The following article by Debbie Loat appeared in the June 2006 edition of Countryman magazine, and has been reproduced with permission. It is included to help explain why it is necessary for the Friends Group to carefully manage the spreading rhododendron in Gledhow Valley Woods.
They look spectacular in full bloom, but leave an ecological wilderness in their wake. As major eradication programmes try to reclaim land from this leafy trespasser, Debbie Loat asks why the rhododendron has run out of friends?
It doesn't look like a killer. With its lavish flowers and spears of dark, glossy leaves, the rhododendron is a familiar spectacle in the British rural scene, swathing hillsides in robes of brilliant spring-time purple. But don't be misled. The rhododendrum ponticum, as it is properly known, is one of the most troublesome plants to have been introduced to Britain in the last three hundred years. This extraordinarily resilient shrub is terrorising whole landscapes, disrupting local ecological systems and destroying the economic potential of vast tracts of countryside.
"Quite simply, it's a bully," sighs Dr Rod Gritten, Ecologist for Snowdonia National Park with thirty years' experience of working with this formidable plant. Wales is one of the key battlegrounds for the rhododendron, with infestations affecting hundreds of hectares. "Snowdonia has such a big problems with this plant, it has done so much damage here."
Rhododendrons cover around two per cent of the Park's 840 square miles, and that figure is increasing all the time. Over the past 25 years, the authority has spent £2 million on control strategies, but Rod knows this is a drop in the ocean. "We could spend £60 million. And you could easily double that if you include removing the seedlings afterwards."
Despite some successes, for instance along the Mawddach estuary and in the Beddgelert region, there are still massive areas of rhododendron that haven't been touched. "It really is a serious conservation problem that is having major economic effects on farmland. There are dozens of acres that are being abandoned by farmers because they just can't get into it."
Nature has provided the rhododendron ponticum with a powerful armoury. Its evergreen leaves are poisonous to animals and produce such dense shade that 95% of the light is blocked out from the vegetation beneath. Few, if any plants, can germinate. With nothing to feed on, the wildlife soon retreats. In just a few years, woodland can be replaced by an impenetrable rhododendron thicket. 'Nothing kills the rhododendron naturally," explains Colin Edwards, one of the top experts in the field, based in Edinburgh at Forest Research, an agency of the Forestry Commission. "These plants will keep on growing until they are cut down. They have no natural enemies, are very long lived and produce masses of seeds."
The rhododendron originally came from Spain and Turkey, first brought to England in 1763. Initially unpopular, by Victorian times it had become a fashionable addition to country estates, planted in gardens for ornamental appeal and in surrounding land for game bird cover. The Victorians exacerbated the problem by using ponticum as a rootstock for other rhododendron varieties. The rootstock invariably took over the whole plant.
Colin is realistic about what can be achieved in rhododendron control. "There is no way we will ever eradiate it from the British Isles, but there are areas we need to protect and we need to take action now. It has the reputation of being difficult to kill, but it is not infallible."
Encouraging work is underway, for example, in pars of North West Scotland, where rhododendrons make undesirable bedfellows with the highly prized Atlantic oak woodlands. The National Trust is taking important strides forward on several estates in the area. Windswept and dramatic Inverewe, on a rocky peninsular beside Loch Ewe, has seen successful trials of a new form of control.
"Inverewe was one of the first estates to use 'stem injection'," explains Rob Dewar, Ranger for the Wester Ross properties including Inverewe and Torridon. "This involves a single injection of herbicide and six months later the plant is dead. It's particularly good if you have one thick stem and it uses less herbicide than the other methods. Also, you can do it in winter, or in drizzly weather. Before, when we were spraying plants, we had to wait for dry weather, usually in the growing season. 'Stem injection' has made a big difference. We are not far off controlling the problem here now. It is 80% clear within the 2,000 acre estate. But its not the miracle answer. We are still cutting back some plants and also painting the stumps with herbicide."
'Stem injection' may be a significant discovery but Colin Edwards is cautious. "It's not panacea for all. It can't be used for multi-stemmed bushes where the plant has been cut down and grown back with lots of stems." Many areas where rhododendrons are a long-term problem have just this sort of re-growth.
The Forestry Commission has been carrying out trials on rhododendron control since the 1930s. "Now the methods are much more sophisticated, and we're doing more research all the time," says Colin. At the moment, the most widely used system is spraying with herbicide. Every leaf must be squirted, to kill the plant. If the bush is too big, it may need to be cut down and all the re-growth sprayed later. Costs can be up to £8,000 per hectare over five years. The treatment must be followed up with the removal of seedlings, by hand.
Exmoor National Park, which has rhododendrons on its craggy northern coastline, has experienced different problems. "At North Hill, near Minehead, there are rhododendrons on heathland that is organically farmed and part of an SSSI," explains Park Ecologist, Alison Cox. "We haven't been able to use herbicides so we've ended up doing a lot manually and using a small digger to get the bushes out and then burning them. Some of the areas are really steep running down to the sea and we've had to use a winch." The cost, she adds, is four times higher than with conventional methods. "The expense of removing rhododendrons is among the things that guides our Park budget. The rhododendron is one of the big factors that prevents many of our key sites being in a favourable condition. There is never enough money for control work."
It is a familiar complaint. All the organisations involved lament the lack of grants. "A major problem is that the cost of clearance exceeds the value of the land once restored," explains Deborah Long, Conservation Officer for Plantlife, which has fought tirelessly to highlight the enormous harm being caused by invasive plants. "Non native invasive plants, like rhododendron ponticum, are the biggest threat to out native plants after habitat destruction," continues Deborah. So concerned is plantlife by the spread of rhododendron that it wants nothing less than a ban on its sale. The organisation's campaign was a key factor in achieving the framework for a ban in legislation passed in Scotland in 2004. Plantlife now wants a similar ban in England and Wales.
A perennial stumbling block, Deborah admits, is persuading people that the rhododendron is a horticultural villain. "We still have a long way to go in raising public awareness. If you see rhododendrons in the wild, they can look beautiful. People don't realise the damage they can do." Colin Edwards agrees. "Education is vital if people are to understand." This, he argues, must be combined with a more strategic national approach. "We need to get more of the organisations involved working together. In Wales there is some good work on the bigger picture approach, but in some areas the agencies haven't even started to speak to each other." Only then, he believes, might it be possible to achieve a louder voice in the quest for urgently needed funds to combat this unwelcome rural ruffian.
New guidelines on rhododendron control have been drawn up by the Forestry Commission. A booklet entitled "The Management and Control of Invasive Rhododendron Ponticum" is available from the Forestry Commission.