ALL TOO MANY HEADLINES in the science section lately speak of trees in trouble, of various forest pests and other pressures that are imperiling these precious living resources. From Dr. Murphy Westwood of Morton Arboretum in Lisle, Illinois, I got a status update on some of the most talked-about issues, including emerald ash borer (above, alongside detail of white ash in fall foliage) and also whether we gardeners and homeowners can play any role in shifting the balance of things toward the positive column.
Westwood (below, right, in the lab) directs the Global Tree Conservation Program at the arboretum, which strives to save threatened trees from extinction through collaborations with botanical gardens and universities, and others in China, Europe, and Mexico, as well as throughout the U.S. She has a particular interest in oaks—including a number of American species in trouble—which we also talked about.
Read along as you listen to the Nov. 6, 2017 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
emerald ash borer and threatened oaks,
with morton’s dr. murphy westwood
Q. Before we get started on trees in trouble, I believe I read that in 2015, the Morton Arboretum had its first millionth annual visitor tally. Is that correct?
A. That’s right.
Q. Tell us a little bit about the place.
A. Oh, it’s wonderful. It’s a 1,700-acre public garden in the western suburbs outside of Chicago. We have over four and a half thousand different species of trees and woody plants on display here. About half of the collection is more formal collections, formal gardens. There’s a hedge garden and children’s garden that’s very popular. The other half of it is restored natural areas, so a really excellent woodland and a prairie restoration that’s been going on for probably about 50 years now. There’s a little bit for everybody here. It’s a fantastic place to visit. [Below, the restored Schulenberg Prairie at the Morton Arboretum.]
Q. I think it was founded in the 1920s, maybe?
A. That’s right, in 1922. We’re already thinking about how to celebrate a hundred years.
Can you give us a quick hint also, kind of what the Global Tree Conservation Program that you direct is about, so that we can have the backdrop of that?
A. We started the Global Tree Conservation Program three years ago, with a focus on protecting threatened tree species as the unit of conservation. The arboretum has a long history of research and conservation effort for forest communities and ecosystems, especially in the Midwest, and locally and regionally here. But as you mentioned in your introduction, the news is full of sometimes some bad-news stories about how we’re losing species diversity around the world, especially in biodiversity hotspots.
Botanical gardens and arboreta have an incredibly important role to play in conservation. We have years and years of expertise in plant identification and collecting and understanding plants’ habitats, biology, anatomy, ecology. We started our program with the goal of deploying some of our expertise and then leveraging the expertise of the broader global botanical-garden community to protect threatened tree species around the world.
We’re really focused on a kind of goal of zero tree extinction, and we do that by working with partners. That can be other gardens and arboreta. It can be NGOs, so we work very closely with a partner organization that’s based in the U.K .called Botanic Gardens Conservation International, which is sort of like our global association or professional network for gardens with a focus on conservation.
Then, we’ll also work more locally with local partners, local NGOs, universities, to conduct research and conservation projects that are tailored to species’ needs. Especially focusing in areas of high biodiversity, where there’s often less capacity and infrastructure for conservation.
Botanical gardens around the world tend to be kind of centered and focused in more urban areas, in more developed countries. There are a lot of botanical gardens in the US, and in Europe, and in Australia, and the Far East.
Q. Makes sense.
A. It doesn’t necessarily overlap with where all of the plant diversity in the world is. We’re just kind of trying to make sure that nothing’s falling between the gaps.
Q. So zero extinctions, O.K. Just a modest goal. Yes? [Laughter.]
A. Yes. It’s overwhelming, but there is really there’s no technical reason why any plant species should go extinct. Between things like seed banks and our living collections that we have in botanical gardens, we should never have a scenario where you can’t see this plant anymore on Earth. Obviously, that’s not ideal. We’d love to have all of these plants healthy and happy, and in their native environment.
Q. Right, in its native range.
A. We’re at a minimum aiming at zero extinction. What we’d love to ensure is these things are still functioning and providing ecosystem services and playing an important role in the community network and framework in which they exist.
