In April 2018, the 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 land-
scape. 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 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.
Study Objectives
• To examine each elm tree on the National
Mall for health and risk assessment
according to the International Society
of Arboriculture Level 2 protocol.
• To sample soils associated with the
elms and analyze their physical, chem-
ical, and biological characteristics
• To summarize opportunities and chal-
lenges to elm management based on
tree assessment and soil analysis
>>
From left: Barbara Neal, Bryan Denig, and Nina Bassuk assess the health of
one of the iconic elms ringing the National Mall. Photo by Yoshiki Harada
The Urban Horticulture Institute
Team Evaluates Condition of
National Mall Elms
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