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Issues of the Environment: UM study provides insights into the future of climate-impacted northern forests in Michigan and beyond

Tree canopy
Wikipedia Media Commons
Tree canopy


  • Ann Arbor, affectionately known as “Tree Town”, is counting on its urban forest to combat climate change. The iTree Eco Analysis calculated the benefits that Ann Arbor's urban forest, both public and private trees, provides to the City. The analysis estimates that Ann Arbor has over 1.45 million trees; these trees remove 405/tons of pollution per year which is equivalent to the pollution produced by 358,000 automobiles annually.  (Source: *directly quoted* https://www.a2gov.org/departments/forestry/Pages/The-Urban-Forest.aspx)
  • It has long been assumed that as the global climate warms, tree species will expand their ranges northward, and the composition of the canopy is likely to reflect that. However, forest ecologists are calling that assumption into question, and how climate change might change our forests appears to be more nuanced, with some tree species adapting better to warmer temperatures than others. 
  • University of Michigan Director of the Institute for Global Change Biology (IGCB) at the School for Environment and Sustainability, Peter Reich, conducted a five-year experiment that was recently published in Nature. It was part of a larger set of studies by researchers who are trying to understand what will happen to northern forests in the U.S., Canada and around the world as the climate changes. It found that even relatively modest climate warming and associated precipitation shifts may dramatically alter Earth’s northernmost forests, which constitute one of the planet’s largest nearly intact forested ecosystems and are home to a big chunk of terrestrial carbon. “Even though sometimes people think, ‘Oh, it’s cold up in Canada and in Scandinavia and even in northern Michigan, or Wisconsin, or Minnesota—won’t warming be good for these forests, they’ll grow faster?’ And unfortunately, the answer is largely no, not entirely no, but largely no,” says Reich. 
  • For the experiment published in Nature, Reich and his team planted 20,000 seedlings—which are heated using infrared lamps above ground and buried wires below soil—in 72 plots of forest. The team then visits these lots to measure growth. One of the findings showed that northern species of trees, including spruce, fir, jack pine and paper birch found in Canada, Northern Michigan, Wisconsin, and Minnesota, don’t grow well with even a degree or two of warming. “Their growth is slower, and they actually die a lot more frequently, like a much greater proportion of the seedlings will die every year.
  • Reich says it turns out to be due, not to just a degree of temperature difference, but the fact that “with a higher temperature…plants and soils lose water much faster, and they dry out faster.”
  • The researchers found that warming alone, or combined with reduced rainfall, increased juvenile mortality of all nine tree species and severely reduced growth in several northern conifer species—balsam fir, white spruce and white pine—that are common in boreal forests. At the same time, modest warming enhanced the growth of some broadleaved hardwoods, including some oaks and maples, which are scarce in the boreal forest but much more common in temperate forests to the south. However, the new study concludes that hardwoods [the dominant species found in the Washtenaw County i.e. maples, oaks, etc..] are likely too rare in the southern boreal forest to rapidly fill the void left by vanishing conifers.
  • Therefore, near-term projected climate change will likely shift present-day boreal forest into "a new state" of altered composition. "That new state is, at best, likely to be a more impoverished version of our current forest," Reich said. "At worst, it could include high levels of invasive woody shrubs, which are already common at the temperate-boreal border and are moving north quickly." (Source: *directly quoted* https://seas.umich.edu/news/study-even-modest-climate-change-may-lead-sweeping-changes-northernmost-forests)


David Fair: This is 89 one WEMU. And I'm David Fair. On today's edition of Issues of the Environment, we're going to talk trees, specifically how climate change is changing the nature of forests and how that may play out in the years to come. Ann Arbor alone has over 1.45 million trees, and that's why we affectionately refer to it as Tree Town. Now, the urban forests in the city, both public and private, do a great deal to help protect the environment. As the climate continues to warm, we've made some assumptions about how that's going to alter the tree canopy and what that will mean for longer-term health of our air, soil and water. These questions and assumptions have been the subject of a five-year experiment conducted by Dr. Peter Reich. Peter is the director of the Institute for Global Change Biology at the University of Michigan's School for Environment and Sustainability, and his findings were recently published in the journal Nature. And, Dr. Reich, thank you so much for the time today.

Dr. Peter Reich
University of Michigan School for Environment and Sustainability
Dr. Peter Reich

Dr. Peter Reich: Well, thank you.

David Fair: How did you go about setting the parameters of what you wanted to learn over a period of five years?

