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You're listening to A Climate Change this is Matt Matern, your host, I've got a great guest on the program today. Dr. Lee Frelich, Director of the University of Minnesota Center for Forest Ecology. Lee was named one of the top 1% of all scientists in the world on ecology and the environment. So welcome to the program late.

Nice to be with you, Matt.

Well, tell us a little bit about your journey. And what led you to studying this area and and what is the mission of the Center for Forest Ecology there at the University of Minnesota?

Okay, well, then, we might as well start when I was five years old, and my grandmother came to visit every couple of weeks. And we would go out in the garden and talk about why this plant was doing well or why it wasn't doing well. And so I started learning about plants and trees as a very young person. And then later, we had to read a book every week, my mother took us to the public library, and we had to read a book every week.

And I pulled this book off the shelf called the vegetation of Wisconsin, by a professor from the University of Wisconsin, it's one of the great classic works in the history of ecology, by John Curtis and I read it about 10 times. And this was when I was 12 years old, and I decided right then I was going to go to the University of Wisconsin, get a PhD in Forest Ecology and continue the research that this professor had done, because he died just before the book was published.

And that's exactly what happened. Wow. And then I got pulled to the University of Minnesota, and formed the Center for Forest Ecology using money from donations from philanthropists and grants that I got. And then basically appointed myself, the director of the center just gives me a little bit more independence, still being within the university, but kind of independent, and I've been doing that for the last 20 years.

So we do everything from forest fires and wind storms, climate change invasive species, I have collaborators in in 25 countries around the world as well as throughout the United States. So we've, we've done lots of studies of the big fires in the Boundary Waters in northern Minnesota, the big wind storms that we get here that flatten hundreds or even 1,000s of square miles of forest, houses of increasing drought frequency and warmer climate is affecting the growth of, of trees. And the earthworm invasion has turned out to be a big thing. Because as Darwin said, earthworms are the most important group of organisms on the planet.

And he was right. And you couldn't really tell until earthworms invaded an area like the Midwest, which didn't have any native worms, that huge change they make in the ecosystem. So those are some of the things that we've been doing at the Center for Forest Ecology.

Well, that's fascinating. So I can't resist the opportunity to ask more about why earthworms are the most important species.

Yeah, well, for 500 million years, they have transformed the structure and the chemistry of the soil over vast tracts across the planet. And of course, that interacts with the chemistry of the atmosphere. The how the soil functions affects what plants can grow there, and that in turn affects what types of wildlife species can live in a given place.

So Darwin actually published a whole book about earthworms it was the last thing he published before he died. So the book was in 1881, so it's way after he did Origin of the Species. And he had done some earthworm research and concluded they were the most important group of organisms and making the earth what it is today, and I think, modern day scientists still agree with that. Humans are going to catch up pretty soon though. I'm to earthworms.

So I mean with glow while warming, they may soon have an even bigger impact. But yeah, it's just amazing what they when you see them invade an ecosystem that didn't have earthworms how huge the impacts are. And ironically, where these earthworms are native in Europe, the ecologists that live there don't even realize what the impact is because they can't see the with and without these earthworms, like we can hear.

So what is the impact in Minnesota and other parts of the US?

Well, we in our forests, they eat the forest floor so that it's a multi year accumulation of leaf litter. It used to be six inches thick, and kind of have the texture of a memory foam mattress when you walk on it. And basically, that leaf litter layer insulates the soil keeps it cooler in the summer, a little bit warmer in the winter, and the decaying organic matter is also the rooting medium for a lot of the native plant species. There's many, many different soil insects and smaller soil fungi that live in that leaf litter.

And then when the earthworms invade, they eat that it's just a big pile of food for them. What an earthworm does for a living is eat dead leaves, basically. So the soils have warmed up about seven or eight degrees Fahrenheit, and the areas where the earthworms have invaded. So essentially, the root systems, our forests have already experienced the level of warming that we expect from the general circulation models that they're projecting for high warming scenario by the end of the century.

So the below the soil part of the ecosystem has already experienced that level of warming. They also cause nutrients to leach out of the ecosystem. And then there are a lot of plant species, especially orchids and some species of firms that are rooted in the organic matter. And they are basically wiped out when the earthworms invade. And tree regeneration is all different there. That's all different species of trees, the trees that were successful in the old environment, pre earthworm, are no longer as successful. And so everything is different.

