Ending the nightmare on elm-lined streets: scientists using survivors to breed tougher generation

(Christian Marks/TNC)

Majestic American elm trees in New England that have survived decades of a ravaging disease are being called upon to help create a genetic armor to help future generations resist the disease’s devastation.

Scientists from The Nature Conservancy are climbing high into trees in a handful of locations this spring to clip small branches in hopes of developing new Dutch elm-disease resistant strains of the stately tree.

“We’ll make the most resistant American elm varieties among them available to the public, as well as planting them in our own floodplain forest restoration projects on the Connecticut River,” said Conservancy ecologist Christian Marks. “One day, maybe, these incredible giants once again will lend their beauty to our parks and streets and their strength to our floodplains.”

American elms, among New England’s largest trees, once dominated the forest canopy, creating an ecological niche that provided shade and absorbed floodwaters, according to The Nature Conservancy.

But the Dutch elm fungus that entered the country in the 1930s changed all that, cutting a swath of destruction that has resulted in the death of some 100 million of the graceful, arching trees.

The disease kills by choking the tree. The fungus clogs the tree's vascular system, which delivers waters to leaves and branches. Eventually the tree withers and dies.

In coming days, aided by Chesterfield arborist Jim McSweeney, Marks will visit several Western Massachusetts sites to take sample branches. Others are also being taken from sites in Connecticut and Eastern New York.

“The disease has had a profound impact on trees that were treasured by so many people in city parks and streets,” Marks said. “It also had a dramatic impact on floodplain forests along New England’s rivers.”

The elm still is the second most abundant tree species in the floodplain forests of the Connecticut River watershed; however, today’s elms are typically much smaller than those that preceded the disease, and the unique niche the larger trees created has largely been lost. Restoring it would benefit these crucial floodplains, according to Marks.

Scientists are crossing samples from the most promising trees among these large elms with American elm selections developed by the U.S. Forest Service that are already proven to be highly tolerant to Dutch elm disease. The offspring from these controlled crosses will be planted at floodplain forest restoration sites. Once the elms reach sufficient size, the trees will be tested for disease resistance.

This is the third year of this elm restoration project. So far, cuttings from nine elms in Connecticut, Massachusetts, New Hampshire, and Vermont have been collected, and 20 crosses have been completed. This March, cuttings will be collected from at least 16 more elms, according to the Conservancy.