Ep. 573 - Great Lakes Climate Refugia

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Hello everyone and welcome to the in-defensive plants podcast, the official podcast of in-defensive plants.com. What's up? This is your host Matt. Welcome to the show. How is everyone doing this week? I'm doing great because we're talking about one of the most fascinating topics in ecology, and that is climate refugia. Where on the landscape are there unique combinations of variables that can keep plants alive in an otherwise inhospitable realm? There's a lot of different ways to attack this topic, but today we're focusing on climate refugia related to lakes and not just any lake, the greatest of the Great Lakes, Lake Superior. Joining us to talk about this is Dr. Ashley Hillman, who's trying to understand how climate refugia not only shaped plant communities in the deep past, but how it might shape plant communities moving into a future wrought with climate change. This is such an interesting topic, so I don't want to keep you from it any longer. Without further ado, here's my conversation with Dr. Ashley Hillman. I hope you enjoy. All right, Dr. Ashley Hillman, welcome to the podcast. I can't wait to talk about your research today, but first let's start with an introduction. Tell everyone a little bit about who you are and what it is you do. Yeah, sure. My name is Ashley. I use she, her pronouns, and I currently work for the Canadian Forest Service out of Alberta, Canada. My current work is looking at modeling forest resilience through using straight and transition models, looking at potential changes in forest structure and composition as a result of climate change. But I think what we mostly want to talk about today is what I covered on my PhD thesis that I finished last year that covers climate refugia, the effects of lakes on buffering climates. That does play into my work I do at Canadian Forest Service a bit as well. But yeah, I would love to talk about lakes and disjunct plant populations and yeah, all that stuff. Talk about it all day. Yeah, when I found your work, it was like, yes, let's talk to her. But yeah, it's a really cool way to kind of go from deep time into future time. And it's all kind of connected as you hinted at there. But what got you interested in refugia, climate change? I mean, was it very plant focused or a more big system, kind of earth science kind of approach? Yeah, I think it I like to talk about my path because it was not linear. I was not a botanist. I did not start out carrying anything about plants. I did my undergrad in zoology and was like, plants who like I just want to study wildlife, some kind of charismatic megafauna. I mean, I think a lot of us start there. But yeah, yeah. And then I got jobs where I started learning to identify plants, and then still didn't love them. But you know, it was it was work. And then kind of over time, they took over my life a little bit. And I kind of went more the plant ecology route. And then that kind of led more into some research projects I was working on as a research assistant at the University of Alberta. They kind of led more into, you know, I would say like more ecosystem based stuff using plants as indicators. And then my supervisor had this idea about refugia and this sort of tied into a larger refugia project that other people in my lab were working on as well. And so I guess to back up, I could talk about what climate refugia even are. Yeah, that was actually going to be my next question is, is let's define that because so much hinges on how we're defining this. Yeah, yeah, absolutely. Okay, so climate refugia refer to places that are sort of projected to be less affected by climate change. And those can be places that are typically driven by some corner landscape features. And you think of things like mountain tops, north facing slopes, so places that might have like a topographic effect that might sort of maintain cooler temperatures. And then you think of things like north facing slopes, you see changes in plant communities, right? Like you tend to see more up here, at least in Northern Canada, we see a lot more like spruce trees on those cold north facing slopes, you see snow lasting longer on those sides of slopes, that kind of thing. We can also have other things. So I had other members of my lab looking at the effect of feetlands on buffering climate change. And so the idea there being that they can serve as not only a source of groundwater recharge during droughts, but they can also buffer fire from adjacent uplands. Yeah, so this idea that there's some feature on the landscape usually driven by topography or some degree of water on the landscape, that's going to maintain some degree of cooler temperatures for longer. And then that refugia gives species a chance to either sort of slow down that warming so they have longer to adapt. Or they can use these little pockets of refugia as like stepping stones to getting to whatever temperatures or ever habitats they're ever suited for sort of as yeah, as the climate gradient warms moving north, they can kind of move north with it using these little refugia pockets. Right on. No, that's a really important thing to bring up is all the different factors that can play into what makes a refugia a refugia. But what I love about your work and anyone else that deals in this world is this idea that, you know, physics doesn't change. So it can help us understand both the past and potentially the future. And you really need both to kind of blend that together and connect the dots. Yeah, absolutely. And I think like in, you know, sort of before a lot of this more recent climate research, this idea of refugia was really referring to like paleo refugia. So when we have things like prior ice glacial periods, where were species persisting during those glacial periods and how were they able to sort of persist in those habitats and then serve as sources of dispersal for recolonization once glaciers retreated. So that's sort of how refugia was used in the past. And that does give us a really good idea of biogeography and things like that, which does play