And then one of the biggest things they do is facilitate the invasion of invasive plant species that come from the home continent out of the earthworms. So, in the Midwest and northeastern part of the United States, that would be things like buckthorn and to Terry and honeysuckle and garlic mustard. Those invasive plants, which are incredibly bad problems for conservation of our forests, are facilitated by the earthworms because they're adapted to the earthworms through evolutionary time on their home continent.

Well, what are the number of questions arise from that? Like, why is our soil seven to eight degrees warmer if the planet has only warmed by, say, you know, one or two degrees? What's the likely effect of this? Meaning the soil getting that much warmer? And are there any ways out of this to solve for this problem?

Yeah, the soil gets that much warmer because the leaf litter used to insulate it during the summer and kept it cool. So during the warmest part of summer, the soils directly exposed to the air instead of having this layer of insulation. So that's why it was able to warm up so much more than the average air temperature. What it does to the plants in addition to the depletion of nutrients that leach away when the earthworms invade is put them under drought stress.

So there's a lot more evaporation from the soil. A lot less water soaks in to the soil because it used to soak into the leaf later and it was like going into a sponge which then slowly dispersed the water into the soil. But now it just hits the soil directly and runs off because it's a hard surface. So it's causing drought stress and heat stress for the trees way more than you would expect just from the increase in air temperatures.

So what do you see is any solution to this particular problem?

Well, we can kill ation problems. Yeah, we can't really get rid of earthworms if we tried to poison them. We would kill hundreds of other species of I have soil fungi and microbes that actually belong in the soil. So that would be a bad thing to do. So we're going to have to learn to live with them, unfortunately. And so that's what we're thinking about. Okay.

So one of the things that I had seen floated and is a trillion trees and that how we can plant a trillion trees, whether this is feasible, what would have to be done to achieve this? We're going into a break right now. But when we come back from the break, Lee, I'd like you to address this.

You're listening to A Climate Change. This is Matt Matern, your host and I've got Dr. Lee Frelich on the program, Director of the University of Minnesota Center for Forest Ecology on the show and he'll be right back to talk to us about a trillion trees is that the future.

You're listening to A Climate Change. This is Matt Matern, your host. I've got Dr. Lee Frelich, director of the University of Minnesota Center for Forest Ecology on the program. And Lee, you were just telling, I was just asking about whether the goal of the trillion trees is feasible, and how could we actually achieve this?

Yes, I think it is feasible. If it was done over a decade. I think we could plant that many trees, it breaks down to about 125 trees per person. And so one of the questions I asked when I'm teaching classes is could we plant 125 seedlings for each person on the planet over the next 10 years? And the students are all nodding their heads?

Yes, of course we can. The only question is, will we do it? The some of the cautions needed are that you need to have local expertise everywhere in the world, because you have to plant the right species a tree on the right soil type. So you really need that local expertise, and you need follow up a lot of planning projects, they plant trees, and just leave and most of them die. And you need to follow up. If some of them die, fill in that planting, pull the weeds if necessary, maybe give them some water in the first few months to make sure they get established.

So the right type of tree in the right place. Make sure their native trees for the region where they're being planted in the follow up is is very important. And that's exactly what our we're doing with our project called green again, Madagascar, which one of our former graduate students, Matt Hill, from the University of Minnesota, moved to Madagascar and started this project to rebuild the rain forest and Madagascar, which was mostly destroyed over the last several decades by deforestation.

And so we now have a nursery there that grow is 58 different species of native trees. And believe it or not, a number of them don't even have a scientific name. We just have the local name that the Malagasy residents have given the tree, but they know all about the species, and we're able to grow them and the local farmers are eager to have plantations of forest on their land.

So and it is part of the plant for the planet project, which is part of the trillion Tree Project. So if you go to to the plant for Planet, for the planet website, there are sites all over the world on a map.

And you can click so they're dots, you can click on those dots. And it will tell you about that site and what the project is doing with tree planting. And one of them you can click on is green, again, Madagascar, and you can you can donate money right off the bat right there if you want to. And that 96% of that goes directly to our employees in Madagascar who are growing and planting the trees. But there are many projects around the world.

So no matter where you're interested in establishing new forests, this plant for the planet website will allow you to to do that. So that's a major platform for bringing the funding needed into the the tree planting arena.

That's fantastic work that you and your students are doing. And tell us a little bit about the progress that's been made in Madagascar in particular, that's a fascinating story of one person just jumping in there and getting it going. Love that. Shout out to your student Matt Hill and then green again Madagascar, people should look that one up, as well as plant for the planet.

