The battle against ash dieback

Paul Binks, highways asset manager at Lancashire County Council, discusses the local authority’s battle against ash dieback.

 

Ash trees are a major component of Lancashire’s landscape and are highly visible alongside the highway and in other public places. The disease has killed between 60 and 90 per cent of the ash in every country it has spread through across Europe and large numbers of dying trees will pose a widespread threat to public safety.

Lancashire County Council is a major landowner and the main impact of ash dieback is upon the trees which grow alongside the more than 7,500km of highways for which it is responsible. However, the authority also has a duty of care to manage the risks associated with trees alongside public rights of way, and in countryside parks, school playing fields and other estates.

With limited budgets, the council enlisted the services of KaarbonTech, through a procurement exercise, to help identify the extent of the risks faced by the council, and enable the development of a detailed ash dieback action plan in line with Tree Council guidance.

 

What is ash dieback?

Hymenoscyphus fraxineus or Chalara is the disease that causes ash dieback and is the most significant tree disease to affect the UK since the Dutch elm disease outbreak in the 1970s. It is expected to lead to the decline and death of the majority of ash trees in Britain and affect the majority of local authorities in some way.

Originating from Asia, its introduction to Europe about 30 years ago has devastated the European ash (Fraxinus excelsior) because our native ash species did not evolve with the fungus and therefore has no natural defence against it.

The fungus overwinters in leaf litter on the ground, particularly on ash leaf stalks. It produces small white fruiting bodies between July and October which release spores into the surrounding atmosphere.

These spores can blow tens of miles away. They land on leaves, stick to and then penetrate into the leaf and beyond. The fungus then grows inside the tree, eventually blocking its water transport systems, causing it to die.

The tree can fight back, but year-on-year infections will eventually kill it.

The presence of the disease in Lancashire was first identified near Clitheroe in 2014, and it has since spread to ash trees in all parts of the county. During the growing season of 2019 it has become apparent that ash dieback in many large specimens is now relatively advanced.

 

The survey

Lancashire County Council undertook a prioritisation exercise using the highway network hierarchy and other risk factors to identify the high-risk routes to be surveyed.

KaarbonTech are well known in the local authority sector for their asset management software and services and have surveyed over 100,000 trees across the country. The Tree SMART software that supported this operation enabled a high-speed collection of georeferenced condition and photographic evidence that will be used as a basis for the council’s action plan.

Lantra qualified professional tree inspectors used the Tree SMART survey module to bring to life the risk-based approach that the council had specified from their desk top research and assessed 423km of highway from May – September 2020. As ash dieback is most noticeable when trees are in leaf, tree inspections are more effective during the summer months.

The result was an identification and physical survey of 5,921 ash trees consisting of 3,146 individual trees and 2,777 within groups.

KaarbonTech recorded the pathogen responsible for Ash Dieback (Hymenoscyphus fraxineus) in 2,238 individual ash trees and 2,777 of the group trees, this equates to 85 per cent of ash trees carrying the disease to some extent.

Understanding the stage of the pathogen’s encroachment was also important. There were 284 individual trees and 124 in groups where ash dieback is at an advanced stage (less than 50 per cent healthy leaf cover) which equates to seven per cent of trees inspected.

Completing a survey of this kind and having geospatial data will allow us to more accurately project budget requirements to remove or prune ash trees considered to pose the greatest risk to the public.

This data will be combined with other council knowledge to project the budget required to continue to manage the network safely and protect Lancashire’s residents for years to come.

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