into some of my vocal species. But yeah, in sort of terms of it's kind of moved into the sort of current climate crisis is like, we should be understanding where these refugia are, what's driving these refugia, can we map them on the landscape, can we incorporate them into protected areas management and that kind of thing. So yeah, and really understanding how species might respond to those refugia where they are. Very cool. Yeah, the idea of connecting deep time to kind of like state of the art, pushing the envelope, predictive power in science is really exciting. But when you think about all of this blended together, it comes at this idea that, yes, we have to come to grasp with the fact that until globally, we get our heads out of our collective, whatever orifice we want to talk about here. It really does come down to protecting biodiversity. And when we think of the climate change crisis, the effects on not only our species, but around the globe, it all comes down to biodiversity and the way other organisms are going to be affected by this. And refugia are really important part of that is you hinted at there. But what makes it, you know, someone like you that was very zoology, very megafauna focused, switched to plants. What is it about plants that helps studying refugia? I would assume you could do it with animals, but do plants make it easier? I think, I don't know, maybe I've become so plant focused that I think plants are easier. I'm like, Hey, look at this, like, you know, we no shade to people who study mammals, but we always heard a joke, like, you know, what's your sample size, like four, you know, like, yes, I think when you're studying the effects of particularly temperature gradients, it's really easy to use plants because the numerous don't move. It's, you know, you can, you can get that sample size you need, you can sort of move at that gradient and know you're going to find that species that you're looking for. There are cases where, you know, it works with mammals too. I think one of the main sort of mammal refugia paper that papers that I'm seeing come from Pica's in the, in the alpine, because they are very, very temperature sensitive. And so super at risk of climate change. And so there's been a lot of work on sort of alpine refugia of Pica's. Yeah, I don't know, I think plants, they make really good model organisms for this because they are adaptive and because they can't move, they kind of have to either adapt where they are or not persist. And so I think that can give us some clues as to what's going on in the environment that's allowing them to persist. Right on. And as you realized, I'm sure many of us do that get into the world of ecology, conservation, wildlife, biology, you do kind of have to spend some time at least understanding the plant communities because that's the foundation of any ecosystem. So really, no matter what angle you want to take this at, studying how the plant communities are shifting, those Pica's are relying on plant communities, right? Like it all kind of ties together and tells this bigger picture. But sample size is so important when it comes to predictive inference. And that's another really strong suit that you brought up there is that statistical power, because so many people want to argue about statistics nowadays, most of which probably don't even understand how it works. But the more sample bigger sample size you have, the more power you have, at least. Yeah. And when like I said, with plants, it's easy because you can travel to them. So you can go to do, in my case, it was, you know, target habitats and say, are they here? Are they not? And I can go into a lot of different habitats in my study area and see if they're there. And that gives you the sample size that you're looking for to really actually see what the trends are. And then to be able to make predictions about that. Yeah. And as you talked about, there's a lot of different factors on the landscape that can really affect this. I mean, any home gardener will understand like the north side of your house is going to be different than the south side of your house or, you know, wherever you're gardening, this concept is kind of there, whether it's talked about as refugee or not is a different story. But you take a particularly interesting take on this subject that really gets, you know, beyond the typical example of just mountains, which are the easiest, you know, in the ecology textbooks to demonstrate what systems did you particularly look at? Yeah. So I focused on lakes as sources of refugia, which was, you know, I didn't, I took like a limnology course in undergrad, maybe that's like, I'm certainly not a lakes biologist, but yeah, there was something that my supervisor had looked at a little bit in terms of lakes as firebreaks in Northern Canada and sort of places like the Canadian Shield that have a really high proportion of lakes on the landscape and how those service firebreaks, things like say on the downwind side of a lake, there's tends to be less fire or this buffer around the lake that doesn't burn because you have this cooling effect of lakes. So anyway, this idea of lake effect, I think is pretty well known, particularly for anyone familiar with the Great Lakes region, you know, the lake effect there, you know, there's huge changes in precipitation, there's, you know, the fruit belts for us in Southern Ontario where, you know, because of the buffering effects of lakes, the climate is different enough to be able to grow like, you know, peaches and things, which is like, it's Canada. There's not very many places where you can grow peaches. I always forget that fact and go, huh? Yeah. So yeah, this idea of lake effect, I think is pretty well known, particularly with really big water bodies like the Great Lakes. And so something that my supervisor knew, having grown up in the Wisconsin area, was that Lake Superior itself has these populations of plants on the shoreline that are otherwise only found in the high Arctic or in the high Alpine. And so there's these weird disjunct populations of Arctic plants just hanging out at Lake Superior