Restoration of the American elm in forested landscapes in the state of Delaware

Collaborators: Vince D’Amico (Forest Service NRS-04), Judy Hough-Goldstein (University of Delaware), Ellen Lake (Ph.D. candidate, University of Delaware).

The American elm was once widely distributed throughout the eastern United States and was a preferred tree for use along city streets and in the yards of many homeowners. The Dutch elm disease (DED) fungal pathogen Ophiostoma ulmi was introduced into the United States in 1930 and in the subsequent years has destroyed millions of American elm trees in the United States and Canada. By 1976 only 34 million of the estimated 77 million elms present in urban locations before introduction of the DED pathogen remained, and far fewer are still present today. Research on the American elm from the 1970s to present focused on the identification of American elm isolates that could withstand the DED pathogen. Over 100,000 American elm trees were tested for resistance to Dutch elm disease. No trees were found that were resistant to DED; however, a few were identified that exhibited good levels of tolerance to the disease. Five of these selections, the Valley Forge, Princeton, New Harmony, R18-2, and Delaware-2, will be used for the restoration effort in Delaware. Ten restoration plots consisting of 6 trees of each of the 5 selections, for a total of 300 trees will be established at locations near Newark, Centerville, and Middletown, Delaware. These plots are located in areas where the trees will be allowed to propagate, evolve, and develop mechanisms that can withstand new forms of the DED fungus. This project will ensure the retention of the American elm in forested landscapes and will provide future trees that are tolerant to new forms of DED for use in urban settings.