Talking Trees with Davey Tree

New Year, New Tree! Plant These Trees Instead in the New Year

December 22, 2022 The Davey Tree Expert Company Season 2 Episode 49
Talking Trees with Davey Tree
New Year, New Tree! Plant These Trees Instead in the New Year
Show Notes Transcript

Dan Herms, vice president of research and development at the Davey Institute, talks about what trees should be planted for changing hardiness zones, his climate change research and why you should be optimistic but realistic about mitigating climate change.  

In this episode we cover:  

  • The research Dan has done on climate change (0:50) 
  • How climate change will impact trees (2:22)  
  • Changing hardiness zones and what to plant (3:10)  
  • Picking the right tree for the future (5:25)  
  • How homeowners can help mitigate climate change (7:54)  
  • Fighting climate change through education (9:05)  
  • Besides planting trees, what else can be done (11:20)  
  • Is it possible to slow or reverse climate change? (13:30) 
  • Is Dan encouraged about the climate change outlook? (14:50)  
  • What Dan would tell those that are scared about climate change (16:40)  


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To learn more about climate change, visit  

To learn more about the effects of climate change on trees, read our blog, Climate Change on Trees. 

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Have topics you'd like us to cover on the podcast? Email us at We want to hear from you!    

Doug Oster: Welcome to the Davey Tree Expert Company's podcast, Talking Trees. I'm your host, Doug Oster. Each week, our expert arborists share advice on seasonal tree care, how to make your trees thrive, arborists' favorite trees, and much, much more. Tune in every Thursday to learn more, because here at the Talking Trees podcast, we know trees are the answer. If you are a long-time listener of the Talking Trees podcast, you will recognize our next guest. That is Dr. Dan Herms. He is the Vice President of Research and Development at the Davey Institute and has done remarkable research concerning climate change and trees. Welcome back, Dan.

Dr. Dan Herms: Thank you, good to be back.

Doug: Let's just start off with this extensive research you've done related to climate change. As I remember, for me, you brought up the memory of that summer of 1988, I think it was. For gardeners and plant lovers alike, that was a tough summer.

Dr. Dan: 1988 was an epic summer, extremely hot, extremely dry. I was conducting research for my PhD in Michigan that summer, and we had a number of days in central Michigan over 100 degrees Fahrenheit, many days over 90 degrees, very little rain. I just saw a lot of tree stress and tree mortality. In fact, Doug, 25% of the white birch trees in the Great Lakes region died in the years following 1988, the several years following 1988 due to a massive bronze birch borer outbreak. Bronze birch borer is a native wood borer that colonizes drought-stressed trees. Their defenses are weakened. Just massive die-off of birch. Other tree stress events, very apparent following that very hot summer of 1988.

Doug: I remember that too. I remember the borer explosion from that and how many birch trees we lost in landscapes around our area. Right now, tell me a little bit about the research that you're doing or have completed.

Dr. Dan: I've been conducting research on how climate change will impact trees and tree health, the trees that should be planted for the future climate, projections on how much the climate will warm in coming years, and how we can anticipate, respond to that, and how trees can contribute to climate change resilience and mitigating the impacts of climate change, especially in urban environments.

Doug: I'm interested in like a change of species of what we should be planting and what you really shouldn't be planting, depending on where you are. That's what we're seeing here, right? Is where there's certain species that we don't think are going to do too well as the climate changes, and that's going to change what we're going to be planting, right?

Dr. Dan: Yes, that's correct. If you're familiar with the USDA climate hardiness zones, the winter hardiness zones, over the next 30 to 50 years, we can anticipate no matter where you are in the country, that your hardiness zone is going to increase by one or two levels. For example, in Kent, Ohio, where my office is, the hardiness zone is projected to change from Zone 6, where it is currently, to Zone 7 or 8 by mid to late century. Just when I was a college student, it was Zone 5. We've already seen an increase from Zone 5 to 6. Won't be long before it's going from Zone 6 to 7 and Zone 8. To provide some perspective on that, Zone 8 would be equivalent to the current climate of Northern Alabama, Southern Tennessee climate. That's what we're looking at. Of course, the trees then that grow in those environments are to a large degree different than the trees that we have here now.

