The Nature Conservancy (TNC) and the United States Forest Service (USFS), along with many other partners, have been working to restore the American Elm (Ulmus americana) to its historical range and prominence on the landscape. NorthWoods has been fortunate to collaborate on this work in Vermont. The focus is on creating a genetically diverse population that is resistant to Dutch Elm Disease. Dutch Elm Disease (DED), which made its way to the US in the 1930s, has decimated elm populations across the country. While some of us may have seen these once majestic trees preserved in urban settings, their true place in the landscape is on the riparian floodplains from the midwest to the east coast. This tree has played an important ecological role in keeping our water clean, mitigating flood intensity, and hosting many important species of wildlife. In its absence, no other tree has managed to fill this ecological niche, leaving these landscapes at risk of colonization by invasive species, more consequential flooding, and loss of ecological diversity.

Trees in the environment referred to as “survivor trees” have shown a natural resistance to DED. This project has focused on locating these individuals and testing their clones and progeny for resistance to DED. There are two types of plantings being done as a part of this project. A few larger plantings, referred to as tolerance trials, include thousands of trees that will be inoculated with DED to test the resistance of specific crosses of Ulmus americana. Multiple smaller restoration sites across the northeast will not be inoculated with DED, but their resistance to the levels of DED in the environment will be assessed through canopy die-back and tree health.

NorthWoods has been working at one of the large sites in Northern Vermont along the Connecticut River with TNC since 2015 to prepare for planting, plant trees, and work to monitor their health. The trees planted at this site are the progeny of 26 individual survivor elms that were found growing in Vermont. Early this April, a group of staff from NorthWoods, along with TNC Conservation Planner Gus Goodwin, returned to the site to prune trees in preparation for their upcoming inoculation.

For the purposes of this trial, the trees will have DED introduced to ensure their resulting resistance can be accurately monitored. Pruning is an important step prior to inoculation as it creates a single trunk at least 4.5’ in height where the inoculant will be introduced and have the best chance of reaching the canopy of the maturing tree. The trees that NorthWoods staff pruned will be inoculated in 2024. As they mature, their level of resistance to DED will become clear, and crosses that do well can be used in riparian restoration projects moving forward.