Tree-eating beetles march north as winters warm

For lovers of the stately pine forests of the Northeast, sightings of a destructive tree-eating beetle in recent years have been nothing short of alarming.

Now, new research from climatologists at Columbia University confirms what ecologists feared: Warmer winters mean the southern pine beetle is here to stay, and is set to march ever northward as temperatures rise.

Historically, the tiny beetles, which starve evergreens to death, were largely unheard-of north of Delaware. The Northeast’s cold winters killed off any intruders.

The winters are no longer cold enough.

Over the last 50 years, average annual temperatures in the northeastern United States have warmed by about 1 degree Fahrenheit. But crucially for the beetles, the year’s coldest nights — which determine whether they survive the winter — have warmed by as much as 7 degrees Fahrenheit.

Southern pine beetles are now frequently spotted in New Jersey, New York and parts of New England. And their range will only grow farther as the planet continues to warm, according to a study published today in the journal Nature Climate Change.

By 2020, swaths of previously unaffected forests along the Atlantic Coast up to Nova Scotia will become vulnerable to a southern pine beetle infestation, the study says.

By midcentury, some 40,000 square miles of the pitch pine forests from eastern Ohio to southern Maine will be hospitable to the beetle. And by 2080, vast areas of forest in the northeastern United States and into Ontario and Quebec will be vulnerable.

“You’ve probably spent summers hiking in the Adirondacks, Cape Cod, Long Island, upstate New York, the New Jersey Pinelands,” said Corey Lesk, a climate scientist at the Columbia University Center for Climate Systems Research and the study’s lead author. “All those forests are now facing a clear threat, directly, from climate change.”

In the South, the beetles have long been a major forest pest. The beetles tunnel through a tree’s bark and feast on a vital layer of tissue that provides the tree with water and nutrients. As the pine dies, its needles fade from green to yellow to red.

The beetle’s northward spreadis a reminder of the seemingly countless ways that climate change can upset the established order of ecosystems.

Matthew P. Ayres, a Dartmouth biologist who researches the beetles but was not involved in the study, said the new analysis could serve as a model for predicting how warmer extremes could alter the ranges of other insects and plants. “It’s reasonable to assume that there are hundreds or thousands of other species that may also be affected,” he said.

The Columbia researchers used climate modeling to predict the beetles’ spread as global warming intensifies. But unlike previous projections, which have tended to assume uniform temperature increases across a region, the researchers focused on temperatures during winter’s coldest nights. Temperatures on those nights must fall to about 8 degrees below zero to kill most beetles, but that is simply not happening across much of the Northeast.

“It’s unique in that it employs our best climate models to project patterns in the coldest night of the winter,” Ayres said of the study. “In biology, that coldest night is more important than average temperatures.”

The situation in the Northeast resembles an outbreak of mountain pine beetles that has ravaged millions of acres of forest across the Western United States and Canada — a devastation that has also been attributed to climate change.

But beetle infestations in the Northeast have been less visible, partly because they have occurred on relatively flat land. Out West, the dead trees that line the mountainsides are hard to miss.

Some scientists say an effort over the years to protect forests from fires could have made the problem worse, leaving the forests overgrown. In the South, overcrowded forests have been especially vulnerable to beetles because the trees are already under stress competing with one another for sunlight, water and nutrients.

Foresters there have brought the pine beetle under control by, among other strategies, thinning even healthy woods, leaving the remaining trees stronger and more ready to withstand a beetle onslaught.

And suppressing any beetle outbreaks before they reach epidemic levels is crucial, scientists say. In the South, forest managers swiftly cut down trees that have been infested, selling the timber to salvage loggers and paper mills — a strategy that pays for itself. But there is not much of an equivalent industry in the Northeast, making felling the trees more expensive.

In New York, the state’s Department of Environmental Conservation has already felled more than 15,000 trees in Long Island to ward off the beetles, a department spokeswoman said in a statement.

“This beetle was given the name southern because it was not found in the north,” the spokeswoman said. “But as our climate continues to warm, these beetles will find more and more of New York’s pine forests suitable for feeding and breeding.”