Foreign invaders threaten UK trees

Seeds and saplings from abroad are causing havoc, reports Geoffrey Lean

RUPERT BROOKE must be turning in his grave. For more and more corners of English fields have become forever foreign.

New research shows that more than nine out of every 10 trees planted in Britain - even traditional native species such as oak, beech and birch - come from overseas. The imported saplings grow less well and, over the long term, threaten the survival of the British tree.

The study, published in the journal of the government-backed Tree Council, calculates that more than 2 billion foreign trees have been planted up and down the country since the Sixties. The report, by Dr Andrew Gordon, in Tree News says: "This is enough to plant nearly 1 million hectares of forest at normal densities and is equivalent to nearly half of the actual British forest area."

The mass invasion of foreign trees - often for planting by the sides of motorways and around supermarkets - is the result of an abrupt, if short-lived, change in Britain's forestry practices.

For centuries foresters and nurserymen collected their own seeds from native broad-leaved trees, but in the Sixties, the Forestry Commission adopted a controversial policy of planting only conifers imported from overseas.

The unsightly new plantations created a storm of protest, and by the early Seventies the Commission started planting broad-leaved varieties again. But in the meantime, the skills of seed collection had almost been lost and it was cheaper and easier to import them, or young trees, from Europe.

Initially they were imported from German, Dutch and Belgian nurseries but these, in turn, have increasingly been importing their own seed from Eastern European countries.

One result, say experts, can be seen around the country each spring where trees of the same species burst into leaf at different times, depending on when they were genetically programmed to do so where they or their ancestors originated.

Further research, by Dr Richard Worrell of Edinburgh University, shows that the imported trees do not grow as well as native ones, and die more easily. Trees, he says, evolve to suit the climate and conditions of the areas where they originate: the further they are moved from them the less well they do. So trees imported from northern Europe to south east England do relatively well, but those that travel longer distances fall behind badly.

He has found that Scots pine, for example, grows less well if it is imported from Germany or Poland, on much the same latitude as Britain, than if it originated locally: but pines brought from Scandinavia or southern Europe grow at only half the rate of home-grown ones. Similarly, birch imported from Finland is twice as likely to die as native trees.

The result, says Dr Worrell, is that a great deal of money is wasted as new plantings die or fail to grow properly.

Worse, the imports can threaten native British trees over the long term by inter-pollinating with them. "It is not good for the genetic make- up of British trees to have these relatively maladapted genes floating around," he says.

He is trying to revive the art of British seed collection - last week he gathered one third of a ton of acorns from native oaks - but says that there is "no foolproof way" of making sure that seeds have genuinely come from British trees rather than from ones imported years ago.

Small fragmented woodlands pose another problem because their trees may have pollinated themselves, again weakening their genetic inheritance. The best places still to find genuinely native trees and to gather their seeds is, he says, in ancient woodland, particularly in Britain's uplands.

n A mystery disease is killing oak trees in Sherwood Forest country park near Mansfield, Nottinghamshire. About three-quarters of the forest's "middle-aged" oaks, dating back to the Napoleonic wars 174 years ago, have been affected.

But 900 veteran trees, some more than 400 years old, including the famous Major Oak, have escaped the bug.

Council forestry officer, Gareth Broome, said: "We don't know what is causing the problem. The oaks lose their leaves and die back. They don't recover. It is a serious situation but not a crisis."