The Road of Elm and Ash

Written by Michael Yallop for Crann Magazine

As I travelled down the country this year on my holidays, I noticed the extent of how Ash dieback (Hymenoscyphus fraxineus) was really affecting our roadside trees. I suppose I didn’t have to look far, outside my front window, the mature Ash trees in my own garden are now succumbing to the disease.   It really wasn’t till this summer that I started to pay any heed to the disease. I think down to the fact like many things, until it started to affect my own trees. Many commercial growers who have been well aware of the issue up to now and have been trying to both deal with the disease in the plantations and deal with government in relation to the planation. I think they also have been trying to point out the significance of what was happening and what was to come. In my own case, it was only when I thought, what trees will be left on our roadsides and hedge rows I seen the scale of the problem we have.  Ash you could say is a dominant tree of height along many of our roads, fields, and hedge rows, so the loss will huge and the impact great across many sectors.

What is Ash Dieback.

Ash dieback, a disease of the Fraxinus spp species especially effecting F. excelsior and F. angustifolia. Recognised symptoms are that of a sparse crown and early leaf loss, maybe showing signs of struggling to produce a full crown and flushes of epicormic growth or shooting along large limbs and branches. Necrotic lesions in the bark and brown/grey discolorations are visible beneath the bark where its peeling in some cases. Black patches can appear in the leaves and unlike autumn colour change, the leaves go a consistent brown. Changes can be seen in the leaf stem, a green to brown to green again like figure 1. 

Figure 1

Figure 1: A diseased leaf which has fallen showing the green and brown discoloration on the stem and the dark brown colour of the leaflets.

The thing that amazed me most was maybe to some, a simple thing. This invasive pathogen was a forest floor leaf decomposer in its native eastern Asia, but when it made its way here, it attacked living trees instead of dead leaves.  Another point of interest is that we did have a variation of this decaying fungus already active on the dead leaves of our own ash, Hymenoscyphus albidus which was harmless to the live tree itself. I suppose all these things make the case clear for Ireland as an island to be tighter on its biosecurity, not the first time that has come up when we saw oak processionary moth make its way over here last year. Coker et al., (2018) has carried out modelling work to better understand mortality rates in the years ahead. From the study concluded that between 50% and 75% of trees were likely to die but this number will probably be much higher. The model outlined that over 30-year period, up to 100% could die. This type of research makes for grim reading and as I walked along my own road the other day, I looked at some mature ash showing minor signs and hoped these could pull through.

Evidence from the past might mirror the future.

Dutch elm disease wreaked havoc in Ireland wiping out most of our Elm population. My own road where I live was made up of Elm and Ash. Overtime the Elm has made a revival and died off again and now it’s the turn of the Ash.

What will be the species of tree that will come along to fill this space and what should we be planning to do for the future. Well, the first answer I feel is that Sycamore (Acer pseudoplatanus) will probably replace the Ash as the most common roadside tree. Fast growing and hardy they would easily create the height in our hedge rows that the ash has done. We should be planning on how we are going to deal with this issue for both landowners and homeowners, so we don’t get a situation where people are just felling trees ad lib. A recent article in the media noted how landowners could be left with the job of dealing with the dead trees in their roadside hedges as the Local Authority Management Agency said ‘’owners or occupiers of land are obliged under the Roads Act, 1993, to take all reasonable steps to ensure that a tree, shrub, hedge or other vegetation on the land is not a hazard or potential hazard to persons using a public road and that it does not obstruct or interfere with the safe use of a public road or the maintenance of a public road’’ (Moran, 2021). My fear would be people clearing roadsides of all vegetation or felling ash trees which are weathering out the storm because they hear all ash trees are dying.

One thing that puzzled me was the way in which the disease was having a more prolific effect on some trees and not so much on others. The answer to this was the chemical make up inside each tree differed. Coumarins, Fraxetin and Esculetin are chemicals found inside Ash trees and help to slow the susceptibility of the tree to the disease as seen in figure 2 (Nemesio-Gorriz et al., 2020).  Hopefully this kind of key information found by the researchers at Teagasc forestry department can point towards the survival of some of our Ash.

Figure 2

Figure 2 right shows a group of ash, some effected, and some are show better resistance to the disease.

The years ahead of us.

For most people right now, the challenge that lies ahead over the next number of years with our Ash trees is relatively unknown. Many will die and be felled, and a tiny pocketful might pull through. I like to get people’s opinions on topics like this to understand their thoughts. Many I talk to know of it but pay little heed to it and others don’t really care. I found many people feel it’s more a forestry problem and don’t think it will affect the giant Ash growing in their front garden like figure 3. My hope is that from this type of article and other publications, people may get a better understanding of the problem on a more local level.

Its safe to say that this is huge topic, and I am only brushing the surface with many issues such as the make up of the fungus, how it spreads and whats going to happen to our mature Ash. Promotion and awareness of ash dieback is key especially for those who manage mature and large trees on roadsides or public places. Get the right advice from a competent Arborist. Our countryside landscape is about to change very rapidly, and so will many housing estates where Ash trees are used in streetscapes. I hope the work that Teagasc and Kew Gardens Research lab are doing can help to better understand this disease and help us to manage it and try to save some of our trees, after all we need hurleys.   

Figure 3

Figure 3 right shows mature Ash in a garden slowly succumbing to the disease, these are along the edge of the road.  

References:

• Coker, T., Rozsypálek, J., Edwards, A., Harwood, T., Butfoy, L. and Buggs, R., 2018. Estimating mortality rates of European ash ( Fraxinus excelsior ) under the ash dieback ( Hymenoscyphus fraxineus ) epidemic. PLANTS, PEOPLE, PLANET, 1(1), pp.48-58.

• Moran, C., 2021. Farmers to be hit with liability for dying roadside trees as disease ravages ash population. The Irish Independant,.

• Nemesio-Gorriz, M., Menezes, R., Paetz, C., Hammerbacher, A., Steenackers, M., Schamp, K., Höfte, M., Svatoš, A., Gershenzon, J. and Douglas, G., 2020. Canditate metabolites for ash dieback tolerance in Fraxinus excelsior. Journal of Experimental Botany, 71(19), pp.6074-6083.