Eastern Hemlocks Are Declining. Here's Why That Matters. (2023)

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ETHAN: Welcome to episode 102 of the Sweaty Penguin: Antarctica’s Hottest Podcast. I’m your host, Ethan Brown. Today we will be talking about trees: the one thing we just can’t seem to make up our mind on when we’re trying to educate children. Seriously, in The Lorax, we’re told to grow and preserve trees; in The Giving Tree, we’re told to just blow the tree to smithereens; and in Harry Potter and the Chamber of Secrets, we’re told that none of that matters because the tree will blow us to smithereens. Are we supposed to like trees, hate trees, be afraid of trees —I don’t understand!

ETHAN: Specifically, we’ll be talking about the Eastern Hemlock: a majestic, ancient tree species that is at risk of losing its place in the ecosystem. The Eastern hemlock is found throughout Eastern United States and Canada, and is actually the state tree of Pennsylvania, which leads to my next question: Eastern Hemlocks, are you a Steelers fan or an Eagles fan? Because if you’re an Eagles fan, I really don’t want to do the rest of this episode. Unfortunately, the Eastern Hemlock is currently fighting for its survival due to climate change and an invasive insect called the hemlock woolly adelgid. Why does this matter? In addition to many other important uses, Eastern Hemlocks are really effective at storing carbon —more so than most other trees —making it really concerning to see their collapse. Today, we’ll discuss why the Eastern Hemlock is significant, what issues it faces, and what we can do to protect them moving forward.

ETHAN: The Sweaty Penguin is presented by Peril and Promise: a public media initiative from The WNET Group in New York, reporting on the issues and solutions around climate change. You can learn more at pbs.org/perilandpromise. If you want to take two minutes to help out The Sweaty Penguin, you can either leave us a five star rating and review or join our Patreon at patreon.com/thesweatypenguin. Doing either earns you a special shoutout at the end of the show; joining the Patreon gets you merch, bonus content, and a whole lot more.

ETHAN: But first, it’s time for Eastern Hemlocks 101. [bell ring] The Eastern Hemlock is an elegant but monstrous tree, growing up to 100 feet tall. Being a conifer, the Eastern Hemlock grows needles instead of leaves, and propagates itself throughout the forest by dispersing small pinecones. It may not turn a vivid red or orange during the fall, but this allows it to hold its needles throughout winter ensuring you don’t have a Charlie Brown tree for Christmas. Not only that, Eastern Hemlocks can live up to 800 years. That’s right! The oldest Eastern Hemlock right now could have been around since 1222, and I bet it’s so proud of all our progress solving world peace, world hunger, and advancing medicine so we never have another Black plague like the one from back then… [“oof” sound] This gentle giant has garnered an affectionate following, even being ​​nicknamed the ‘redwood of the east. Now I would argue that redwoods are the hemlocks of the west, but whatever. I know you always have to make it about you, California.

ETHAN: Unfortunately, the Eastern Hemlock is under threat. Enter the Hemlock woolly Adelgid, or HWA, First of their Name, invaders of the East and Destroyers of Forests. The insect is an invasive species native to East Asia, first detected in North America in the early 1950s. Because the pest isn’t native to the U.S., it actually has no natural predators, meaning the population was able to grow extremely fast. You’d think predator species would be down to try some new exotic food, but I guess they just don’t have a refined palate. In the subsequent six decades after HWA’s initial discovery in America, the adelgid has established populations in 19 states. That’s three more states than Del Taco, ten more states than Bertucci’s, and one more state than the National Hockey League. That’s right! Insects 1, hockey 0! It’s also three states shy of the National Football League, although we’ll see if it falls apart when Gisele starts dating Pete Davidson and Tom Brady wins eight more Super Bowls out of sheer resentment.

ETHAN: The HWA is only about 1.41 millimeters long, but never underestimate a Short King. Around late September to early October, they create white woolly follicles on the underside of branches, containing hundreds of eggs that create the next generation of the species. Adult adelgids reside at the base of a needle, where they insert a mouthpiece to feed on the tree’s nutrients and water storage cells. And I know what you’re thinking, no, the needle doesn’t like it. Get your mind out of the gutter. In fact, this feeding causes the needles to die, turn gray, and drop from the tree. Buds are also killed by their feeding behavior, resulting in no new growth on the infested branches and the eventual death of the tree. How big of an impact does this have on an Eastern Hemlock forest? Just listen to Dr. Bill Hargrove, research ecologist at the USDA Forest Service, explain what researchers are able to observe from their satellite images.

