IN full springtime bloom, they are truly a spectacular sight as their purple flowers decorate Scotland's countryside.

But conservationists are calling for a huge increase in spending to eradicate wild rhododendrons due to the threat they pose to the country's native woodlands.

The Woodland Trust charity fears unique habitats such as the west-coast rainforest, home to rare species of mosses and other small plants, could be lost unless the present £2 million a year spent on killing off the non-native plants is boosted.

Rhododendron ponticum was first brought to the UK, most likely from Portugal or Spain, in the 16th century for botanical gardens and country estates, but it has spread out of control, swamping woodlands in a blanket of dense green foliage and preventing new trees from taking root.

In Victorian times, the plant was hybridised with North American species that are hardy to cold and wet conditions and some experts believe this has created a “complex hybrid swarm” - in effect a new species perfectly adapted to Scotland’s climate.

Forestry Commission Scotland (FCS) has calculated that £400 million would have to be spent over just 10 years to eradicate the plant completely from 131,000 acres of Scotland known to have it.

The Trust says complete eradication is the only sure way of stopping it from spreading again.

But FCS has admitted that a total of just £2m or so a year is being spent, part of it by its own Forest Enterprise commercial arm to clear its own estates, and the rest in grants to landowners to root out the plant under the Scottish Rural Development Programme.

Adam Harrison is in charge of trying to preserve Scotland’s unique west coast woodlands on behalf of the Woodland Trust. Many of those woodlands have become infested with the rhododendron ponticum, often as a result of Victorian estates planting “rhodies” as cover for game.

“Rhododendrons are a huge problem on the west coast in particular – one in ten of the woodlands has got rhododendron in them,” he said. “It’s spread right across the landscape, and it’s going to be a big job to get rid of it.

“At the moment the government is spending about a million itself and then about a million in grants to other landowners to get rid of it, but that’s not nearly enough. They reckon at the moment the bill would be something like £400m to get rid of all the rhododendron in Scotland and so we’re spending just a tiny fraction what we ought to be doing. Unless we get on top of it now that bill will be £100m bigger in 20 years’ time.

“If you clear just the most important sites in the protected areas you are always going to have them surrounded by rhododendron that can reinvade. Eventually the whole landscape will get filled and choked with this.”

He pointed to a project that shows what could be done at Glen Creran near Oban, where £96,000 is being spent to stop the rhododendrons threatening internationally important oak woodlands.

He said the whole valley needs to be cleared, adding: “It only takes one plant flowering maybe miles away for the seed to arrive and reinvade a site, so the effort needs to go into making sure that everyone’s signed up to the effort and is doing their bit, whether that’s the neighbouring landowner, whether it’s in a garden or whether it’s the stuff growing along the road which is the responsibility of the local council.”

A spokesman for Forestry Commission Scotland, which deals with the issue for the Scottish Government, said the estimate for eradication was based on average costs for the area of known ponticum.

He added: “Forest Enterprise Scotland’s removal programme is ongoing – as budgets and work programmes allow – and has so far resulted in initial clearance of mature rhododendron ponticum from a gross area of 22,000 hectares (54,000 acres) of the National Forest Estate.

“Forestry Commission Scotland guidance emphasises that the successful eradication of rhododendron ponticum can best be achieved through a collaborative approach amongst landowners.

“Grant support to assist with removal operations is also available ¬– but such is the desire among landowners to help remove this species from the landscape that funding is already committed for the next two years.”