Elm trees on the Isle of Man saved by bad weather!

Dutch Elm at Ballachrink, Isle of Man
Image: P. Davey

A paper published in the latest issue of New Journal of Botany suggests that thousands of healthy elm trees on the Isle of Man have avoided infection by Dutch elm disease thanks to the island's weather being too cold and windy for the pathogen to take hold. 

The island has an estimated 300,000 elms and only around one per cent of them have been lost to Dutch elm disease since the fungal pathogen was first noticed on the Island in 1992. This is a very different picture from that seen on the British mainland, where the disease has eradicated between 25-75 million trees since the 1970s.

Dutch Elm (top), English Elm (below)
Image: M. Coleman

Dr Max Coleman of the Royal Botanic Garden Edinburgh was the lead author on the paper and said "The weather appears to be the key to understanding the remarkable survival of these elms thanks to the way it controls dispersal of the beetles that spread disease. Dutch elm disease is a fungus that hitchhikes on the bodies of tiny elm bark beetles and is completely reliant on them to get from tree to tree. These beetles are fairly harmless to the tree on their own. However, when they are covered in spores of the deadly fungus they can potentially infect healthy trees.

“We know the beetles need a temperature of at least 20 degrees to fly and if wind speed exceeds five metres per second flight is inhibited. By analysing local weather data from 1995 to 2015 we found that only one year out of 20 could be regarded as a good year for the beetles and the disease to spread".

The findings of the research have major implications for the future of elms on the Isle of Man. Dr Philippa Tomlinson, BSBI County Recorder for the Isle of Man and of Manx Biodiversity, the partnership organisation that provides a biological records service to the Isle of Man Government, said: "Understanding that the island's elms are likely to be just as vulnerable as elms elsewhere highlights the importance of measures to control Dutch elm disease. Although the cooler and windier conditions experienced on the Isle of Man appear to have kept disease at bay, this cannot be relied upon in the future with the uncertainties of climate change."

Dutch Elm, East Baldwin Valley,
 Isle of Man
Image: P. Davey

Ian Denholm, Editor-in-Chief of New Journal of Botany, concluded: “Combining research on elm genetics with consideration of beetle ecology has led to a convincing and elegant explanation of why the spread of disease has been constrained in the Isle of Man compared with much of the UK. Such inter-disciplinary studies highlight the extreme importance of understanding how climate affects interactions between organisms as well as its impact on individual species. 

"Elms are a complex group; unambiguous identification of types present also helps ensure the accuracy of BSBI’s database of plant records encompassing the whole of Britain, Ireland, Isle of Man and the Channel Islands.”.

New Journal of Botany is usually only available to BSBI members and institutional subscribers - it is one of the perks of membership! - but our publishers, Taylor & Francis, have kindly made this paper available to everybody until the end of March. Just click here to read the paper.