BILL HARGROVE: If you look during the wintertime in a location that was predominantly hemlock, you see a decrease in the amount of greenness that is seen from the satellite. That’s caused by the loss of evergreen species, and this is almost like a signature of hemlock woolly adelgid activity and the resultant hemlock decline.

ETHAN: According to Dr. Hargrove, he and other researchers can see the hemlock stand losses from space, and that really puts the impact of this invasive species into perspective. In 2007, the Virginia Tech College of Agriculture and Life Sciences reported an estimated 50 percent of the Eastern Hemlock range had been affected. Why? Well, the hemlock woolly adelgid is actually a certified girlboss. All HWAs are female and asexual, meaning they can reproduce by themselves, and they do so two times a year. Who needs men, right? If there weren’t salsa jars to open, we’d have no use at all! And not only that, the winter generation can lay up to 300 eggs in total, while the spring generation will lay up to 75! That’s enough to raise an army…and be warned, Eastern Hemlocks: winter is coming [GAME OF THRONES-ESQUE MUSIC STING]. The sheer volume of their reproduction means the Eastern Hemlocks get overpowered and drained of their carbohydrates and sugars extremely quickly. Take that, ‘tummy tea’!’ And perhaps the most notable feature of the Hemlock woolly Adelgid is how efficient they are at killing Eastern Hemlocks. These tiny hit men, or I guess I should say hit women, can kill a Hemlock within just 4 years of initial contact. That’s an extremely short timeline for an invasive species, and it’s one of the major reasons adelgid are able to eradicate whole stands of trees before the infestation is noticed. For all these reasons, you can see why Dr. Hargrove would be encountering the collapse of entire forests on satellite images.

ETHAN: Despite their certified girlbossery, there’s one characteristic of HWAs that should be making their forest invasions more complicated, and that is that they’re a wingless insect. They must rely on other modes of transportation to move between forests, and since they don’t own an e-scooter or RipStick, they need to catch a ride. That can happen naturally through the wind or animals, but more often than not, they hitch a ride with us: humans. We help the spread of this invasive pest by moving infested plants from a natural setting or nurseries to new locations. Because we are moving the plants in controlled and safe situations, it’s unfortunately very effective for aiding in the spread of HWA, who go on to infect even more Eastern Hemlocks.

ETHAN: And if that wasn’t enough, humans are only making the situation worse due to climate change. Take Maine, the one state that has more Subarus than people. Just a few weeks ago, hemlock woolly adelgids were found for the first time in Acadia National Park, one of the top ten most visited national parks in America. In the past when HWAs have made their way into Maine, they die out pretty quickly due to Maine’s cold winter temperatures. But in a Q&A last week following this latest invasion, Maine Forest Service entomologist Colleen Teerling explained that winters just aren’t cold enough anymore.

(Video) Eastern Hemlock Health Update

COLLEEN TEERLING: For a long time, we did have winters that did protect us somewhat because hemlock woolly adelgid is somewhat knocked down by cold winters. The thing is we’re not getting the cold winters we used to get, and so we can’t count on winters to protect us any longer. We used to get winters that would give us 90 some percent mortality in the winter generation, and now we’re getting maybe 60 percent mortality. 60 percent mortality might sound like a lot, but it’s not much when you think about hemlock woolly adelgid.

ETHAN: Are we sure it’s cold temperatures, or are they just really scared of being in the same state as Stephen King? Look, I would be too. Even girlbosses can have its kryptonite, it’s okay. If we defer to the expert, though, Colleen says “we can’t count on winters to protect us any longer,” and that’s pretty noteworthy to hear such a forceful statement from a state scientist. She’s not wrong though, climate change is having an extreme effect on Maine’s ability to sustain HWA invasions. Like I said earlier, since HWAs don’t need to mate to reproduce and lay so many eggs at one time, even small changes to their mortality rate can be the difference between the population’s death and its explosion. As such, it’s no surprise that a Colby College project found in 2010, based on regional climates, 7.5 percent of Eastern Hemlock forests in Maine were at risk of HWA infestations. In 2050, that number is projected to go up to 96.8 percent. I know when we talk about climate change as one or two degrees Celsius of average global warming, it sounds pretty small. But with a species as good at reproducing as the hemlock woolly adelgid, those small shifts can turn an entire state from unsuitable for HWAs to suitable just like that, completely changing the game according to Colleen.

