New England's Stately Oaks and Hemlocks Give Way as the Region Warms

By Doug Struck, for the Daily Climate

Biologist David R. Foster of the Polly Hill Arboretum on Martha's Vineyard walks through a stand of trees killed by a caterpillar outbreak. Scientists link the die-off to a warmer climate that allows the insects to thrive. (Photo by Doug Struck)

WEST TISBURY, Mass. – Spring did not come for the oaks of Martha's Vineyard.

For three years, the residents here watched a stunning outbreak of caterpillars that stripped an oak tree bare in a week, then wafted on gossamer threads to another. 

The islanders fought through clouds of drifting filaments with brooms, brushed off the showers of excrement after they walked under trees, and tiptoed through a maze of half-inch worms on the sidewalks. The local newspapers ran pictures of building sides covered with caterpillars, looking like horror-movie outtakes. 

“They were gross,” recalled Barbara Hoffman, 53, with a visible shudder. “You could hear them munching. I said spray 'em.”

Most trees recovered in the first year; fewer survived the second. But as the bugs struck again in late 2007, an accomplice drought hit the weakened trees, leaving the island now with swaths of stark, barren and lifeless branches.

“You just watched the trees and realized they weren't coming back,” said Kathy Tackabury, 58, who lost seven oaks on her property.

Scientists see a fingerprint of climate change in the denuded branches, and a pattern of things to come. The effects of climate change, they say, are unlikely to be gradual or predictable. Warming winters will throw into confusion old orders of species, nurturing unexpected predators and weakening age-old relationships that helped form forests.

“You can get unexpected dynamics in nature as we generate new combinations with climate change,” said David Foster, director of the Harvard Forest, who heads a research group financed by the National Science Foundation to study the Martha's Vineyard die-off. 

Forests elsewhere in the U.S. are victims of such surprise. 

In Canada and the Pacific Northwest, vast stretches of pine are being denuded by mountain pine beetles marching eastward. 

In the upper Midwest, deer and earthworms are flourishing in the warmth, stripping the forest groundfloor and pushing out natural conifers. 

In New England, the majestic hemlocks that were grist for Longfellow and Frost are doomed by the steady advance of a pest in warmer winters.

“To see hundreds of acres of dead forest like this in New England is remarkable,” said Foster. 

He moved with long strides through a thick underbrush of huckleberry and cat brier recently to a crest of the island, crowned with ashen-colored trunks of dead oak. The view of dead trees, he said, was “startling.”

Farther north and west in Massachusetts, Foster and others are studying the devastation of the stately hemlocks. 

An insect brought from Japan, called the hemlock woolly adelgid, is moving steadily northward into New England. It already has infested much of the US South, bringing what forestry officials call “an ecological disaster” to the iconic Great Smokey Mountains and Blue Ridge Parkway. With warmer temperatures in New England-some studies put the average winter increase at 4 degrees in 40 years-the pest is advancing.

“The northward spread is being kept in check by cold winters. As winters warm, which is what is projected, that all falls apart,” said Wyatt Oswald, an assistant professor of science at Emerson college who is studying the hemlocks. “At some point, climate change will allow all these hemlock to be wiped out.”

Stands of dead oak on Martha's Vineyard stand in contrast to other species untouched by the caterpillar that ravaged oak trees here (courtesy of David Foster)

The same simultaneous decline in Cape Cod oaks and hemlocks in northeastern North America occurred 5,500 years ago, two die-offs that were long thought to be separate events. But sedimentary records showing a sudden severe drought at the same time implicates climate in both events, Foster said. Bugs may have delivered the blow, but the bugs were fostered by climate change.

“We might get really severe drought, and we might get major outbreaks of insects or really severe weather impacts,” Foster said. “Unexpected events will lead to unexpected and rapid changes.”

Certainly the residents here were perplexed at the caterpillar outbreaks from 2004 to 2007. Although several insects were at work, the prime culprit was eventually identified as a fall cankerworm, a long-time resident of the island that no one recalled having done more than minimal damage. This outbreak was a full-fledged invasion.

“It was disgusting,” said Jason Gale, 39. He recalls glancing back at the island from his lobster boat, and being shocked by the stretches of dead trees.

Timothy Boland, head of the Polly Hill Arboretum on the island, was thrust into the middle of a growing community debate about whether to attempt wide-spread spraying. The pesticide, Conserve, is a bacterial substance considered greener than most insecticides, but it is very expensive. And it can be toxic to aquatic life and bees. Boland urged patience.

“Typically, in the second year population, the moths can't sustain themselves and the population crashes,” he said. “But it did not happen.” He ordered the spraying of the most valuable trees on his 70-acre arboretum, advised residents to spray their favorite trees, and let the rest go.

“It was a funny position for me as a tree man to argue that we should let these trees die,” he said. 

West Tisbury tree warden Jeremiah Brown (courtesy Doug Struck)

Jeremiah Brown, 39, is a burly landscaper and elected tree warden of West Tisbury, an island community of 2600 year-round residents. He has healthy, stately oaks next to his shaded home. He sprayed them. Next door, his neighbor did not. The trees there are dead fingers reaching leafless to the sky.

“People were looking to me to save the day,” he said ruefully. “They said I should have a helicopter over town spraying everything.” 

Town officials in several communities on the island voted emergency funds for limited spraying. In West Tisbury, Brown said he sprayed about 150 of the most critical trees on public grounds. As other trees died, they began to rot in 18 months, and communities have had to pay to remove trees threatening roads.

“I don't want to cut trees down,” said Brown. “I'd like to, naturally, plant a few things and have the town be proud of me in 100 years. But all I do now is cut down trees because of those darned caterpillars.”

The worst stretches of dead trees are on the elevated moraines of the island away from the roads. The suddenly open sky has created new opportunities. A profusion of beech, now free from the oak shade, is sprouting. Blackberry and blueberry shrubs are promising bumper crops. Foster, Boland, and other scientists are fascinated to watch the progression of a forest as the oaks are replaced. Residents see the dead trunks as fodder for their wood stoves. Not everyone has taken the same lesson from the die-off.

“I don't believe in climate change. I think it's just the way the world is. That's nature,” said Judy Jahries, 70, emerging from a West Tisbury grocery. 

“It's a sign we are out of balance,” countered Jackie Clason, 56. “If a person is sick, they are open to diseases. It's the same with the planet and trees.”

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