Tell us how many trees has, has plant for the planet planted since it started and how many other organizations out there doing similar things as the US government funding a major tree planting? And where do our efforts stand? And how much more do we need to ramp them up?

Yeah, I actually don't know the number for all of plant for the planet. I mean, we're plus 50,000 Trees already at Green again, Madagascar, I'm sure they're in the millions, or even 10s of millions for plant for the planet.

Yeah, and there are other efforts that the US Forest Service, The Nature Conservancy, there are a lot of organizations, organizations that plant trees in areas that need to be reforest that there's a bout 2.2 billion acres of land on the planet that's been identified, that has a climate that will support for us, but is not forested at the current time and not needed for agriculture.

So there's plenty of land that we've deforested around the world. And a lot of these plant for the planet sites covered have very wide geographic coverage of those areas around the world. So I think we need to ramp it up by another order of magnitude, though, and then keep that up for about 10 years.

And what would happen at that point, if we actually planted a trillion trees in the next 10 years, over the next 40 to 50 years, they would grow. And we think that they could take as much as 100 parts per million of CO2 out of the atmosphere.

And that's about the amount of the increase that we would expect from CO2 emissions over the next 40 to 50 years. So in other words, they would help to stabilize the CO2 level of the atmosphere, if we had that mass of a planting of trees, would help stabilize the CO2 level of the atmosphere for a few decades while we switch to renewable energy sources. So that's my personal solution for climate change.

So it's in terms of the US Forest Service, do they have a goal as to how many trees they're planted to plant in the US over the next 510 years?

I don't know their exact goal. But they, of course, they have their own lands, you know, the about 150 million acres of national forests. And they have areas that need to be reforested. And their goal is just to get the vegetation cover that they desire on those lands.

And I think they're making pretty good progress towards doing that, of course, what's happening now is some of these big forest fires and droughts in some of the national forests are starting to kill trees faster than they're being planted.

And it's making it difficult in terms of trying to find species that are more drought tolerant for the new plantings, having to be more careful about whether you plant something on a south slope versus a north slope. So they're trying to learn about all of those things. And what's the best way to go forward, given that there's some warming of the climate locked in.

So it becomes very complicated, and with the warming climate, because if we go on a high warming scenario, like a business as usual scenario, and say, we fail to plant all these trees, and we get behind the curve, and a lot of this land that is available that has a climate that will support trees right now will no longer support trees, then we really get behind the curve.

Lots of forests start to die, they start giving off carbon, it's a it's a feedback towards higher carbon. So we really need to get ahead of the curve right now. And I think we need to ramp up everything by an order of magnitude in the in the tree planting world to do that, and then keep that up for at least 10 years.

Now in terms of the order of the magnitude that you're talking about, is it two times 10 times 100 times and kind of a related question industry driven production targets are forcing, some say excessive amounts of wood being put up for sale on public lands. What's what's the solution for that?

Yeah, well, ecologists, forest ecologist think that we need to let forests get older. And other words, we need to learn from the natural disturbance regimes that we have historically had, how often fires occur how often when storms occur, we've been harvesting on cycles that are shorter. And the younger the average age of trees on the landscape, the less carbon is being stored in the trees.

So we need to do what we call close to nature forestry, where we try to to emulate the natural disturbance regime, which often allows trees to get older than we have in a harvesting system. And so this is something that's been pointed out by forest ecologists that we need to do emulate natural disturbances and also allow forests that do have these big fires and wind storms to recover naturally.

You might be surprised that upwards of 80 or 90% of the carbon is still present, even after a big forest fire, even the big intense forest fires they've had in California, most of the carbon is in the big tree trunks and the most of the the trunks only have the outer part burned.

So most of the carbon is still there, the new little seedlings are trying to grow. And if you go in and salvage that not only does the equipment emit CO2, but you squish all the germinating seedlings, and you remove all that dead wood, which is an important part of the function of the ecosystem in recovery, because it rots and releases nutrients as the new trees grow. So it can really limit the recovery and the amount of carbon that the next generation of forests can can accumulate.

You're listening to A Climate Change. This is Matt Matern, your host, and I've got Dr. Lee Frelich, on the program - Director of the University of Minnesota Center for Forest Ecology. We'll be right back to talk to Lee about some very important questions facing our country and the rest of the world.

You're listening to A Climate Change. This is Matt Matern, your host. I've got Dr. Lee Frelich, Director of the University of Minnesota Center for Forest Ecology. And Lee, I want to ask you a question about Minnesota, Minnesota, historically, has the three T's taconite tourism and two timber. How do you strike the right balance between these three competing interests? Given that Minnesota is said to maybe become the new Kansas if we don't make changes to the way we're treating the environment?

