Mountain bikers urged to help beat deadly tree disease at Bwlch Nant yr Arian

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Mountain bikers are being asked to do their bit to minimise the impact of a fatal tree disease that has now been discovered in mid Wales.

An outbreak of Phytophthora ramorum has been found in a small number of Japanese larch trees at the Bwlch Nant yr Arian visitor centre, near Aberystwyth, which is home to three single track mountain bike routes.

P. ramorum is a fungus-like pathogen that kills many of the trees that it infects. Infected Japanese larch trees produce high numbers of the spores that spread the disease with the result that a lot of these trees can become infected very quickly.

In an attempt to minimise the impact of the outbreak at Bwlch Nant yr Arian, Forestry Commission Wales will fell up to 60 trees that are currently infected. This work will take a couple of weeks to complete and will be carried out with as little disruption as possible to visitors.

P. ramorum is not harmful to humans or animals and all walking and mountain bike trails, plus the visitor centre, remain open to the public.

While the felling of infected trees takes place, the last section of the three mountain bike trails will be closed for a short period of time and a diversion put in place.

Bwlch Nant yr Arian is managed by Forestry Commission Wales on behalf of the Welsh Assembly Government.

Mountain Bike Ranger, Andy Braund, is appealing to mountain bikers to help keep the routes at Bwlch Nant yr Arian open by following some simple biosecurity measures.

Andy said, "We are working hard to minimise the impact of this serious disease on our woodlands and the support of the mountain bike community is vital.

"Everyone who works in or visits the affected woodlands is being asked to observe some simple biosecurity measures so that they don’t inadvertently spread this pathogen.

"For mountain bikers, this means keeping to the trails and washing their bikes and kit thoroughly to remove all dirt and plant material before they leave the forest - a bike wash is available at the visitor centre.  They should also wash their clothing between visits to forests.”

Forestry Commission Wales staff will continue to monitor trees at Bwlch Nant yr Arian for signs of infection but, in many cases, symptoms may not become evident until next spring when larch trees – which are deciduous conifers – renew their needles.

Andy added, “Phytophthora ramorum is a serious disease and, by felling infected trees, we hope to limit the production of the spores that spread the infection.

“As Bwlch Nant yr Arian is a popular site, it is also important that we fell infected trees before they die and become unstable, thus presenting a potential risk to visitors."

P. ramorum was first discovered on Japanese larch trees in Great Britain in 2009 in South West England. It was then found on larch in public woodlands in South Wales in June 2010.

Further information about P. ramorum can be found on the Forestry Commission’s website at

Mountain bike trails at Bwlch Nant yr Arian

The Summit trail offers awesome riding on flowing twisty single track, taking in superb views.

The Syfydrin Trail is an epic ride in epic countryside, taking in the entire Summit trail.

The Pendam Trail is the shortest route at Nant yr Arian and combines sections of the 'Summit' and 'Syfydrin' trails to give a taste of the fantastic riding and scenery.


  1. P. ramorum is a ‘quarantine’ organism under European Union law and its suspected presence must be notified to the relevant authorities (the Forestry Commission, Fera, the Welsh Assembly Government or the Scottish Government). It was first found in Britain on a viburnum plant in a nursery in 2002.
  2. P. ramorum can kill many of the plants that it infects, but symptoms vary according to the species. On Japanese larch (Larix kaempferi) trees, it causes shoot tips to wilt and needles to turn black and fall prematurely. Cankers that bleed resin can appear on the branches and upper trunk. Infected Japanese larch trees produce particularly high numbers of the spores that spread the disease – five times the level produced on rhododendron - meaning the disease can quickly affect a large number of trees and shrubs.
  3. P. ramorum has not been found infecting any European larch (Larix decidua) or hybrid larch (Larix x eurolepsis) trees, which are the other two species of larch grown in Britain, but these species are being kept under close surveillance.
  4. P. ramorum can be spread on footwear, vehicle wheels, tools and machinery that have been used in infected forests, or by the movement of infected plants. It can also be spread in rain splash, mists and air currents.
  5. P. ramorum was first discovered on Japanese larch trees in Great Britain in 2009 in South West England. It was then found on larch in South Wales in June 2010 in public woodlands in the Afan Valley, near Port Talbot, in the Garw Valley, near Bridgend and in the Vale of Glamorgan. Felling of infected larch trees in South Wales is underway and Forestry Commission Wales is working with timber processors and others to ensure biosecurity measures are in place to allow logs from the infected trees to be taken to mills for conversion into timber.
  6. P. ramorum has not been found on any trees in Scotland.
  7. P. ramorum is not harmful to humans or animals.
  8. P. ramorum causes the disease known as "sudden oak death" in the USA, where it has killed millions of American native oak and tanoak trees. However, this name is a misnomer in Britain, where laboratory tests have shown that our two native species of oak, sessile and pedunculate oak, are much more resistant to P. ramorum than their American cousins. Fewer than five native oak trees have been confirmed with P. ramorum infection in Britain.
  9. P. ramorum should not be confused with acute oak decline (AOD), which is a separate disease affecting oak trees in the Midlands and parts of Wales and South East England, and in which a newly discovered bacterium species appears to be involved.
  10. Larch is a durable, versatile timber that tolerates changes between wet and dry conditions very well, and resists rotting when used in the ground. It is therefore in demand for outdoor uses such as fence posts, fence panels, exterior wall cladding, boats, sheds and furniture, as well as indoor uses such as flooring and chipboard. It is easily stained, worked and finished. Complete figures are not available for Japanese larch numbers alone, but all three larch species together cover an estimated 134,000 hectares in Britain, or about 5 per cent of total woodland. Individual country figures are:
    • Wales – 23,000ha / 8 per cent;
    • England – 43,000ha / 4.3 per cent;
    • Scotland – 65,000 ha / 5.1 per cent.
    • (To convert hectares to acres, multiply by 2.47)
  11. About 14 per cent of Wales is covered by woodlands. Of this, 38% (126,000 hectares/311,000 acres) is owned by the Welsh Assembly Government. Forestry Commission Wales is the Welsh Assembly Government’s department of forestry and manages these woodlands on its behalf. Forestry Commission Wales provides advice on forestry policy to the Minister responsible for forestry. It provides grant aid to other woodland owners and regulates forestry by issuing felling licences. It is also part of Forestry Commission GB and contributes to the international forestry agenda. More information on the woodlands of Wales is available on
  12. In July, the Forestry Commission announced a £600,000 support package for woodland owners in South West England and Wales to help tackle the outbreak of P. ramorum infection on larch trees. The package is part of Defra’s £25 million, five-year Phytophthora management programme.
  13. Forestry Commission Wales is developing an additional programme of support for private woodland owners who have P. ramorum confirmed on their land. Details of this support will be announced later this month.


For information about P. ramorum: