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MICHAEL DUNNE: I'm Michael Dunne. For decades and decades, majestic herds of elk have bounded up and down the meadows and river banks of the upper Yellowstone National Park, delighting many visitors to the region. But this wonderful natural scene is actually not that natural, and quietly illustrates a huge problem for the park. Those elk herds exploded in numbers, and their insatiable appetite for native aspen trees created an ecosystem and retreat. Luckily, along came the wolves today on the show, you'll hear from an Oregon State University instructor whose recent study proves that restoring wolves to Yellowstone is improving the habitat and ecosystem for all by returning to their natural place atop the food chain, wolves are helping aspens return as well. Luke Painter, an instructor of ecology and conservation at Oregon State University's College of Agricultural Sciences, thanks so much for coming on and talking with us.
LUKE PAINTER: Well, thank you for having me.
MICHAEL DUNNE: I read information about a study you were the lead author, lead author of about wolves and Yellowstone, specifically around aspen trees. Why don't you talk about the study that you conducted?
LUKE PAINTER: All right, yes, this took place in northern Yellowstone, and this is an area that is home to what's called the northern Yellowstone elk herd and some of the lower river valleys in the area, like the Yellowstone River and the Lamar River. Some people might be familiar with the Lamar Valley, which is a famous place where people go to see wolves and bison and other things in the summer. Well, this elk herd had, over the 20th century had been quite large and had suppressed the growth of young Aspen and willows and cottonwood trees, and prevented the Aspen stands from regenerating from for they would grow new sprouts, but then the sprouts couldn't get any larger, and so the stands basically had older trees that, by this point, were all larger than 20 centimeters. DBH, you know, a lot of them were like a foot in diameter, and those were dying out, and then there wasn't any new growth underneath young aspens to replace those older trees. And this was a matter of some concern all the way back into the 50s and 60s, when people notice this happening and when the after the wolves were reintroduced in 1994 1995 there really wasn't much expectation that they were going to make a big difference in this situation, but the combination of wolves and other factors like cougars and bears and hunting outside the park and things like that, the elk population went down and continued to decrease in northern Yellowstone, and this led to a new situation where so the Aspen were were able to escape from this constant browsing pressure. Browsing is what we call it, when the animals eat woody plants. And so, the Aspen were able to escape from this browsing pressure and begin to grow taller. We first noticed this back in about 2007 and I, the study I did really began in 1998 when 1997 98 when Eric Larson from Oregon State University, working with Bill ripple there, laid out some randomly selected stands In the in Yellowstone Area and selected random plots in those and did a general survey of the Aspen, and found that at that point in the late 90s, you know, right after the wolf reintroduction, there weren't any young Aspen in any of those plots that were taller than about a meter. They weren't getting tall enough to escape from the Elk. They weren't getting tall enough to replace the trees, but in 2012 I went back to 87 of these randomly selected locations, and I found a really noticeable difference in the growth of these young trees and browsing had which pre winter when the elk would. Come down into these valleys, and they don't have a lot of other things to eat where the browsing of these plants reduced down into the range of, you know, 50 to 60% of them getting browsed. And some stand much lower. And so, this allowed them to start to grow taller and this was very noticeable in my 2012 study. And then in 2020 and 2021, I went back to those same locations and measured them again. So, we have a time sequence here of three different visits to these sites.
MICHAEL DUNNE: What might it mean for that environment, that ecosystem, what benefits now that sort of balance has been restored? What benefits do you think you know these taller, non-browsed upon aspen trees can mean for that area?