at like a way far south latitude. And so I mean, I think when these populations were first discovered, there was some idea that of course, this is due to the lake effect to some degree, but we didn't really know a lot about that. We didn't really know like, why are they here? What is it about the lake itself that sort of creates this cool habitat for these species to be able to be here and so separate from their sort of next adjacent population that may be, you know, 500 to 1000 kilometers away? Oh, wow. Okay. Yeah. That was another question is, yeah, it's all regional bias, right? And you hear Lake Superior to me, I'm like, ooh, a chili northern, almost tundra-esque, but it's not. And that's a really important fact to talk about in your work is just how much latitude makes a difference the closer you get to the poles. So that is a huge disjunction when you think about tiny plants. Absolutely. And then Lake Superior, I think, is really unique as a model system for this, because it is also latitude and we at this sort of gradient where we get like more deciduous mixed forests, like maple forests, starting to transition into the cold boreal forest that we have throughout most of Northern Canada. So it serves as a really good model of like, what is, if we have that transition happening, is there something about the lake that's like affecting that transition from sort of warmer adapted hardwood forests into these like cooler conifer based boreal forests. So it's a really good way to sort of spatially test this on this like latitudinal gradient. So we, if we have an idea of like from the south side of the lake, so what is down near Sault Ste. Marie, all the way up to the north part of the lake, which is, yeah, it's quite far, it's a very big lake. Yeah. Yeah, actually part of our, I had done some species distribution modeling, I'm part of our fields testing of our models, so let's verify them. So I drove from Sault Ste. Marie all the way around the lake to Duluth, in Minnesota. And it's like, wow, this is a really, really big lake. It's a great one, you might say. Yes. How long of a drive is that to put that into context? I think it took us four days. Oh, yeah. Okay. Yeah. So yeah, I mean, I don't think unless you grow up near them, people really appreciate how big the Great Lakes truly are. And it's one of those situations where you just said four days, that's what I think of driving from east coast to west coast across North America. Yeah. Now granted, it's a complex sort of border to get around there. And there's all these other things going on, but they're massive. And when you think about that much water on the landscape, it really shouldn't surprise people that there's going to be a lot of lake effect. But this is reading your work really the first time in a long time, I've thought about lake effect as someone who grew up between Erie and Ontario as not just solely based on snow storms. Like lake effect is a big concept. Yeah. And so I think, yeah, going back to these little disjunct species. Yeah, what we sort of wanted to look at for my thesis was this idea that refugia of course, as all things with conservation is scale dependent and it's species dependent. And so we wanted to look at this lake effect at this variety of scales. So knowing that these little disjunct plants were sitting on the shoreline, it's like, okay, well, that's this sort of like micro scale. So that's this this lake effect at this very localized scale at sort of, you know, the size of the shoreline where these species are going to exist. And so the idea of why these species are here is that likely as the glaciers were retreating and sort of exposing this like new sort of, I guess, scraped down habitat that would have sort of allowed for some sort of primary succession to happen is that these little disjunct arctic plants or these arctic plants, which would not have been disjuncted for a time, were probably very widespread. And because as the glaciers were retreating, that sort of area in front of them was very cold. Still, it was, you know, not very good habitat, not very good soil development, things like that. So these little plants that are really adapted to those really bad environments did really great. And then so probably they were quite widespread. And then as the glaciers continued to retreat, the climate warmed, that ban in front of the glaciers was warmer, is when we started to get sort of the growth of forests and other, you know, other sort of more dominant shrubs, forest types. And because these little guys just don't have that competitive advantage over taller plants, they were probably just outcompeted. And the rest of the area between became forest. And so yeah, forests grew up as the glaciers were treated. But because Lake Superior, which was formed by the glaciers, maintained these cool temperatures, those species have stayed there. So they've really been there since the glaciers were treated, I think about 10,000 years ago, roughly, is when Lake Superior was formed. So yeah, so they kind of have been there this whole time, which is great. But then it's kind of like, well, why? Like, what is it about the lake? We know it's big and it's cold and it's deep. But you know, like, to allow these species to persist is really cool. Yeah, yeah, when you think of the timescale is involved, it's some people struggle to keep a plant alive through a season, let alone 10,000 years plus worth of them. And I love this idea that like, it's always been a story of micro climates for these plants, because you know, the glaciers, that big frozen chunk of water, not just an open body, is its own micro climate creator kind of thing. And that was rapidly changing too. But let's think about the players themselves. What were some of these species that really kind of tell this story for you? Yeah, I think, I mean, there's a whole slew of them. But I think when you think of like typical of Arctic alpine plants, it's like saxophrasias, there is like, saxophrasia, pinaculata, which is more common in sort of the East Coast. So in Canada, it's more of a coastal maritime plant occurring really