The range of the iconic American elm, Ulmus americana, spans across the eastern United States, from Texas to Florida, Maine to North Dakota, and in parts of seven Canadian provinces. Before the arrival of the non-native Dutch elm disease, American elms provided benefits to wildlife and people alike. In the spring, elm seed served as a source of food for mice, squirrels, opossum, and many migratory bird species. Elms also provided thermal cover and nesting sites for a variety of cavity-nesting birds.
American elm’s tall height coupled with its vase-like shape offered a uniquely graceful tree that was historically planted along city streets and boulevards, delivering the benefits of cleaner air and cooler temperatures. Indeed, one large American elm located on the southern side of a home can intercept 2,384 gallons of storm water, conserve 107 kWh of energy, and sequester 518 pounds of CO2 annually.
A fungal disease affecting elms was first described in 1919 in the Netherlands, and was therefore named Dutch elm disease (DED). From this initial outbreak, DED spread rapidly throughout Europe and, by 1934, was found across the continent. The disease, which entered the United States on European shipments of unpeeled veneer logs, was first observed in Ohio in 1930. By 1976 only 34 million of the estimated 77 million elms present in urban locations remained, and far fewer are present today – making DED one of the most commonly known and destructive tree diseases in the world.
Research on American elm from the 1970s to the present has focused in large part on the identification of American elm individuals that can withstand the DED pathogen. Of the over 100,000 American elm trees tested for resistance to DED, fewer than a dozen have exhibited adequate levels of DED tolerance. This narrow genetic pool makes American elm vulnerable to other diseases as well as potential changes in the DED fungus itself. Therefore, to increase American elm’s long-term recovery as a canopy tree, it is crucial to increase the genetic variation of tolerant elms available for planting in urban and rural settings.
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Support our Research
Researchers at the Northern Research Station would like to expand current efforts to screen American elm trees that may be tolerant or resistant to Dutch elm disease (DED). To facilitate this effort we are asking for the help of state foresters, park employees, and the interested public to identify large American elm trees on their landscapes.