Ash dieback

A fatal fungal disease of ash trees

First confirmed in the UK in 2012, ash dieback, also known as 'Chalara' or Chalara ash dieback, is a disease of ash trees caused by a fungus called Hymenoscyphus fraxineus.

This disease has spread quickly and is now affecting woodlands across the UK, leading to the death of thousands of trees. It has already caused widespread damage in continental Europe.

What is ash dieback?

Ash dieback is a disease that affects ash trees, caused by a fungus called Hymenoscyphus fraxineus. The fungus has two stages to its lifecycle - a sexual stage, which helps the fungus spread, and an asexual stage, which is what grows on the tree and causes damage. The fungus blocks water transport in the tree, leading to lesions in the bark, leaf loss and the dieback of the crown.

Ash dieback fungus is believed to have originated in Asia. It was first discovered in Europe in Poland in 1992, and is now found widely across the continent. The first confirmed case in the UK came in 2012, since when it has spread across England and to Scotland, Wales, Northern Ireland, and the Isle of Man.

Ash dieback symptoms

The main symptoms of ash dieback are:

Dead branches
Blackening of leaves which often hang on the tree
Discoloured stems often with a diamond-shape lesion where a leaf was attached

Trees may eventually drop limbs, collapse or fall. The symptoms are often easier to spot in mid-late summer when a healthy ash should be in full leaf. It becomes much harder in autumn when leaves are naturally changing colour and falling.

Once a tree is infected the disease is usually fatal, either directly, or indirectly by weakening the tree to the point where it succumbs more readily to attacks by other pests or pathogens, such as honey fungus. These secondary pathogens can cause butt or root rot, leading to the tree falling.

How does it spread?

The disease may spread locally (over tens of miles) by wind dispersal. The reproductive stage of the fungus grows on the previous year's fallen leaves, producing fruiting bodies that release spores between June and September. These spores are dispersed by the wind and settle on the leaves of healthy trees. If a healthy tree receives a high enough dose of spores, it too will become infected. Over longer distances, the disease may be spread by the movement of infected ash plants.

Management

There is no cure for ash dieback, but some trees are less susceptible to the disease. Investigating this natural resistance could be the best way to secure the future of the UK's ash trees. Ash dieback causes trees to slowly die, drop limbs, collapse or fall. In places where infected trees grow beside roads and footpaths, they are likely to pose a threat to public safety. As a result, in some cases infected ash trees are removed for the safety of site users and to help control the spread of the disease. In these cases, ecological surveys are important to check for the presence of protected species such as badgers and dormice, enabling the appropriate mitigation to be undertaken.

What you can do

Biosecurity is important to help manage the spread of the disease. Simple steps such as washing your footwear before and after walking in woodland, sticking to footpaths and washing bike and car tyres can all help reduce the risk of spores being spread.

Ash dieback in Cheshire

Ash is one of our larger tree species in Cheshire, often making up part of the upper canopy of the majority of broadleaf woodlands in the county. We estimate that ash trees make up around 20% of broadleaf trees in Cheshire and their density in our woodland can range from up to 80% in some cases. With the threat of ash dieback spreading across the area and causing around 90% of ash trees to die, this will have a significant impact on our woodlands and farmland trees for years to come.

We work collaboratively with other Wildlife Trusts across the UK to ensure a robust strategy and framework for dealing with the effects of ash dieback. As tree owners we are responsible for keeping our trees safe.

Safety of the public and the resilience of habitats are at the core of our work. We carry out an annual professional tree inspection of all our woodlands to ensure they are safe for people to visit. Tree diseases highlight the sensitive nature of habitats and how we need to ensure resilience in our woodlands through proactive management.

Ash trees can regenerate and those that do will produce offspring that can be resilient to the effects of dieback. We aim to retain as many trees as possible rather than felling. Deadwood, in particular standing dead trees, is highly valuable for wildlife and is considered one of the rarest habitats in the UK. Tree felling in areas with a high-density of ash trees could allow for too much exposure to the elements and lead to the failure of the remaining trees. However, tree felling in areas of low-density of ash trees can benefit wildlife and allow ground flora to thrive and become more resilient with younger tree stock.

To tackle Ash dieback in Cheshire, we must consider all options. This may include diverting footpaths or closing sites. This is a complex decision-making process, with public safety and wildlife at the centre.

Nature Reserves impacted by Ash dieback

Warburtons Wood

Warburtons Wood, near Kingsley, is an ancient woodland and Site of Special Scientific Interest (SSSI) with large areas of the woodland dominated by tall Ash trees. It is one of the best examples of woodland ground flora in Cheshire. Felling would be damaging to biodiversity and could lead to more failure of the remaining trees. Therefore, the footpath through the wood was diverted in summer 2023 around the neighbouring Hunters Wood. This will allow natural processes to occur and wildlife to benefit whilst keeping people safe.

Owley Wood

Owley Wood in Weaverham is an ancient, semi-natural woodland on a steep slope leading down to the old navigation of the River Weaver. Ash trees make up less than 10% of trees within the woodland. They are mainly sparse, however some dense areas are present. Thinning these trees out will allow light back into the woodland, encouraging regeneration of ground flora and encourage new sapling development. The denser areas will be re-stocked to enhance the species diversity of trees within the woodland, which is dominated by Sycamore. Our aim is to future proof the woodland against diseases that may affect Sycamore. Planned work will start winter 2024 and likely carry on through 2025.

Pumphouse Wood

Pumphouse Wood, on the edge of Barnton, is a small semi-natural woodland. Backing onto houses and a school, it is well used by the local community. The upper canopy is dominated by Ash trees with an estimated 80% of the upper canopy likely to die.

The primary concern at this site, is that the remaining 20% could become open to wind and other elements that they have previously been sheltered from and therefore subject to failure. We will be looking at clear felling large areas of the woodland. We are still in the process of planning our work at this site, however it will take place later in 2024.

Poors Wood

Poors Wood is a semi-natural broadleaved woodland on the steep banks of the River Weaver. The canopy is dominated by Ash and Sycamore, with frequent Beech and English Oak. There will be minimal felling at this site as there are few Ash trees present.