ETHAN: So okay, a random tree is dying out. What’s the big deal? Well, losing Eastern Hemlocks could bring a number of consequences. For one, they are actually amazing at capturing and storing carbon dioxide, like a fart jar on a family road trip, making Eastern Hemlocks an important factor in combating climate change. Eastern Hemlocks have the potential to grow up to 100 feet in height, up to 6 feet in diameter, and to a volume of 1,300 cubic feet. This, combined with the fact that they can live for over 800 years, means they can store a substantial amount of carbon in biomass, surrounding soil, and leaf litter, far more than many of their surrounding species. What’s more? The Eastern Hemlock’s leaf litter, which consists of twigs, bark, and needles, has some special properties that make it less prone to decomposing. It has high quantities of a polymer called lignin which makes the tree more rigid, it is high in tannic acid which has been shown to slow decomposition by decreasing soil pH, and just in general, needles decompose at a much slower rate than leaves. All of these factors make Eastern Hemlocks carbon storing machines. If they were smart, they’d be charging for all that storage. Can they take my iCloud photos next?

ETHAN: But when the hemlock woolly adelgid comes through, these dying Hemlocks release all that pent up carbon. And the tree that generally replaces Hemlock stands are Black Birches, which are not nearly as good at storing carbon. It’s like replacing Santino Fontana with Skylar Astin. Like, who would do that? A 2018 study in Ecosphere examining trees and soil carbon found that 80-to 90-year-old hemlocks stored 6.8 times more soil carbon than black birches of the same age. So not only are dying Hemlock stands releasing carbon, but it’s not getting reabsorbed. And that’s a vicious cycle. We have climate change aiding the spread of hemlock woolly adelgids, leading to the death of more Eastern Hemlocks. And we have dying Eastern Hemlocks releasing massive quantities of stored carbon into the atmosphere, which further drives climate change. That’s really concerning, and that’s why even though this may seem like a very random episode topic, I found it to be very much worth discussing.

ETHAN: Eastern Hemlocks specifically are also essential to the survival of many animals, fungi, and other vegetation in many forest ecosystems, as Cornell University Extension Associate Caroline Marschner explains.

CAROLINE MARSCHNER: They support a food web, lots of different animals and plants depend on them for food or for shelter. If you walk into a hemlock grove in the summertime, you’ll feel that you walk into this cool quiet space. The air underneath a hemlock canopy is up to 10 degrees centigrade cooler in the summertime than the air above the canopy. So it provides a really nice cool refuge for animals in the summertime. In the wintertime we go into a hemlock grove you’ll notice that there’s less wind under that canopy, and maybe a little bit warmer.

ETHAN: I’ve never been to a hemlock grove myself, so I obviously can’t speak to this, but according to Caroline, there is a noticeable effect from the Eastern Hemlocks on the climate around then. It sounds from Caroline’s description like they have a cooling effect in the summer, a warming effect in the winter, and a calming effect year round. That phenomenon helps explain why a lot of species rely on the Eastern Hemlock for their survival. Larger animals like Ruffed Grouse, Wild Turkey, and White-tailed Deer rely on the dense, low branches of young trees to provide winter cover and help prevent deep snow that can inhibit their movement. For Porcupines, Hemlock bark and twigs give winter nutrition, while the seeds provide food for Red Squirrels, Snowshoe Hares, Deer Mice, Southern Red-backed Voles, and other rodents. Because of its dense foliage, many species use the eastern hemlock as their nesting site to get protection from wind, cold, and precipitation especially during the winter months. Without Hemlock trees, many birds like Red-shouldered Hawks, Mourning Doves, Yellow-rumped Warblers, Green-tittied grouse and others would be in trouble when it comes to surviving the winter and reproducing. Ok fine, I made up the green-tittied grouse, but you believed me didn’t you!!! In fact, the Eastern Hemlock provides crucial shelter, food, and protection for over 120 vertebrates, meaning the loss of Eastern Hemlocks would have devastating effects on the surrounding biodiversity, whether or not that includes the deep-throated titmouse. And that one’s real! [“nice”] Okay, fine, it’s not.