Q. To shift, then, to one that is in the headlines a lot lately, and who knows what’s going to happen with it, because it sounds like it’s really in trouble: the ash. The American ash [Fraxinus americana, the white ash], and other ash species as well, or how many ashes?
A. Yes. We recently completed threat assessments for the International Union for Conservation of Nature, the IUCN. They administer and run a program called the Red List, which is a list of threatened species. It’s basically the international gold standard for evaluating the extinction risk of plant and animal species.
We completed six threat assessments for the six native U.S. ash species that are Eastern U.S. The point being that these are the species whose distributions are centered where the emerald ash borer was originally introduced, around Detroit in the late 1990s. These are the species that are currently being just decimated by the explosion of the emerald ash borer population here in the U.S. We have evaluated six, but there are many other ash species in the Western U.S. and around the world. We’re also working to complete those assessments, as well, but I focused initially on the Eastern U.S. because of the urgency.
Q. I see on the interactive map; I think it’s from the USDA’s Collaborative Emerald Ash Borer Project. Well, you know the map that I’m talking about.
A. Right. Yes. It’s an excellent resource.
Q. Yes, and it’s updated so it tells you what date you’re looking at, the last tally, and it shows you within counties where the first report was or whatever. Then, it shows areas that are under quarantine, and I saw that it has crept into Texas, Oklahoma, Kansas. This is emerald ash borer that we’re talking about. Nebraska and even Colorado; there’s an isolated little area in Colorado that’s been marked on the map.
A. That’s right.
Q. Is this a problem just in North America, or is this elsewhere in the world as well?
A. The ash borer itself is native to Asia, and Eastern Asia mainly, so China and bits of Russia. It’s been introduced here in North America. There’s also reports of it I think around Moscow, so farther West in Russia. If that is the case, and if it is reproducing and happy there, it’s probably just a matter of time before it works its way into Europe.
Q. I see. When you say, “introduced here,” meaning North America, last year, I did an interview with Dr. Gary Lovett at the Cary Institute in New York State, and we talked about how that happens: methods like wooden packing materials from abroad and so forth that may carry some of these inadvertently imported forest pests. I’ll link people to that if they want to know a little bit more of how did this happen. From where we are now, we have a big problem not just because it’s moved into so many areas, but it’s a very voracious pest. What is it about it that makes it so terrifying?
A. That’s right. Basically, the insects will lay their eggs on the bark of ash trees, and then the larvae bury into the vasculature of the tree–basically, the circulatory system of the tree–and that’s where it feeds and overwinters. It creates these extensive galleries in the bark of the tree [above], which effectively girdles the trees, so it suffocates it. It can’t move nutrients and water around.
Because the insect larvae are pretty big, and you may have several in any one tree at a time, they can choke off and effectively kill the tree within three, four, five years, very effectively.
And the insects are very happy here. They have no natural predators, and so they’re breeding like crazy. If the borer takes hold in a stand of trees, it can wipe out the entire standing stock of mature ash trees. Anything really over an inch in diameter, it will infest and attack. The trees die within a few years, and it’s like 99 to 100 percent kill rate.
Q. Sometimes we see in our areas, if we live in the East … or actually, when we say East, we mean east of the Rockies, not even east as in just the East, or beginning of the Midwest.
Q. It’s a big area.
A. Basically the whole eastern half of the Mid-Atlantic.
Q. Yes, that map is looking like it wants to be the eastern two-thirds of the U.S., do you know what I mean? It looks like it wants to push; it’s kind of scary. How does it happen that an area becomes quarantined? I noted on the map that there’s some of areas that are marked off.
I’ve seen these big traps out in my area, where I don’t think we yet have reports [of EAB], but are they kind of purple or blue, or they’re like these big canister things up in the trees—these traps to monitor and see if the pest has been seen locally.
A. Yes, there are many different stakeholders who are interested in tracking the distribution and spread of the borer. Certainly, the government agencies, the USDA, but states and even municipalities like local towns and communities, have monitoring efforts in place. Botanical gardens have monitoring efforts in place where they have their eyes out for this. I’m not sure exactly what the process is for the USDA to declare a zone a quarantine zone, but there are a lot of different players and people that have a vested interest in understanding where this thing is and why.