only, yeah, in the East Coast, maritime and then on Lake Superior. And that's kind of its distribution in Canada. Things like pink wicula vulgaris, so common butter warts, which is here and more of a like lower alpine, but hill species. And maybe in like low Arctic. Things like purple, purple, and saxophage, saxophagia opposite, opposite of folia, which is very high alpine, very high Arctic tundra plant. So this is like the furthest North occurring plant on the province and the planet is, is I did not find that species, I think there's like one or two occurrence records from the shoreline and probably accessed by boat, which sadly we were not able to do. And yeah, things like, yeah, moss campion also like a really typical sort of high alpine or high Arctic plant, just yeah, these little teeny tiny, sometimes cushion forming little plants that just yeah, normally you would see in the alpine. Right, yeah, when you're walking around a shoreline where, you know, look, there's probably a bunch of good forest over there. It does, it's got to be weird as someone that's getting familiar with plants or has deep familiarity to see the stuff go and what are you doing here? They seem out of place, right? Yeah, why are you 1000 kilometers away from where you're supposed to be? Sure, mother no. Yeah, exactly. Wander away. Alright, so how do you go about trying to understand this? I mean, you think about this concept, I'm sure, you know, these are not unique finds in terms of the most recent decade or so of a floristic study. These are things people have known about for some time. And yeah, where do you go to start chiseling off a piece that's understandable and approach this from a scientific perspective to kind of strike at something that tells that story a little bit better? Yeah, so first we kind of looked at doing some desktop modeling of occurrences, I did species distribution modeling, mostly because also I started my PhD January of 2020. Oh, no, this is going to go so well. I'm a loner. So the intention was to do fieldwork that year, but because of, you know, fluid restrictions, I wasn't able to. So we're like, okay, I guess we're doing a desktop analysis. So yeah, it became sort of this, which actually turned into one of my favorite papers on my thesis. Oh, awesome. Yeah, when life goes through a pandemic, right here, right of paper. Yeah, so we did, yeah, some species distribution modeling to look okay, where we have known occurrence records, like what are the environmental variables there. And so we use both like terrestrial variables, so like things like land surface temperature, like adjacent forest cover, things like that, and then a lot of little lake variables. So what's the depth within, you know, a certain window offshore, what's the water surface temperature, what's the wind speed, some of this data is really easily accessible, some of it is not. I will do a pitch for NOAA because I know there's strong wind down there, but you know, I got a lot of my data from NOAA and that was really important to me. So awesome. Such valuable data. But yeah, so we, yeah, we did this sort of model to look at, okay, we know there's certain areas of the shoreline that are, have a higher richness and abundance of these species and why is that. And so we really found that it really has to do with the water temperature and the depth of the water offshore and directionality. So really in the northeast corner of the lake is where we see the highest abundance and richness of species. And that has to do with sort of the way that lakes appear is shaped, it's like east-west, and so you get all this wind blowing across like these vast stretches of the lake, but then you also get it crossing kind of the deepest part of the water, picking up both cold temperatures that are sort of brought to the surface when there's like upwellings of water or when the water is circulating during the lake's like, you know, annual turnover. So it picks up those cold temperatures that because the wind has had so much like surface to build up, it picks that east shore and then the waves hit that east shore in particular. And so partly it's that the temperatures are quite a bit colder, but then you also have a lot of wave action on the shoreline and that's sort of stopping forest encroachment as well. So you have this cold temperatures, but you also have a habitat still available. So that's kind of what mostly leads to these little hotspots. Yeah, this jump that we see. That's a really cool insight because you have this weird combination of physics, you know, the specific key to water and how that changes the time rate it takes to change water, any amount of degree. Yeah, then you have the thing I needed to know until my candidacy exam. It's like, oh, oh, no, water physics and university. I am I am humbled. Yeah. But then you have quarks of geology, you know, how deep the lake is, but also the scouring of it creating that habitat, all kind of combining in one region of the lake and not to say that like, you know, the lake is cold everywhere, relatively speaking, but having it kind of show you there's these concentrations and having that sanity check, especially of like, no, these are what the real world data also support. It's got to feel pretty cool to have that kind of like, oh, wow, moment of it all coming together to tell a little bit more of a fine resolution picture. Yeah, absolutely. It was very cool. And then that was really, I hadn't really been to these field sites yet. So, but you know, I had this idea, we're like, okay, these are these hotspots. And then kind of going later to validate some of those models in the field and then do other field studies, it was like, oh, no, like, this is where they are. And then when you go to places that don't have those really high rates of exposure on the shoreline, so places where there's maybe islands or little bays, like right offshore, there's no habitat, you get forests cover right up to the shoreline. So when you don't have those like, high wind speeds and wave actions, as well as ice that as it's sort of thawing, it'll go up on the shoreline and scour out without