Ash Dieback

This document is now out of date in many respects, our latest information about managing Ash Dieback on the reserves can be found here.

Ash dieback is a disease of ash trees caused by the ascomycete fungus Chalara fraxinea (more properly known by the name of its sexual teleomorph*, Hymenoscyphus pseudoalbidus).

The fungus infects ash trees via the spread of spores, and it causes leaf loss and crown dieback, leading to the death of the tree. Ash trees suffering with this infection were first recorded in Poland in 1992. It is now known to be widespread in mainland Europe where in some countries it has severely impacted the ash component of the woodland landscape.

Leaf necrosis in ash die back - photo courtesy of The Food and Environment Research Agency (Fera), Crown Copyright

Leaf necrosis in ash die back – photo courtesy of The Food and Environment Research Agency (Fera), Crown Copyright

The Forestry Commission website reports the first UK record as February 2012 when a batch of young trees imported to England from the Netherlands were found to be infected; the UK imports a large volume of young trees from mainland Europe each year (including those grown on from UK seed). Subsequent checks have revealed the fungus at an array of locations both in nursery stock and, in east England, in established woodland. The Forestry Commission report that on 08 November 2012 a total of 135 confirmed sites (15 nursery sites, 55 recently planted sites and 65 in the wider environment) had been identified.

So far in Wales, at time of writing, only one positive site has been recorded; a recently planted site in Carmarthenshire. However, checks on WTSWW sites are being performed by Forestry Commission Wales, and Wildlife Trust staff are being vigilant during their visits to their woodlands. Ash is a key species on many of our nature reserves as it is across the country- for example Kilvrough Woods on Gower is part of the Gower Ashwoods Special Area of Conservation (a site of European importance) and mature ash trees at West Williamston in Pembrokeshire are the ‘master’ trees critical to the life cycle of the brown hairstreak butterfly.

It is important to recognise that we do not yet know what impact this disease will have in Wales. It is known that there is some natural resistance to the disease, and the genetic diversity of our ash population will hopefully confer some resilience against its spread. Also, landscape history, woodland ecology and environmental conditions are not the same in the UK as in mainland Europe. A reasoned response to this outbreak will work to contain the disease, but not to the detriment of the population’s natural ability to recover. There is always the risk that an ill-considered response where speed is the main criterion can be as damaging as the outbreak itself. WTSWW will keep a keen eye on developments, complying with any emerging legislation, but also working to ensure the right decisions are made for the right reasons.

wilted shoot of ash from ash dieback

wilted shoot of ash from ash dieback

So, how can you help? Learning to recognise the signs and symptoms of the disease is key. There is some great information available via the Forestry Commission, including a pictorial guide and a video to help recognise the disease in the field

If you suspect ash dieback, please check your observations carefully against these references- remember leaf discolouration is normal in autumn! But do report any potential outbreaks to the Chalara helpline on 08459 33 55 77 (open 8am – 6pm every day) or by email to If it is on a Wildlife Trust nature reserve please also let the Trust know on 01656 724100.

It is important to remember that with change, always comes opportunity. Even if this disease does cause major mortality in Wales’ ash trees, the ecosystem will recover, as it has following Dutch Elm Disease. More standing dead wood will add ecological value to many Welsh woodlands, and if the outbreak encourages future policies that favour natural regeneration over high density stocking, that too would be beneficial.

We will keep you up to date with news over the coming months via this newsletter.

*This fungus has a life cycle where it reproduces both sexually and asexually, the stage where the fungus produces sexual spores is known as the teleomorph (or perfect stage), where it reproduces asexually this stage is known as anamorph (or imperfect stage) – ref