Dutch elm disease ravaged Canadian cities. Can we help trees protect themselves? — Scientists in the state of Vermont have spent the summer spreading Dutch elm disease to thousands of trees.
Researchers with the U.S. Forest Service and the Nature Conservancy want to see if a new generation of elms — bred from survivors of the disease — might have resistance to the fungus spread by bark beetles that has been decimating elm populations in the U.S. and Canada for decades.
The goal is one day repopulating areas where towering elms were once ubiquitous, lining city streets and thriving along river banks.
"The loss of the trees over the years has been devastating," Gus Goodwin, a senior conservation planner for The Nature Conservancy, told The Associated Press.
Time will tell if the Vermont experiment will result in a strain of trees resistant to Dutch elm disease (DED). Researchers working on similar efforts here in Canada hope science will offer solutions at a time when the disease is becoming a threat in new areas.
"We're not losing our elm population," said Alison Morrison, a manager at the University of Guelph arboretum which operates the Elm Recovery Project. "What we've lost is our elms' ability to grow old."
Fredericton was once known as the "City of Stately Elms" until the disease spread there and elsewhere in eastern Canada in the 1960s and 70s, leading to the loss of an estimated 10,000 trees. Now there's only about 1,000 mature trees left standing.
University of New Brunswick forest management professor Anthony Taylor has several elms on his property outside Fredericton, ones that survived the first wave of DED.
"But now I see there's another wave of the disease killing some of the trees on my woodlot," he said, "which is sad to see."
When bark beetles carrying the DED spores colonize a hospitable elm, the disease attacks its vascular system and blocks the water-conducting tissue, depriving the foliage and branches of water, preventing photosynthesis and eventually killing the entire tree.
That can happen within one to four years of infection.
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The beetles further spread the fungus by laying eggs in an infected tree, creating a new generation of carriers that can then fly to the next healthy tree. The fungus can also spread through roots.
In order to control DED, Taylor says, infected elms are immediately cut down and disposed of.