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Q&A with a Forest Ecologist: Getting smarter about imported forest pests

A Way to Garden Podcast: Interview with Dr. Gary Lovett

Imported forest pests: a Q&A with Dr. Gary Lovett

Q. Yours is very interesting work—though a little terrifying to read about. I’ve probably been gardening for 30-something years. I feel like when I began, I perhaps knew the names of two such pests, and now I can enumerate a lot—and I am not an expert. I’m seeing more headlines about them, too. Are introduced forest pests accelerating?

A. Actually if you look at the data for the number of pests introduced to the U.S., it’s a fairly constant line. They’re continuing to be imported, but it doesn’t appear to be at an accelerating rate.

What happens is that they don’t go away, so the number of pests is accumulating in the system, so we have a lot more than we used to. The other thing that’s going on is that some of the ones that were introduced recently are very destructive, like the Asian longhorned beetle and the emerald ash borer and some of the ones you mentioned.

Q. How do you quantify what’s at risk, in terms of acreage, or dollars?

A. Some of the pieces of the problem we can quantify pretty well. There has been a Forest Service study that shows that something like 825 million acres of forest land in the U.S. is at risk for further damage from the pests that are already here—and that’s not even considering any new ones. That’s like 63 percent of the forest land in the U.S.

Worcester, MA street before and after asian longhorned beetle infestation. Credit: Dermott O'Donnell


Q. Oh my goodness.

A. Another way to quantify it is with cost, and there was a recent study on that that we’re paying over $4 billion a year as a nation in responding to these pest outbreaks. Most of the costs are being borne by individual homeowners or by local governments, like cities and towns. That cost is for takedown and removal of trees that die from these pests. Since it’s a forest pest you might expect it to be a forestry-problem, but really the big problem economically is in cities and towns.

Q. In the Tree-SMART Trade information, I read about Worcester, Massachusetts, for example. Let’s tell people that example, which is pretty horrifying.

A. Worcester, Mass., is a small city, or medium-sized city. It had an infestation of the Asian longhorned beetle. This is a beetle that’s imported from Asia in wooden packing materials. It came into Worcester, which is an industrial area, in wooden packing crates that were used to import machinery. The crates were left out in the yard, and the bugs got out of the crates, so they had an infestation of this beetle.

This beetle likes maple trees the best, but it eats a lot of different hardwood trees. They found this infestation and the only way to get rid of the infestation is to take down the trees. [Above and below photos, respectively, a Worcester street before and after.]

The Federal government came in, and the combination of the Federal and local government started taking down trees in Worcester to stop this outbreak. So far they have taken down over 34,000 trees from Worcester, Mass., and they’re not done yet.

Q. And that began in 2008, and they’re already at that number of total takedowns.

A. Right.

Q. One can visualize what a small or medium-sized city looks like—in the Northeast we should say for context, because it’s not a desert landscape—without 34,000 trees and counting.

A. And you were asking about cost, and we can quantify the cost of taking down all those trees, and maybe the cost of replacing them. But if you see the pictures of Worcester, and you see these neighborhoods once had tree-lined streets, and now they’re completely bare.

I guess you can quantify the reduction in property values, but you can’t quantify the change in the quality of life, when your neighborhood loses all its trees.

Q. You said packing materials, so is that one of the carriers—is that a primary way that these pests find their way into the United States?

A. Yes, there are two primary ways, and that’s one of them. It’s solid-wood packing materials, the crates and pallets that are made out of solid wood. If they’re made out of processed wood like plywood, strand board [flakeboard] or any of the processed wood products, the processing kills the bugs, so those are not a problem. It’s only those made of solid wood.

The other main way that these things get into the country is through live plants that are imported for the horticultural trade, for landscaping for the most part. So you bring in a tree from Asia and that tree might have a disease or insect riding on it that might get out, and it wreaks havoc.

Q. And it wreaks havoc because… Well, I suppose we should have a very quick 101 on why an introduced pest—and it could be a plant, an insect, a disease—why do they prosper so well in the new environment?

A. That’s a great question. In their native environment, the trees have evolved to deal with these pests. Let’s say the ecosystem has changed organisms. The trees might have chemicals that keep the insect from feeding, and there are also natural enemies for these pests—things that eat the bug, or somehow devour the fungus or something. This might be birds that eat bugs, or spiders or other insects that eat the pest insect.

But when this thing is transported into the U.S., it finds a tree that’s similar enough to its native host tree that it can reproduce on it, but the native tree won’t have that resistance because it hasn’t been evolved, and the enemies won’t be around. So the combination of those two things allows the introduced pest to explode.

Q. People have probably heard of historical examples that led to near-extinction or at least elimination of the chestnut, for example, or Dutch elm disease. Those pests came into the country in 1900 and 1930ish, I believe. I was surprised to see that some of the pests that I hear about today, like gypsy moth and another I can’t recall right now, have been in the country even longer than that. Some have been here a very long time.

