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Using the Garden State as a barometer, researchers from Columbia University, the University of Vermont, and the U.S. Forest Service measured temperatures and their relationship to where the beetles were spreading.
They found that the temperature of tree bark on the coldest night of the year is critical. The destructive pests feed on the living tissue under the bark, introducing blue stain fungi. If the bark remains cold enough, the pests can't do their damage.
But the temperature on the coldest night of the year in New Jersey has been rising due to climate change, the researchers say, creating a path for the insect to start an invasion that eventually will spread into the northern United States and southern Canada. The lows are rising much faster than average temperatures, they said.
Southern New Jersey is critical because of its 440,000 acres of pine forests. The researchers picked the southern pine beetle as a climate change focus because it seems so sensitive to temperature. And it is responsible for destroying $1.7 billion worth of timber between 1990 and 2014 in southeastern states.
"I think the presence and destructiveness of the southern pine beetle in New Jersey is well-established. It's been a problem for 15 years," said co-author Corey Lesk, a doctoral candidate at Columbia's Center for Climate Systems Research. The study was published Monday in the research journal Nature Climate Change.
"But it's spreading north rather quickly," Lesk said. "Our study uses the data from southern New Jersey in relation to how it's moving north. The coldest night of the winter seems to dictate whether the southern pine beetle can live."
The group established that bark temperature of about -10 Celsius, or about 14 degrees Fahrenheit, is the limit at which the beetle can survive.
Since 1980, they found, the coldest night of the year above 14 degrees has migrated north in New Jersey by about 40 miles a decade. And the beetles have been moving north, too, by about 53 miles a decade since 2002.
The cold-weather connection has long been known. But the new study predicts how far and fast the beetles will spread, given warming temperatures.
Using historic climate data, the team projects that the annual minimum air temperature will continue to rise a few degrees a year in the northeast.
"Given this warming trend and our criteria for southern pine beetle-suitable climates, vast areas across the northeastern United States and southern Ontario and Quebec are projected to become climatically hospitable" to the beetle before 2080, the researchers wrote. However, the study notes that the beetle will become established along the Atlantic coastline into Maine by 2020 because of the more moderate temperatures there. It will take more time to roam further inland.
The authors acknowledge shortcomings of the peer-reviewed study, including the complexity of biosystems and the inability to predict the success of efforts to curb the pests' advance.
In New Jersey, the beetle has definitely made its mark, according to Ron Corcory, the southern pine beetle project manager for the state's Forest Service. He said the beetle has affected about 46,000 acres statewide since the early 2000s.
However, Corcory has noticed that the damage has stabilized the last two years, with most of it closer to the coast, "sort of hugging the Route 9 corridor." The state uses flyovers three times a week to survey the canopy of the Pinelands National Reserve and outside its borders to assess the damage, he said.
"I would say clearly we see it from Cape May up through Ocean County," Corcory said.
"We're not seeing it necessarily north of that. But you're not going to eradicate it."
The state prefers not to use insecticide as a means of control because that would kill off clerid beetles, known as checkered beetles — a big predator of southern pine beetles. Rather, Corcory said, the state manages beetle outbreaks by cutting down nearby trees to increase the space between them, interrupting pheromone, or chemical, communication between the insects.
The study's authors note that the beetle has made its way from New Jersey to Long Island and Connecticut, estimating it will find a home in pine-dense Canadian forests by 2050.