Eighty-eight American elms now line the long block of Pennsylvania Avenue in front of the White House. Even in their youthful state, and awaiting spring leaf growth, these trees symbolize the rebirth of America's Main Street after a decade of security-driven restrictions and barriers.
But they also mark the return of a great American tree. The elm, in precipitous decline in recent decades, was once the quintessential civic tree of city and hamlet alike, rising to 100 feet, vase-shaped and coming together from both sides of a street to form a protective arch over the communities it shaded.
A 20-foot Princeton elm moved by crane to its own tree box on Pennsylvania Avenue.
(Bill O'Leary -- The Washington Post)
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"It's really the most popular and loved tree," said Dan Smith of the Casey Trees Endowment Fund, "so its loss had strong emotional impact."
Dutch elm disease, a blight carried by a burrowing beetle, arrived in the 1930s and spread throughout the land, decimating elms in parks, streets, campuses and gardens. Only diligent care has kept old specimens alive. The urban landscape changed, and the substitutes -- Norway maples, zelkovas and honeylocusts among them -- could never attain the elm's toughness, stature or magic.
But as the new White House elms attest, a handful of disease-tolerant specimens emerged, some by serendipity, others through single-minded research.
None is immune to the disease, but they cope with it, especially with good care. Thus the American elm once more is a choice not only for stewards of public spaces, but in home gardens with enough room -- as an avenue, perhaps, leading to a large suburban lot, or to mark a point of transition in the landscape.
The elms grow fast and, in maturity, provide the best kind of sun-screening for woodland bulbs, perennials, shrubs and small trees growing below -- shade that is high and dappled.
The variety planted now along Pennsylvania Avenue is called Princeton and has been around the longest. It was a seedling bred in the 1920s by William Flemer Jr., owner of Princeton Nurseries in New Jersey. Flemer's selection turned out to be one in a million -- actually, one in tens of millions -- and it survives, famously, as a 75-year-old row of elms along Washington Road in Princeton.
More recently, at the Agricultural Research Service's test fields in Glenn Dale, Md., Alden Townsend headed a small team of scientists who spent much of their careers developing resistant elms. Townsend, who retired in January, introduced two varieties 10 years ago that had superior tolerance, one named Valley Forge, the other New Harmony.
The National Park Service recently released another, named Jefferson, cloned from a survivor on Jefferson Drive S.W. near the Freer Gallery of Art. It won't be available to consumers for another four or five years, said James Sherald, chief of natural resources and science for the Park Service's National Capital Region. He called its form "as classic as can be."
For the Pennsylvania Avenue plantings, a committee of Park Service horticulturists picked the Princeton variety, based on its long track record, upright habit and availability. Townsend, in an interview, concedes that his most disease-resistant selection, Valley Forge, is not as classically formed as Princeton. He is not disappointed that Valley Forge or New Harmony was not chosen -- "Our job is to do the science, not push a product" -- though he says it is important that cities not plant Princeton alone. "I think a mixture of clones is the best idea," to avoid a future disaster by planting only one type, he said.
Townsend co-wrote a scientific paper published in the March issue of the Journal of Environmental Horticulture that reiterated the value of certain varieties and revealed new ones that show promising tolerance to the disease.
On most American elms, the fungus spreads through the tree's vascular system, clogging and killing limbs and, eventually, the trunk. Tolerant varieties still get the disease but are able to build internal walls that prevent it from spreading.
The research team inoculated a number of nine-year-old American elms with the disease. In one key measure -- of dieback in the crown of the tree after two years -- Valley Forge, Princeton and Jefferson showed no symptoms. Two unnamed clones suffered just 1 percent dieback, and five others, including New Harmony, suffered 8 percent or less.
A standard American elm, used as a control, had 42 percent dieback, according to the report, which Townsend wrote with Susan Bentz, a horticulturist at the Agricultural Research Service, and Larry Douglass, professor of biostatistics at the University of Maryland.
Surviving old trees are kept alive by pruning out diseased branches and injecting with a systemic fungicide. Of the 106,000 street trees in the District of Columbia in 2002, 8,588 were American elms, according to Casey Trees. Approximately 250 of the elms die each year, though. Casey Trees was established four years ago with a $50 million endowment from local philanthropist Betty Brown Casey to save the city's ailing urban forest. "Washington probably has the largest and healthiest population of elms in the country," said Smith, the group's spokesman.
Working with community volunteers, the organization has planted almost 600 Princeton elms over the past two years in various neighborhoods across the city to replace elms that had died.
The White House block of Pennsylvania Avenue was closed for most of 2004 while workers removed concrete barriers and other security structures, replaced them with new guardhouses, and rebuilt the road surface and sidewalks as a pedestrian boulevard. The street opened to pedestrians last November, and the elms were craned in this month to their tree wells, set opposite each other so the elms will form their classic arch. They replace a planting of willow oaks.
The elm trunks are four to five inches across (at the garden center, a two-inch caliper is considered a stout young tree). The five-year-old elms now stand 20 feet high and were raised by Roger Holloway of Riveredge Farms, a nursery based in Atlanta.
Needless to say, he is the Princeton's fiercest champion, noting that it has not only survived the longest of the tolerant varieties, but was chosen for its beauty, not its disease resistance. It is more upright in habit than the standard species, making it easier for street-tree crews to maintain. He started raising Princeton elms in 1997 and has seen public interest grow alongside the saplings. "There's no other tree in our country that seems to stir up so much passion," he said.
Sources:
Riveredge Farms, Atlanta. Princeton elm: trees, 2 1/2 to 4 feet, $39.95; 5 to 6 feet, 59.95; 6 feet, $89.95. Shipping extra. Larger sizes are available through retail nurseries. Call 888-680-1922, or click on www.americanelm.com.
Botany Shop, Joplin, Mo. Princeton elm: sizes range from 18 inches to 6 1/2 feet, priced from $30 to $125, shipping included. Valley Forge and New Harmony: 3 to 4 feet, $50; 6 1/2 feet, $95. Call 888-855-3300, or click on www.botanyshop.com.
