Dutch elm disease proves a challenge for Dartmouth’s trees

by Lucy Turnipseed | 4/26/19 2:05am

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There are around 2,000 trees across the 200 acres that comprise Dartmouth's campus.

In his 1971 book “The Lorax,” Theodor Geisel '25 wrote that the titular creature “speaks for the trees.” 

But if Dr. Seuss were to give that label today, the recipient would not be the Lorax, but rather, the College’s arborist Brian Beaty, who cares for the roughly 2,000 trees on campus, often monitoring for signs of Dutch elm disease.

Dutch elm disease, which has largely eradicated elm trees in North America, remains a problem on Dartmouth’s campus as well, threatening the trees that surround the Green, among others. However, with the help of the Beaty and a committed grounds-keeping staff, a rare amount of healthy elms remain a part of Dartmouth’s aesthetic image. 

Paul Marino ’04, who worked on research regarding the vectors of Dutch elm disease with biology professor Matthew Ayres, said he was struck by the elm trees on campus when he was a student. 

“I suppose a lot of people are [struck by the number of trees], which is why they’re worth fighting for,” Marino said.

Dutch elm disease originated in the Himalaya region and first manifested in Europe, according to both Marino and Ayres. It then traveled across the Atlantic to North America as global trade proliferated, either through wooden pallets or live plants, before again going back to Europe in an evolved form. 

“With this research, we were understanding some of the complexities that we missed in the past,” Marino said.

The 2006 study that Ayres and Marino worked on — looking at the community ecology of the disease in the Upper Valley of New Hampshire and Galicia, Spain — focused on one of these new complexities: mites. 

According to Ayres, the vector of the disease is a bark beetle that spreads a fungus. He added that the fungi establishes itself in the outer branches of the tree and affects the cells in the leaves that control the stomata, essentially paralyzing the water control of the tree and permanently dehydrating it. 

Once the fungi gets into the vascular tissue of the tree, it eventually makes its way into the trunk unless steps to intervene are taken. 

“[The elm] was an iconic urban tree, and within a matter of a few years, they were all gone,” Ayres said of the first outbreak of the disease, which occurred in the United States in the 1950s. 

“We’re lucky at Dartmouth — we have some of the biggest elm trees you’ll see almost any place.”

Ayres and Marino’s principal focus in the 2006 study was the discovery of mites traveling on the bark beetles. They, along with their research team, hypothesized that these mites were mutualists that carried and cultivated the spores for the fungi, which the mites then consumed.

Although the study brought scientists closer to understanding how the disease spreads, a cure is not on the horizon, according to Ayres and Marino. They both added that Dutch elm disease continues to evolve and is quite aggressive — the combination of which proves impossible to halt completely. 

But, over the course of the next thousands of years, Marino is hopeful that the elms will have developed an immunity on their own. 

“If they can survive global capitalism, then I think they’ll stick around,” Marino said.

In the meantime, Beaty keeps a vigilant eye out for Dutch elm disease on the 200 acres that comprise main campus. Nowadays, Dutch elm disease is by far the biggest threat to tree health at Dartmouth, he added.

There are typically four to five cases a year of Dutch elm disease on campus, according to Beaty. He added that the yellowing of branches is a sign that they need to be cut off because the effects of the disease cannot be reversed. 

Beaty said he closely watches trees with a diameter of over 18 inches, as trees smaller than that are young and easily replaceable. All the new elms planted on campus are genetically engineered to be resistant to the disease. These trees are not immune but fare much better when infected with Dutch elm, according to Beaty.

Additionally, as a preventative measure, fungicide is pumped into most of the elm trees on campus every three years or so.

Beaty said that, as the arborist, he feels some pressure to keep up the aesthetic image of Dartmouth. Part of this focus may come from the founding myth of the Lone Pine and the centrality of nature to the College’s identity, Beaty said. He added that the College is very supportive of all the work he does for the trees.

One of the difficulties facing the preservation of tree health on campus is construction projects, Beaty said. He noted that during construction, trees can be damaged by equipment. Beaty said he has been in communication with the crew working on the new Arthur L. Institute for Energy and Society to protect the safety of the trees in the surrounding area. 

According to Beaty, most organizations and people across the College cooperate in maintaining tree health; however, he noted that when a tree that resides on a fraternity’s property is in need of treatment, there have been times when he has not been given permission by the organization to treat the tree.

“It’s just politics,” Beaty said. “There’s a lot of times conflict between the frats and the College about controlling property.”

Chelsea-Starr Jones, who is a prospective ’23 who was recently on campus for Dimensions of Dartmouth, said the tree upkeep is a “noble” cause. 

“At a lot of the other colleges I’ve visited, the trees haven’t really been cared for, but here they are and I think that’s really important at a place that’s so focused on the outdoors,” Jones said.

Scott Tamkin ’22 said that a major reason he decided to come to Dartmouth was because he was impressed by the image the trees created on campus.

Elm trees can be recognized by a few defining factors, according to Marino. Their asymmetrical leaf patterns, staggered branch growth, overhanging limbs, distinctive forks and a vertical bark pattern.

“People just have to keep looking up,” Beaty said.

Marino is a former member of the Dartmouth staff.