Meet Nick Johnson, from the Northumbria Veteran Tree Project. We have been online friends for a while, but it was great to meet with him when he came to Rothbury to measure two iconic and very beautiful weeping ash trees. Over a lovely lunch in Bewick's, I told him that I was surprised that the trees were not yet in leaf. 'Oh dear', Nick responded. 'I do not like the sound of that'. Do you know, I had not even thought of these dear trees being affected by this awful disease.
Ash dieback can affect ash trees of all ages, but these beauties are by no means youngsters. Nick pointed out to me the telltale signs.
Leaves develop dark patches in the summer.
They then wilt and discolour to black. Leaves might shed early.
Dieback of the shoots and leaves is visible in the summer.
Lesions develop where branches meet the trunk. These are often diamond-shaped and dark brown.
Inner bark looks brownish-grey under the lesions.
New growth from previously dormant buds further down the trunk. This is known as epicormic growth and is a common response to stress in trees.
I asked him, 'What actually IS Ash dieback'? Nick told me that Ash dieback (Hymenoscyphus fraxineus) is a fungus which originated in Asia. It doesn’t cause much damage on its native hosts of the Manchurian ash (Fraxinus mandshurica) and the Chinese ash (Fraxinus chinensis) in its native range. However, 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 this means it has no natural defence against it.
I admit to having not realised the terrible calamity of this disease. 'Nick' I asked, hopefully, 'Is there any natural disease tolerance'?
He showed me what the Woodland Trust has to say about it:
There is hope on the horizon. Initial findings suggest that we might have some trees that are tolerant to ash dieback, meaning that the population could eventually recover over time (likely over 50 years).
However, tolerance to the disease is complicated because a number of factors play into it including genetic traits, the health of the tree and the number of ash dieback spores in the atmosphere.
Nick is not the only person I have been asking about this. Alastair Hardie is also very sickened and saddened to see what is happening. On Facebook recently Alastair posted this:
THE CATASTROPHE OF ASH DIEBACK.
I wonder how many realise the importance of the ash tree in our local landscape. When we moved to Westfield House Farm from Branton around 30 years ago there was still evidence of an earlier pandemic - rotting stumps where ancient elms had stood before succumbing to Dutch Elm disease. The ash was the dominant remaining tree and we took our lead from that when planting, over the years, mixed woodland and over a mile of hedgerows. They are thriving and grow strong and straight. But not, I fear, for long. The contrasting photos show two of our ash trees, each maybe over 150 years old. One is in it’s death throes, the other is seemingly in it’s summer glory but looking up the fence line and wondering what comes next. The prognosis is not good. There is a very high mortality rate. I have recorded, for the benefit of future generations, all of the mature ash trees on the farm. We are now planting oak, beech, sycamore, chestnut and field maple as well as smaller trees such as rowan, birch, hazel, holly, thorn, cherry etc. etc.
Here is an article from the Journal of Ecology: Landscape epidemiology of ash dieback: Landscape epidemiology of ash dieback - Grosdidier - 2020 - Journal of Ecology - Wiley Online Library