Ash Dieback Survey

As a landowner, if you possess ash trees, it is incumbent upon you to conduct regular surveys for disease indicators. Should the disease be detected, you are obliged to respond appropriately, considering any potential risks to public safety.

What is ash dieback?

Ash dieback, also known as 'Chalara,' is a highly contagious fungal disease poised to decimate over 90% of native ash trees, along with most other ash species. The disease compromises the tree by infiltrating its network of vessels responsible for transporting water, nutrients, and gases, swiftly diminishing the tree's essential functions. This leads to vessel obstruction, branch girdling, and ultimately, the death of the affected part. The majority of trees infected with Ash dieback are likely to perish, either from the disease itself or from secondary infections like Honey fungus, which exploit the tree's compromised state and weakened defences. However, a small proportion of ash trees seem to be resistant to the disease, and their genetic markers are being studied in hopes of cultivating disease-resistant ash trees for the future.

Ash species affected

While our sole native ash species (Fraxinus excelsior) and its varieties are particularly vulnerable, it is also recognized that Narrow-leaved ash is susceptible. The RHS has identified the following non-native trees as vulnerable:

• Manna Ash
• Black Ash, Green or Red Ash
• White Ash
• Manchurian Ash
• Among these, White Ash and Manchurian Ash are considered to be the least susceptible. It is important to note that Mountain Ash trees (Sorbus aucuparia sp) are actually a separate botanical species and are not affected.

You will need to consider whether active intervention is required or not.

Key things to be aware of are:

• Trees on your land are your responsibility
• Once ash die back has infected an ash tree the tree can be at considerable risk of structural failure. The tree can shed branches and limbs, or the whole tree may even collapse.
• Large trees have the potential to kill or seriously injure people and damage property and vehicles – this should be the paramount consideration for tree owners when deciding how to manage ash trees affected by ash die back.
• A key health & safety consideration for tree owners should be “what is in the target area around the tree should it fall or shed limbs?”. For example the risk posed by the tree to infrastructure (power lines, gas lines & telecoms), highways, areas around occupied buildings (especially schools, hospitals, shops, housing & offices etc) and other peopled areas, should be very carefully considered.
• Preventing Access to Trees – if a tree owner has concerns about the safety of a tree, it may be prudent to cordon off the tree(s) to prevent access to the area where a tree may fall, as a short-term measure until a tree can be properly inspected.
• Inspection of Trees should, it is recommended, be carried out initially by a competent tree inspector who has relevant professional expertise and qualifications to assess the tree and recommend an appropriate course of action i.e. to carry out tree surgery /removal, or to do nothing and /or monitor the situation. A robust monitoring system would then involve interim inspections by landowners in between professional inspections.
• Tree Surgery should always be carried out by a competent tree surgeon who has relevant expertise and qualifications.
• Disclaimer – this is not intended to be an exhaustive Health & Safety Guide, only a list of the key considerations for tree owners.

Useful guidance on managing and mapping the risks from trees can be found at the National Tree Safety Group Guidance. Whilst ash dieback is not specifically mentioned it is considered the document is comprehensive enough in its guidance and scenarios that parallels can readily be taken and applied to management of tress infected by the disease.