As if the emerald ash borer’s incursion into northern New England wasn’t enough, now there’s another potentially devastating forest pest marching this way: the southern pine beetle.
Dendroctonus frontalis – the first name means “tree murderer,” we should note – is only a fraction of an inch long. But during outbreaks, they reproduce by the millions and can kill trees in a matter of weeks.
“They’re one of the most aggressive tree-killing insects in the world,” said Matthew Ayres, a biology professor at Dartmouth College who has studied the species for 25 years.
A relative of the mountain pine beetle, which periodically ravage the lodgepole- and ponderosa-pine forests of the intermountain West, the southern pine beetle is native to the vast pine forests in the southeastern US.
But now, thanks to a warming climate, the beetle is moving north. It’s established itself in New Jersey, Rhode Island, Connecticut, and probably Massachusetts, according to Ayres. In New York, it’s on Long Island and has been trapped near Albany.
“There’s no doubt that northern forests in New Hampshire and Vermont are going to be challenged in the next few years – sooner rather than later – by southern pine beetles,” said Ayres.
The Red-cockaded Woodpecker evolved in old-growth, open-understory pine forests of the southeastern United States—particularly in longleaf pine—that was naturally maintained by lightning-started fires every one to five years. This habitat was once extensive, but almost disappeared during logging in the twentieth century. The birds are now often found in mature loblolly, slash, shortleaf, Virginia, pond, and pitch pine forests......Will they follow their Southern Pine Beetle prey north into the mid-atlantic states?
Range of The Red-cockaded Woodpecker
The Red-cockaded Woodpecker evolved in old-growth, open-understory pine forests of the southeastern United States—particularly in longleaf pine—that was naturally maintained by lightning-started fires every one to five years. This habitat was once extensive, but almost disappeared during logging in the twentieth century. The birds are now often found in mature loblolly, slash, shortleaf, Virginia, pond, and pitch pine forests......Will they follow their Southern Pine Beetle prey north into the mid-atlantic states?
Range of The Red-cockaded Woodpecker
Writing in the journal Nature Climate Change earlier this year, a team of researchers predicted “a plausible new threat” from the beetle “to vast areas of pine forest in eastern North America by 2050 and into subarctic Canada after 2080 under continued climate change.”
“It is a very big deal” for the northeastern US,” said Kevin Dodds, a forest entomologist with the US Forest Service and one of the authors of the article. “It’s definitely a considerable forest pest.”
Cold winters have traditionally limited southern pine beetle’s range. One night at zero degrees Fahrenheit and most beetles are killed, said Ayres. At five degrees below zero, they’re pretty much all dead. The problem: “In the last 50 years [in our region], the coldest night of winter has warmed by 7 to 8 degrees,” said Ayres. In the next 50 years, it could rise another 10 degrees.
Dead pines in northeastern Oklahoma, where some forests have been hit hard by beetles.
Credit: Kevin Krajick/Lamont-Doherty Earth Observatory
Cold winters have traditionally limited southern pine beetle’s range. One night at zero degrees Fahrenheit and most beetles are killed, said Ayres. At five degrees below zero, they’re pretty much all dead. The problem: “In the last 50 years [in our region], the coldest night of winter has warmed by 7 to 8 degrees,” said Ayres. In the next 50 years, it could rise another 10 degrees.
Adult female beetles are the ones who seek out new host trees. When they find a vulnerable pine, they burrow into the bark and release pheromones that alert other beetles, which swarm to the tree. Scientists call this a “mass attack.” The tree tries to fight back with resin, but the sheer number of invaders overwhelms its defenses. Beetles carve tunnels into the inner bark and lay eggs. After hatching, the larvae tunnel out and fly off to another tree. They can fly up to two miles and can produce multiple generations in a year.
During periodic outbreaks, the beetle’s numbers swell. They spread rapidly and kill pines in vast numbers. They then typically crash. In the south, outbreaks occur roughly on a 6-10 year cycle, though patterns can vary widely.
“The southern pine beetle has been recorded attacking and killing every species of pine with which they come into contact, and that’s more than a dozen,” said Ayres. It favors the “hard” pines like loblolly pine and shortleaf pine. It will kill pitch pines, and the pitch-pine barrens along the Atlantic coast from New Jersey to Maine are very vulnerable. It’s likely to go after jack pine and red pine, too.
Southern Pine Beetle larvae emerging from trunk of tree
Southern Pine Beetle larvae emerging from trunk of tree
The big unanswered question is how it will treat white pines.
