South Mall Campus Master Plan Public Comments

January 12, 2018

Matthew Flis
National Capital Planning Commission
401 9th Street NW
Washington, D.C. 20004

Re: South Mall Campus Master Plan Draft Environmental Impact Statement (EIS)

Dear Matthew Flis,

Casey Trees is a Washington, D.C.-based nonprofit, with a mission “to restore, enhance, and protect the tree canopy of the nation’s capital.” To fulfill this mission, we plant trees; monitor the city’s tree canopy; and work with government officials, developers, and residents to prioritize the District’s trees. We are dedicated to helping D.C. reach its 40 percent tree canopy goal by 2032. As a city, we will achieve this goal when development projects and city plans ensure no net loss in tree canopy. Therefore, we are excited to provide comments on the Draft Environmental Impact Statement (EIS) for the South Mall Campus Master Plan.

The Smithsonian Institution’s (SI) master plan to renovate the south mall campus involves replacing the roof system of the underground Quadrangle Building situated below the Enid A. Haupt Garden (the Garden). The most recent version of the EIS identifies Master Plan Alternatives B, D, and F.

After reviewing all alternatives in detail, we urge the National Capital Planning Commission (NCPC) and SI to select Alternative B as the ideal master plan and adopt the recommendations below:

1. Select Alternative B to Preserve Tree Canopy and Comply with the Federal Comprehensive Plan

Alternative B would replace all existing trees and, in turn, preserve the Garden’s “intimate garden spaces” that SI has committed to maintain after renovation. Alternative B also complies with policy FE.G.2 of the Federal Comprehensive Plan, which states “when tree removal is necessary, trees should be replaced to prevent a net tree loss to the project area.” Specifically, smaller trees with a 10 inch diameter or less must be replaced at a minimum of a one-to-one basis. Larger trees with a diameter greater than 10 inches must be replaced at a rate derived from a formula developed by the International Society of Arboriculture.

2. Adopt A 20% Tree Canopy Goal in the Final Master Plan

Our analysis shows that 20% of the south mall campus is covered by tree canopy today (Figure 1). The EIS is an opportunity to highlight the importance of tree habitat by committing to covering no less than 20% of the south mall with tree canopy post-construction. Today, 35% of the south mall campus is plantable space (Figure 2). A 20% tree canopy will be easily attainable by adopting Alternative B, which strives to maintain the same area of plantable space long term.

Maintaining a 20% tree canopy will also provide a vital connection to the future tree-lined pedestrian corridor along 10th Street SW, established in the Southwest EcoDistrict plan, which will intersect with and lead pedestrians directly to the Garden.

3. Include Trees in All Bioretention Areas

One of the stated goals of the EIS is to establish multiple bioretention areas within the south mall campus. Any bioretention areas designed to manage stormwater runoff should include trees. Trees in bioretention areas further slow stormwater runoff and reduce pollution through interception, evapotranspiration, and nutrient removal. Casey Trees’ Urban Tree Selection Guide can be consulted to select trees that perform best in bioretention areas.

4. Incorporate Four Edits into the Draft EIS

  1. In sections and under “Direct Impacts,” it is noted that Alternatives D and F “may alter the secluded and intimate character” of the Garden, resulting in a “moderate, long-term, adverse impact.” When discussing the intimate character of the Garden – preserved in Alternative B – it should be noted that this secluded nature is created through the use of trees and vegetation, and that removing trees and vegetation, even temporarily, results in a direct, major, long-term, beneficial impact.
  2. Move the “Wildlife and Vegetation” impact topic from section 4.2, which highlights resources eliminated from further analysis, to section 4.3, which covers resources to be included in further analysis. Trees provide their maximum benefits at maturity. For this reason, we also recommend changing the language describing the impact of removing vegetation from “negligible, short-term, direct, adverse” to “major, long-term, direct, adverse.” Removing and reestablishing vegetation is a long-term impact because it will take at least 5-10 years, depending on the tree species selected, for new trees to grow to a comparable level of maturity and supply the same benefits.
  3. Throughout the EIS, it is mentioned that soils will be temporarily displaced. Amend these statements to indicate that both soils and vegetation will be temporarily displaced.
  4. As written in sections and about Alternatives D and F, indirect impacts include changes to the landscape features of the central greensward, which would be mitigated by replanting four rows of elm trees on the National Mall near the Hirshhorn Sculpture Garden. Include a map or detailed description in the EIS to clarify what trees will be replanted and where.

Thank you for the opportunity to comment. Casey Trees would be happy to work with you to provide tree-related analyses for the EIS or become a member of the landscape design task force. If you have any questions about these recommendations, please feel free to contact me at

Kristin Taddei
Planning Advocate

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