ETHAN: And it’s not only land animals that are affected by the decline of Eastern Hemlocks. While their dense canopies act as a great temperature regulator for rivers and streams, Eastern Hemlocks also have roots that prevent soil erosion and act as a filtration system. If waterways were to become warmer due to the loss of these Eastern Hemlocks, it would be impossible for Brook trout to spawn, meaning their population would decline drastically. Many of these fish like Brook, Brown, and Rainbow Trout are game fish, and in addition to being your grandpa’s only topic of conversation, these fish help support the multi-million dollar sport fishing industries in New York and Pennsylvania —an industry which also drives tourism and creates thousands of jobs in these areas.

ETHAN: And the Eastern Hemlock’s economic value doesn’t stop there. Listen to the University of Kentucky’s Laurie Thomas explain some of the many other uses for these trees.

LAURIE THOMAS: Eastern Hemlock wood is used primarily as construction timber for light framing, roofing, subflooring, boxes, crates, and pulpwood. It is also widely used as an ornamental tree for landscaping. The graceful tree is handsome throughout the year, with a much softer form than most of our other conifers. It responds well to pruning and shearing and is often used as a hedge. […] From the 1880s to the 1930s, Eastern Hemlock was extensively harvested for its bark, which was used in the leather tanning industry.

ETHAN: I know what you’re thinking —no, leather tanning is not when cows go to the beach. Obviously, that’s called “beef by the reef.” [short tropical music sting] Laurie suggests that the Eastern Hemlock has a multitude of uses, and there’s a reason. For one, they respond well to pruning and shearing as she says, making them great ornamental trees. They also don’t lose leaves in the winter because, well, they don’t have any to begin with, and that makes them nice to look at year round. But they also provide an economic value. Eastern Hemlock wood is a softwood, and although it doesn’t have the density and longevity of a hardwood, it does bring some advantages —it’s less expensive and it can be used for a wider variety of applications. As such, it’s no surprise that 80 percent of all timber products come from softwoods. In fact, in the 19th century, the Eastern Hemlock’s tannin-rich bark was so popular that the leather tanning industry would cut down the trees, strip them of their bark, and leave them to rot on the forest floor, wrecking massive destruction on the species. Luckily, demand dropped as the leather tanning industry shrunk, so once again, it’s vegans to the rescue. Apparently plants do like vegans, who knew? So because of the special properties that Laurie lays out, Eastern Hemlocks have brought a lot of economic and aesthetic value.

(Video) Tree of the Week: Eastern Hemlock

ETHAN: Eastern Hemlocks also have a certain amount of cultural value. I mentioned that it’s the state tree of Pennsylvania, but even before Eastern Hemlocks were industrialized, Indigenous people in the eastern United States and Canada used them for traditional medicine. Certain ailments like rheumatism, arthritis, colds, coughs, fever, skin conditions, stiff joints, soreness, and scurvy, were remedied through different methods like creating a Hemlock poultice or tea. Step aside Advil, it’s Hemlocks! [SUPERHERO MUSIC]

ETHAN: So how do we save this tree that brings so much environmental, economic, and cultural significance? Typically, a go-to solution with invasive pests is some sort of pesticide, but with the hemlock woolly adelgid, that presents a lot of challenges. (1) Eastern Hemlocks often grow near sensitive stream areas which could be harmed by pesticide chemicals, (2) spraying entire stands would be really expensive, and (3) because HWAs spread so rapidly, pesticides would have to be applied to massive areas, which would be really hard to achieve. But there’s other possibilities as well. Currently, scientists are introducing a small black beetle called the Laricobius nigrinus, which is a predator of the HWA, and obviously a Slytherin. I mean, hero or not, you know that thing’s related to the Malfoys. Even with that name though, the non-scientific name is even worse! These unfortunate bugs have been nicknamed Tooth-Necked Fungus Beetles. Honestly who named these guys, playground bullies? But for all the awful luck these beetles are getting in the name department, according to entomologist Dr. Richard McDonald, this beetle could be used to control HWA populations.

RICHARD MCDONALD: This is a winter active predator, it comes out in October right when the adelgid breaks estivation, summer estivation, this thing is synced up with this with this adelgid. And this beetle feeds on 6-8 adelgids a day and really what it’s doing is it’s prepping itself for that cold period in the winter where it’s going to get a whole bunch of fat bodies, and then we might have what we have this time where you know January and February is just cold as could be, couldn’t collect there weren’t beetles out cause they’d all fed and they just go down and hide in the needle duff and wait for it to get warm again.

