In April 2018, the Cornell Urban Horticulture Institute team of Nina Bassuk, Bryan Denig, Yoshiki Harada, and Barbara Neal released an extensive report on the elms (including American elms) of the National Mall in Washington, D.C. The report details a study conducted at the request of the National Park Service to examine the current conditions of the trees and soils on the tree panels of the National Mall, and it includes a fascinating history of the landscape. Here are some highlights from the report.
The National Mall elm trees are an important planting in the monumental core, yet they face several challenges. The soils of the tree panels are very compacted, most likely due to the constant pedestrian use and the numerous large organized events that take place on the Mall. Unevenness in the size and distribution of the tree canopy has resulted from decades of mortality (often due to Dutch Elm Disease) and the planting of certain elm varieties with growth forms that are seen as incompatible with the planting as a whole.
From June 17–20, 2017, the research team conducted a tree inventory and collected soil data and samples for later analysis. In addition, in November 2017, ground penetrating radar done by Council member Gary Raffel was used to document root growth for seventeen of the trees. This report deals with the current tree and soil conditions, while management recommendations are in a separate report to be released in late 2018 or early 2019.