Q. In articles about the emerald ash borer, I see quotes not just from scientists such as yourself, but also sometimes from pest-control companies and arborists about injecting or spraying infested trees, sort of implying that there’s remedial help possibly. How does that work and what can it really do? You’re describing a situation that’s widespread, moving fast, and a voracious pest, so what would be … how does that work? [Above, ash impacted by EAB die quickly.]
A. For a little bit of context, the Red List assessment that we did, where we determined that these ash species are critically endangered because of the emerald ash borer threat, so critically endangered of extinction. That takes into account really only the wild population, so anything cultivated we don’t consider, which actually paints a more bleak picture than it really is because of exactly what you just said.
We do have some ways of treating some of the trees in order for them to not be so severely impacted by the borer, and that’s exactly why in ash’s case, we’re hoping it will not go extinct. We will always be able to keep some of these trees alive.
That is definitely something that homeowners can consider. So a lot of communities, a lot of private homeowners, a lot of landowners, municipalities are treating really important or valuable street trees. We treat trees here in our collection that are important and valuable in our collection, so that they are not overcome by the emerald ash borer.
Q. I see.
A. And that is absolutely something that people can do to maintain ash in their landscape. The thing to consider though is that is obviously you have to keep treating over the years. It’s not a solution for saving ash in terms of them being a functional species in our Eastern forest, but it is a solution—although, an expensive solution—in communities, for homeowners. If that’s something that homeowners have the capacity to do, and the passion to do, then that is definitely a good solution for the short term, and keeping in mind that yo have to keep that sort of interference or that effort in over time.
Q. Are there breeding efforts, or is there anything else being done? There’s the monitoring, as you said, different agencies and levels of government and nonprofits and whatever. Counties, and states, and so forth, are watching, and there are quarantines, and there’s trying to stem the spread, so to speak.
A. Slow it, yes.
Q. Yes, slow it and contain wherever is possible. I’m assuming that trees that have been identified as having it are destroyed? Are they then destroyed, because you don’t want to spread it, you don’t want to …
A. There are some silver linings. We’ve learned a lot about the spread and monitoring of invasive pests through this whole process. There is a lot of new and interesting research that’s happening about understanding what might be replacing some of these trees in our forests, so what sort of species and what will the plant community look like in the future, where we’re filling the gap. In places like in Ohio, you might have up to 15 or 20 percent of the forest is made up out of ash. That’s a big gap to fill.
We’re trying to take this as a learning experience, but there’s also some proactive things that are happening. There are breeding programs. One of the challenges is that a lot of our native ash species are far enough removed and evolved from the common ancestors they share with the Asian species that it’s not easy to breed between them.
So chestnut is a good example, American chestnut, which we have a really good program that the American Chestnut Foundation‘s been doing for decades now, with Chinese chestnut to try to breed in resistance to the blight that came and wiped out a lot of our chestnut. This is different, because it’s actually very hard, and in many cases, impossible, for these species to breed with their Asian counterparts. That is challenging. We are trying to understand some of the underlying mechanisms of why the Asian species are more resistant to the borer, but that sort of genetic work is kind of a slow and long process.
A. What is happening is some researchers, the Forest Service, and some universities like Notre Dame are doing some research on what we call lingering ash, which are trees in our regular forest matrix that, for whatever reason, appear to be surviving and living a little bit longer and looking healthier than everything else around them, which dies very quickly.
Those are being identified, and something else that people can do, if they find … they’re walking through the forest, and they see an ash that’s mature and healthy and all the other ash are dead in the Eastern U.S., in the area where there’s been a long infestation of EAB, call me or email [laughter]…
Q. 1-800 Murphy. [Laughter.]
A. Yes. There’s the U.S. Forest Service would love to hear about that.
Q. Yes, O.K.
A. There are some lingering ash, and that is essentially us trying to use our own U.S. species, their own inherent genetic variability, to see if one of them happens to have some tricks up its sleeve–some natural genetic variation that makes it more resistant than its neighbors. Then there’s also some … they’re releasing some parasitoid wasp, I believe.
