Nonnative Invasive Forest Pests A Concern For Northeast U.S.

Aug 10, 2016

Over the past few years, state officials and forest biologists have been very worried about invasive pests that have been encroaching on our landscape. A new paper published in the journal Ecological Applications suggests that the United States needs to be doing more to fight the spread of invasive forest pests before our landscape is changed irrevocably.

A co-author on the paper is Matthew Ayres, a biological sciences professor at Dartmouth College who studies the population biology of forest insects. On Tuesday's Vermont Edition, Ayres talked about the paper's subject matter, including examples of nonnative invasive forest pests and what prevention measures can be implemented.

The threat posed by nonnative forest invasives

The paper doesn't pull any punches. Right in the beginning it says that for many U.S. forests and trees, "the most serious and urgent near-term ecological threat"  is invasive pests. The paper also states the damage from these pests is already likely measured in the billions of dollars per year, mostly falling on homeowners, property owners and municipalities.

So why are invasive pests such a problem in this country?

"Totally because there are so many of them flooding into our country and other countries around the world," Ayres says. "It's associated with global trade and global commerce."

The paper looks at insects and pathogens that are not from North America, rather than those native pests moving within the continent – though Ayres does acknowledge that "range expansions of native insects is another factor which is rocking the forests of New England." Additionally, the paper looked specifically at the impacts on forest and trees, but not crops that are primarily grown for agricultural purposes.

"A special problem with nonnatives is that you run the risk of extirpating whole plant species." - Matthew Ayres, biological sciences professor at Dartmouth College

"A special problem with nonnatives is that you run the risk of extirpating whole plant species," Ayres explains, saying that "functional extinction" could even be a possibility as the populations are decimated.

One species at such risk in North America is the ash tree, with Ayres adding "that will probably be more or less done within another one or two decades."

What are some nonnative forest invasives?

The paper includes a table with 18 species of "nonnative forest insects and pathogens in North America with current or potential future high impacts."

One invasive forest pest specifically referenced is the emerald ash borer, the cause of that extirpation of ash trees. In the paper, this beetle is referred to as "the most destructive and costliest forest insect to invade North America to date," before going on to say that addressing it could potentially cost $12.7 billion through 2020.

This March 13, 2007 photo shows Tom Coleman, a forest entomologist at the University of Georgia, holding a branch with hemlock woolly adelgid in Athens, Ga. Biologist Matthew Ayre told Vermont Edition recently that hemlock woolly adelgid is likely now an established invasive in southern Vermont and New Hampshire.
Credit John Bazemore / AP

Another mentioned is the hemlock woolly adelgid. Ayres explains that it has "a piercing sucking mouth part that it uses to suck on the leaf cells of hemlock trees and it turns out that it is lethal to eastern hemlock," and that the insect is likely now an established invasive in southern Vermont and New Hampshire. Yet another is a winter moth whose caterpillars defoliate trees and it has been spreading in the New England region, Ayres says.

Why are invasives an issue in the Northeast?

The paper says that in the United States, the Northeast and the upper Midwest are the two areas at greatest risk from the threat of nonnative species.

"New England is a global hot spot for diversity of invasive insects," Ayres says. "There are about 50 nonnative forest insects that we know of in New Hampshire [and] Vermont."

Ayres says that number grows to about 60 species if you include other Northeast states like New York and Maine. He continues with a few reasons as to why this is the case.

"One of them is certainly that the Eastern Seaboard – New York City, for example – is a global commerce hub," Ayres explains. "And so lots and lots of trade comes in, including lots of things that are packed on wooden pallets, and those wooden pallets are one of the main ways that some of these insects get transmitted between continents."

"New England is a global hot spot for diversity of invasive insects. There are about 50 nonnative forest insects that we know of in New Hampshire [and] Vermont." - Matthew Ayres

Another reason that Ayres gives is that because the area's forests are diverse, nonnative insects can generally find similar tree species to those they would use as a host in their native region. Like in the case of ash trees, Ayres explains, sometimes these North American plants don't have the defenses in place to deal with these new creatures.

A third reason that Ayres mentions is global warming and the rising temperatures in the region.

"Previously, there were many insects that would arrive in these ports and then die in their first winter," Ayres says. "Now the climate is becoming more benign, so the number of ports which a nonnative insect might be able to establish from is becoming greater and extending farther into our region."

What can be done to address forest invasives?

"There are a handful of very simple and sensible things that can be done," Ayres says. "They're probably going to require legislation, but they include switching to non-solid wood packaging to get away from these wood pallet problems. And we have the technology to do that.

"Another is to become better at detecting pests early when they've just arrived. So expanding early detection and rapid response programs. If we catch these things when they're still at low numbers, we're sometimes able to extirpate them. Once they become widely established, extirpating them is usually an impossibility."

Ayres adds that working with trade partners to create risk-minimizing practices would be another possibility, as would be placing restrictions on importing live woody plants.

"There's an enormous number of woody plants that get shipped into the U.S. to be sold here, and ... it's very, very challenging when you're shipping that material around to be absolutely sure that they're pest-free," Ayres says.

Not all the prevention has to be large-scale though. For example, Ayres says you shouldn't move firewood to different locations as that is a way that pests continue to get spread around.

"If we catch these things when they're still at low numbers, we're sometimes able to extirpate them. Once they become widely established, extirpating them is usually an impossibility." - Matthew Ayres

Recalling the paper's estimate that the damage caused by invasive pests is likely billions of dollars annually, Ayres reiterates who he feels will reap the financial benefit of addressing them.

"My suggestion would be that the real benefits to this are going to go to tens of thousands, millions of individual homeowners, landowners and members of local governments because that's where these costs are coming down," Ayres says. "What happens when your town suddenly has to spend a million dollars in the next two years to cut down hazard trees which are otherwise going to be falling on houses and power lines and cars? Where do those millions of dollars come from? Well, they come out of the school budget, the road maintenance."

He adds that he thinks contacting legislators to find out what they plan to do about preventing new invasives could put things in motion to address these pests.