Ayres said the beetle has killed white pines in Alabama, Kentucky, and New Jersey. “We know they’re susceptible. What we don’t know well is how well the beetles reproduce in white pines.”
Kyle Lombard, the forest health program coordinator for the New Hampshire Division of Forests and Lands, said his office is monitoring the bug’s progress. But “We are not overly concerned it will be a real threat to our New Hampshire forests. We just don’t have a lot of the preferred host, and the winter temps in New England would severely knock it back or completely control it.”
In their mass attacks, southern pine beetles tend to favor forests where the trees grow close together. In New England, white pine doesn’t usually grow in pure stands, but as single trees throughout the woods. That may discourage the beetle.
Unlike with emerald ash borer, where there’s virtually nothing humans can do but wring their hands, the thinning of uninfected pine stands can help control the southern pine beetle.
“The best management strategy to discourage southern pine beetle outbreaks is to maintain healthy pine stands, and that is another advantage New Hampshire has – we are not averse to managing forests,” said Lombard.
“We can manage it, and we should,” said Ayres. “But we should also take this as a harbinger of other changes and challenges that could be facing northern woodlands. This won’t be the last.”
Joe Rankin lives in Maine.
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New knowledge for managing tree-killing bark beetles
Outbreaks of the southern pine beetle can't be stopped by its main predator, but risks to forests from this tree-killing insect can be predicted with a simple, inexpensive monitoring program, according to a study by Dartmouth College and other institutions.
The findings appear in the journal Ecography. The study included researchers from Dartmouth, the U.S. Forest Service and Texas A&M University.
The northward march of the southern pine beetle can't be stopped by its main predator, but forest risks can be predicted and better managed with a simple, inexpensive monitoring program, according to a Dartmouth-led study.
Credit: Dartmouth College
The southern pine beetle has coexisted with North American pines for millions of years, but recent warming of winter temperatures has allowed the beetle's range to extend as far north as New York and Massachusetts.
The researchers used data from a forest monitoring program to evaluate how forest risk varies from location to location and to evaluate whether the southern pine beetle's natural predator, the checkered beetle, can stop outbreaks. Their results show that southern pine beetle outbreaks rise and fall remarkably synchronously across hundreds of miles. This means that the risks in any year and any region can be predicted with a simple, inexpensive monitoring program that measures their abundance by using traps baited with the pheromones that the southern pine beetles use themselves to find each other. The results also provide further evidence that weather, such as the coldest night of the winter, influences pest abundance and affects epidemics.
"The checkered beetle tracks the abundance of the southern pine beetle very closely," says senior author Matt Ayres, a professor of biological sciences at Dartmouth. "Unfortunately, the pest affects the predator more than the predator affects the pest. Thus, the predator cannot be relied upon to stop outbreaks and epidemics can persist for years, kill enormous numbers of pine trees and change forests in ways that last for decades or longer."
Pine beetle outbreaks have historically affected virtually all aspects of southern pine ecosystems and caused incalculable costs to local communities, state economies and the enormous forest products industry based on southern pines. Now, the pest is killing pine trees much farther north, raising major challenges to natural resource management and the maintenance of ecosystem services.
"Our study provides a rare empirical assessment of how local processes scale up to produce landscape patterns that influence forest ecology and forest management," says lead author Aaron Weed, a former postdoctoral researcher at Dartmouth and now an ecologist with the National Park Service "Our findings confirm that inexpensive monitoring that measures the abundance of southern pine beetles using traps baited with the pheromones is an effective method of assessing forest risks. Since the 19th century, the checkered beetle has been considered as a possible natural biological control for suppressing southern pine beetles, but our findings indicate that the predator cannot be relied upon to stop outbreaks."
Fortunately, entomologists and forest managers have developed techniques that do not require insecticides and can greatly reduce impacts from southern pine beetles. These include removing individual trees that are crowded with beetles and thinning overstocked forests before they are infested.
"One challenge is that climate change has allowed the pest to expand its range into more northerly regions, where landowners and forest managers do not have experience with these techniques nor the resources to implement them," Ayres says.
Story Source:
Materials provided by Dartmouth College. Note: Content may be edited for style and length.
Journal Reference:
- Aaron S. Weed, Matthew P. Ayres, Andrew M. Liebhold, Ronald F. Billings. Spatio-temporal dynamics of a tree-killing beetle and its predator. Ecography, 2016; DOI: 10.1111/ecog.02046
- March 24, 2016
- Dartmouth College
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