Big changes afoot: managing Ash Dieback on WTSWW nature reserves

Ash tree on Carmel Nature Reserve. Photo: Lizzie Wilberforce

Ash tree on Carmel Nature Reserve. Photo: Lizzie Wilberforce

Many of our members and supporters will have heard of ash dieback – a disease of ash trees, which was first reported in the UK in 2012, and a year later was reported in native woodland in Wales (and in WTSWW’s patch) for the first time – in Ferryside, Carmarthenshire.

What is ash dieback?

Ash dieback is a fungus (Hymenoscyphus fraxineus) which originated in Asia. It doesn’t cause much harm to its native hosts, but since its introduction to Europe about 30 years ago, it has devastated our native ash (Fraxinus excelsior), which has no natural defence against it.

Ash dieback has spread rapidly through the Welsh countryside and in the seven years since it was first reported, has affected almost all of WTSWW’s nature reserves with ash trees.

What is the impact on ash trees?

Ash is infected by the spores of the fungus, through the tree’s leaves; the cycle then continues via overwintering leaf litter which re-infects trees the following spring. The fungus grows inside the tree, and blocks its water transport system, causing the tree to die.  The extent of resistance to the fungus is not known, but a recent analysis of surveys of ash dieback across Europe reveals mortality rates as high as 85 percent in plantations and 70 percent in woodlands[1]. Latest trial data from Forest Research shows that over 5 years, less than 1 % of the trees showed tolerance to dieback symptoms[2]. The current safety guidance is that it should be assumed that any tree showing symptoms is going to die; however, the disease progresses at different speeds in different trees.

 

What is the impact on WTSWW nature reserves?

We have ash on a great many of our nature reserves. Some of our sites on limestone (such as Cwm Ivy and Llanrhidian Hill on Gower, Carmel in Carmarthenshire and West Williamston in Pembrokeshire) have woodland canopies heavily dominated by ash. Many other sites of mixed woodlands (such as Coed y Bedw in Glamorgan and Pant Da in Ceredigion) still have some substantial ash trees on them. Ash is one of our most common tree species in Wales. Please check reserve pages for the latest updates.

During the summer of 2019, the WTSWW conservation team visited all our high risk areas (where ash trees are a risk to people, for example near houses and roads) to assess the ash trees present. What we found was that already, about half of our ash trees are in Ash Health Class 3 or 4 (i.e. they have less than half of the canopy of a healthy tree). In other words, we have a very significant problem developing, with dead and dying trees in locations that will directly affect people’s safety.

Ash Dieback casualty tree in Cwm Ivy Nov 19

Fallen dead ash at Cwm Ivy & Betty Church nature reserve, Gower. This tree was tagged as suffering from ash dieback symptoms in summer 2019.

What are WTSWW going to do?

Our staff team have spent several months surveying and carefully planning our response. We need to meet our obligations to keep people safe, but we also need to try and minimise the negative impact on the species on our nature reserves, and still encourage visitors where we can.

Our duty of care to visitors is significant; warning people of the risk does not reduce our liability. Where we are inviting the public onto our land, we have to ensure the access we provide is as safe and that we address any hazards we identify.

Our first and most important principle is not to fell a tree if we don’t have to. We are only assessing ash trees in high risk areas (these being the areas of high public presence); all other ash will be left to stand.

Many of our less well visited reserves fall into this low risk, non-intervention category. This is important for allowing any resistance to manifest, and also to support the many species that depend on ash (such as scarce lichens) and even if they die, to ensure the fantastic standing dead wood resource is available to the species that use it.

Our second step is to try and remove the risk, so that we can leave the tree standing. That means making sure that people do not come near the dangerous trees. With regret, this means that we are considering closing a few reserves, or closing paths within nature reserves- but the advantage is that we do not then have to undertake major works that will significantly affect the ecology of those sites. We will endeavour to keep alternative routes open where we can and will continue to re-assess these sites regularly.

Third: in high risk areas, where we cannot reduce the risk, we need to act to make the tree(s) safe. This will mean some substantial work to some large ash trees in the coming years, based on a hierarchy of priority. This is not something we want to do (for either the ecological or financial consequences) but the potential risk to life makes it essential, as it would for any other dying tree in a high risk location.

The way we apply this hierarchy of action may change in space and time, as we learn more about Ash Dieback and as we undertake mitigation work on our nature reserves. We are working with other Wildlife Trusts and organisations across Wales and the UK to keep our approach and decision making as up to date as possible.

Read our latest Ash Die Back Action Plan.

What will happen to the areas where ash trees have been lost?

Our preferred approach is not to re-stock (i.e. we will not plant in new trees). Instead we wish to allow the natural regeneration of whatever is available from the local provenance seed. This avoids the import of compost, plastic tubes and so on. This is even more important when you consider this was one route by which this disease reached Wales in the first place. It also ensures that whatever grows is locally appropriate. We will monitor these areas however, and intervene if there are any barriers to the regrowth of the canopy in the long term. We may also re-stock when required to by others (for example as a condition of a felling licence).

What can you do?

Here are a few things we would be incredibly grateful to our volunteers, members and supporters, to consider supporting us with:

·         Helping us share our decision making and thinking on managing ash dieback with others

·         Respecting signage and closures of paths and reserves, and encouraging others to do the same: they are there for your safety and based on detailed inspection.

·         Checking the website for any updates on reserve closures

·         Consider donating and supporting the Trust’s core work. The requirement for essential tree work is going to cost WTSWW many thousands of pounds that we would prefer to be using for conservation. Every penny helps and we are incredibly grateful for the ongoing support we receive.

Where can I find out more?

We are just in the process of producing an Ash Dieback Action Plan which will provide more details of our approach. Alternatively for site-specific queries, please contact your local Conservation Manager:

Kerry Rogers (Cardiff, Bridgend, Vale): k.rogers@welshwildlife.org

Lizzie Wilberforce (Pembs, Carms, Ceredigion, Swansea, Neath Port Talbot): l.wilberforce@welshwildlife.org

Sarah Woodcock (Valleys, Brecknock): s.woodcock@welshwildlife.org

[1] https://www.sciencedaily.com/releases/2018/12/181205093651.htm accessed 15-11-19
[2] https://www.forestresearch.gov.uk/research/chalara-ash-dieback-resistance-trials/ accessed 15-11-19