Yeah, well, the tech a night actually comes from a pretty small portion of the state. And we're happy that we provide most of the iron for the for the United States, I think it's like 90% of all the iron comes from Minnesota. And so it comes out of the Northern, the boreal forest in northern Minnesota and goes on a train down to Duluth and gets on ships and goes to Gary, Indiana, or to Detroit and gets turned into steel.

But that's not all that disruptive. It's not a very big area that's disrupted. It's just the Iron Range, which is only a few miles wide and about 100 miles long, and it's a very small proportion of Minnesota. The timber in the tourism, though, that is really going to depend in the future on what type of a warming scenario we have. So we have two very different alternate futures for Minnesota. One is the reduced emission scenario and according to my research, where we mapped out the the different biomes.

So we have the boreal forest biome, which are the coldest forests on the planet in northern Minnesota and then temperate forest which is more like maple and oak, then there's some grassland along the western margin of the state. So for a reduced emission scenario 80% or more reduction, the climate would only warm up a little bit and Minnesota would still be pretty much the same. We would still have boreal forests and temperate forests with our all of our 1000s of lakes.

However, if we do the business as usual scenario, the amount of evaporation during long growing season and much hotter summer yours would outstrip rainfall to such an extent that the climate would be too dry to support trees in Minnesota. So what we call the prairie forest border, which is the the edge between the grassland climate and the forest climate would move 300 miles to the north and east.

And that would essentially turn the Boundary Waters in northern Minnesota from a boreal forest into grassland, and maybe some groves of oak trees interspersed, what we call oak savanna. And there'd only be a little bit of forest in the very northeastern tip of Minnesota. And so I was doing a story in the Washington Post, and I made the quote that we have perfectly good Kansas now, and we don't need a second Kansas in Minnesota.

And the ended up in the light being the first line of headline story in the Washington Post, which allowed me to discover what it's like to get worldwide feedback from people who do and don't believe in climate change. But yeah, the the prairie forest border goes from Minnesota, all the way up to Edmonton, Alberta.

You know, 1,500 miles, if that moves 300 miles to the north, and that southern most 300 miles of the Boreal Forest turns into grassland, all of that wood is going to decay and become carbon dioxide, and the trees will die and not be replaced like other trees like they normally would, after a normally functioning forest after a forest fire will regenerate to forest.

Well, that wouldn't happen because the climate would no longer support trees. And that's one reason why the IPCC report, Intergovernmental Panel on Climate Change shows the margin of the Southern margin of the Boreal Forest in northern North America as a climate tipping point. And Minnesota as part of that, that tipping point. So everybody loves the fact that we have three biomes in the state.

And we don't even have to cheat like California and have mountains in order to have several biomes. It's a flat state, and we still have three biomes. It's one of only two places in the world where those three biomes come together in one place, you know, the other being Kazakhstan, by the way.

So it's a very unique place on the planet because of that, and therefore you lose the boreal biome, then Minnesota will be less unique, you won't be able to go from a prairie landscape to a rocky boreal forest landscape. I mean, it's amazingly diverse. Northern Minnesota has a climate almost like the central part of Alaska. And the southwestern part of the state is actually quite dry and has a grassland climate. So it's way more diverse than you think.

That is fascinating. Having spent a little time at the Boundary Waters when I was around nine years old, it is a beautiful area, and it's the thought of losing such a treasure is devastating to the US, it is one of the many treasures we have. So what do we do to protect this? These three biomes in Minnesota and places all over the world that are suffering stress from from climate change.

Well, we've got to reduce CO2 emissions as much as possible get ahead of the curve. So we don't start having these feedbacks kick in that where we no longer can control the amount of CO2 in the atmosphere.

So that means doing the trillion tree project going full steam ahead with renewable energy projects. eating more plants, I mean, I hate to tell people what their diet should be like. But we know that plant based agriculture emits a lot less CO2 than animal based agriculture. Moving to electric vehicles, with the electricity, of course produced from power plants that are using renewable electricity.

If we do all those things, and we do them all quite rapidly, then we can go on that low emission scenario and there won't there will be very minimal changes in the locations of biomes. So the sense of place will stay the same in most areas.

So what has been done in Minnesota in terms of combating climate change in terms of replanting forest and in the scenarios that you had discussed where climate change kind of goes out of control basically, with the business as usual, what would happen to the 10,000 lakes in Minnesota? Are we looking at them drying up? Or what, what what happens next?