ETHAN: First the hemlock woolly adelgids are all females and now the beetles are on the same cycle? I don’t know, this sounds like it might get out of hand. Dr. McDonald seems to be optimistic about this idea though, in large part because the HWA is synced up with the tooth-necked fungus beetles…you know what, I can’t, they need a better name. The pearly white necked mushroom beetles? Gorgeous. Anyway, even with similar timelines, these beetles aren’t entirely effective in eradicating the HWA, and this is because HWAs produces two generations a year: a winter generation and a spring generation. You know, like Vogue! Might as well call them Adelgid Wintour with their winter and spring lines! And the beetle is able to chow down on the winter generations, but as the weather turns warmer, the beetle goes dormant in the leaf litter while the adelgid is out debuting its Spring fashions. Now, there are ways to address this shortcoming —one possibility is the silver fly who are spring feeders and could be used as a complement to our beetle friends — though silver flies are very difficult to capture and breed. But it remains the case that as excited as Dr. McDonald may be about this beetle, it’s certainly not a silver bullet solution. You also have to consider the fact that introducing a new species to a region can always bring a lot of unintended consequences. Remember, that’s how we ended up with the hemlock woolly adelgid problem in the first place. Who knows what a beetle that’s been bullied all its life is capable of?

ETHAN: How about Hemlock stands that have already been eradicated or infested? Replacing the area with similar trees could be an option. The Chinese Hemlock, for example, is actually immune to the strain of hemlock woolly adelgid found in the Eastern United States and Canada, because they’ve already encountered it back in China. Again, there’s always uncertainty introducing a new plant, just ask my two succulents that get into fist fights on a weekly basis. But if these vaccinated trees do turn out to be a viable replacement, they could provide similar forest structure, store similar amounts of carbon, and even be used as a line of defense to slow the HWA as it travels to new forest stands.

ETHAN: Of course, in order to implement ideas such as these, there needs to be both awareness and funding. As such, helping people learn how to identify and report HWAs could be a useful way to prevent their spread. And on the money side, there’s been some efforts already, with Canada and the United States each putting in federal funds. Certainly, considering the best sources of funding and how that funding is utilized would be important steps here as well.

ETHAN: I know the cycle of climate change hurting Eastern Hemlocks and Eastern Hemlock deaths exacerbating climate change sounds like an unbreakable one. But obviously, we discuss ways to mitigate climate change all the time, and as that process unfolds, we do have some exciting options to try to keep the issue under control. If we can keep the hemlock woolly adelgid at bay, we’ll protect the climate, conserve the ecosystems of many animals and fish, and ensure the HWA doesn’t invade more states than the National Football League.


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ETHAN: The Sweaty Penguin is presented by Peril and Promise: a public media initiative from The WNET Group in New York, reporting on the issues and solutions around climate change. You can learn more at pbs.org/perilandpromise.

ETHAN: Welcome back to The Sweaty Penguin. With me today is Dr. Danielle Ignace, Associate Professor of Indigenous Natural Sciences at the University of British Columbia. Dr. Ignace, welcome to the show.

(Video) Identifying eastern hemlock

IGNACE: Thank you so much.

ETHAN: First off, could you tell us a bit about your background and your research interests?

IGNACE: I am an indigenous eco physiologist. So, what does that mean? I am an indigenous person. I am a member of the Coeur d’Alene tribe which is in northern Idaho and that’s on my father’s side, and also Menominee through my mother’s side and that’s in northern Wisconsin. And I guess I have all my training over the years, from undergrad, and graduate school primarily in Environmental Studies, as well as plant physiology. And I’ve essentially taken a lot of those concepts and then expanded them to become an eco physiologist. So looking at all the impacts of global change, including big disturbances, climate change, invasive species and how all of those impact ecosystem health.

ETHAN: Being an indigenous scientist working with indigenous communities, how do you feel that that perspective influences your work?

IGNACE: I have to say that really for a long time it didn’t influence my work, and there are various reasons for that and I suppose if we think about how Western science has typically operated and has not included indigenous perspectives, knowledge or values, as well as the system of Academia, in a lot of places has not really truly valued or supported these. And of course this, this isn’t necessarily 100% of places, but I found in the past that I didn’t feel supported or valued and having that indigenous perspective and bringing that to the table. And so I would say early days of my career and what I worked on, it was not included at all. And that’s, that’s really unfortunate and sad, but things have changed quite a bit and I would say especially in the past several years. You know I’ve switched institutions, I almost left Academia because of this issue but I found a place that truly valued and supported indigenous people as well as their perspectives and knowledge. And so now my work very much is guided by those ideas and principles, and so now to kind of have this just resurgence of a career as well as new work coming out and partnerships and collaborations. It’s a really exciting time to do this work. And in one sense it’s really sad because of the climate change and nature emergency. On the other hand, it’s exciting to actually come to a place where we can finally truly engage with indigenous communities, and actually have that be a part of finding solutions, or finding ways to adapt.

