Brighton in Sussex is home to Britain’s largest population of Elm trees. These 19,000 elm trees are known as The National Collection. Elm trees are increasingly rare due to the blight brought by Dutch Elm disease principally in the 1970s. Initially this came into the UK as long ago as 1926. Dutch Elm disease is a fungus carried by beetles and affects only elm trees. In response to this attack, an elm tree will automatically produce tyloses, an effective natural defence against the 1926 strain of Dutch Elm disease. Tyloses occur in the xylem - water conducting vessels of the plant / tree, sealing them off and restricting the movement of the pathogen.
However in the early 1970's, a new strain of Dutch Elm disease was imported from channel ports, linked directly to the Canadian Rock Elm. This strain travels faster through the elm trees and kills them before they can produce tyloses. Since the introduction of this strain of Dutch Elm disease to Britain, the number of elm trees has gone down from about 3 million to fewer than 200,000 and many of these are very young ones which will certainly succumb to the disease. Elm trees reproduce by root stalks more often than by seed and so this transmission mechanism quickly spreads the disease between elm trees and along elm hedgerows.
Brighton’s National Collection of elm trees has been preserved by preventing Dutch Elm disease from getting into Brighton. The South Downs and The English Channel form natural defences across which the disease cannot easily travel. Brighton’s elm trees are most threatened, according to elm tree expert Rob Greenland, from the Chichester planes and from the Shoreham direction. The tracking of beetles using pheromone traps and tactical pruning of infected boughs is used by the council to help stop Dutch Elm disease spreading.
Can elm trees in the rest of Britain survive Dutch Elm disease?
Elm trees can also be protected through chemical treatment, which is effective although expensive. Other techniques such as reproducing elms which are genetically immune to Dutch Elm disease are being developed: one example is the propogation programme of Paul King. The cost of failure is high in terms of biodiversity as Elm trees support a range of other species. For example, the White Letter Hairstreak butterfly and many other species depend on the elm tree for nutrition and survival, and so they too are also in danger as a result of Dutch Elm disease. Aside from biodiversity if the Brighton National Collection were to get infected, Rob Greenland estimates it could cost £20 million in remedial and replanting work to clear up and replace these elms with other species.
Meeting Rob Greenland is an education in the world of elm trees. He is so enthusiastic about elms that his car number plate is R2 ELM. He has a website dedicated to elm trees and even though he is now retired Rob is happy to show people round Brighton’s National Collection.
As he says, ‘’The National Collection in Brighton is like a fortress with heavy stone walls, but all the buildings inside are made of wood in the fight against Dutch Elm disease."