those sort of wind wave effects. There's like, no habitat for these guys whatsoever, you just get outcompeted by trees. No, it's heroic really, like the worst conditions for these behemoths of plant growth and architecture sets the stage for these dainty little Arctic lands. Yeah, just eakin out their little existences. Okay, you start this in a global pandemic, a lot of this is developing models to try to understand some of the major drivers here. What does that field validation look like? What do you go to set out once you have kind of a concept and an idea? How do you take that to the field? And what are you trying to understand once you're out there? Yeah, so when we did our field validation, when we drove from Suzane region, we really just chose, okay, we kind of split the lake into like three regions just to make it a little bit easier. We're like, okay, in this region, let's just go to areas that are predicted to have high abundance or that our models predicted to have high abundance. Let's just see, are these species there? How many of them are there? You know, and what abundance are they there? Which species are there? And just see how true our models were. And they ended up being really close, which was nice. We like good predictive power. Particularly in that northeast shore, it ended up being true that that is where the highest richness is. Our models sort of showed us where it has sort of targets the rest of our field studies, which was really helpful. That is super encouraging, because that's another thing you hear, especially as popular science makes it out to the public. This idea of, well, it's just a model, how much can it reflect reality? But the amount of field validation that goes into these sorts of things and the amount of real world data that feeds in, it's got to feel so encouraging to go, no, this is truly the story we're seeing here. And it's really kind of puts wind in the sails, so to speak, of future work. So where do you take it then? Like, what was some of the next steps in this process to try to understand this? Yeah, so sort of keeping with this multiple scale aspects of the study. So still sticking at this micro habitat scale, we then did some focus surveys on the shoreline. So we go like, hey, we know they're here, but what is it about these specific habitats? Is there more micro habitat availability? And by that, I mean, so typically these plants are growing only in like cracks in the bedrock, where like the tiniest amount of soil has developed. So, you know, it's like, but some different types of rock will weather in different ways. So some will weather in a way that they fracture a lot, and they create a lot of opportunities for these cracks to form and fill with soil. And some weather, so they're very smooth. So there's maybe changes in bedrock type that could be driving like why these species are in families in some places or others. Is it things like soil pH, which can also be an effect of the base rock weathering? Is it, you know, height above the shore or distance from the water? Yeah, things like that is at the presence of competing species. So like really common boreal species. So we did these really targeted surveys on the shoreline. We measured the cracks and the these little splash pools that they grow around. We did, you know, individual stem counts to get abundance and richness, data and, yeah, to sort of look at, you know, like what is, what are these like multifaceted aspects of their immediate habitat that are sort of maybe informing why they are places that they are. And yeah, it really found that a lot of these sort of micro scale site features don't tend to matter so much. Which I guess makes sense. A lot of these species are really highly adaptable to a variety of habitats. So they kind of can grow in like really harsh conditions. But their main limiting factor is usually competition. And so we didn't find a huge effect of competition. But I think it may be that we just targeted habitats where these species already were. So because we know that when in the absence of suitable habitat, they are out competed by forests. And so, but in general, yeah, it didn't tend to be more these site conditions that tended to be those broader climatic effects that sort of still drove the distribution. And endless species abundance and richness was still more based on their like opportunistically, this habitats here so will grow here, but it is more larger climate variables that are driving it. Yeah, yeah, I love this natural history aspect of it because it's such a big picture sort of theoretical start that really drills into what is driving this. And it's so variable species by species that yeah, you have to think about, okay, big picture across a region, it's X. But local scale could be Y or Z. But you don't know until you go looking, we can make these anecdotes up all we want until you test it. You don't know. And I really like this idea of these destructive sort of landscape level events like glaciation, setting a stage for a highly adaptable plant that's only in adaptable to this big climate picture, not once it's bigger bullies come around. Right. That's true. Yeah, it just, it's like I will grow in this really awful spot and be perfectly happy to do so. But then yeah, something taller than it comes along and it just can't compete. As soon as things get too luxurious. Yeah, they're just too slow growing and just too, yeah, not the greatest disversers in the world. So yeah, they just, they just can't compete. But when you think about a water body like Lake Superior, you start to ask this question of how big is this effect? I mean, obviously, competition plays a role in the farther you get away from that scouring the cold, all the things that kind of combine to keep competition down. You're still probably seeing a signal of refugia of buffering, at least if not complete decoupling. I know that's a probably a much more niche concept when you start thinking about refugia. But did you get any insights into like, okay, besides these species, how big is the lake effect of a lake like Lake Superior? Yeah, absolutely. So we