A Tree Walk with Rob DeFeo

On September 27, 2011, a large group of foresters and a few lucky tourists gathered outside the metro; some balanced sandwiches and notebooks, others chatted together expectantly. In the middle of our group was Robert DeFeo, ready to share his wealth of information with us. Rob DeFeo is the Chief Horticulturist of the National Capitol Area of the National Park Service. As part of his job, Rob is responsible for the health and well - being of more than 18,000 trees within the National Mall and Memorial Parks.

Our tree tour took us first to a Jefferson Elm near the Smithsonian castle, which was planted around 1930 and is remarkable for its unusually high tolerance to Dutch Elm Disease. An extra chromosome in its DNA makes the Jefferson Elm tolerant –so tolerant that geneticists are searching wild plants for the extra chromosome in order to continue breeding tolerance to Dutch Elm Disease. For us in the forestry community, it comes as no surprise that much of the work Rob does on the National Mall is geared toward preventing and treating Dutch Elm Disease. Rob has a

dedicated staff that, with well-trained eyes, can catch Dutch Elm Disease before it affects a critical 10% of the tree’s canopy and often before it reaches a threshold of 5%. The affected part of the canopy is removed by pruning and the tree is treated with Alamo.

One SAF member, Eric Norland, was very appreciative of the opportunity to learn more about the trees, ―What a great program. The elms on the Mall are a national treasure and the National Park Service arborists are doing a tremendous job in keeping these trees healthy and monitoring for Dutch Elm Disease.

Genetic diversity is one of the first lines of defense against the disease. Of the 3,000 elms around the National Mall, half are Dutch Elm Disease-tolerant cultivars, and no more than 10% are the same cultivar, ensuring a certain amount of genetic diversity in the population. But the young nursery stock often leave a bit to be desired in terms of branching form, and many never grow into the gnarled, reaching specimens that Frederick Law Olmstead had in mind. Proper pruning early in their lives can give the young trees nicer structure over time and helps prevent damage from storms or age.

As our group of 35 made its way along the Mall, participants swapped tree stories and introduced themselves to one another. Old friends and new chatted about their experiences with tree disease, pruning, and success stories. Many of our group were first timers to the SAF Luncheon scene. Karl Dalla Rosa said, ―Who wouldn’t take advantage of an opportunity to spend lunchtime walking with a bunch of foresters on the National Mall, learning more about our urban forestry heritage?

It is clear from our tree walk that Rob has forgotten more about Elm trees than most of us could hope to know, and so it was reluctantly that we left the National Mall and proceeded to the tidal basin, where the famous Cherry trees beckoned. The original Japanese Cherry trees were a gift from the city of Tokyo to the people of Washington in 1910, but a sweeping disease left the original gift decimated and a new shipment arrived in 1912. Some of these 1912 trees are still living and have survived a century of Washington tourists.

Fred Blott said, ―The walk provided a real appreciation for the dedication and efforts of Rob’s staff of eight arborists who personally tend to the cherry trees throughout the year and ensure their continued survival in a very challenging environment.

Beginning at 15th street, we followed the edge of the tidal basin, ducking under aged limbs and admiring twisted branches. Not everyone delights in the splendor of the low twisting cherry limbs, however, as Americans with Disabilities Act lawyers have a perennial request that the branches be cut to provide clearance to 7 feet.

On the other side of the bridge, we left the busy street side and again ducked under twisting branches where we found the stone lantern that was gifted with the cherry trees one hundred years ago. Here were some of the oldest of the cherry trees, an entire grove of centurions. These are the trees Rob is most concerned about. They have survived up to now by the good luck of being tucked away from the most popular spots, away from monuments. Keith Cline, Urban and Community Forestry Program Manager at the Forest Service said, ―Rob and his staff of certified arborists do an impressive job of fine pruning and caring for the health of these historic cherry trees.

With the opening of the Martin Luther King, Jr. Memorial, however, the protected site of the grove has changed. Already, we could hear voices and movement just steps from the grove. Rob says he expects foot traffic around the trees to increase significantly, tamping down the soil and impacting the trees’ roots. Along the National Mall, the soil around the elms has the density of cinder block and the sturdy trees were selected, in part, for just such an inevitability. But what will happen to these cherry trees if the soil here became similarly compacted? While we may not be able to predict the future of the cherry trees, we can be sure of one thing: Rob and his team will continue to give their all for the protection of the magnificent trees that make our National capital parks what they are.

—Paula Randler—