Doug: You've talked about it before, and I've heard this said, sugar maple is a good example. It loves that Zone 5, Zone 6, right?

Dr. Dan: Sugar maple, Zone 5, Zone 6, Zone 4. It's a tree that's like an iconic tree in New England and Northeast US and in Northern Michigan. The fall color, the maple syrup, and it's projected that the Ohio climate by mid to late century will not be very hospitable to sugar maple, for example.

Doug: When we're thinking about planting something, what would be a choice? Okay, I don't want to plant a sugar maple because I don't want it to struggle in the future. What would I put in there? Would I pick another maple that would be more for this climate? Do I look for a different species altogether, you think?

Dr. Dan: Yes. Well, there are maples that will do well in, say, the Northeast Ohio climate in the future. For example, red maple. You can look at other species. To think about it in a more general sense, I think about looking at trees that do well here now, but are also doing well farther south in warmer climates. We have to plant a tree that's going to tolerate today's environment, but the climate is changing rapidly enough that the tree we plant today will be experiencing a different climate within the course of its lifetime. We hope that we plant a tree today and it'll still be here in 100 years from now. That's going to be really different, the climate.

Yes, think about trees that do well now. That can be challenging because this weekend, the forecast as we head to Christmas Eve and Christmas were predicted in Northeast Ohio to get below zero. We have to plant a tree that will tolerate that winter weather. We're seeing a big cold blast coming down from the Arctic. Tolerate that now, but then tolerate the heat of the future.

Doug: Some people might be excited by that. They might say, "Well, gosh, now I'll be able to plant a crepe myrtle and I won't have to worry about it dying back eventually." This is a scary thing, climate change and all the changes that we're seeing. Trees, certainly, but insects too, it's changing everything.

Dr. Dan: It certainly is, yes. We have insects spreading north, trees, haywire weather. That Gulf Stream this weekend, it's sweeping way up North into Alaska, taking really warm air up there, bringing that cold air down here. We're experiencing a lot more variation. Even though it's getting below zero, that doesn't mean that climate is not warming.

Doug: What are some things we can do as homeowners to help mitigate this?

Dr. Dan: Planting trees is a great way to help mitigate climate change at the very local level where we live. You plant a tree, well, it provides shade, which cools our environment, our house, our yards, our city, can reduce the urban heat island effect. Cities are warming even more than the rest of the environment because of all the asphalt, the buildings that absorb and re-radiate that heat. Trees can really mitigate that impact in many parts of the country, including the Eastern, including Ohio and Eastern US, we're seeing more heavy precipitation events. Stormwater runoff is challenging our sewage systems and trees can really reduce stormwater runoff in the urban environment.

A lot of beneficial impacts of trees. Of course, not to mention sequestering and storing carbon have a direct impact on the because of climate change.

Doug: Talk a little bit about fighting climate change through education, because there are some people that they just don't believe that climate change is real, but from a science point of view, from your research, we know things are changing. Talk a little bit about how we can spread the word a little bit in a gentle way to help our climate in general.

Dr. Dan: I was just reading an article in the paper today about a survey of people's impressions and thoughts about climate change. What a positive take home is that? Most people in the United States appreciate and understand that the climate is changing and that it's getting warm. That's a big start. There is a lot of disagreement about the cost

of that but if we focus on the fact that the climate is warming and the evidence is overwhelming especially those of us with white beards that have been around for a while we remember how different the climate was when we were children than it is now. Glaciers are disappearing that's a documented fact in the Glacier National Park. Spring is coming, earlier fall is staying later, sea level is rising. I was in Charleston South Carolina this weekend on vacation I saw some flooded streets on a nice sunny day at high tide. Obviously, those streets were being flooded when they were built sea levels rising so the evidence of climate change is apparent. Whether or not we agree on the cause and the evidence is overwhelming that the cause is due to greenhouse gas emissions. Whether we agree on that or not trees are really beneficial to mitigating the effect of that warming climate.

Doug: I guess we just have to be careful about which trees we choose to plant again. Oftentimes the example is the sugar maple but there's lots of other species too. Besides planting trees, what else would you suggest we do to help?

Dr. Dan: Well, sticking with the topic of trees taking care and preserving the trees we have is really important and so yes planting young trees is really important but most of those benefits, those young trees are have years out. The trees provide their most benefits as they mature and become large and so preserving those mature trees that we already have is really important and so that requires focusing on tree health and tree health care program. Monitoring those trees, taking good care of those trees.

