An invasive species was making news last week in PEI after the City of Charlottetown announced that it would be removing over 300 elm trees (over half of the elms in the city) from its streetscape. The trees are being removed to prevent the further spread of Dutch Elm Disease.
Dutch Elm Disease (DED) is an introduced, fungal disease caused by a vascular wilt fungus (Ophiostoma ulmi). DED affects the conductive tissues of trees. Conductive tissues in trees are like human veins. They carry water, minerals, amino acids and sugars to every part of the tree, like our veins carry blood. Without the flow of these liquids, diseased trees begin to wilt and eventually die.
DED is spread through several pathways: by the movement of wood from diseased trees, through the trees’ root systems, and by bark beetles. Bark beetles burrow into dying elm trees to reproduce in the fall, and remain there for the winter. In spring, the beetles go in search of healthy elm trees to feed on, carrying Ophiostoma ulmi spores with them and further spreading DED.
Ophiostoma ulmi was introduced to North America in the 1930s as a result of a shipment of lumber that was carrying the fungus. DED made it to Eastern Canada in 1940. It was first recorded in PEI in the late 1970s, and first discovered in Charlottetown in 1996. Since then, the disease has continued to spread. Today, 323 of Charlottetown’s 583 elms are diseased.
DED is an issue across Canada, except in BC and Alberta where the disease is absent. Montreal streets were once home to over 32,000 elms. Today only a few remain, as a result of DED. Montreal is taking a similar approach to Charlottetown and is aggressively protecting its remaining healthy elms by taking down diseased trees.
Charlottetown’s plan is to remove the elms by the end of April, when the bark beetles are still dormant. Removing diseased trees will give the remaining elm trees a chance at surviving. The city will continue to monitor the remaining elm trees for signs of disease and take appropriate action if needed.
With the removal of over 300 large trees, there is no doubt that our cityscape will change. Cityscapes across this whole continent have changed… All because of a fungus that hitched a ride on some lumber almost one hundred years ago. It certainly makes a case for us to be more careful in our own lives. A plant, animal or disease that we introduce into our environments, whether intentionally or accidentally, may create unimaginable, unintended consequences in the future.
For more information on Dutch Elm Disease, check out the following links: