Tens of thousands of trees are being felled on National Trust-owned forests in the southwest of England in an attempt to stop a disease spreading which threatens to destroy up to 100 species of hardwoods and conifers.

The disease, known as "sudden oak death", was discovered in shrubs in Cornwall, Devon and Somerset five years ago after it was introduced by an infected plant from the United States. It has also been found in Ireland.

It has since been discovered in the larch, a conifer, and most significantly in rhododendrons, which have defied efforts over decades by foresters to get rid of the pest that was brought into the UK in the 19th century.

Nearly 60,000 larch trees are being felled in two forests in Somerset in an attempt to stop the spread of the airborne fungus, which has already been found in more than 2,000 hectares of land in the region.

Properly known as Phytophthora ramorum, the disease causes seeping or bleeding areas on the trunk of the three, followed by fading foliage, attack by beetles on the weakened timber and the arrival of fungal growth on the bark.

"Dutch Elm disease, while it did a lot of damage, was a pathogen that affected one tree. This disease is a multispecies pathogen which is known to affect over 100 species," said the trust's expert on the disease, Ian Wright. "The spread of Phytophthora ramorum into woodlands is a real concern as it represents a significant and worrying progression of a disease that was up to 2009 predominately garden-focused."

Besides felling the larch, the trust began last September to clear 10 hectares of rhododendron ponticum.

The capacity of the disease to spread so easily between species is causing major concern: "And what might we expect with the changing climate, the warmth of the summers, the cold winters and the wetter summers of the future?" said Alison Field of the forestry commission.

Researchers in the US have warned that 50 different forms of the fungus have been identified in the last decades, though their ecological role remains largely unknown, according the US department of agriculture.