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Researchers cross-breed elms to resist disease

Photo: Two men, one in uniform, stand in field of young trees. One holds large syringe.
Research biologist and project leader Jim Slavicek (left) of the Northern Research Station and Deer River District Ranger Chad Kirschbaum of the Chippewa National Forest prepare to inoculate an American elm tree as part of a long-term study on the forest. Forest Service photo by Scott Farley.

Three research plots, established by Northern Research Station scientists and carefully tended by Chippewa National Forest staff for nearly a decade, will be instrumental in restoring American elm to Minnesota forests.

Scientists Jim Slavicek and Charlie Flower worked with forest crews to inoculate 1,200 American elm trees with Dutch elm disease June 13–15. In eight weeks, Slavicek and Flower will return to the forest to evaluate the trees for signs of Dutch elm disease. Next spring they will return for a final analysis of which trees survived both Dutch elm disease and winter temperatures. Trees that do not display sufficient disease and cold tolerance will be culled, leaving the forest with a seed orchard that can be used for reforestation projects.

Slavicek and scientists at the station’s lab in Delaware, Ohio, propagated the trees by crossing “surviving elm” (American elm trees that have been exposed to Dutch elm disease and survived) from the Chippewa National Forest with a few of the strains of disease-resistant American elm that have been developed. Forest staff installed exclosure fences around the plots to prevent damage from deer browse and over the years have maintained the elm plantations by hand-pulling weeds and mowing the grass to reduce damage from rodents.

Until Dutch elm disease eliminated virtually all mature trees, American elm was an important part of hardwood forests and urban landscapes throughout the eastern United States. The research collaboration with Chippewa National Forest is part of a larger Forest Service effort to create enough genetic diversity in Dutch elm disease-resistant American elm so that the tree can be successfully restored in forests and cities throughout its native range. Learn more about American elm research on Chippewa National Forest on Northern Research Station’s website.