ETHAN: Yeah, I’m glad to hear you’ve been able to find more support now, I think that at least from my learning about climate change, there’s just so much to learn from indigenous communities with land management, resource management, just valuing nature, and certainly so many solution ideas come from there. So I would hope that more and more academic communities would see the light there. I wanted to talk today about your work with Eastern Hemlocks, which I actually hadn’t heard of prior to working on this episode. So first off, why did this tree in particular pique your interest?

IGNACE: Several years ago, I had started my position as an assistant professor at Smith college, which is in Western Massachusetts. And you know when you arrive at a new place, you can just kind of make your observations about the surroundings, the different plants. I found myself exploring quite a bit and trying to get a handle on actually just working with trees, which I hadn’t really done before. And of course, this problem here of Eastern Hemlocks, you know, in the eastern United States that are being threatened and decimated in some parts of the Eastern United States by an invasive pest, the hemlock woolly adelgid. And so being aware of this problem and actually seing it with my own eyes and just the telltale signs of when you have that pest present on your hemlock trees. I really knew that there was a big story to tell with that because in some areas of the Eastern United States, we have just a complete decimation in as fast as four years, it could be five to seven years that we lose vast landscapes of Eastern hemlock trees. We’ve certainly seen that in areas south of where I was working on this in Massachusetts. And so I knew that it was something to be explored because it was spreading, it continues to spread North. We see it in Canada and it just keeps expanding its range. And we don’t really have a fantastic solution to this problem. There are a lot of challenges with dealing with this particular pest, and I just knew that, well, this is a very special tree species. It’s a foundation tree species, meaning that no other species in this area has the particular and unique role that this species has in these ecosystems. It provides a very unique environment for bird communities, for, you know, essentially all the organisms that are in the area that depend on it. And it also has some really important functional roles, you know, filtering water quality in nearby streams, it creates a ton of shade, it’s a very shady environment and it creates a very special soil environment as well. So, in a sense, only very particular species can survive or do well in this, in the Eastern Hemlock Forest.

ETHAN: And we’ll dive into all of this more, but a lot of your work, like you said, looked into how the decline of Eastern hemlocks could release stored carbon and contribute to climate change. And I thought some of the ways that you structured these experiments were actually really cool. But could you tell us a bit about that research that you’ve done?

IGNACE: We knew that we had to kind of, I guess investigate this problem from different perspectives and in this way, because getting back to my Arizona days and having kind of done a lot at measuring plant function at the leaf level, I really couldn’t do that here. We just didn’t have the infrastructure or huge scaffolding towers for me to climb up and actually get to the leaf level. So what that meant was, I turned to the soil and that, there’s a lot of information to be gained from the soil. We see now that science is moving in a way that rather than treating soil this a black box of kind of just deep mystery that we don’t know what the processes are, we’re starting to see more research get involved in that, which is exciting. And so, I just knew that I think just for feasibility that I had to go into the soil as well. And we know with the Eastern hemlock tree species that because of the special environment that it creates, it has very acidic soil properties that it creates, and that’s essentially because of its, the compositions of its, of its needles. It’s, you know, it’s a, it’s an evergreen Conifer species. So that when these needles fall to the ground, they don’t decompose very easily. So we essentially get this big build-up of all this litter in the soil profile. So, if you go digging into the soil, you will see just this huge deep layer of all that organic material, that doesn’t decompose very quickly. And so what that means is that there’s a lot of the Eastern Hemlock litter that has gone into that, doesn’t decompose very quickly, it’s high in carbon. And what we found was that over years of looking at the soil, one aspect was to dig into the soil, and look at that soil organic layer, and measure the percent carbon found within that layer. And we just lost a huge amount of stored carbon potential. So if we lose out on Eastern hemlocks what we typically see are that tree associates in the area such as Black Birch, typically replace those Eastern Hemlock Forest. It’s a completely different tree species. It’s a deciduous tree species, so, meaning that it drops all its leaves in the Fall. So it’s not an evergreen. And it just has completely different influences on the environments as well as the soil properties. So, those leaves, actually, when they drop, they decompose much quicker than what we see for the Evergreen Conifer species of Eastern Hemlock. So we lose out on all that carbon.

