Alien invaders face being exterminated

THE beautiful oak woodland at Coille Mhor, near Kyle of Lochalsh, is home to plants that are unique to Scotland.

Mosses and lichens that grow nowhere else in the world can be seen on the forest floor and the trunks of the trees, creating a local environment so distinctive it is officially designated a site of special scientific interest (SSSI).

But this fragile ecosystem is under threat, menaced by an aggressive foreign invader that, left unchecked, will choke the life out of the woodland.

Rhododendrons, introduced to Scotland from Africa in the 18th century, may be pretty, but they are also lethal.

"As soon as you get rhododendrons in there, they shut out all the light out and kill all the mosses on the floor of the wood and on the trunks of the trees," said Richard Luxmoore, of the National Trust for Scotland, whose volunteers have been battling the fast-growing invaders at Scottish sites, including Coille Mhor, for several years.

The rhododendron is one of at least 988 "invasive non-native species" in Scotland - unwelcome plants, worms, crustaceans, mammals and birds that scientists increasingly fear are threatening our ecosystem and even our economy.

For years, a ragtag alliance of wildlife groups, gardeners, birdwatchers, anglers and concerned locals have fought the invasion as best they can, trapping, shooting and uprooting the invaders in an effort to preserve the natural order of things.

But resistance has been piecemeal, with no central leadership and only limited support from government, and no clear plan or policy to help. Now, though, that could be about to change.

The Westminster government and the Scottish Executive are discussing a new UK-wide strategy that could result in renewed efforts to curtail the spread of harmful species or even eradicate them outright.

"The Invasive Non-Native Species Framework Strategy for Great Britain", a draft plan that has been circulated among government officials and ecology campaigners, outlines "a more preventative approach" towards the newcomers.

Effectively declaring war on non-native species, the strategy declares: "We should be guided by the principle that, where it is shown beyond reasonable doubt that a non-native species is having or is likely to have a substantial negative ecological, social or economic impact, and eradication or control measures are technically and financially feasible, acceptably humane and safe for people and native wildlife populations, then such eradication or control measures should be instigated."

Scotland will provide many battlefields in the war to come, foremost among them the River Tweed.

The river and its tributaries draw anglers from around the world, hoping to hook the king of fish, the Scottish salmon. Yet, in recent years, the Tweed and its cherished fish stocks have come under relentless attack from the signal crayfish.

Originally brought to Britain nearly 30 years ago to satisfy our increasingly cosmopolitan tastes, the American crayfish have long since moved beyond restaurants, also infiltrating the Clyde and its tributaries in Dumfries and Galloway.

The crustaceans are continuing their apparently relentless spread through the Tweed and its tributaries. No longer confined to smaller burns, they are now routinely found in main channels.

Everywhere, they voraciously devour the eggs of salmon and trout, threatening what is both a popular pastime and an important local industry. Only this week, the River Tweed Commission approved a new £20,000 project aimed at finding new ways of controlling the crayfish.

Nick Yonge, director of the Tweed Foundation, said moves towards a coherent national plan on alien species were "welcome but overdue". He said: "We have been almost in despair about the fact there is no single government agency to take responsibility for this, but it looks as if things could finally be about to change."

Professor Colin Galbraith, director of science of Scottish Natural Heritage, also welcomed the moves towards a single UK strategy. "We've got to get a collective view on alien species and the damage they can do - we're building public awareness, but there is much still to do."

As an example, he cited the grey squirrel, which carries a virus fatal to their smaller, indigenous red cousins. "People look at species like the grey squirrel and they're very cute and fluffy, but they can do real harm," he said.

INCOMERS THAT PEOPLE WELCOME

NOT every alien animal arriving on these shores is unwelcome.

Goosanders and mergansers, types of saw-bill ducks, arrived in Scotland in the 1950s as their range extended northwards.

It is perfectly natural for animals and plants to expand into new areas, and global warming is expected to bring more new arrivals.

Mike Donaghy, of WWF Scotland, said: "We have to allow natural migrations, the natural expansion of animals' range, to take place. Saw-billed ducks started coming up from the south in the middle of the 20th century - 100 years ago you wouldn't have seen them."

Trees such as the larch and sycamore are other non-natives which live in relative harmony with "native" Scots flora and fauna, while rainbow trout, sheep, cows and cats are all human introductions.

The wallabies living on an island in Loch Lomond and a fruit-bearing peach tree in Aberfeldy are more exotic examples. Ring-necked parakeets could also be heading Scotland's way if the temperature warms up a bit - they live and breed in the wilds of central London.

HEDGEHOGS

HEDGEHOGS were noted in the Western Isles in 1982, but only in 1995 was it realised how they harmed the wader population. A cull was started to wipe out about 5,000 hedgehogs, to protect birds such as dunlin, redshank and lapwing.

KNOTWEED

JAPANESE knotweed was introduced to Scotland as an ornamental plant in the mid-19th century. It spreads easily and is hard to eradicate. It out-competes native plants and can damage structures and road surfaces.

GIANT HOGWEED

GIANT hogweed was brought to Britain in the late 17th century. It grows to more than 15ft tall and each flowerhead produces up to 50,000 seeds. Its sap can blister the skin and each year people are harmed by contact with this plant.

BALSAM

HIMALAYAN balsam is an attractive invader that escaped into the wild from gardens. Often found along riverbanks, it outgrows native grasses, creating an ecologically harmful monoculture. It is hard to eradicate.

RUDDY DUCK

THE ruddy duck, native to the Americas, became a menace after escaping from bird collections in England and settling in Fife, Tayside and the Lothians. They wipe out native ducks through inter-breeding and competition for food.

FLATWORMS

NEW Zealand flatworms grow up to 15cm long, are pointed, have numerous eyes and prey on earthworms. Since arriving in the 1960s in imported pot plants,

they have cut some populations of earthworms to below detectable levels.

MINK

AMERICAN mink first invaded the countryside in the 1930s after escaping from fur farms. They are carnivores with a wide range of prey, including seabird chicks, which has led to the extinction of several seabird colonies on Scottish islands.

RED SQUIRREL

GREY squirrels threaten our native red squirrel with extinction, as they carry a disease fatal to reds and compete with them for food. The economic cost of grey squirrel damage to beech, sycamore and oak woodland is up to £10 million a year.

RHODODENDRON

RHODODENDRON is widely invasive and its dense growth means it can eliminate most other species from an area. Particular damage has been caused to mosses and lichens in woodlands in the west of Scotland.

SIKA DEER

SIKA deer are deemed to be forest pests because they eat young trees and remove bark. They also threaten the genetic integrity of red deer through cross-breeding. It is illegal to release sika into the wild or allow them to escape from captivity.

SWAMP STONECROP

AUSTRALIAN swamp stonecrop, aka New Zealand pygmyweed, is often wrongly sold in shops as Tillaea recurva or Tillaea helmsii. It causes problems in freshwater habitats, out-competing native species and choking ditches.

MITTEN CRABS

CHINESE mitten crabs, which grow to the size of a dinner plate, are heading up the east coast of England towards Scotland after arriving in ships' ballast water. They feed on salmon eggs and destabilise river banks by burrowing holes.