Sadly, we are well aware of the nationwide spread of the disease, Chalara, also referred to as ash dieback. Previously on this platform, we have discussed the look and spread of the Chalara disease as well as how to make the best of the felled timber it entailed.

Is ash dieback diminishing? No. But there are national efforts to limit its impact and recovery is imminent. What’s more, while the disease’s impact is at its peak, Danish expert Iben Margrete Thomsen warns that overreaction by automatic preventive felling is just as harmful as ignoring the issue.

What is Ash Dieback?

Firstly, it is important to distinguish between the symptom (dieback) and the disease (Chalara).

Originally an Asian disease of ash trees that infiltrated English flora through Poland and the Netherlands around ten years ago, Chalara is a disease caused by the Hymenoscyphus Fraxinea fungi that affects the vascular system of ash trees. The disease causes ash dieback, which manifests in leaf loss and crown dieback (shrinkage or defoliation), posing a threat to approximately sixty native varieties of ash trees.

From July to October, the fungi spores in the leaf litter form a fruiting body before releasing more spores. It’s been theorised that these spores can travel dozens of miles in the right conditions, latching onto other Ash leaves, preventing the leaf from carrying out photosynthesis and leading to the leaf dying and prematurely dropping off.

What Does Ash Dieback Look Like?

(Taken from The Spread of Ash Dieback (Chalara) in the UK)

The symptoms of ash dieback in trees infected by Chalara include:

  • Black/browning leaves, often spreading down the stem
  • Wilted, shrivelled or contorted leaves in summer
  • Black leaves may not drop as quickly as usual in autumn
  • Wound-like lesions and spots on the bark

Chalara or Ash Dieback in the UK

The situation is widespread and ongoing, and a few grave points made in a recent Small Woods Association publication are worth discussing.

  • In Europe, Britain has the highest percentage of native ash population. The expectation is a 97% loss of ash trees across the country, although this is strongly rebuffed by forest pathologist and Chalara expert, Iben Margrete Thomsen (see below).
  • Decaying ash trees are widespread in woodlands and roadside edges, posing a safety hazard to passers-by on paths and highways
  • Is the safety of passers-by fully taken into account?
  • Secondary factors such as honey fungus may accelerate decay.

Although sobering, it is worth specifying that these points were made in an advertisement by a tree-felling business, so may need to be taken with a pinch of salt. Thomsen, on the other hand, is a world-renowned expert on Ash Dieback and is a voice of calm and reason in her articles on the matter.

The idea that the majority of ash trees were dead or dying, she says, was never true. “We do observe a progressive decline in health (…) but most ash trees with moderate crown symptoms stay alive for years, even in forest conditions with lots of honey fungus attacks.”

She also points out that Ash Dieback impact is most visible and severe about ten years after the disease makes an appearance, which is where Britain is now. It’s not surprising, therefore, that most current discourse on Ash Dieback are reactions from those opposed to the widespread preventive felling of ash trees. The visible mortality of the ash tree species, combined with “the expectation of future mortality”, are causing waves of frustration and unease across those whose concerned.

During her international conferences, however, her message is always the same: don’t panic, just be aware of where and how to deal with sick ash trees… if sick trees they really be.

As pointed out by Roy Miller and Ian Willoughby in their Ash Fightback article, the general symptoms of ash dieback in large, mature trees—crown thinning, yellowing and branch dieback—can also be caused by root disease and waterlogging, for example. In other words, stress-related issues, not a pathogen-carried disease. Although the term `ash dieback’ is generally used to describe the sick trees, the role of Chalara, the actual pathogenic disease, may have been exaggerated in the many manifestations of ash dieback in the past few years.

Nonetheless, the makeup of UK woodlands and landscapes will be dramatically affected in years to come. At the moment, timber yards such as ours are overflowing with Ash logs, many of which were preventatively felled, both as a curtailing measure and to remove any risk to members of the public passing by. The real driver for felling at such a fast rate was public liability issues for landowners and local authorises.

What To Do About Ash Dieback and How Is It Prevented?

Don’t panic, and only cut down trees that pose a threat to the public, says Thomsen. The assumption that it would be best to cut down all ash now rather than come back in two years to cut down dead and dying trees is erroneous: most infected trees with slight and mild symptoms can be seen as likely survivors rather than doomed victims. It’s better and greener to keep an eye on ash trees and surgically remove individual cases, especially to avoid losing thousands of trees without good reason. This is more costly in the long term than automated blanket cutting, but the latter is far worse for the environment.

Ash dieback, Thomsen argues, only affects the integrity of trees in severe cases and therefore should be treated as an additional stress factor, not a death warrant. To decide if an ash tree should be preventatively felled, two simple guidelines should suffice:

  1. Trees with over 50% defoliation in the past two years.
  2. Trees with severe crown symptoms combined with extensive dead bark at the stem base.

You cannot truly prevent ash dieback, nor is it really feasible to halt it in its tracks. An ash tree may survive one infection of Chalara, but repeated cases every year will kill it, so it is advisable to photographically record how many times a tree contracts the disease. If you suspect a case of Ash Dieback, report it to the Forestry Commission by calling 0131 314 6414 or contacting [email protected].

Remember, trees infected with ash dieback should only be cut down when presenting a threat to the public. This is necessary to preserve natural diversity and allow nature to take its course, letting trees succumb or develop resilience for future diseases and climate change. When trees are cut down, the replacements that are planted need species to maintain the genetic diversity that is key to tree evolution. 

WL West & Sons Ltd is a timber merchant and sawmill business with 150 years of experience. We provide a wide range of air-dried oak and kiln-dried oak timber products and supplies. We also build and install custom projects for our customers.

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