Ash dieback, also known as Chalara dieback of ash, is a fungal disease that affects all species of ash trees (Fraxinus). The disease has spread west across the country and is now affecting almost all parts of Wales.
The fungus (Hymenoscyphus fraxineus) attaches itself to the leaves of ash trees and spreads through to the branches, causing the tree to eventually die.
Ash dieback is a Europe-wide problem and 90% of ash trees are expected to die from it. It's a massive problem for landowners and councils across the UK who have ash trees on their land. Affected trees can collapse without warning on people, property, power lines and roads.
Some rural councils in England think as many as 500,000 ash trees on their land have been affected by ash dieback. In Powys we've estimated around 23,000 ash trees will need felling because of the disease, though the final figure could be much higher.
To stop ash trees from hurting people or damaging property we're starting a programme of ash tree inspection and felling that will take a number of years to complete. But by acting now we'll be able to protect people and property from a disease that can't be ignored.
How are ash trees affected by the disease?
The disease affects ash trees by blocking the water transport systems, causing leaf loss, lesions in the wood and on the bark. This leads to the dieback of the crown of the tree.
Trees become brittle over time with branches breaking away from the main body of the tree. If they are not dealt with, trees are at risk of collapsing, presenting an immediate danger to the surrounding area.
What does ash dieback look like
How we are tackling ash dieback
There is no known cure or practical way to prevent the disease from spreading. It is estimated that around 90% of ash trees in the UK will be killed by ash dieback.
There are thousands of ash trees on public land in Powys and many more on private land. The only way to remove the risk posed by badly affected trees is to fell them.
We will only be dealing with trees on Authority owned public land - parks, housing estates, schools, on roadsides etc.
Surveys are ongoing to identify ash trees that require urgent felling. The surveys will take many months to complete and then we will be re-surveying on an annual basis until the disease has run its course.
Over the next few years, ash trees on public land will be assessed to establish how the disease has affected them - and how quickly they need to be felled.
Ash trees affected by ash dieback will be categorised in one of four categories. This will help us determine which ones are in need of removal. Trees in category one are either unaffected by ash dieback or show early signs of the disease. Trees in category four will be heavily affected by the disease with a large amount of leaf loss and brittle branches - these trees will become a priority for removal.
Some ash trees show good levels of resistance to the disease and should not be considered for removal - These trees are very important for the ecological value they retain in the environment and may help repopulate the species in the future.
What can you do
There is no need for the public to report ash trees on public land to us. We will be carrying out a full survey across the county.
If you have ash trees on your land that could potentially fall on neighbouring land, roads or property, it is important that the trees are assessed by a suitably qualified or experienced arboriculturalist to establish their health and the level of risk they pose.
Private landowners have a duty of care under common law to ensure they do all that is reasonably practicable to prevent injury or damage to neighbours and under the Occupiers Liability Acts, visitors to their land, as well as trespassers. The Highways Act also requires them to ensure their trees do not endanger people on roads and footpaths.
Businesses have additional requirements under the Health and Safety at Work Act to ensure their work places are safe.
For single householders this may require you to keep checking the condition of your ash trees, for larger landowners and businesses you will need to:
- Identify how many ash trees you have and where they are
- Assess their current condition - use percentage of canopy cover remaining
- Identify where affected trees pose a risk
- Remove hazardous trees
After the initial assessment and mitigation, we recommend you make a plan of ongoing inspections and note expected decline of the ash trees you have. This will enable you to budget for future work that will be required. Affected trees are expected to lose 10-15% of their canopy per year although the decline can be quicker than this. Trees with 25% to 0% of canopy remaining should be felled if they are near people or property. It can be predicted when trees with 50% to 25% canopy cover remaining will become hazardous.
Planning and Tree Preservation Orders (TPOs)
No ash species should be approved in landscape schemes.
The full implications of the disease are still unknown, so it is not felt necessary to fell healthy trees. Applications for consent to fell unaffected trees (under tree preservation orders and conservation areas) remain to be judged on their own merits, and the potential for infection by Chalara will not be a significant consideration. Trees confirmed to be infected by Chalara will again be judged on their merits against the likely outcome of infection, the value of disease control, and the theory that mature trees may provide a source of resistant stock. Felling infected trees under Statutory Plant Health Orders will be an exception.
Until further notice, the potential risk of infection by Chalara will not be considered a significant justification for not making a TPO, although a confirmed case of Chalara is likely to be a significant factor weighing against making an order.
Frequently asked questions on ash dieback
What happens if you don't do this?
There will be several thousand large dangerous trees standing and potentially falling close to roads, schools, properties and public spaces.
How quickly does it spread from tree to tree?
The disease is caused by airborne fungal spores and can easily spread more than 20km per year. The spread from tree to tree depends more on the natural resistance of the particular tree as the spores are released in the billions and are literally everywhere.
How long will it take?
The removal of diseased ash trees may take several years as trees decline over time. Each affected tree will decline by 10 to 20 percent each year depending on several environmental factors.
Is the council using this an excuse to get rid of more trees?
No. This disease is highly regrettable and a disaster for the natural environment. The loss of so many trees and the ecosystems they support cannot be underestimated.
Are you going to cut down other species of trees?
Not due to ash dieback. The only other trees being removed by the County Council are day to day dead, dying and dangerous trees that are removed for public safety.
Are you cutting down ash trees that don't need cutting down?
Definitely not. All trees felled will be assessed prior to any work and retained for as long as safety permits.
Are some ash trees going to be resistant to the disease and how will we protect them?
There are some ash trees that appear to be resistant or highly resistant to the disease. These trees are incredibly important for the ecological value they retain in the landscape. We will continue to monitor the decline or resistance of all the retained trees over a number of years. All trees showing good resistance will be noted and departmental owners of those trees will be notified.
Are you going to replace what is lost?
Eventually we will begin to replace what has been lost but this will be in the longer term and part of the council's environmental and greening strategy across the county.
What happens to all the wood?
We will be extracting the wood for sale or use where it is economical to do so. This may take some time to organise and to equip ourselves to do.