Assisting the migration of plants is something that has already been carried out in a limited way to help them respond to climate change. The concern is that some plants are either unable to migrate in response to climate change, due to habitat destruction, or because they will migrate too slowly to keep pace with the changes. Moving them, translocation in the jargon, to areas with a climate that will become increasingly suitable in the future is something we can do to help.

The same idea can be applied to the threat posed by disease. The aim in this case is to move those individuals that appear to have greater resilience to disease to places where disease is yet to become established. This spreads well-adapted genetic traits more rapidly than would happen naturally. This is a solution that works with nature by making use of those plants that have emerged as survivors from the process of natural selection.

Dutch elm disease (Ophiostoma novo-ulmi) has been spreading north since its accidental introduction on infected logs into southern English ports in the late 1960s. The death of elms in vast numbers changed the landscape and had knock on impacts for species that rely on elm. The scale and speed of loss in England, in the 1970s and 1980s, was such that the ongoing northward spread in Scotland has not been given the attention it deserves. During summer 2024 I was told about disease in areas of northern Scotland previously unaffected by the fungus in Assynt on the west coast and at Berriedale on the east coast.

The fungus is a wilt disease as the plants response to infection is to block water-conducting vessels. The result is symptoms of drought and leaves that rapidly turn brown and hang on the tree for several weeks. A tree can go from full health to dead in as little as a month. The symptoms are very distinctive and can be seen in the pictures taken this summer.

The fungus is spread by beetles that have a minimum temperature requirement for flight and as the disease spreads north the number of days warm enough for spread is reduced. Whether the disease will spread rapidly in the new areas it has recently colonised is hard to predict.

The Garden’s Scottish Plant Recovery project includes wych elm (Ulmus glabra) and the approach to recovery has involved crossing trees that have shown resilience to disease. This process is explained in a previous post. The breeding work carried out in spring 2024 has produced over 2,000 seedlings and these will be planted out in spring 2025.

Recently, I visited Glencoe to meet the National Trust for Scotland team that manages this dramatic part of the Scottish Highlands. The glen has remnant populations of wych elm on the more base-rich rocks and soils and is currently free of disease. As elm bark beetles can probably hitch a ride on vehicles, the busy road passing though the glen will increase the risk of Dutch elm disease arriving in the area. Our plan is to plant some of the potentially resilient seedlings near to existing elm populations to establish a new generation of trees that may survive a likely future wave of disease that would probably kill the indigenous elms. Unfortunately, the gloomy prognosis for the Glencoe elms is based on experience elsewhere in Scotland.

The planted elms will be the same species but not the local genetic stock, although some local seedlings will be part of the planting mix. Our search for resilience has focussed on those parts of southern Scotland that have the longest history of infection. Inevitably, planting will alter the genetic makeup of the Glencoe elm population, but for good reason. To do nothing risks the near total loss of the Glencoe elms if disease does arrive, as seems very likely. Intervention like this is not done on a whim and the pros and cons have been weighed. In this case, the severe impact of disease is such that moving elms around Scotland seems an acceptable response that we hope will assist recovery.

In Assynt the community is getting involved in an elm and disease awareness campaign. On the 14 December 2024 the Culag Community Woodland Trust is running a public charcoal burning session to share elm stories and the latest news on disease reported for the first time in 2024. The focus is on what individuals can do to help. Early reporting of disease is something anyone can do and the pictures in this post will help people know what to look for. Understanding how the disease can be spread accidentally on chainsaws that have not been properly cleaned between uses is another simple message that needs to be communicated. Some of the Assynt cases may have arisen in this way through poor tree surgery practice.

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Acknowledgement: The two images of the tree at Lochinver were kindly supplied by Chris Puddephatt who has completed a year-long photographic project to document the elms of Assynt. Chris’ work is available online here.