Expert: N.H. Forests Are Global Hotspot For Destructive Non-Native Insects

Jun 19, 2018

There are at least 50 species of non-native insects established in the state, including the Emerald Ash Borer, which has devastated the local ash tree population. Poised to join this list is another wood-boring bug, which could have a similar impact on more of New Hampshire’s trees: the Southern Pine Beetle.

“In New Hampshire, we live in a global hotspot of non-native forest insects,” said Matthew Ayres, Professor of Biological Sciences at Dartmouth.

Ayres joined The Exchange along with Jeff Garnas, Assistant Professor in the Department of Natural Resources and the Environment at UNH, to discuss current and future threats from these insects. (Listen here for the full conversation.)

“The Southern Pine Beetle is one of the most aggressive tree-killing insects in the world,” said Ayres.

The species has been confirmed in Massachusetts and as far north as Albany, New York, and poses a threat to virtually any pine tree. In particular, however, they flourish in pitch pines.

“Pitch pine in this area occurs in what we call the Pine Barrens,” said Garnas, “which are kind of pine-oak scrubland habitats. They’re very ecologically unique.”

New Hampshire’s Pine Barrens form a small but significant portion of the state’s forests, as these unique habitats are home to many species of plants and animals that don’t appear anywhere else in the state.

“They’re not the kind of ecosystems that we want to lose, or have significantly impacted by this beetle,” Garnas said.

In addition to supporting biodiversity, pitch pines and all of the state’s trees serve many ecological purposes. Trees and forests affect the way water is filtered through the earth and into lakes, rivers and even our drinking water. Then there’s the matter of the air we breathe.

“People like to think about trees and forests as the ‘lungs of the earth,’” Garnas said. “It’s not a perfect analogy, but they do take in carbon dioxide and release oxygen, which is a very important ecosystem service.”

If New Hampshire loses a significant portion of its pine population, there will be many fewer trees to support this service.

Ayres explained that the Southern Pine Beetles’ distribution has extended by over 100 miles in the last few decades, moving from its native habitat in the southeast to the forests of New Jersey, Rhode Island, New York and Massachusetts. This has been spurred, for the most part, by the warming of the coldest night of winter.

In the past 50 years, Ayres said, the coldest night of the winter has warmed by 7 or 8 degrees Fahrenheit. This, he says, is an “enormous amount” from an ecological standpoint.

“In the past, this would have produced mortality in the beetles, at least every few years,” Ayres said, “and thus put a cap on how far north they could come.”

As it moves northward out of its natural range, the Southern Pine Beetle could have an enormous impact on forests in the northeast, including in New Hampshire, especially given how quickly the beetles can destroy their chosen hosts.

“The genus is Dendroctonus, which in Greek means ‘tree killer,’” Ayres said, “and they really are tree killers.”

The Southern Pine Beetle is particularly dangerous to trees because of the way in which it attacks, releasing pheromones to attract more of its own species and enabling thousands of beetles to attack a single tree at once. This means that the beetles can kill a healthy, adult tree in a matter of months.

Although these concentrated attacks can ravage trees, Ayres says they can make management of the beetles easier than some other insects.

“The management of the Southern Pine Beetle is one of the great success stories in the history of forest entomology in its traditional range in the southeast,” he said.

By monitoring forests from small aircraft, forest services can identify outbreaks early on by spotting patches of dying trees, and then can cut and remove the infested trees before the beetles have a chance to move on to others nearby.

“You can stop the growth of a local spot by judiciously cutting down a few of the trees where the attacks are being concentrated,” Ayres said.  Local forest services are already monitoring for the beetles.

While New Hampshire braces itself for the potential impact of the Southern Pine Beetle, another non-native tree-killer, the Emerald Ash Borer, continues to take a toll. This invasive species was brought to the U.S from Asia in 2002, and made its way into New Hampshire in 2013, most likely via firewood brought from out of state.

“There were early attempts to eradicate it, and there were [firewood] quarantines early on,” Garnas said, “but they were unsuccessful. It spreads too quickly, especially when aided by humans on firewood.”

Now, Garnas says, the Emerald Ash Borer is present in 34 states and is likely to eventually spread across the entire continental U.S.

Like the pitch pines favored by the Southern Pine Beetle, ash trees don’t make up a huge percentage of New Hampshire’s tree population. Overall, ash makes up about 6 percent of the state’s forests. However, Garnas says that’s still a lot of trees, about 25 million adult trees statewide, according to the Society for the Protection of New Hampshire Forests.

Garnas also said that a large number of the ash trees in New Hampshire are street trees, planted in residential and commercial areas, after elm trees were mostly killed off by Dutch Elm Disease.

“[Ash trees] were kind of the second line as far as trees that grow well in urban settings,” Garnas said. “So this is bad news for cities and homeowners.”

Efforts to introduce natural predators of the Ash Borer have had some success in reducing the populations, but it’s unlikely that the insects will ever be completely wiped out. Like the elm trees that were essentially wiped out by disease, New Hampshire’s ash population will likely not be bouncing back any time soon.

“I’m afraid that I can’t be optimistic about the ash,” said Ayres. “I think that the best thing that we can do is to try and prevent the next Emerald Ash Borer from coming into North America, and we can do that.”