A. That’s true. spongy moth was introduced around 1869, and beech bark disease around 1890—so each of these pests has its own trajectory, how fast it spreads, and how fast it is at killing the trees. Something like chestnut blight spread very fast; within a couple of decades it had pretty much obliterated the chestnut population in the Eastern U.S.  Dutch elm disease was somewhat slower, but it moved pretty fast.

Now we’re watching emerald ash borer—another of these fast-spreading pests. It was introduced in the 90s, and first found in 2002 in Detroit, and it is spreading throughout the country really fast.

Q. About emerald ash borer. What is it doing to the trees, and why is it so capable?

A. It’s just a really lethal pest. It reproduces very well. For listeners who don’t know it, it’s a tiny green beetle. If you see it magnified picture of it, it’s actually very beautiful.

Q. It is beautiful; the macro pictures are lovely. 

Emerald Ash Borer. Credit: Chesapeake Bay Program

A. A lot of these pests in real life are just gorgeous insects; it’s too bad that they destroy our trees. This one burrows under the bark and creates these galleries—these long feeding tubes under the bark  [Below right, detail of galleries; below left, an inspector checks solid-wood packaging.]  It reproduces enough that there are so many of these larvae burrowing under the bark that it girdles the trees and kills them. It can do that in a couple of years.

As soon as there is a tree that’s damaged by them, it attracts more beetles and feeds more beetles. The trees that are dying become incubators for more beetles. So it has an enormous potential to increase in population, and it’s also very good at spreading.

I should mention that we’re very good at spreading it, and one of the main ways it spreads is in firewood.


Q. Firewood, yes. I’m on the MA-CT-NY border, and in recent years the rules have changed about moving firewood across the border—there are more restrictions.

A. And this is why, because these bugs can get buried in the firewood and you wouldn’t see them. You wouldn’t know it. But then you go take some firewood with you when you go camping in the next state, and let’s say you don’t burn it but leave some at the campsite, and then the bug gets out and you’ve spread the bug.  A lot of the new infestations of emerald ash borer are found near campsites.

Q. I attended an invasive species walk at Cary this summer, which is when I learned that the state I live in (and Cary is situated in)– New York—is like a bullseye of this insidious pest activity. Which regions are most affected and why? Why does New York have more than any other?

A. It’s great to be Number 1, isn’t it? [Laughter.]

Q. I don’t think so. I’d like to get rid of that.

A. We could forego that one, yes. It varies in different areas of the country, but all 50 states are affected buy this, and Canada, and this is a problem throughout the world. It’s not just us.

There are pests in the West, in the Rocky Mountains, but the Northeast and the Upper Midwest have the worst problems. I think are a couple of reasons for that. One thing is that these pests are brought in on global trade, and we’ve had a lot of global trade in the Northeast for a long period of time. As I said, these pests accumulate, and as you mentioned, chestnut blight was brought in in 1900, gypsy moth in the 1860s, so it’s been going on for a long time.

The other is that a lot of the most recent pests are being brought in from Asia—Japan, Korea, China—and our forests here in the Northeast and the Upper Midwest have a lot of tree genera in common with the forests of Asia.

In Asia they have oaks, hickory, ash, maples, pine trees. That wouldn’t be the case with, say, Africa. So a bug that’s adapted to ash trees in China, when it gets over here finds a tree that is similar enough to feed on but doesn’t have the enemies we were talking about before.

Q. Every region of the country does have issues, yes?

A. We can think about the Western U.S, in California and Oregon in particular. They have a big problem with sudden oak death, a disease that affects oaks and tanoak trees. In Southern California they have this new bug called the polyphagous shot-hole borer, which infests a lot of different trees, including avocadoes.

The Southeastern U.S. has something called laurel wilt, which is killing all the laurel and bay trees. So just about every area of the country has a problem.

Hemlock Woolly Adelgid, CC Cary Institute
Hemlock woolly adelgid. Credit: Cary Institute

Q. Is our changing climate also providing greater opportunities for these pests?

A. For the introduced pests, it’s kind of hard to tell. If you introduce a pest and it starts to spread, you don’t know whether it would have spread less if the climate was different—we don’t have that comparison that we can make.

There’s one good example that people are quite sure of, and that’s the hemlock woolly adelgid. That research shows that it’s sensitive to cold temperatures. As it has moved north—it was introduced into Virginia—as it’s moving north into the mid-Atlantic states, the rate of spread is slowing down and the amount of time it takes to kill the hemlock trees is also increasing. So it seems to be becoming less virulent as it’s going north, in the sense that it takes longer to kill a tree.

On the other hand, we know that with climate change—the bug is sensitive to cold winter nights, so if it gets really cold on a winter night, it kills a lot of them.  There is been some research that shows that they are evolving as they move north, so the populations at the northern end of the range are more cold-tolerant that the ones at the southern end of the range.

So the bug is basically adapting and that’s not good news for hemlock trees.

Q. We’ve mentioned Dutch elm and chestnut blight and spongy moth—then there is dogwood anthracnose, which has been around a long time, and came in in the 1860s too. But it seems like much more recently that it did wholesale damage in areas of our native flowering dogwood (Cornus florida).