ETHAN: Yeah, and it’s interesting because I think it can sometimes be difficult to get people to care about a plant as much as especially just a random tree in a forest in the northeast of the United States. And I think that obviously this work you’re doing, linking it to climate change, really important. Some of these ecosystem dynamics, really important. But what would you say to someone who’s just kind of like why should I care that there’s this tree that’s getting decimated?

IGNACE: We’re tending to see you know a higher frequency of these unusually warm winters. If we have a warmer winter, it actually creates just the right environment for this invasive pest to kind of flourish and take off. Because if we have really cold winters, that tends to keep this pest population down, it has a very complicated life cycle actually, it’s really good at I guess dealing with the elements especially when we have a warming climate. And so we’ll tend to see more and more of this pest show up. You can actually see the signs unless you have a dead hemlock tree there. You can actually see the signs of the invasive pest present looking across the street, just seeing these little – they look like cotton balls, they’re these egg sacs, these white tufts at the base of the needles, and they are just off the charts this year. If folks can’t quite, I guess see the bigger picture that this is really impacting climate or feedbacks to climate change. All this carbon that was stored in the soil gets emitted back out to the atmosphere. That worsens global warming, that will contribute more to climate change because these ecosystems are being a source for CO2. We’re starting to see people can actually visually see the impacts just on their recreational activities, and by that, last year there were reports that beachgoers in Maine were walking on the beach and then there were reports of some sort of black substance staining their feet. So there were concerns that this was some hazardous material or maybe there was some sort of, you know, toxic leak in the water and it was washing up on the beach. What it actually was were all of these invasive pests just having a really, you know, ridiculously high abundance here. And they washed up on the beach and because there is such high numbers they actually stained the skin on beachgoers.

(Video) The Hemlock Woolly Adelgid Problem

ETHAN: That’s really interesting that you say our friends, the hemlock woody adelgid are actually growing more because of these warm winters. Do you see that then as creating a positive feedback loop where they’re doing better because of climate change, but then their impact also drives climate change? Because I know obviously these trees aren’t the biggest climate driver in the world. But certainly that’s a very interesting relationship.

IGNACE: I think, the way you just described it is really accurate, that we have warming, a warming climate creating more warm winters, creating the opportunity for these pests to really flourish, therefore damaging more Eastern hemlocks and then therefore decimating huge landscapes of Eastern hemlock trees and and contributing more to climate change. It’s important to note as well in this particular area of the United States that we don’t really have the natural predators that that are would have, would be seen in other parts of the continent or where they were originally from. So we also don’t have an Eastern Hemlock resistance or at least not, you know, any known resistance to the hemlock woolly adelgid. So this creates this, you know, just a big opportunity for this past just to flourish because we don’t really see these natural predators keeping its population down. There is some work out there and others trying to take natural predators of the woolly adelgid from the Western, you know, part of the country and release them in the eastern part. We have yet to see what that will do. If that is enough to keep down the population, it can’t bring back the Eastern hemlocks we’ve already lost, but perhaps, maybe I’ll remain cautiously optimistic whether that kind of biological control will help keep these populations down.

ETHAN: And in most of my reading, it really just was the invasive pest issue that was coming up as driving the decline of Eastern hemlocks. But I want to ask, would you characterize invasive insects as far and away the biggest threat? Or are there other threats that we should be concerned about?

IGNACE: I would say it’s the interactive effects that we should be most, I guess, devoting our attention to. It’s complicated, right? We know that generally if we have, you know, warmer, warmer seasons, if we, if we lose out on snow melts we lose out on water availability to trees. If we have, you know, droughts, we’re having a horrible drought, right now, as well, in addition to these heat waves that we’re dealing with here. We’re also having just these extensive droughts. We’ve hardly seen any rain here. So these are all factors that of course, are results of climate change in affecting this region, but that makes trees more susceptible to these pests. And and so yes, these invasive pests come in and they’re maybe they’re having a great year for various reasons, but if you have drought, you have all these these stressors, environmental stressors weakening your trees or various species and plus you have this invasive pests, that is just a double dose of just an extreme environment and extreme stress. So I would say it’s the interactive effects we need to look at.

ETHAN: The northeastern US is quite familiar with invasive species. We’ve done an episode on gypsy moths, the Spotted Lanternfly has been in the news at the time we’re recording. Is there anything that stands out to you about the Hemlock Woody Adelgid as different or or unique from some of these other notable invasive insects in the region?

