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."
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.