap weed is quite a pretty little plant but when it gets a foothold in a rock pool the anemones, crabs, small fish and all the other seaweeds there are completely swamped. It can clog waterways and marine slipways and foul the bottoms of boats, so it has also had an economic impact.”
Jap weed probably arrived in British waters clinging to the hulls of ships or in their ballast. It can regrow from a fragment and the only way to keep it in check is physical removal.
Until recently the Horse Pond at Corfe Castle, Dorset, was a refuge for the great crested newt and a site of special scientific interest. Now it is covered by a matted layer of decaying vegetable matter, the result of the spectacular spread of the chillingly named swamp stonecrop, also known as New Zealand pygmy weed.
Other invasive plants that thrive in their new home are the hottentot fig, a succulent that covers cliffs in glistening gelatinous balls, rhododendron ponticum and Himalayan balsam.
Preliminary trials on National Trust land have shown that native species can return once the invader has been evicted. The clearance of knotweed from one Cornish valley helped bluebells to survive, as well as wetland plants including purple loosestrife, marsh marigold and bog pimpernel.
The Be Plantwise campaign being announced by the Department for Environment, Food and Rural Affairs today will concentrate on aquatic weeds such as parrot feather and water fern, pretty enough in garden ponds but a menace in the wild.
Mr Irranca-Davies said: “Gardeners can do their bit by knowing what they grow in ponds and disposing of unwanted plants with the utmost care.”
Water primrose, one of the most recent arrivals, is believed to have spread from waterways in France, where it has infested 500 sites and costs millions of euros a year to keep under control. Eradication may be impossible. Every habitat is feeling the impact of invaders, and they are spreading because of climate change. Mr Ford said: “Until a few years ago holm oak was only recorded on the South Coast, now it has reached the Cotswolds.
“At Studland in Dorset we have a problem with piri piri burr, which covers sand dunes and closes the niche occupied by rare plants and animals such as lizards.”
Another invader making its way up the southwest peninsula is the three- cornered leek, which looks exactly like a bluebell, except it reeks of garlic. Again climate change is believed to have encouraged its spread. Mr Ford said: “The flowers look nice but don’t take them indoors unless you want your house to smell of onions.”
From http://www.timesonline.co.uk, see original source.
Simon de Bruxelles] They sneak in along coastal creeks or are carried by the wind. Some escape from garden centres, others are borne by waterbirds. The invading horde of alien plant species has been identified as the second-greatest threat to Britain’s wildlife after climate change. Some were introduced as decorative additions to garden borders, others appear to have arrived from nowhere, found a comfortable home and filled it. Keeping the unwelcome guests under control costs the country an estimated £2.7 billion a year, according to the National Trust.