Yeah, though, the lakes, probably, while some of them would dry up, it would be a, it depends on the context of each lake, it depends on the shape of its basin, the level of of its outlet, if there's an outflow, some lakes just depend on the level of groundwater. And that would fall in a warmer climate because the evaporation rates would go up and the water table would fall and other lakes depend on streams flowing into them until it fills up to the outlet where it spills over.

So there would be really different effects in different lakes. But now limnology, just told me maybe 40, or 50% of the lakes in Minnesota could dry up if we go on that maximum warming scenario. So we are one of the leaders in Minnesota in going to renewable electricity sources. So and the governor has been in support of that, who was reelected, that we continuously go to higher and higher proportions of our electricity coming from new renewable sources.

And there are lots of different tree planting efforts in Minnesota. And there are some experiments to experimenting with some trees from a little bit further south because we're going to have some warming and just see how they do here. For example, though, I live in Minneapolis, and the Minneapolis park board planted London plane trees in Minneapolis. It's a type of Sycamore that actually is from London. And I was just shocked that they actually survived here.

So that tells you something about how milder winters have become that you can plant a London plane tree in Minneapolis, and it doesn't die during the winter. You know, we used to get 30 or 35 below zero temperatures here in the winter. And now we can hardly squeak out 20 below zero. So for us that means it's it's pretty mild. So that's one of the positive sides of a slightly warmer climate is there's more species of trees that we can plant here.

So Nature Conservancy is doing some of these experiments, the Forest Service is doing some of these experiments, because there's a lot of national forest land in northern Minnesota. So if we can do that reduced warming scenario, those forests will stay in good health. And I think we'll be in very good shape.

I guess one of the concerns is putting species that aren't indigenous to the area in in another place and what those outcomes will be course we've done that all over the world and planted things that aren't indigenous, and we've seen some pretty bad repercussions. I'd love to get your take on that after we get back from the break.

You're listening to A Climate Change, this is Matt Matern, your hos,t and I've got Dr. Lee Frelich, Director for the Center for Forest Ecology at the University of Minnesota. We'll be back in just one minute.

You're listening to A Climate Change, this is Matt Matern, your host. I've got Dr. Lee Frelich, Director of the Center for Forest Ecology at the University of Minnesota.

Lee just wanted to talk to you a bit about fire season and fire management practices. Is this a result of bad forest management? Or we have too many monocultures? Are we just not calling the Forest properly? What's what's causing these historically large fires to occur? And how can we decrease them going forward?

Yeah, that's a great question. And actually, there's two things involved. One is we've suppressed a lot of fires over the last 100 years. So a lot of the areas were managed by Native Americans and they did these frequent low intensity burns and kept the density of trees low in some areas and the amount of fuel at a lower level. So that has stopped in a lot of areas. And a lot of people are resistant to the Forest Service starting up prescribed burns in order to get back to that regime.

Because there have been some escaped prescribed fires that have caused disasters for people. So that's one of the two things. And the other is that growing seasons or the the fire season, the length of the warm season is much longer, even with the warming we've already had, and there are droughts that are much more severe. So the vegetation has a lot longer time to dry out. So we have historically dry conditions.

And those two things together are fueling these huge fires. And it's not just in California and Oregon, it's all over the world. I mean, they had a fire that was 10s of millions of acres in size last year in Russia. And there have been fires in northern Scandinavia. And across the boreal forest, which is the spruce and fir and pine that kind of runs from central Alaska across Canada dips into northern Minnesota a little bit and goes out to Labrador.

The boreal forest is experiencing more frequent fires because droughts that were warm enough and dry enough for a big high intensity forest fire are occurring more often now. And what's happening is at the time of the second fire, the conifers aren't old enough to bear seeds. So say you get a big high intensity fire and Jack Pine, which is a important species in the boreal forest regenerates.

And then 15 years later, there's another fire but Jack Pine doesn't get cones until it's 20 years old. So it's really exterminated by those events where you get two fires in close proximity and what happens it changes the forest of birch and Aspen because the seeds of birch and Aspen can blow in from miles away. They have really tiny seeds and the Aspen seeds have plumes on them. So we're seeing a conversion of coniferous boreal forest over to these broadleaf deciduous birch and Aspen species in the boreal forest.

