What Does it Take to Protect the 20,000+ Trees on the National Mall?

The cherry trees on the National Mall are a beloved cultural symbol and annual destination that draw in visitors from around the world to our nation’s capital. Living symbols of friendship and diplomacy, the trees have adorned the National Mall waterfront since 1912, when the Mayor of Tokyo gifted cherry trees to the United States. The pink and white blossoms are a symbol of Spring, renewal, hope, beauty, and the lasting international friendship between the United States and Japan.

The care of these trees, however, lasts much longer than their 2–3-week bloom season. The National Mall and Memorial Parks (NAMA) Division of the National Park Service employs a small team to ensure the health of the trees on the National Mall. The Trust for the National Mall interviewed Supervisory Arborist for National Mall and Memorial Parks, Matthew Morrison, along with his arborist crew, to learn how this small team cares for the nearly 4,000 cherry trees and more than 20,000+ trees on the 1,100 acres making up National Mall and Memorial Parks.

Year-Round Root-to-Branch Care

Morrison emphasizes the need to care for the entire tree, from the roots to the canopy, and he has implemented new practices of year-round care on the National Mall to do just that.

The cherry trees always receive massive public attention beginning in March as we anxiously await their iconic blossoms. Four months earlier, however, the NAMA arborist team is already planning how quickly they can get to work preparing the trees for bloom season.

"Always, we prefer to start earlier. We’re always in a crunch up to cherry blossoms,” says NAMA arborist Patrick Quin, “We have to balance care of the cherry trees with the care of more than 20,000 other trees around the National Mall.”

Compacted soil and exposed tree roots around the Tidal Basin render our cherry blossom trees stressed and in various stages of decline.

The pruning process can begin as early as November and continue up to the time of bloom. This process involves removing dead, diseased, or damaged wood as well as any branches that pose a safety threat to visitors. Using a variety of tools, including hand snips, hand saws, pole saws, and chain saws, the arborists use scientifically based arboricultural practices to ensure the tree can effectively heal after the cuts are made.

Once bloom season is over, the arborist team surveys the health of the cherry trees throughout the park. The team collects tree tissue and soil samples from trees that are damaged to take to plant pathology labs, where they analyze what is ailing the tree and what can be done to fix it.

Compacted soil and exposed tree roots around the Tidal Basin render our cherry blossom trees stressed and in various stages of decline.

“NAMA sees approximately 25 million visitors annually; that is more than the Grand Canyon, Yosemite, and Yellowstone combined,” says Morrison, “the foot-traffic alone has a terrible compacting effect on the critical root zones of our trees, on the turf, and on the soils, not to mention the equipment used to keep the park clean and healthy.”

He continues, “Compacted soils are a problem in our park. With constant foot traffic, the roots of the cheery trees become exposed, risking continuous damage that prevents the tree from ever healing.”

Since Matthew Morrison joined the NAMA team in September 2019, he has been a revolutionary force in reforming tree care on the National Mall. As Morrison himself states, “These trees are now receiving the best care that they’ve received, quite possibly, in their lives.”

One of the new practices that Morrison implemented for the park’s cherry trees is blanketing the root systems in hundreds of cubic yards of in-house generated wood chips to protect soil and tree roots around the most heavily trafficked areas of the Tidal Basin.

Morrison and his team began the wood chip program to protect the cherry trees during pre and post degradation; “The soil from which our cherry trees grow require access to air so that the roots may respire or breathe … Wood chips are the byproduct of our tree work. Using them on site negates the carbon footprint and expense of hauling them off campus.”

The NAMA tree crew uses ground protection mats for conveying and staging trucks during off-road use to protect turf, soil, and tree roots.

The wood chips provide several benefits to the tree, including:

Cushioning the soil to prevent soil compaction around the tree roots.
Coarse texture of the solid chip allows air to enter the tree’s growing media.
Insulating the roots, providing a more consistent temperature through extreme heat and cold.
Retaining moisture in the soil to keep it soft and habitable.
Provide nutrients and oxygen to the soil, benefitting the health and growth of the trees.
Removing the need of lawnmowers, weed cutters, and herbicides which harm the trees.

Morrison says that all of the benefits that the wood chips provide “make the overhead canopy of the tree really prosper, and we see that the buds swell beautifully, leaf development is great, growth is great, and for the first time in these trees’ history they are now really thriving and doing better than they ever have before.”

The team is also actively working to acquire equipment with “flotation” tires, which do not have the damaging effects on soil and tree roots as traditional maintenance vehicles. NAMA holds its tree work contractors to the same standards as the in-house Arborist Team, requiring all turf, soil, and tree roots to be protected from compaction caused by trucks and equipment of typical highway tires.

The Best Care Possible

Matthew and his team additionally focus on the importance of “education and strenuous work” to mediate the problems that have historically plagued the trees on the National Mall. For the first time since the cherries were planted on the Mall, they are being cared for in a way that is backed by science and best arboricultural practices.

“Historically, we have had partnership groups and other volunteers help our tree crew prune our world-famous cherry trees, however, the parasitic effect caused by uneducated, enthusiastic, good-natured, volunteers have proven to have an ill effect on this otherwise stressed stand of nearly 4,000 cherry trees. Incorporating knowledge of basic tree biology, tree anatomy and proper pruning procedures ensures the current cherry tree pruning operation is arguably the best in our the park’s history.”

Advancement in Technology for the National Mall

Technology plays a key role in protecting the natural resources on the National Mall, but it is also used to protect park visitors. The Arborist team employs a Geographic Information System (GIS) to hold all records of man-made variables in the National Mall and Memorial Park system;  for example, park benches and playgrounds. The GIS has been adopted by the  Arborist  team  to log all trees and record natural variables. 

Matthew explains the value of utilizing GIS for multiple purposes of park record-keeping:

“Every single tree logged into our GIS system and that we have accurate data documenting each tree including an identifying photo, hazard analysis, field notes, health and safety concerns [as a] form  of mitigation and a level of urgency. These data entries combined with budget and cyclic monitoring information are at the nucleus of the decisions I make that keep the park visitors safe and the trees healthy… As sappy as it may sound, my mission is that all our workers and visitors go home as healthy as they arrived and that we leave a good healthy park as a legacy for future generations to come. “ 

Why are the Cherry Trees Worth Preserving?

Morrison says that in caring for the trees, “I love more than anything else leaving a positive effect on these trees and leaving a legacy for future generations. I’m leaving these trees for them in as good a shape as I can.”

Arborist Patrick Quin says the one thing he’d like to ask of visitors is that they do their part in protecting the trees: “They’re here for everybody to enjoy, but please stay off of them.”

“What may seem harmless can cause a lot of work,” Arborist Kevin Freeman says, “Folks pull off branches for flowers, and we have to go back and fix those breaks in the tree every year. Your number one responsibility in caring for the trees is ensuring you don't cause more damage.”

Quin also shares that he thinks the cherry trees are worth protecting because “it’s a whole landscape. This is what the National Mall is; it's all about the cherry trees. They’re a gift from afar and we’d like to maintain that gift.”