A. I don’t know the specific case for dogwood anthracnose, but with some of these pests, sometimes the pest is introduced at one point, and then a more virulent strain is introduced at a later time. The taxonomy of fungi [dogwood anthracnose is a fungal disease] is not well known, so it might be difficult to tell. Here at the Cary Institute, which is a 2,000-acre property in the Hudson Valley of New York, we lost something like 90 percent of our dogwood trees to this anthracnose—mostly in the 80s and 90s.

asian longhorned beetle
Asian longhorned beetle. Credit: Bugwood

Q. What about the Asian longhorned beetle? Every time I see the native longhorned beetle species we have here, a sawyer, that looks somewhat like it except for a little white dot I think—I panic, and grab it, and put it under a glass and look it up to make sure it’s not Asian longhorned beetle.

A. The Asian longhorned beetle was brought in on wood packing materials, and introduced in several different places. It’s from Asia, from China and Japan. The first introduction in the U.S. was in the New York City area, and there were several outbreaks around New York City, and then there have been outbreaks in Toronto, Chicago, Worcester, Bethel in Ohio.

The USDA jumps on these outbreaks really fast, and tries to eradicate them. They’re been successful in some areas, and have them contained. They’re still working on it in other areas, like Worcester, that we talked about.

It’s a very destructive pest, and is not yet widespread in the native forest. But if it does become widespread in the native forests, we’re in deep trouble. Its main food is maple, and those are the dominant forest trees throughout the Northeastern U.S.

Q. Out West, I have read about white pine blister rust in white bark pines.

A. White pine blister rust is a fungal disease that was introduced again in the early 1900s, in the Eastern U.S., and had a minor effect on our native white pines here. As you know white pine is a stately, beautiful tree here. As the disease spread west, it encountered other pines in the same family, and it’s doing even more damage to those. You mentioned white bark pine [Pinus albicaulis], which is a high-elevation tree in the Sierras and Rockies, where it is now actually on the endangered species list, or a candidate for listing on the endangered species list, because this pest has done such damage to it, in combination with the bark beetle that are spreading out there.

There are other pests in the West like balsam woolly adelgid, which hits a lot of the firs.

Q. There is no shortage of pests.

Let’s talk about Tree-SMART Trade, and what both the government—those who govern trade, what the action items for them are—and also what can we individuals be on the lookout for, and do? How can we be smarter?

A. In terms of the government, when we were looking at this problem we really didn’t see any policy action—we realized it was a severe problem throughout the country, and we really didn’t see any policy action happening. So we first listed a number of options, then narrowed them down to some high-priority actions that we think make a lot of sense.

We are now in the process of trying to push those actions to get some legislation that would enact these.

The kinds of actions we are talking about are: phasing out solid-wood packing materials; restricting the importation of live woody plants, so that we’re not bringing in diseases and insects on these live woody plants; increasing our surveillance capability, so that if something does get through the ports and starts a small population near a port or industrial facility, we can pick that up and eradicate that before it spreads.

I should mention that all these recommendations are focused on preventing the pests from getting into the country. It’s much easier and makes much more sense to try to prevent these things from getting into the country in the first place than to try to deal with them after they’re already here.

We can also try to tighten enforcement of regulations that already exist—some are basically unenforced, or enforced by a slap on the wrist by those who are not in compliance.

And I think we could tighten our pest-prevention policies we have with out trading partners, to make sure that shipments coming into the country are clean before they leave the port they’re being shipped from. By creating these trade partnerships we can clean up the shipments before they arrive here.

Q. As a gardener and homeowner—like I said, every time I see another kind of longhorned beetle I’m always wondering if I will be the person in my area to file a report. Should we be looking? You mentioned we have to be careful about firewood—but are there other things? [Above, the ALB.]

A. I think gardeners can be really helpful, because gardeners are special people—they’re very aware of what is going on in the environment around them. They’re also not afraid to pick up a bug and look at it closely and see what’s going on.

Q. [Laughter.]

A. Like you said, you picked up that big beetle and put it under a glass and looked at it. [Laughter.] That’s great.

Q. Many times since I first read about the Asian longhorned beetle, I have done that.

A. Gardeners also tend to be pretty well attached to trees—except when they shade the garden, right? [Laughter.] So one thing that gardeners can do for sure is buy only U.S.-grown native plants for landscaping. I think a lot of gardeners appreciate the need for native landscaping.

Q. So this is another reason to think native.

A. And as you said, you can keep your eyes open for new pests and diseases. If you see trees that are staring to die for some reason, that isn’t obvious to you, it’s worth look around to see if you see holes, for instance. Ask the Cooperative Extension, or the state forester in your region if this is something unusual that you should be aware of.

They don’t mind you doing that.

The other thing gardeners can do is contact Congressional representatives or Senators to tell them that you are concerned about this issue, and you can do that either individually, or if you’re a member of a garden club or some other organization, you can encourage your club to support these Tree-SMART Trade policies.

As soon as the government understands that people are concerned about this and consider it a big problem, that’s when the action is going to happen.

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