Alden “Denny” Townsend, a tree geneticist for USDA’s Agricultural Research Service based in a U.S. National Arboretum facility in Glenn Dale, Maryland, saw quite a few elm-lined streets while growing up. The son of an oft-transferred manager for a large chemical company, Townsend was born in Oklahoma, lived in several Ohio towns and one West Virginia town, and graduated from high school in New Jersey, but he doesn’t remember any special attachment to the elms lining the streets of any of the places he lived. “I did love being out in the woods,” he recalls. “I was always out camping or hiking. I was interested in science and the outdoors, but I don’t recall any special calling to study elms.”

Today, Townsend is the leader of a U.S. Department of Agriculture effort to save the American elm. He has spent most of his career doggedly testing and propagating thousands of seedlings searching for an American elm that can stand up to Dutch elm disease. Townsend is more than happy to tell you he has not discovered a disease-immune elm, but he has come achingly close.

In collaboration with USDA plant pathologist Larry Schreiber and agricultural research technician Warren Masters, Townsend has discovered two disease-tolerant American elms called “New Harmony” and “Valley Forge,” cultivars that could bring the elm back into use as an urban tree. “New Harmony and Valley Forge are not impervious to the disease, but they are tolerant of its effects,” Townsend explains. “These two cultivars will show signs of the disease, but by the second year, when most susceptible elms are dying, these trees start to recover.”

“Denny’s great contribution is that he has developed resistant American elms that retain the classic vase shape with overarching limbs,” says Penn State tree geneticist Henry Gerhold. “Most of the resistant European and Asian elms planted after the disease outbreak didn’t have that distinctive, beautiful crown.”

Ironically, the popularity and versatility of the American elm was directly responsible for its downfall. Town after town, impressed by the usefulness of the tree, had planted elms along city streets. Elms were planted in clusters, without using any other species to vary the landscape. In plant science, growing just one variety of plant is called a monoculture, a condition that makes the plant or crop extremely vulnerable to the outbreak of disease. “American elms turned out to be the species most susceptible to Dutch elm disease,” Townsend says. “They also were grown close together, which made the disease easy to spread.”

USDA began research to find disease-resistant elms in 1937, and Townsend has been on the case for more than 25 years. The story of how he and others came to help save the American elm combines determined research with a few episodes of blind luck.

As a boy, Townsend developed an interest in tree science. At 15, he started a nursery using gray birch trees he transplanted from a wild grove behind his suburban house in New Jersey. After graduating from high school in 1960, Townsend applied to Penn State to find a career where he could work outdoors. “I took a test when I arrived, which told me that I had an aptitude for science. I started in geology, but I found it boring. Also, during the first week, a geology professor told us that there were 20,000 geologists out of work.”

Townsend knew he had found his niche when he took a course in dendrology—the naming and identification of trees. In 1964, armed with a bachelor’s degree in forest science, Townsend started working as a forester with the U.S. Forest Service. Stationed initially in the Mount Hood National Forest in Oregon, he later was transferred to a regional project, looking throughout Oregon for trees resistant to white pine blister rust. Blister rust is a slow-acting fungus that infects western white pine, sugar pine, and eastern white pine, eventually killing the trees. “It was really a great experience to apply tree genetics on a large scale,” he says.

Townsend’s interest in genetics led him back indoors to the Yale School of Forestry, where he earned a master’s degree, and finally to Michigan State University for a doctorate in plant genetics. In 1970, he arrived ready to start his research career at the USDA research station in Delaware, Ohio—right outside Columbus. “My assignment was to develop a breeding program for better urban trees,” he says.

Townsend’s assignment included the improvement of other urban trees such as red maple, spruce, and alder, but finding a disease-tolerant American elm is the work that has captured national attention in such magazines as Smithsonian, Audubon, and Business Week. He started by making scores of controlled pollinations between European and Asiatic elms, germinating the seed and growing the hybrid saplings before inoculating them with the disease-causing fungus to test tolerance or resistance. The trees that seemed most resistant were cloned and again inoculated with the disease. “It was a long-term process. It takes four years for the hybrid trees to grow large enough for inoculation,” he explains. “It takes two more years to check the trees’ response to the pathogen, and four more years before you can start the process of intensively screening the superior clones.”