Tighter controls are to be imposed on plant imports to halt an invasion of diseases that put Britain's trees in peril. At least eight major new foreign threats have been identified, with important species including oak, beech and larch in danger.
With forestry worth £7.2bn a year to the British economy, ministers fear a severe outbreak could wipe millions from the industry at a time when the Treasury wants to rebalance the economy.
Next month Caroline Spelman, the Environment Secretary, will unveil a strategy to keep the invaders at bay. She is studying import controls to prevent new strains from entering the UK, and examining extra biosecurity measures.
It is hoped the blueprint will secure a cut in the damage caused by pests and pathogens, including the considerable cost of felling diseased trees, which even if they survive grow more slowly, reducing timber yields. Ministers also want to prevent infected plants from reaching garden centres and private gardens.
In a speech today, Ms Spelman will warn that "many of our native trees are dying". "A bright future for our natural environment is not a given. It is hard won," she will tell the Conservative Party conference. "These exotic diseases have escalated in the past 10 years. We are going to combat the scourge of these diseases which threaten to change our landscape for ever unless we act."
The Government is especially concerned about "potentially very damaging pests", including emerald ash borer from North America, and oak wilt disease. Both could enter the UK if biosecurity measures are not in place, officials admit. "We have to grasp the problem. Otherwise those trees and the habitats they support will be lost," Ms Spelman will say.
There are more than three million hectares of woodland in the UK. Scotland is the most wooded: 18 per cent of land is given over to forests, with conifers dominant. Ten per cent of England is wooded, mostly broad-leaved trees, compared with 14 per cent of Wales and 5 per cent of Northern Ireland.
Last month, Dr Keith Kirby from Natural England warned that the future of Britain's oak trees was far from secure. And a survey by Hull University suggested the leaf miner caterpillar, which targets horse chestnuts, could threaten the traditional game of conkers by making the trees more vulnerable to other diseases.
More than half the UK's total woodland area is made up of conifers. However, the commercial forestry sector faces the "potentially serious" prospect of the Phytophthora ramorum pathogen on larch and red band needle blight on pines triggering a crisis. Two thousand hectares of larch have been felled since 2009 as a result of the invasion of P. ramorum in the UK.
Earlier this year, Ms Spelman was forced to abandon plans to sell much of the state-owned woodland managed by the Forestry Commission after a backlash from campaign groups. However, almost three-quarters of the UK's woodlands are already privately owned.
Oak wilt disease is found in the US and poses a "serious potential threat" to the UK if border controls are not tightened.
Pine pitch canker is a "potentially major" danger to Britain if it spreads from California.
Emerald ash borer is highly destructive and incurable. It's found in North America, and its potential scale of damage has been compared with the devastation from Dutch elm disease.
Larch trees are targeted by Phytophthora ramorum, a fungus which was barely known in the UK until 2009 when Japanese larch trees in the South-west were struck down. Now found in Wales, Northern Ireland, Lancashire, Cumbria, the Lake District and the island of Mull in western Scotland.
Oak trees are endangered by sudden oak death, a form of P. ramorum, which thrives on rhododendron. Acute oak decline can kill a tree in as little as four years. Dark fluid bleeds from splits in the bark. Oak processionary moth is also a major problem.
Red band needle blight targets pine trees. Needles develop yellow and tan spots and bands, limiting timber yields and eventually killing trees. Since 2005 this has become widespread. Scots pine was thought to be less susceptible but the disease has become more severe.