Ash dieback disease (Chalara)

January 7, 2020

(Hymenoscyphus fraxineus)

As recently touched on in our ‘The Art of Collaboration’ article there is a serious threat to our ash trees, in fact it is predicted that 95% of ash trees will be lost in the UK. This is due to ash dieback disease which is most prevalent in the south-east of England where it was first recorded in 2012.

‘Ash dieback will kill up to 95% of ash trees across the UK. At a cost of billions, the effects will be staggering. It will change the landscape forever and threaten many species which rely on ash.’ 1

Our workshop is in a rural location in Bosham, near Chichester and Ed himself lives in rural West Sussex. On his journey each day he has noticed the significant amount of ash trees that have been felled along the roadside. However, felling ash trees will not stop the spread of this wind-dispersed disease, rather it is a case for safety from falling branches and trees causing injury, damage and hazards as they become increasingly unstable.

In fact, is had been suggested that leaving them standing has a benefit, as Forest Research explains about the countryside at large, ‘…by keeping as many ash trees standing as possible, we can identify individuals which appear to survive exposure to the fungus and which can be used for breeding tolerant ash trees for the future.’ 2

As mentioned, ash dieback is caused by a fungus that originated in Asia. Fortunately, it doesn’t have such harsh consequences for the Asian native trees, Manchurian ash and Chinese ash. However, it has grave ramifications for the European ash that did not evolve with the fungus, and therefore has no natural defence system against it.

So how did it arrive here?
The spores of the fungus can be carried easily by the wind. It is possible that it arrived naturally in the UK this way from mainland Europe where the disease was first recorded about 30 years’ ago. However, ‘it was also inadvertently imported on ash saplings. The UK was importing thousands of ash plants from infected parts of Europe until a ban came into place in 2012’. 3

What happens to the tree?
‘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.’ 4

Of course, this is a terrible plight for the ash tree, and not too dissimilar to the decimation of the elm tree population in the not too distant past, although elms are now making a steady recovery albeit with relatively younger trees and not the giants that once graced our landscape.

Unfortunately, once ash dieback disease has a hold, it also renders the timber unusable, save for firewood before the timber begins to powder. With this is mind, we envisage (although don’t quote us on this!) that current stock levels of ash will continue or even rise in the short-term as managed forests fell their healthy trees, with shortages in the years to come alongside the impact on our countryside, landscape and natural woodlands.

NOTES:
1. The Woodland Trust – www.woodlandtrust.org
2. Forest Research – www.forestresearch.gov.uk
3. The Woodland Trust – www.woodlandtrust.org
4. The Woodland Trust – www.woodlandtrust.org

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