also set up these transects that went inland from the lake at multiple spots around the lake to sort of capture that same sort of spatial gradient of parts of the lake that were very exposed versus parts on the west side of the lake that don't have that exposure. And we set up these temperature loggers moving right at the shoreline and then moving all the way out to 100 kilometers inland to see like, okay, at what point do we stop seeing these cooler temperatures or potential changes in forest type? And on that northeast shore, it was like still 10 kilometers, I don't know, like at least two to three degrees cooler than our sort of control plots under can and that's on average, the shorelines and some of those northeast shores were, you know, up to five, six degrees cooler on average than the far inland sites. The hottest day of the year, it was like, the shoreline was almost 20 degrees colder than 100 kilometers inland. So that's a really dramatic change and like, yeah, I've averaged out over the year, maybe not so much. But you do get these pockets where like, that's really hot days are really not being experienced on the shoreline. And so, or even up to 10 kilometers inland. And so that has to have some effect on the forest, for sure. And like what species can can kind of go there, we did do species, survey plots, those inland transects as well, and sort of anecdotally, I don't know that there was like a huge species compositional difference that you couldn't also account to things like riparian effect of the lake. But definitely things like the proportion of coniferous trees was noticeably like a higher proportion of coniferous trees were closer to the shoreline than ever they're out. And as I was sort of saying, when you have that something like Lake Superior on that transitional gradient between deciduous trees and coniferous trees, when we talk about forest transitions under climate change, and this idea that there's like a increase in deciduous driven forests and a lot this overall loss of coniferous forest, things like these refugia that can expand out this far from the lake, and sort of maintain those temperatures for conifer growth, hopefully into the future, but you know, at least for now. Yeah, I mean, you think of the timeframes already we're talking about 10,000 plus years. That's impressive. Now granted, we're changing things very fast, but it gives you a better more complete picture. And of course, you know, when you start getting into the bigger concept of the species pool, the regional filtering that was already in place, I'm sure the differences and the nuances become even more nuanced. But when you start thinking about that temperature distance alone is pretty remarkable. And you think of things like phenology, emergence times, you know, kind of these mutualisms and symbiosis or even antagonistic interactions, how do they change over time? And that's where I think even just kind of starting to scrape away at the surface of this opens the door to so many more questions when it comes to trying to understand, why are these species here? How did they hold on for this long? And how might they change into the future? Because 20 degrees, yeah, okay, it might average out over time, but any amount of that percentage difference could mean something unique to every little combination you can think of. Yeah, absolutely. And we did also, I guess, even expanded the scale study, the final chapter of my thesis is like, extremely like landscape scale. So we did the same inland transects that we did at Lake Superior, and we expanded that to this network of lakes across Western Canada to sort of look at, okay, if something as big as Lake Superior has this effect, how big does a lake need to be before it can have this effect? And so we looked at, you know, a range of lakes that were, you know, maybe small and deep or small and shallow. Of course, nothing's as big as Lake Superior, but we have a great slave lake up in the Northwest Territories that's also very big and very deep. And yeah, we didn't see as much of a cooling effect at pretty much any other lake at Lake Superior in terms of this like dramatic shoreline cooling effect, which was kind of a bummer, I think, to be like, oh, there's maybe this dramatic lake effect, but there is still an effect. And when you talk about phenology, that is where we saw kind of the biggest effect is that particularly on the downwind side of some of these lakes, you might experience spring leaf out a week, two weeks later than forests for their inland. And so sometimes that's offset by maybe the fall temperatures stay warmer for longer. And so you just get the shifting of the growing season, but in lakes that were a little bit bigger, it's sort of like you don't get that offset. And so you just get this delayed spring leaf out and this delay in spring phenology, but not an extension in the fall. So really, you're shortening the growing season. And so I think that also will favor things like conifers, a more cold adapted species when you have this things that are adapted to a shorter growing season like that. Not as dramatic as we're hoping, but there are these signals there showing us that it is affecting phenology for sure. Yeah, you mess with the big dog. You got the biggest answer, right? Everything is going to be much smaller, but having any signal I think is really interesting because it kind of gets at this idea of landscape heterogeneity. We know in ecology how important that can be, what creates it. We have the typical examples of disturbance regimes, fire, that sort of stuff. But okay, where are the water bodies at? And how does that lengthen or shorten growing seasons? How does that affect the insects that feed on these things? The birds that then come up and feed on those insects. And it complicates things, obviously, because now you got a bunch of permutations to try to think about, but it does make you start to appreciate a little bit more of the amount that this planet and the biosphere that we understand today has changed and gone through changes. And what might that look like now with us thrown into the