The College on Friday removed two diseased American elm trees -- one on the Green near the flag poles and one on Tuck Mall in front of Streeter Hall -- and trimmed one in front of Baker Library to contain the spread of Dutch Elm Disease.
By removing the infected trees promptly, Facilities, Operations and Management hopes to prevent cross-contamination of nearby healthy trees by the highly contagious disease, grounds supervisor Bob Thebodo said yesterday.
Similarly, infection of disease-free portions of trees can be prevented by removing the affected portions.
But not all cases of Dutch Elm Disease can be stopped this way, Thebodo said, since root grafting -- where the roots of neighboring trees grow into each other, spreading the infection -- is hard to control.
As the situation warrants it, removed trees will be replaced with disease-resistant elms. The Elm Research Institute in Keene, N.H. and other companies have developed genetically-modified elms tolerant of Dutch Elm Disease.
The wet spring and early summer heat, Thebodo said, have been especially conducive to the spread of Dutch Elm Disease, a fungus first introduced to North America in the early 1930s with disastrous results for the American elm stock.
The disease is spread by bark beetles, which take advantage of the weakened tree to burrow into it. According to the Elm Research Institute, 100 million U.S. elm trees have died as a result of the fungus since the disease first appeared here.
As the summer progresses, "the more likely we'll see infections that are either from this year or infections that can be physically removed from the trees," Thebodo added.
The removed elms had been included on a running list of unhealthy trees.
The College was last hit with a major Dutch Elm outbreak "about 20 or 30 years ago," Thebodo said, when "a rather substantial number of elms were lost on campus, large trees." In that case, the trees were "over-mature" and therefore vulnerable, especially the older trees in front of Dartmouth Hall and on the Green.
Dartmouth's campus is home to roughly 2,000 trees, Thebodo said. Of these, roughly 90 are American elms, according to an email from Wheeler-Richardson community director Fouad Saleet.
Though several trees are removed each year, Dartmouth's tree maintenance program is better than that found in most places in the country where trees often die young, Thebodo said.
"Within 50 feet of the road the life expectancy is less than seven years," he said, adding that "the trees we've been removing so far have far exceed that age."
The tree removal is part of an annual review of trees by the College's tree warden, Dave Dibenedetto, Thebodo said. Dibenedetto's job, he explained, is to identify potentially infected trees and then make arrangements to climb into them to take further samples to confirm that they are, in fact, diseased.
Between $30,000 and $50,000 is spent annually on maintenance of the elm trees, Saleet wrote. These expenses include the costs of injecting insecticide and fungicide into the trees and the pruning of infected areas.
Tree maintenance by the College is not simply limited to elms, Thebodo said.
Much of the grounds crew's efforts with trees is spent on maintaining the thousands of trees on campus by fertilizing, watering and trimming them, placing supports and braces and planting new trees when needed.
While some campus trees die, Thebodo said he does not see that as a setback. "All living things have to die," Thebodo said.
