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Ash trees at risk from infectious disease

Branches of an Ash tree against a blue sky

A large proportion of England’s Ash trees, including Sheffield’s 250,000, are at risk from Ash Dieback, an infectious Asian tree disease sweeping across the country.

The highly infectious, incurable disease which only affects Ash trees, is spreading rapidly across Europe and was first recorded in Britain in 2012. The disease is now widespread across England, with the most advanced effects in southern and eastern counties.

The Peak District and other parts of Derbyshire and Yorkshire have already seen a significant impact, and it has now begun to spread across Sheffield.

It is expected that around 90% of England’s Ash trees will die from the disease. Sheffield is home to around 253,000 Ash trees and could lose between 127,000 and 215,000, which means preventative action now is essential to restore and protect the city’s existing and future Ash population. Approximately 153,000 of Sheffield’s Ash trees grow on public land and the remaining 100,000 are on private land.

Affected trees become unpredictably brittle and dangerous as the disease takes hold. They can drop limbs or fall entirely in the later stages of the disease. It is critical that trees on both public and private land are identified and monitored.

Sheffield City Council’s parks and countryside service and its Streets Ahead contractor Amey carry out tree inspections for all trees on council land and are monitoring all Ash trees for signs of infection.

The only way to remove the risk posed by badly affected trees is to remove them. In addition to felling badly-affected trees, some trees in hard to access locations may need to come down in the early stages of the disease to ensure the safety of tree operatives.

Tree contractors are at the greatest risk of harm from dying ash trees, so it is vital that they are fully qualified and insured and aware of the particular dangers of dealing with Ash Dieback affected trees. People who are not qualified should not, under any circumstances, attempt to work on trees affected with the disease, nor should landowners appoint contractors who are not skilled in this field, for everyone’s safety.

Whilst infected trees need to be taken down before they become a public danger, those that may be resistant to the disease must be retained so that a new generation of more resilient Ash can establish. It is thought that up to 10% of Ash trees may have some resistance to the disease and assessments are already taking place to identify those trees with resistance in Sheffield.

Councillor Mary Lea, Cabinet Member for Culture, Parks and Leisure at Sheffield City Council said: “In most cases this disease is fatal for Ash trees and we have been monitoring the situation across England closely, in preparation for it taking hold here in Sheffield.

“It is airborne and incurable, and we know from countries overseas and what has happened in the south of England that sadly we stand to lose a huge percentage of our Ash trees.

“Infected trees become very dangerous. To manage the risks we must remove them at the right time, before it becomes unsafe for an arborist to carry out the work. Due to the serious risks involved for operatives I must stress the importance of appointing a qualified professional to complete any work. For their own safety, those who are not qualified, should not be offered or accept work on trees with Ash Dieback.

“I understand that there may naturally be some concerns about the removal of trees and I want to reassure people that it’s the last thing we want to do. However, we have to prioritise the safety of people and so we are closely following national guidance from The Tree Council to manage this situation as best we can, and make sure we retain as many Ash trees as possible.

“A small number of Ash trees will be resistant, which is why we will only take trees down at absolutely the right time. We will work with and listen to the advice and experience of experts so that we can protect the species and encourage a new, more resilient generation of Ash trees.”

Last year Sheffield City Council held an Ash Dieback conference at the Botanical Gardens. Representatives from Sheffield Tree Action Group (STAG), The Forestry Commission, utility companies, wildlife charities and the farmers’ union, were invited, as well as tree contractors and representatives of private landowners. The conference was used to share the latest information on Ash Dieback and start a local resilience forum for Yorkshire, with representatives from all affected bodies.

The city’s Ash trees will be managed in line with the Council’s Trees and Woodlands strategy, in which they have committed to planting 10,000 trees per year, at least 100,000 trees over the strategy’s 10 year period; and the recently launched new Street Tree Strategy, which comes following months of partnership working between representatives from Sheffield City Council, Amey, Sheffield & Rotherham Wildlife Trust, Sheffield Tree Action Groups, The Woodland Trust and tree valuation experts.

Christine King, Co-chair of the STAG Steering Group, said: "It is deeply saddening that Sheffield will lose so many native large canopy Ash trees in the coming years as a result of Ash Dieback.

“We recognise the need to ensure the safety of both the public and those who work on trees as these trees decline. We will therefore continue to work collaboratively with Streets Ahead, as we have done this last two years, to ensure that felling is only done when individual street trees have declined sufficiently to justify it.

“Through the new Street Tree Partnership, we are working with Streets Ahead, Sheffield City Council and other stakeholders, to ensure we learn the lessons of Ash Dieback and Dutch Elm Disease. This means increasing the overall diversity of Sheffield's street trees, maximising their future resilience to the continually emerging new pest and disease threats all UK trees sadly face."

Those with Ash trees on private land that could potentially fall on neighbouring land, roads or property, should have trees assessed by a suitably qualified or experienced arborist to establish the health and level of risk posed.

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.

Larger landowners and businesses need to take the following steps, and it is essential that a qualified professional is used to carry out any tree work:

    • 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


    • Appoint qualified tree specialists to remove hazardous trees

There are many resources available from The Forestry Commission and The Tree Council about managing Ash Dieback.





Further technical information and questions relating to managing Ash Dieback is available on the council's website.

For more information contact the council's Parks and Countryside service at or call 0114 2500 500. Follow on social media @parksheffield on Twitter & Instagram, or @sheffieldparks on FB