Q. I wondered about biological controls, yes …
A. There’s some research being done for biological controls, too. So we’ll have to see how that goes.
Q. All right. Sort of shifting gears now to a different issue: I believe oaks are signature species of the Morton Arboretum, and I was surprised this fall to read about a Red List—you spoke about the Red List for the ash—but a Red List of United States oaks being published. There are some that have not such good conservation status, some of our native species. And oaks are, as you just described a couple of minutes ago about how the ashes in your region are a large amount of the forest, meaning it’s a keystone species. Would that be the correct expression?
Q. And oaks are often a keystone species, aren’t they, in their forests?
Q. These are really important trees, not an insignificant species, right?
A. Yes. We actually looked at all 91 native U.S. oak species, and compiled the Red List threat assessment for all 91 of the oaks, as well as these six Eastern ash species. For the oaks—I guess it’s the case for the ash, too—but I think it can be very easy to take some of these keystone species for granted because they are so common, you see them everywhere. You sort of think, “Oh, they’ll be here forever,” and it’s not necessarily the case.
There are about a quarter of our U.S. oak species that are threatened with extinction, so in one of the three threat categories that the IUCN defines, as well as near threatened, which is a category just before the threat category that says if trends keep continuing, then this thing could sort of creep above these thresholds and become a threatened species.
The oak story’s interesting, because with ash there’s such an obvious front-runner threat, and it’s for all the species, and it’s all the same thing, and it’s very easy to identify. With oaks, that’s not necessarily the case. We looked at our native oak species, which are pretty much distributed across the entire U.S. I think Idaho is the only state that doesn’t have native. Our oak richness is really highest, the species richness, is highest in the Eastern U.S., and throughout the Southern U.S., and then along the West Coast.
Our threatened species also follow that general area, so the Southeastern U.S.—Texas, Arizona, California. Our threatened species are kind of distributed across the entire country.
Q. I saw that on the map and in the report. It was kind of shocking how many of those were in trouble. [Seedlings of one of the threatened oaks, Boynton’s post oak, above.]
A. Yes, and there’s really no one front-runner threat, so habitat shifting, fire and fire suppression, so changing fire regimes, farming, ranching, climate change …
Q. I knew you were going to say climate change.
A. … urban development–all of these things play a role.
Q. I knew the phrase “climate change” had to come up because it seems like the straw that breaks the camel’s back. It’s such a factor that is influencing so many species.
A. It is, and we’re especially worried about climate change because trees are so long-lived. Like all plants, they’re stuck where they are, but their life cycle is so slow that their populations and species can’t shift their ranges nearly as quickly as fast-growing or annual plants, or animals, for example, where they can get up and move around. We’re especially worried about trees and climate change in the U.S.
Q. Is there another thing that you’re really focused on right now in your work? Anything else on the front burner besides these two things we’ve been speaking about?
A. Yes, these Red List efforts are part of a broader effort. We have to evaluate the threat level for oaks across the entire world.
A. Yes, and that’s about 450 species. We’re really only a quarter of the way there. [Laughter.] We anticipate actually the picture to be a little bit worse, because oak centers, the two oak centers of diversity are in Mexico and Southeast Asia; that’s where they’re the highest species richness. We are working now on Mexico and Central America, and looking at oaks there. You can’t just stop with doing the threat evaluation. You have to then move forward and say that, “Now I know what to prioritize, now that I know what’s threatened, what am I going to do about it?”
That is kind of the happy side of my job, which is we have projects on the ground targeting some of these species, so we’re collecting acorns, we’re growing them in botanical gardens, we’re conducting research to understand why some of these species aren’t regenerating in the wild. That’s the more positive note, is that we really can have an impact and try to reverse some of these trends.
more about the morton arboretum
- The Morton Arboretum website
- Emerald ash borer information
- Science and conservation at Morton Arboretum
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its seventh year in March 2016. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the Nov. 6, 2017 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
(Photos from Morton Arboretum, except ash borer insect closeup, from Pennsylvania Depart of Conservation via Wikipedia.)