IGNACE: I would say that just the speed in which it can impact the tree species. As I mentioned before, we can see impacts of it as early as four years, just huge die-offs of Eastern hemlock trees. So, rather than waiting to see just the weakening of trees over time and waiting, I don’t know, 10 to 20 years, this is happening as early as four years, 5-7 years, and then we just get these huge replacements of the Eastern Hemlock stands. So, to me, this is, it’s a unique pest because of that, it also is just really specialized. So it has, it’s an aphidlike insect, it has these, you know, its morphology is such that it really pierces into the tree cells and just, you know, takes away the sap of the trees. It really takes away all of those necessary nutrients and resources to the tree. So that’s how it’s able to do it so quickly. And so, I think what makes this unique is just the speed in which it can kill off large areas of Eastern Hemlock, as well as now, we’re seeing it creep north, more and more to the north.

ETHAN: Obviously, it’s really really hard to control invasive species outbreaks, but it certainly seems like this one is worth taking seriously. You mentioned one strategy of introducing some predators. But are there any steps that you have seen that seem intriguing to you? That can be taken here to address the issue?

IGNACE: Certainly others have implemented you know pesticides or a chemical solution. That’s usually not the best. I mean they do work, it’s very expensive. So you could implement that on an individual tree and see outcomes from that, that would help that particular tree. But to do that, on huge landscapes would be, I think, I think not the best idea given it’s a chemical solution and could affect a lot of different other processes and organisms in the area as well as it not being very cost effective. So that, that is a problem. Back in the day that used to be salvage logging. So in the way to kind of, get ahead of the pest, there would be logging to kind of stop the pest in its tracks, but of course, that means we were, we were eliminating completely healthy Eastern, hemlock trees and therefore contributing even more to this problem of, you know, being more carbon, or losing all that stored carbon in the system, so not great solutions, right? These natural predators, I think if that works, it doesn’t affect negatively, or too negatively and other processes. I, you know, I think that could be, I will remain cautiously optimistic about that as a solution.

ETHAN: My last question for you. What are some of the next questions that you hope to answer through your research?

IGNACE: I’m also, as you know, at the University of British Columbia, and there’s lots of Western Hemlock there and as I mentioned that there’s a different relationship with this invasive pest there. So it’ll be really interesting to see just do this big cross-continental comparison of this particular, you know, aphid-like insect having differential impacts on these different species and what that means for carbon storage, biodiversity and any potential feedbacks to climate change. In addition to that, you know, as an indigenous woman in STEM working with indigenous communities is also my big priority here so it won’t be just in the context of eastern and western Hemlock. But other ecosystems that I am starting to get, get my kind of researcher hat on and going to those systems and actually talking to the communities involving communities, local communities in how they are impacted by either invasive pests or any invasive and climate change and, and just working with those communities early and often.

ETHAN: I’ll be excited to keep up with that. Dr. Ignace, thank you so much for joining us.

(Video) My Favorite Trees - Eastern Hemlock

IGNACE: Thank you so much.

ETHAN: This wraps up episode 102 of The Sweaty Penguin. Take two minutes, help out the show, and get a shoutout at the end of the show by leaving us a five star rating and review on Apple or Podcast Addict, or join our Patreon at patreon.com/thesweatypenguin. You get merch, bonus content, and more. Clips today came from Stone Age Man, Mid Coast Conservancy, CCE Anandaga, Forestry and Natural Resources Extention, and Living Web Farms. Special thanks to our Emperor Penguin patrons Lawrence Harris and Brownies Central. The Sweaty Penguin is presented by Peril and Promise: a public media initiative from The WNET Group in New York, reporting on the issues and solutions around climate change. You can learn more at pbs.org/perilandpromise. The opinions expressed in this podcast are those of the host and guests, they do not necessarily reflect the opinions or views of Peril and Promise or the WNET Group. Thank you all for listening, and I’ll see you next week.


1. Michigan DNR invasive species expert explains Eastern hemlock tree infestation
2. ID That Tree: Eastern Hemlock
(Purdue Extension - Forestry and Natural Resources)
3. Will the Decline of Eastern Hemlock Affect Mushroom Biodiversity?
4. Old Growth Rising
(Granby Public Library)
5. 99% of DMZ Players WON'T do this..
6. Tree ID Clip: eastern hemlock
(OSU South Centers)


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