LUKE PAINTER: Oh, that's a good question. Yes, the Aspen are a really very important component of the habitat diversity, and therefore the species diversity of the northern rocky mountain ecosystem, because they're the Aspen are almost the only deciduous tree that grows in this region. In these higher elevation areas, you know, they're dominated by coniferous forests, but Aspen grows there and creates some variation in that habitat. And the other, the other deciduous tree that grows in this area is cottonwood trees, but they're only along the rivers. So Aspen is up on the hillsides. They're out in some of these other areas. And there is a kind of a succession sequence that can happen, where, after a fire, or some event like that, it wipes out some of the trees. And Aspen can, can, can flourish, and then over time, coniferous trees can take them over. And some of that's going on too, and so, but without the ability for the new trees to regenerate, that cycle can get lost and the Aspen can disappear. And this was what we were worried was going to happen from the elk eating them all. And with those Aspen stands in there, they have kind of a filtered sunlight through the trees. They're not completely blocking out the sunlight. So, you get a lot of different plants that grow in there, raspberries and other things like that, that animals like to eat. It's a popular place for songbirds to make their nests. The sapsucker birds like to feed on aspen trees, lots of insects and plants that you find there that you don't really find so much in other places. So, it just creates a lot of diversity in the ecosystem. And this is a normal part of this northern Rockies ecosystem. Aspen is also important for beavers. Beavers like to eat them. And so, there's a, there's some symbiosis there that helps to support beavers. And so seeing them come back really indicates that this, this situation, has been restored to a, as you said, a balance that's more similar to what we would expect for the region, and probably more like what was there before the disturbances that led to the heavy browsing pressure from Elk, the high numbers of elk in the 20th century, and this actually was a goal of the park in the 20th century, to try to control the elk and help these plants to regenerate. And they had a calling program where they were, they were shooting elk in the winter up until the 60s to try to reduce them. And it was just they had to do so much of it to see even a small effect that eventually they gave up. But now it seems that wolves have taken over that and they're helping to accomplish that result, that goal, without human intervention. So that's also interesting. I want to note that in this new study in 2021 this is the first time that we found, or really that anybody has reported in in many decades, that we found as young aspen trees getting to a diameter of five centimeters, which, you know, is a few inches in diameter, which many researchers have said is kind of a threshold of indicating they're now old enough we can consider them to be adult trees. They're going to be growing into the over story. They're, they're, they're very likely to survive and contribute to the future of the stand. So that's one of the notable results that came out of our recent study.
MICHAEL DUNNE: It's interesting because, you know, when wolves were absent, there still were other predators. There were grizzly bears, black bears, cougars, and you mentioned humans hunting and so on and so forth. But, obviously, it certainly seems like boy wolves are really effective predators. Talk a little bit about that.
LUKE PAINTER: As I said, there was a calling program where they shot elk in the park and also captured them and transported them out. But that ended in 1968 and they just gave up on it. And the elk population after that really took off. So, in the 80s and 90s, 1980s 1990s the elk population was at record highs. I mean, it was very, very dense relative to other places where we have elk, and also relative to the history of the park. And so, the pressure was very high at that time. And studies that were done of elk calf survival during this time found that when that of the elk calves that died in their first year, almost all of that mortality was in the winter from starvation. In fact, almost every winter, 1000s of elk would be dying from starvation, and some winters would be much higher depending on the severity of the winter. So that was what was controlling the population. So, they essentially had hit what ecologists call carrying capacity, which means they're going to run out of food if there's any more of them, and they'll and they keep reproducing. So, the limit is that they starve. And so, this was happening, and in the 80s and 90s, and so the predation by cougars and bears that were present, then it was happening, but it's what we call compensatory. It wasn't really making a big difference on the population. And now, with the population being much lower, and we could, we could discuss why that happened, there was a combination of factors. Like, there was a really severe winter in 1997 after the wolves were reintroduced, they knocked the population down from mass starvation and also from a lot of hunting. As the elk left the park because they were starving, there was a big hunting harvest, so that happened right at that point. But unlike previous times when there had been events like that in the 80s and 90s, this time, the elk population didn't rebound. It just kept on going down and staying down because of this additional predation pressure and with this lower elk populations, a study was done in 2008 and they found that almost all the mortality of calves in that study was not from starvation, as it had been before, but now from predators. And so now all the predation from the bears and cougars and wolves, it all adds together to keep the elk population from expanding to that point where they eat themselves out of food and are entered in, entering into mass starvation. So that's keeping them at lower densities overall, which maintains a healthier herd and also controls their effects on the rest of the ecosystem.
MICHAEL DUNNE: I know your study was conducted in Yellowstone, but obviously you and I are speaking in a state that now has wolves that came over from Idaho, and so we're now seeing, maybe not a robust wolf population, but, but it's here. It's here in Oregon. And I'm wondering, you know, based on what your study showed in Yellowstone, what impacts might you be able to extrapolate for what might happen here in Oregon?
LUKE PAINTER: That's an interesting question, and frankly, one that's a little difficult to answer, because the Yellowstone situation is very clear cut. Okay, we have a national park. There's no hunting inside the park. There's hunting when they leave the park, but inside the park there's no hunting. And then the elk population was very high, and the Aspen were clearly suppressed. So, is that going to translate to areas outside the park? Well, there are places where ungulates, that's what we call these hoofed animals like elk and deer, where they suppress Aspen and willows and cottonwoods. This has been a problem for some riparian restoration efforts out in the Blue Mountains of Oregon. But there's other factors involved there. There are also cattle that are eating Aspen. And then there's the fact that, because of concerns about wolves preying on cattle and. They might not get to what we call ecologically effective densities, because they're because of controls on the wolves, and people don't want them everywhere. And so, it's a little bit harder to see if that's going to play out in some of these other areas. And of course, the situation with elk is different, because you know, they're hunted, their populations are already a bit lower, and cougar predation is pretty significant there in the Blue Mountains as well. So, we really don't know. We have to, we have to see how this is going to play out. But we don't have the kind of clear-cut situations to measure it against, like we had there in Yellowstone. So, this really created the National Park. Created a laboratory setting where we could really observe these effects. And we think these effects are going to translate into some other places, but it's probably going to be more diffuse, harder to pin down, because of these other factors involved, these confounding factors of cattle and humans hunting the elk and also hunting the wolves or lethally controlling them, in the case of Oregon, so as to where it whether that these ecological effects are going to translate outside the park. And kind of the answer, I guess, is it depends.