And the other thing that's happening as we're getting big wind storms, they're huge wind storms we had a windstorm in in 1999 in northern Minnesota that level four or 500,000 acres of forest in about an hour with 120 mile an hour winds. So just a big thunderstorm with a high intensity down. And then you have 50 to 100 tons per acre of blown down dead trees.

And it's too remote to salvage any of that. And when you get a drought and it burns, it's an extraordinarily high intensity fire. But instead of the fire being our crown fire, it's like a crown fire sitting right on the surface of the soil.

And so it's extraordinarily high intensity and it kills any remaining conifers, all the seeds, all the seedlings, everything and it's just regeneration of birch and Aspen afterwards. So both two fires in a row and wind followed by fire is causing this conversion of boreal forests from conifer to the deciduous.

So what kind of forest management practices should we adopt to to combat these changes?

Well, we we should reinstate some of this understory burning and try to do it over a bigger area. I'm not sure we can get back to the level that that this continent was at when the Native Americans were managing everything.

But we should do more of that so that when a high intensity fire hits those areas where the fuel has been reduced by these more frequent low intensity fires, it will at least drop from to a lower intensity no longer via high intensity crown fire and be at a level where you can actually fight the fire. mean you can't fight up a crown fire in a coniferous forest the intensity is way too high to have an impact through firefighting.

But if the density of fuel is lower because the forest is managed to have big trees, and not a lot of small trees and underbrush, the intensity of the fire will be lower. And that was the structure a lot of forests had before the European settlers. So we should try to get back to that. And hopefully we can do that along with reducing CO2 emissions so we can at least keep the same forest type and restore it to those conditions where it's more resilient to fire, it's less susceptible to fire and so that we can continue to have the same forest types and enjoy all the benefits in terms of the wildlife that lives there.

The tourism, the fishing, if you don't have healthy forests, you're not going to have healthy waters either. And, of course, the timber industry. So there's just a lot of reasons to do that.

Tell us a little bit about bringing in the non-native trees and what problems those cause along with tree diseases and how we're managing those problems. And then one other question related to what you just said is, can the forest managing services go in after those fires?

Where say, a certain pine tree has been wiped out because of successive fires and replant those? Or is it just too difficult to do after something like that has occurred?

Yeah, it is, it is possible to restore a lot of times. Either seedlings can be planted by crews on the ground or can be receipted areally, you can get seeds and distribute them with a helicopter. So that can be done. If the area of the fire of fires becomes too huge, it might become difficult, but it can generally be done. The question about bringing in new species, which we call Neo native, so there are species which are native just to the south. But with a warmer climate, you can plant them further north.

That's a it's a good question. People are always worried that some of these will become invasive species and spread really fast. I think that concern is a little overblown, based on my experience. And in nature, what we've observed is trees are doing that themselves. For example, in the Boundary Waters in northern Minnesota, we had 2000 randomly located plots throughout the wilderness, and every one of them had the seedlings of red maple, which is not a boreal forest species

It's a temperate forest species. And they have spread in there on their own in response to the warming climate. So I think we're going to have to do that. Because all species of trees will not be able to adjust fast enough to the warming climate, especially if we ended up with the high warming scenario, we might have to actually assist trees in in migrating in order to have species of trees that can tolerate the new climate, it might be too warm for the former species.

But of course, going back to the low emission scenario, we wouldn't have to do very much of bringing in these neo-native species with that scenario. And then with regard to diseases, one of the problems with climate change for insect pests and diseases is when trees are under drought stress. They're more susceptible to insects, and the insects and diseases can live in places they couldn't live before.

For example, emerald ash borer is killing ash trees in southern Minnesota, and that it's an insect that comes from Asia. And it can't move into northern Minnesota right now, because we're still getting temperatures between 50 and 60, below zero every four or five years. And the insect can't tolerate that temperature.

But if it warmed up enough, they could move in and we have over a billion black ash trees in northern Minnesota, that for a high warming scenario would then be susceptible to Emerald Ash Borer and would be killed. So there are lots of insect pests that are limited by cold temperatures. So you know, we have this saying in Minnesota, we want to keep the North cold. You know, we like our extreme cold. It keeps the riffraff out and it keeps invasive species out and it keeps insects and diseases out.

There's a lot of benefits to being frozen.

Well, it's been a pleasure talking with you. Dr. Frelich. It's a lot of great work that you're doing and in particular plant for the planet which you had talked about and there, everybody should go to their website and donate to them because they're planting millions of trees to help reforest the planet.

You're listening to A Climate Change. This is Matt Matern, your host, and we'll be back next week. Thanks for listening.