Since the arrival of the Dutch Elm disease at the beginning of 20th century wych elm, considered to be the only truly native elm to the UK, has been at danger of extinction. After the catastrophic outbreak of the disease in the 1970s it is in fact now classified as vulnerable. The disease is mainly spread by elm bark beetles that carve out tunnels in the sapwood under the bark to lay their eggs. While beautiful (see below) these engravings signify a horrific and irreparable interference in the tree’s vital systems. The larvae that hatch then feed on the sapwood and the fungus interferes with the tree’s vascular structure, essentially blocking its water transport system. Leaves and branches then start wilting, and the tree dies within one to three years. Now the summer is almost here it is a good time to observe the elms and unfortunately it is almost guaranteed that you will see some succumbing to the fungus – watch out for yellowing, wilting leaves and imagine that this is what’s happening under the bark:

Ronnie Nijboer, CC0, via Wikimedia Commons

The Dutch Elm disease can also be spread by the root systems, not just the beetles. This may be why the more hardy and disease resistant elms happen to grow from seed, after an exchange of pollen between male and female reproductive systems. In this case genetic variations occur over time and the new elms can be seen evolving to be more resistant. The alternative, elms that develop from each other’s root systems, trunks and those that are cultivated by planting cuttings are clones of each other and therefore pass to each other their vulnerability to the disease. Unfortunately, while no wych elms are immune to the disease, some variations have been observed to be less prone to it and/or perish slower.

So, what does this mean for our native elms?

The Dutch Elm disease, which was accidentally brought to the UK from USA on imported elm logs, has wreaked havoc on on the trees yet there are signs that the whole species might not be wiped out. Currently most wych elms only manage to grow as small trees and shrubs before they succumb to the plague, however current instances of fully grown elms (up to 30m tall) indicate that there is hope. If we assume that genetic modifications have occurred over time and that wych elms that have managed to grow tall have resisted the disease cultivating from those trees would be a step forward. It is important to remember though that on the whole specialists agree that fully grown, strong elms may just have been lucky.

Our tree surgery team cultivate wych elm seedlings and saplings from tall, healthy trees

Among other botanical organisations the Kew Gardens in London are active in the fight against the disease. They point to the fact that ‘before the decimation of the British elm population, they were the second most important broadleaf timber trees in Britain after oak. Elms are also highly valued for adding beauty to our landscapes and supporting many other species in UK native woodlands, such as the White-letter hairstreak butterfly.’ Kew Gardens launched the UK National Tree Seed Project in 2013 which is about collecting good quality seeds and therefore preserving, supporting and encouraging a healthy elm population. While all the tree and shrub seeds collected are important, the wych elm and ash (species also greatly suffering from a destructive fungal disease, ash dieback) seed collections are of particular relevance to us.

Sadly it is too late for some of the most distinguished elms; after developing the disease the distinguished 400 year old English Elm in Brighton had to be felled. Despite the best efforts to try and stop the spread of the fungus by girdling (removing the bark from the affected area) one of the oldest elms in the world had to be cut down in 2019. It was lovingly known as one half of the Preston Park twins and this shows how integral trees can become to a place and its people, and how important it is to do everything in our power to help these trees survive and thrive. Due its immense value to Brighton and beyond the condemned elm was turned into a sculpture and placed nearby its surviving twin.

While in the US some advise fungicide injections to the trees to protect from Dutch Elm disease the Royal Horticultural Society dismiss it as not ‘feasible’ and ‘completely impractical’ in controlling the beetles. In fact they suggest not planting the native varieties of elm at all due to their susceptibility to the disease; instead, they suggest genetically modified varieties.

So here we are, it seems that this ongoing fight is nowhere near the end but there might be hope for the wych elm. The only viable condition though is that it changes and develops with the times that do not favour it… Only by natural genetic changes and our interference in encouraging those changes can this magnificent tree survive, and even this optimistic but premature declaration will have most arboriculturalists and scientists frown with disagreement.