Bracken threatens historic monuments

Of the 839 monuments, which include prehistoric burial mounds, medieval field systems, ancient boundaries, as well as buildings, 42 per cent are at high or medium risk.

Graham Lee, the park authority's senior archaeological conservation officer, says it can take years of intensive work to eradicate the bracken.

He added: "The roots of the bracken are like a fishing net, and go everywhere. As a result roots develop, layer on layer, and do extensive damage to archaeological remains, of which the National Park has a great wealth.

"Bracken blankets an area and makes it impossible to locate monuments.It is labour intensive to control, and while air-spraying has been used in the past, there are concerns about using aircraft because the spray can cover a much wider area."

But an environmental stewardship system run in the National Park has led to the restoration of the kilns at Rosedale East Mines, Mulgrave Castle, and Danby Castle, the one-time home of Henry VIII's wife Katherine Parr, now licensed for civil wedding ceremonies.

The National Park teamed up with English Heritage and the Dawnay and Mulgrave Estates for the work which also included making a range of old agricultural buildings them watertight.

The park has been given 20,000 for two years by English Heritage, match-funded by the Park Authority, and which is being used to target monuments which are seen as being at high risk of deterioration.

Park chiefs are now targeting 17 monuments, working with landowners, the Forestry Commission and the National Trust, to remove the bracken.