Backyard battle of the space invaders

Britain's native flora and fauna are under siege from a range of vigorous and rude alien plants and animals, reports Mark Rowe

IT WAS an uneven struggle: a light-devouring conifer with a reputation for prodigious growth against a powerful lobby of neighbours furious at having their garden sunlight blocked.

The Leylandii, an American hybrid conifer, has provoked a string of acrimonious and expensive court cases between neighbours. Councils have received hundreds of complaints from people who say their views and light have been blocked out by Leylandii. One official described the tree as a "monster"; other victims compare it to "Triffids". Gardeners complain that it also sucks the goodness from the soil, killing other plants.

There is even a victim support group, Hedgeline, set up by Michael Jones, from Selly Oak in Birmingham, who spent pounds 100,000 in legal fees fighting the Leylandii at the bottom of his garden. Some people claim they have been forced to move by the "curse of the Leylandii" and that it has cut thousands of pounds from the value of their properties.

Last week, the Department of the Environment hinted that it will give some form of legal redress to those who suffer from the trees, which can grow at a rate of 4ft a year and, unchecked, reach heights of up to 100ft.

But now, after laying low the Leylandii, where next for the twitching pruning clippers of Middle England? The sycamore and rhododendron should be watching their backs.

Rhododendron grows to a maximum of 25ft high, but can also grow 20ft in width and is described as a "good coloniser" by Adam Pascoe, editor of BBC's Gardeners' World magazine. "The rhododendron is not a fast grower but casts extremely dense shade," said Hilary Allison, of the Woodland Trust.

The sycamore is viewed by some conservationists as an invasive foreign weed rather than a tree. The sycamore does not arouse the same violent feelings as Leylandii but Ms Allison said: "The sycamore is a fairly rapidly spreading tree in certain circumstances. In native woodland it can spread like wildfire and shade out younger trees. It can be a bit of a pest."

The point is backed by Mr Pascoe. "The sycamore does spread itself around with a vengeance and most of its seeds do germinate. Unless you dig them out they can become a problem. It is an invasive tree species."

Cupressocyparis Leylandii, which arrived from the United States at the turn of the century, is one of a number of animal and plantlife imports that have taken root in the UK at the expense of our own native species. The ruddy duck, introduced in the 1940s to this country, has imperilled Europe's only stiff-tailed duck, the white- headed duck, distinguished by its blue bill and awkward penguin walk when on land. The white-headed duck is already under threat from loss of habitat and the hybrids from inter-breeding between the two are threatening to swamp the white- headed duck.

Similarly, the grey squirrel has created havoc among Britain's red squirrel population since its introduction from North America in 1876. The number of the more aggressive grey squirrels is now estimated to have reached 2.5 million nationwide. In contrast, the red squirrel, which has a fussier diet, has dwindled to just 160,000.

The graceful, chocolate-coloured European mink is also under threat from its stockier American cousin, which is invading Europe in droves. The European mink has disappeared from Western Europe, only surviving in Belarus and Ukraine, with researchers blaming the aggressive habits of the American species.

The reason the American species do well so quickly is that the eco-system to which they are accustomed, which controls their numbers and limits their food sources, does not apply in Britain.

"All the checks and balances in the US are not present here. The predators and food supply will be very different," Ms Allison explaind. "It's better in an ecological context not to introduce a plant without checks first."

It is not only American fauna and flora that are attracted by our environment. Muntjac deer (China), rhododendrons (Middle East and Himalayas), and knot-weed pond plant (Japan) have all flourished, with the knot-weed crowding out native water plants.

"It isn't as drastic as genetic imperialism or super-species," said Ms Allison. "Sooner or later some animal comes along that the local environment suits down to the ground. There was a niche in Britain for a small-dog- sized deer, which the Muntjac has filled."

The British climate also enables foreign species to flourish, according to Mr Pascoe. "Our climate is similar to some climate zones in the US, but our winters tend to be wetter."

However, there is another school of opinion that suggests the Leylandii has been unfairly maligned. This holds that the plant first appeared as a natural hybrid in Montgomeryshire in 1888, so there is a case for attributing blame for the whole problem to the Welsh.