This is where a certified arborist can be really useful like your family doctor call your certified arborist to come inspect your trees, identify problems before they become severe, nip those problems in the bud, provide a preventative health care program, maintain those mature trees and the benefits that they're providing.

Doug: Dan, I think too when I think about just smart growth including trees in new construction, new areas instead of just flattening an area to the ground and throwing asphalt down there. I think that's important too.

Dr. Dan: Absolutely. I'm gratified to see that this is happening more and more urban planners thinking about requiring that trees be replanted, incorporating green space into the environment to help keep the environment cooler. Having trees and green space has been shown by number of research projects and papers now to have really important benefits for health and wellness reducing crime and so forth. Making people healthier so that's another benefit of trees that's really starting to become appreciated.

Doug: Do you think there's any way we can actually reverse this or at least slow it.

Dr. Dan: Well, we can certainly slow climate change. That's going to require reducing greenhouse gas emissions. The overall average temperature of the earth is a direct function of the accumulation of greenhouse gas emissions. If we can reduce greenhouse gas emissions, we would have to get that to net zero before we would stop warming because carbon dioxide in the atmosphere is permanent really least on the scale of hundreds to a thousand of years.

We need to the degree that we reduce greenhouse gas emissions carbon dioxide and methane primarily we can slow warming. To stop warming, we would have to get to net zero. To start cooling the climate, we would have to remove carbon dioxide from the atmosphere through carbon storage and sequestration. Large-scale tree planting programs can play a role there but that alone is not going to be adequate.

Doug: Are you encouraged when you see some of that data that at least people are aware of it as we said, a lot of people argue about the reason but so many people are aware of it. It seems just from looking at our culture in general, we're moving towards electric vehicles that sort of thing, is there some encouragement from just seeing people are aware and wanting to make this change?

Dr. Dan: Absolutely, I'm encouraged by changes in the awareness of people over the last 10 years regarding climate change. I think you see things like these in stronger hurricanes, the wildfires out west, the way that the reservoirs in the western United States are drying up, the impacts of climate change are becoming very personal, tangible to many people. I'm also encouraged by market forces that are at work driving the increase in electric vehicles, for instance, increase in renewable energy use, and then also policy decisions. The inflation reduction act just passed and the incentives that are driving increase in renewable energy and electric cars and so forth. I've seen a lot of positive change.

Doug: That's the encouraging side but there is also a scary side to this, a very scary side to this. When you do make something like this political as opposed to like a scientific decision, it's just basically terrifying for somebody like me who wants to pass on a world that's better to the next generation so many of us are doing and have been for a long time doing everything we can to help the environment whether it's composting planting trees, planting things, what do you say to people when they do have that feeling like I do that

I'm scared about this.

Dr. Dan: Well, I think you're justified in being scared as much as the progress that we've made, carbon dioxide emissions are still continuing to increase year-over-year and they really need to start decreasing rapidly if we're going to limit warming to things that can be manageable. I think the momentum is starting to shift in that direction but the impacts of that momentum are not yet showing up in terms of reduced carbon dioxide emissions in the atmosphere. The trend is not changing yet I'm optimistic that it will and I'm optimistic about changes in attitudes but we still have a lot of work that has to be done.

Doug: Well, Dan, I'm going to leave it right there because I like those two words, the two times you used optimistic because I do want to be optimistic about this but also realistic.

Dr. Dan: We need to be realistic.

Doug: Yes, so as always thank you so much for all this great information and as longtime listeners know, we will be talking to you again, Dr. Herms, for sure.

Dr. Dan: Thank you, Doug. It's always a pleasure speaking with you.

Doug: I always learn something new when talking with Dr. Dan Herms, that's for sure and I hope you did too. Tune in every Thursday to the Talking Trees podcast from the Davey Tree Expert company. I'm your host Doug Oster and do me a favor, subscribe to the podcast so that you'll never miss an episode. Hey, you have an idea for a show or some feedback, send us an email at, that's P-O-D-C-A-S-T-S @ D-A-V-E-Y .com. As always we like to remind you on the Talking Trees podcast, trees are the answer.

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