mix? Yes. And I think knowing some of this stuff now is really important, but also being able to think about it into the future. So things like, so yeah, we have great slave lake in the Northwest Territories, very big lake and very deep. But we didn't really notice that much of a dramatic difference. But I think a lot of what drives Lake Superior's difference is that for the latitude it's at, there's this huge temperature differential between the water temperature and the air temperature. And I think as you move further north, you don't get that massive difference because the air temperature doesn't get as hot as it does further south. And so it'd be curious to see as the climate warms, are we going to start seeing some of these more northern lakes become, have this much larger refugee effect or not, maybe, hard to say. But it really emphasizes this need for science for science sake. I mean, you and your colleagues understand why understanding the past can help us predict the future. But when you hear examples like this about, you know, true real world examples of today, we see this because of what happened 5,000, 10,000 years ago. That's where, you know, the work you're doing now. This is why it's so cool to have done this work and now be in a position like you're in professionally to say, hey, we actually can use these kinds of data to move forward into the future to help us understand truly a crisis when it comes to the climate, but also its effects on biodiversity. Yeah, absolutely. And actually, this came into play for in my job now. I mean, this was a project that was already existing and I kind of came into it. Having had this like lake knowledge now and the field data was sort of looking more at very large scales. So for using like, you know, regional climate models to predict how climate is going to change, a lot of those climate models don't incorporate lakes into those predictions. And so now we can say, well, if we are downscaling some of these models and trying to get more accurate results, if we include lakes in the mix, do we see a difference? And we do. You include lakes on the landscape. You do see this sort of, in our case, we're looking at climate velocity. So how fast climate will change. You do see this reduction in predicted climate velocity by just having this, this inclusion of lakes on the landscape. And so I think that gives us maybe a more realistic picture of how the climate will change when we sort of incorporate those aspects of the landscape onto, like, into these big models. Big time. Yeah. And you start thinking about these concepts, especially the farther north and latitude you move is like albedo changes, those air temperature differentials that you mentioned to, I would imagine play another level of needing to include lakes and that differential into the mix. Yeah, absolutely. It's so complicated. And especially because, you know, things like with Lake Superior, yes, it's, it's, it's much cooler than surrounding air and that makes a huge difference, but it's much cooler than the surrounding air because it freezes. And, you know, over the last several, you know, decades, the amount of ice that forms on Lake Superior, each winter is decreasing. And so you start to get, yeah, less ice input, more sunlight entering the water column for longer through the year, you get like an earlier spring turnover that can affect also phenology. So it's like these like trickle effects of less ice coverage, basically. And so the northern lakes still have a lot of ice coverage, but that may also change as things get warmer. So the possibility, again, possibility being highly emphasized here that the idea of this, the system as a refugia could change based on all of these factors and more like its role can morph over time as we change more and more of those variables. Yeah. And unfortunately, working in climate refugia, the big question most people have is like, well, how long, how long is this going to be a refugia? And it's just like, as with all things in ecology, it depends. It depends on so many factors that we just can't predict. Speaking about tangents. Yeah, there's been a lot of work in the refugia world of sort of being like, okay, how can we incorporate this into like land management, protected areas, planning, like, let's look at where these refugia are now and are sort of predicted to be in the future and focus our conservation efforts there. And yeah, hopefully that, using the best of our knowledge and sort of help. It's, it's sadly comical how much they ingrain in you in grad school. It depends is not a good answer when it is like the only answer you can confidently say anywhere professionally. I don't know what to tell you. It depends. It's like, pay me, I'll run more models. Come on. Please. Yeah, I think it's like sort of coming up, you know, as you have to with your thesis of sort of like implications for this research and like next steps or future future work and it's sort of like, okay, what are the conservation implications of this? Okay, if we want to do, if we want to maintain some of these shoreline populations for, you know, whatever reason, maybe they're genetically distinct because some degree of speciation has gone on. Actually, side tangent, that was, I am not a geneticist, but that was a project that would super interest me is, what is the genetic makeup of these species or even the, you know, like functional traits? Have they changed from like other populations? Like superior is cold, but it is still warmer at those southern latitudes than it is in the Arctic. So they are exposed to warmer temperatures. Like it has some degree of adaptation or speciation occurred. Yeah. Or even getting to this idea of like a total genetic novice here myself, like how long ago were they cut off? Like can you use DNA to kind of look a little bit farther back and get resolution? Like when were these populations no longer mixing? Yeah, like, roughly going to say like probably about 8,000 years. There has been some work, I can't remember the species, but there was a paper, someone who did genetic work on different disjunct species in the Great