MICHAEL DUNNE: I also noticed in information about your study that that bison is also kind of part of this equation. Talk about that.
LUKE PAINTER: So, bison were really not part of this when we started the study back in the late 90s, but since then, they have really increased in our study area here in northern Yellowstone, in fact, increased four to five times since about 2012 when I, when I started this study, up until recent numbers and so where we had maybe averaged a few 100 or 2000 bison in at the time I was I was First looking into this. Now there's typically about 4000 bison in northern Yellowstone, and that looks to continue that way, and they're having some increased impacts. They also browse on the Aspen, and actually will break down Aspen saplings with their horns. I have a paper that came out on that last year, and so we're watching that as an increasing effect that's kind of counteracting some of the changes with, with the elk population being reduced.
MICHAEL DUNNE: I My last question for you is this, you know, obviously, tremendous concern that we, many have about climate change and how it's impacting the environment. And I'm, I'm wondering, you know, again, with, with, like, a study that you've done, and the idea of reintroducing species that were there that man took away, and now reintroducing, you know, what benefits might that have? What's your what you saw in your study in Yellowstone, but just generally speaking about, you know, again, I think I probably used it too much in this talk, but restoring balance to an ecosystem when, let's be honest, with climate change, global warming, much of the environment is out of balance.
LUKE PAINTER: Well, so about that word balance…I don't usually use that in my classes, because the student’s kind of have the idea that there's some kind of ideal situation, okay, you know, but really, all, all ecosystems are in some kind of balance, right there, whatever factors are there, and we might look at them and go, that's not in balance, because it's not the way we expect it to be. And that's kind of how it was in northern Yellowstone. It's not the way we would that we would expect this ecosystem to normally function. And so, then we go, Well, that seems out of balance, but you know, there's always some kind of balance of forces, and climate change, the changing climate becomes one of those. And so, we expect that a lot of places are going to enter into a new balance with climate change and with the forces of human development and everything. And so, one thing that's happened in restoration ecology is we don't really expect to restore places back to situations that they had in the past. We're thinking more about, well, what's, what could be an appropriate goal for this place in the present, but an interesting factor that is connected to climate change here is the restoration of beavers. You know, beavers can help to hold moisture in the mountains and thereby counteract some of the drying effects of climate change. And if ungulates, like elk and I would include cattle in there, you know, if they're eating all the willows and the aspens and the cottonwoods, which they like to eat then that the beavers can't live there. And so, in what we have now in Yellowstone is a situation where, because of the restoration back toward a balance more similar to what we'd expect for a functioning ecosystem here. So beavers are beginning to return to some of the streams in northern Yellowstone, and we may see some restoration of the effects of beavers in those areas, which then expands wetlands and supports habitat diversity on a broad scale for many species. So, this is one thing that we're hopeful can happen with this, and also that with fires. You know, fires are likely, possibly to be even more frequent, but many of these places are fire prone anyway, as fires go through and they take out these plants that I just mentioned, these important plants, the willows and the cottonwoods and the Aspen, well, that often stimulates those plants to grow. Aspen responds to this with lots of growth, but if you have too many animals eating them, they can't grow back. And so, there's also a balance that has to be there for that to succeed, you have to have not too many ungulates, not too many elk and deer eating these things. And so, we're hopeful that having the predators restored into these systems will help to restore this balance of fire and herbivory and regrowth of these plants, and that also can support the beavers and so we can get a large ecosystem effect from some of these basic changes in the ecosystem.
MICHAEL DUNNE: Luke Painter, who is with the Oregon State University College of Agricultural Sciences, where he teaches ecology and conservation. Really appreciate you coming on and talking about this fascinating topic.
LUKE PAINTER: Well, thank you so much for having me. I really appreciate the opportunity to talk to your audience.
MICHAEL DUNNE: That's the show for today. All episodes of Oregon On The Record are available as a podcast at KLCC.org. Monday on the show, we'll check in with Oregon Speaker of the House, Representative Julie Fahey of Eugene. Her party did a lot in the last legislative session, but a massive transportation package failed at the last minute. We'll talk about wins and losses in the session. I'm Michael Dunne, and this has been Oregon On The Record from KLCC, thanks for listening.
