Scientists monitor resilient elm trees
KEENE VALLEY — A once iconic species of tree that has been hammered by a foreign disease may have found some hope in Keene Valley.
At the end of February, experts on elm trees came to the Adirondack hamlet to collect pollen from a large tree that has somehow withstood the onslaught of Dutch elm disease.
Gus Goodwin, who interned for The Nature Conservancy’s Adirondack branch in 2007 and worked for the Adirondack Park Invasive Plant Program, was en route to the Adirondack chapter’s offices when he noticed a large elm tree at the former site of the famous red barn at the intersection of state routes 73 and 9N. Goodwin now works for TNC Vermont.
Goodwin and TNC Connecticut River Program floodplain forest ecologist Christian Marks collected pollen from the large elm.
“Each winter, I harvest flower buds from such exceptional elms to collect pollen which we use in our program to breed more disease-resistant native elm trees,” Marks wrote in an email this week. “The idea is that some of these surviving elms were likely exposed to Dutch elm disease numerous times over their long lives, yet survived because of an elevated disease resistance.”
Marks is based in Massachusetts, but the elm work involves numerous northeastern states.
“Together with the Northern Research Station of the USDA Forest Service, we implement controlled crosses between disease-resistant elms, grow seedlings from the seed and test the disease resistance of those seedlings in field trial plots to select the best ones for further breeding and eventually restoration of the species in the wild,” he wrote.
Marks and Goodwin, along with some local TNC staff, successfully collected pollen from the large tree, which Marks said was greater than 3 feet in diameter, and that pollen will be used to germinate elm seeds that are, hopefully, more resistant to the disease.
“We successfully collected pollen and implemented pollinations with that pollen at the northern research station of the Forest Service, near Columbus Ohio,” he wrote. “We will collect the seed from these crosses when they mature in May and plant them in the greenhouse.”
Once the seeds have successfully germinated in the greenhouse, Marks and his colleagues will move the seedlings to test plots in northern Vermont, which has a climate similar to the Adirondacks, for study over the next 10 years or so.
Marks said collecting small branches for the project should not have any affect on the vigor of the tree, but that cutting large branches could.
“Pruning large branches in the summer (as is sometimes done along utility lines) can create a larger injury that can attract the bark beetles that spread the disease,” he wrote. “If one does need to prune large branches off an elm, it should always be done in the winter for that reason.
“Once the seedlings are over an inch in diameter we can test them for disease resistance by injecting them with the disease and monitoring the amount of symptoms that they develop and their survival,” he said. “The whole process can take almost a decade, which means it will be some time before we know if the Adirondack elm has disease resistance.”
The elm tree was once a staple of the American dream, lining the streets of suburbia with its elegant branches and gnarled bark.
Dutch elm disease may be a bit of a misnomer, as the fungi is believed to have originated in Asia. However, it was identified in 1921 by a trio of Dutch scientists after it had already been introduced to Europe. The disease is now found in Europe, Asia, North America and New Zealand.
Dutch elm disease (DED) was first found in the United States in 1928 in a shipment of wood from the Netherlands. But strict quarantine and cleaning procedures kept the disease at bay until the outbreak of World War II, when demands for raw materials led to a loosening of the regulations.
The disease spread across the country from the northeast, and reached as far west as Chicago and Minneapolis by the 1970s. According to a New York Times article from 1989, DED had killed more than 75 percent of the estimated 77 million elm trees that were in the U. S.
The disease is spread through beetles, including the native elm bark beetle. The beetles feed on the bark and introduce the disease through the feeding wounds.
The disease kills the tree by triggering the tree’s own defense mechanism, which plugs xylem and phloem tubes in an effort to prevent further spread of the infection. However, these plugs prevent the tree from feeding itself, and the tree eventually wilts and dies.
Some of the signs of an infection are failure of leaves and new growth to develop in the spring and the yellowing and dying of leaves and branches well before the normal fall leaf-drop.
While there are numerous ways to attempt the treatment of the disease, wild stands of elm that are not isolated from surrounding forests are difficult and expensive to treat.
But Marks hopes that his work will lead to a new generation of elm trees that can survive the infection and restore to glory one of the original statesmen of the North American hardwood world.
“Finding native elms with elevated disease tolerance is important not just to breeding more disease-resistant elms, but also to increasing the genetic diversity of the resistant elms that can be planted for restoring the species in the wild,” he said. “This diversity will insure that the species can co-evolve with the pathogen in the future, as well as insuring that we have a disease resistant elm population that is adapted to a broad range of environments.”
For more information on Marks’ program, go to www.nature.org/ourinitiatives/regions/northamerica/areas/connecticutriver/index.htm.