If one were given God-like powers to create the perfect street tree, the result would likely be the American elm. As one observer noted, it is “the ultimate in arboreal elegance and grace.” As a sapling, it maintains a narrow profile, its branches not impinging on street or sidewalk. But as it grows, it radiates into a vase shape, eventually arching into cathedral splendor. This amazing tree is also fast-growing, long-lived, and can withstand air pollution, soil compaction, drought, flooding, and even deicing salts. And to top it all off, it produces no big seeds and very little leaf litter. No wonder that in towns and cities across the US in the early 20th century, fully 75 percent of street trees were elms, and “Elm” streets were ubiquitous....That is, until eco-disaster struck in the form of a lethal fungus, spread by bark beetles, that began invading these trees’ vascular systems, killing them in the millions.

Adding to the Woes of the Great Depression

Fortuitously, when the original Glen Ridge Shade Tree Commission was established in 1910 and given the mandate to plant along the streets of the rapidly developing borough, elm trees were experiencing a fluke upsurge of bark beetle infestation. To be clear, these insects were not carrying DED. However, they did bore into the tree to eat its tissue and could infect the tree with other types of fungi, albeit not as lethal as DED.

Consequently, the Commission chose London planetrees and pin oaks over elms during the crucial next few years. There were, however, over 500 public elm trees scattered around town. During the next 5 decades, almost all of these died of DED. Four survivor elms remain, one in front of RAS and three on the municipal lawn across the street. Presumably, they had some natural immunity when they were young. But at this point, they are treated on a regular basis to prevent DED.

Coming out of World War II there was a sense that all problems could be dealt with through innovation and chemistry. During the war, a synthetic insecticide, DDT, had been used to fight the spread of typhus and malaria in the South Pacific. So, even though it had never been properly tested for its environmental or human impact or its effectiveness against bark beetles, DDT became the “major weapon” against DED, beginning in 1946. Not only was it sprayed on street trees, but also, indiscriminately from airplanes, on forests containing elm trees. 

In 1962, Rachel Carson’s blockbuster book, Silent Spring, blew the lid off the eco-catastrophe that DDT had wrought. As she pointed out, it took only 11 earthworms that had fed on leaves made toxic by DDT to kill a bird. “It would be tragic to lose the elms,” she concluded, “but it would be doubly tragic if, in vain efforts to save them, we plunge vast segments of our bird population into the night of extinction.” Why were these efforts in vain? Turns out the DDT had virtually no effect on bark beetles. 



Further studies showed that DDT persisted in the environment for 10 to 15 years after exposure. It has also been connected to human cancers. It was finally banned in the US in 1972. By that time, over 75 million elms had succumbed to DED, and it had made its way to California.

The DED-Resistant Elm Crusade

It is hard to exaggerate the public determination to eradicate DED and bring back the American elm. No substitutes would do. As one observer noted, “no single tree, including all the modern elm hybrids [Asian elms] has the positive architectural qualities and the environmental flexibility” of the American elm. From the start, however, it was noticed that certain native elm trees appeared to have a natural immunity, or at least a reduced susceptibility, to DED. Ultimately, these trees provided the germplasm necessary to develop DED-resistant trees.

Of the 600 elms planted on the National Mall in Washington, DC, in the 1930s, one survived -- the Jefferson elm.

As early as 1937, the US Department of Agriculture (USDA) began spraying saplings cloned from these survivor trees with heavy doses of fungus with the plan to further breed those that survived. As promising as these efforts might have been, they were aborted due to war. 

The gauntlet was again taken up in the 1960s. A privately funded elm screening program was begun at the University of Michigan. For the next 20 years, more than 60,000 seedlings from survivor trees were subjected to blasts of DED, leading to the development of the DED-resistant “Liberty Elm.”

But the most definitive work was done by the USDA at the National Arboretum in Maryland, led by geneticist Denny Townsend. This exhaustive program led to the development of nine of the ten DED-resistant cultivars on the market today. In addition, the program’s scientific rigors were a vital ingredient in convincing nurseries to begin breeding and selling these trees and the Department of Forestry to reintroduce them into America’s forests. 

It had taken more than 70 years, but the American elm was back!

Five years ago, the Shade Tree Commission began planting DED-resistant American elms. It started with only a few. This spring, a total of 18 are being planted. As these saplings grow, they provide clear evidence as to why these elms are the ultimate street tree.