National Air & Space Museum Environmental Assessment Comments

May 1, 2017

Vivian Lee
Urban Planner
National Capital Planning Commission

Jane Passman
Senior Facilities Master Planner
Office of Facilities Engineering and Operations Smithsonian Institution

RE: National Air & Space Museum Environmental Assessment

Dear Vivian Lee and Jane Passman,

Casey Trees is a Washington, DC-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 decision makers, developers, and residents to encourage tree planting and protection on both public and private property. We are dedicated to helping the District reach a 40 percent tree canopy goal by 2032. As a city, we will achieve this goal when development projects achieve a net gain in tree canopy. We are excited to work with Smithsonian Institution (SI) and the National Capital Planning Commission (NCPC) to ensure that trees are prioritized in the renovation of the National Air & Space Museum on the National Mall.

Today, the National Air & Space Museum is surrounded by a diverse palette of trees. We applaud SI and NCPC for proposing a landscaping plan that improves visitor access to trees, includes new shade trees in the northwest and southwest sections, and protects the grove of trees north of the Delta Solar sculpture.

It is crucial that the museum’s tree canopy is maintained so there is no net loss in tree canopy after the renovation. The tree canopy that shades the museum today provides comfortable spaces for visitors and essential ecosystem services by managing stormwater and filtering air in bustling downtown DC. To create the best possible visitor experience, we recommend the following:

1. Replace the tree canopy lost during construction: The National Air and Space Museum is home to approximately 250 trees. These trees provide a lush, shady space for visitors. To maintain the environmental benefits associated with the museum’s extensive tree canopy, provide adequate tree protection fencing around the grove of trees north of the Delta Solar sculpture, plant shade trees in all planting beds with at least 1,000 cubic feet of soil, and replace lost trees in at least a 1:1 ratio.

2. Create a larger planting bed near the north entrance: Expand the 5’3” planting bed in the north entrance section into the space designated as a 12′ walkway to its south. This will still allow SI and NCPC to increase the number of walkways from two to three, while providing additional space to plant trees that will offer shade to visitors and passersby (Figure 1).

3. Plant a diverse tree palette: Increase tree diversity that exists at the museum today. With approximately 25 tree species on site, the museum is close to achieving the 10-20-30 rule for tree diversity: include only 10% of any one species, 20% of any one genus, and 30% of any family of trees. Consider working with Casey Trees to establish a planting plan or reference our Urban Tree Selection Guide to identify trees ideal for achieving the 10-20-30 rule.

Thank you for the opportunity to comment. Casey Trees would be happy to work with you to provide tree-related analyses for the National Air & Space Museum renovation. If you have any questions about these recommendations, please feel free to contact me at

Kristin Taddei

Figure 1. Section of the proposed north entrance with the 5’3″ planting bed and 12′ walkway highlighted.

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