Lakes region, like it wasn't these arctic alpine, it was like disjunct from some other habitat. And they did notice that there was some degree of genetic drift already happening. So yeah, I don't, no one's done that work on these species. So if anyone wants to, that would be so interesting. But where is I going in this? Oh yeah, conservation is sort of like, what are your conservation actions? Like I guess if you want to conserve those populations, you could try to do, you know, like focus removal of competing species, you could try to do transplantation to like there is somewhat adjacent habitats in like canyon systems nearby and things, but yeah, like I don't know the conservation is really just like stop climate change. Slow down. Yeah, so it's tricky, it's tricky to like, you know, do all these models and find out these neat things about these plants, but then it's like, well, what do we do about it? Well, I mean, you bring up such an important concept there is you can do all of the science, get objective data and have relative confidence and predictive power. The value system is what we do afterwards with all this knowledge, right? And that becomes a very different kind of philosophical debate. And this is why I think some people are so hesitant to make recommendations because, you know, we don't have anywhere near a complete picture. I mean, you've just illustrated so many different ways that this can get infinitely more complicated. So like to go into this with like a hubris of, well, I know what to do. It's not that simple. And I'm not saying everyone acts that way. I think it's a, you know, the tail end of a bell curve that thinks they know what to do and another tail end that thinks we shouldn't do anything. Where do we find that beautiful middle ground of like balancing conservation and practicality and not creating more of a mess out of an already highly disturbed, messy system? Yeah, absolutely. I think, like I said, the bit of work that I know has been done is incorporating climate refugia into protected areas playing, I think has been a good step. Or just even some like gap analysis of like, okay, where are protected areas, where are the refugia and how well are we already doing? Right. Like to some degree, not bad. I mean, a lot of the key area of like superior is a national park. And so that's great. That's already protected. And those populations should be hopefully good to go for a while unless there's other like climate related things. But yeah, but then also looking at, I guess, this is more philosophical discussion of like, protected areas that are dynamic. And so, you know, maybe what we consider to be important now is going to change as, as ecosystems changed. And so, yeah, I don't know, maybe we have to look at changing where these areas might be over time, if that's a whole other. Oh, yeah. Yeah. I mean, the idea of winners and losers is not emphasized enough. Like not everything's going to be equally affected. And sometimes rare will become common and vice versa. And I mean, that's a whole nother infinite can of worms we could open up right now. But they're all important ideas to get people thinking though, because this is where I think bringing as many minds and backgrounds to the table is where the strength really starts to occur. Because you never know where that one kernel of an idea can evolve into something actually practical and doable, you know, and that's, that's why the more voices please more insights and more input in this process. And I think, you know, emphasis in the past, we've done a lot of emphasis on conservation of like single species. And I think in a lot of places, we've moved away from that more to like conserve the process and conserve the forest is just why we do that like allow more burning in places because that's a natural process and things like that. So yeah, I don't know. I don't know what an answer for that. Yeah, I think at like superiors, like that's the process is these cold, cold temperatures and that's currently allowed to happen on. Yeah, a lot of that shoreline is protected. And that's great. That's an encouraging first step. Make sure that it stays that way. Big time. Well, Dr. Hillman, this is incredible. I mean, it's really obvious now why this just consumed you and dragged you into it kicking and screaming into the plant world. But I'm so thankful you did this work. I'm so thankful your colleagues continue to do this work and that you've been able to evolve the process into looking towards a really uncertain future for not only us, but so many of these species. But most importantly, thank you so much for talking to us about it today. Yeah, thank you for having me. This was great. I will always talk about climate refugia. It's super fun topic. Careful what you say. I might ask you back. No problem with that. All right. Well, in the meantime, keep up the amazing work and thanks for talking with us. All right. Thank you. Cheers. All right. Phenomenal and fascinating work. I thank Dr. Hillman for taking time out of her busy schedule to talk with us about climate refugia. And as always, go check the show notes over at IndefensibleLants.com because that's where I put all of the links so that you can learn more about this work and all of the work we discuss on this show. Climate refugia are so important to understand and are going to play an increasingly important role for biodiversity moving into the future. And of course, conversations like this don't happen unless you support IndefensibleLants. There's so many great ways to do that. As I mentioned at the beginning, we have a Patreon that gives you access to an entirely separate podcast about learning how to garden better. Patrons make this podcast possible. I can't do it without them. And I have a big shout out to the latest producers on this podcast. A big, big thank you goes out to Joe, Drew Soffola, S. Heller, and Andy. All of them have recently signed up at the producer credit level, so they're maximizing their support of IndefensibleLants and getting all the great kickbacks in the process. 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