By Doug Struck
Globe correspondent

Federal officials are increasingly alarmed by the toll of climate change on the nation’s forests, as vast tracts of the West and Southwest erupt in flames, and bark beetles and other bugs turn swaths of lush green into dead, brown moonscapes.

A report by the U.S. Department of Agriculture in February predicted that “wildfires, insect infestations, pulses of erosion and flooding, and drought-induced tree mortality are all expected to increase during the 21st century.”

Last week, Agriculture Secretary Tom Vilsack said we have to do something about it. In announcing the creation of seven USDA hub offices to help farmers and foresters deal with global warming consequences, he offered up blunt testimony on the need:

“I am not here today to give a scientific lecture on climate change. I’m here to tell you what we’re seeing on the ground,” he said at the National Press Club. “We’re seeing more severe storms. We’re facing more invasive species. More intense forest fire threatens communities each year.

“The latest science tells us that the threat of a changing climate is new and different from anything we’ve ever tackled,” he warned.

New Englanders would seem, at first, to be in an enviable position. Climate change will bring both winners and losers, and New England forests are likely to experience a longer growing season, warmer temperatures, more moisture, and an increase in the carbon dioxide that trees convert to food.

“There will be effects that sound like a good deal. Some of the effects will lead to increased growth,” said David R. Foster, head of the Harvard Forest, a 3,500-acre research tract in Petersham.

“This is not the West, where we have to worry about the forest burning up. Dead trees are not going to lead to catastrophic forest fires here,” he said in a telephone interview.

But an altered climate will change the mix of trees, favoring some species and stressing others. That changing mix will invite new pests and diseases, some of which will thrive in a warmer climate.

There already are signs. A tiny insect called the woolly adelgid is spreading northward with more mild winters. It has devastated forests in the Great Smokey Mountains, and is likely to eventually wipe out the stately hemlocks from the northeast, Foster said.

And on Martha’s Vineyard, an outbreak of native caterpillars—surviving through warmer winters that in the past would have killed them—have wiped out hundreds of acres of stately oaks.

“The native species went into an outbreak mode that hasn’t been seen before,” Foster marveled. “That really hasn’t happened in great numbers elsewhere. It hasn’t happened since. Those kinds of things will happen more and more, but they will be unexpected.”

New England is the most forested region in the country, with forests covering 33 million of its 42 million acres. The forests here rebounded from the clear-cutting of colonists, but the wooded area peaked toward the end of the last century, and is declining. Foster and others are campaigning to reduce the losses in order to preserve large unfragmented tracts of forests that are resilient and sustainable.

They are faced with both the impacts of climate change and the encroachment of humans on the forests. The worst scenario is where one feeds the other, he said.

“The last thing you want to do is act abruptly and make quick decision” because of climate change, he said. “There’s a natural tendency to try to go in and fix things, to cut down dead trees, eliminate things that ‘look bad.’ But you often do much bigger damage by coming in with heavy equipment that damages the forests even more.”

“The single best thing we can do is conserve as much as we have now, as much as we can,” he said. “The more that we fragment and perforate and compromise existing natural systems by putting housing in the middle of them and influencing them in the variety of ways that we do, the more stress that’s going to be put on them.”