Dr. Peter Reich: That's a great question. What we set out to do is to run a unique experiment in the forest. This was in two locations in northern Minnesota, where we raised the temperature both of the soil, roots, and aboveground parts of the plants by air, by either about one and a half degrees or three degrees Celsius, which is roughly around three and a half or four Fahrenheit and seven or so Fahrenheit, to see whether this kind of warming would change the survival and growth of different tree species that are common to the temperate and boreal forest throughout the lake states and much of the eastern US and Canada, and see whether some of them would thrive under the warmer conditions and some of them would suffer poor growth and poor survival. And so, we really were trying to understand the implications of ongoing climate change to the health and composition and diversity of the forest and this transition between the temperate zone and the boreal zone and also what that meant for soil health and overall forest productivity looking to the future.

David Fair: So, how well did they fare with even minor increases in temperature?

Dr. Peter Reich: Well, the trees in northern Michigan, Minnesota, Wisconsin and similar areas and in nearby Canada produces like balsam fir and white spruce, they did not fare well at all. They have much higher mortality and much, much lower growth rate with the warmer conditions during that five-year period and also in several other versions of the experiment we've run with the same facility since 2009 until just this last year. A couple of the species that are more common in southern Michigan, oaks and maples, did better with the warming in terms of growth and survived only slightly less well with the warming. And so, there is some hope that at least some of our species might be able to continue growing well and doing well where they already exist.

David Fair: Here's what I know. It wasn't so long ago that there were no Buckeye trees in the state of Michigan, and I think most Michiganders actually appreciate that fact. It's no longer the case. Not only has the changing climate helped that species of tree migrate north, but I believe you can find them north of Traverse City right now. And that's happened alone in this century. Are the northern forests and tree canopies changing and adapting to the warming climate more quickly than we thought they would? Or are they in more danger?

Dr. Peter Reich: Probably, the answer is yes to both of those. Tree species, such as the Buckeye you mentioned and red maples and the like, are moving north faster than we might have thought they could through intentional and unintentional help by humans and through their own capacities. However, climate is changing even faster. And so, the notion that, on their own, tree species from further south will replace those doing poorly further north in northern Michigan or northern Wisconsin or Ontario, the like. Unfortunately, it's not going to happen sufficiently to keep the forests as healthy as we'd like them to be. That migration is real and is helping replace species that aren't regenerating well that are more sensitive to warmer temperatures. The other thing that I want to bring up is that climate change isn't just that the temperatures get into a little warmer everywhere in a steady way. We're also seeing much increased events. And by events, I mean--

David Fair: Severe weather, right?

Dr. Peter Reich: Severe weather events, including heatwaves and ice storms and windstorms and heavy snowstorms that break trees and floods in the spring and droughts in late summer. And those increased levels of disturbance events are something that trees aren't well equipped to cope with anywhere in their ranges. So, you know, even if the Buckeye red maple can migrate up north fast and keeping track with the average temperature, if they face more fresh kinds of destructive storms, that's going to have consequences for their ability to grow tall and straight and create the kinds of crowns that we value for ecological and recreation and economic purposes. And so, you know, anyone who's wandered around in the city or in the woods in the last few years sees lots more, you know, broken tree crowns and trees on the ground because of the various storms. And that doesn't bode well for either our urban forests or our rural forests.

David Fair: We're talking climate change and the impact on northern forests with Dr. Peter Reich on WEMU's Issues of the Environment. He's director of the Institute for Global Change Biology at the University of Michigan's School for Environment and Sustainability. We always hear people talk about reaching the tipping point and exceeding it and where there is no point of return when it comes to climate change and its impacts. Would we be more effective by becoming far more focused and invested in what we do right now—this month, this year?

Dr. Peter Reich: Absolutely. Let me step back, though, to your notion of tipping points. The idea of tipping points is a good one. I believe they do exist for certain kinds of processes and patterns, But I'm not at all hopeless that we are going to globally reach a tipping point where nature just, like, fails us or we've failed it. Therefore, it fails us in a way that's catastrophic. I think it's much more incremental. And nature is much, much cleverer than we are or that we give it credit for. And so, climate change is already having huge impacts and will have even larger impacts on the capacity of nature to do the kinds of things that we view as services to us: providing food and climate regulation and clean air and clean water. And so, yes. We do need to change our behavior collectively at individual, but also governmental and corporate levels yesterday, if at all possible, because it's going to take a while to slow climate change down and stop the catastrophic consequences that will be increasingly coming along. And here's where I'm actually an optimist, and I'll give a couple of examples. One is simply that plants--green plants on land and soils--have 300 times more carbon that exists than is burned every year in our burning fossil fuels. So, we only need to change a tiny percent of that 300-fold greater amount of carbon and store a tiny percent more in the trees and soils to offset a big part of the CO2 we put in the earth from burning fossil fuels. So, there is enormous potential in agriculture and forestry in rural areas and in cities to just store a little bit more carbon everywhere. Now, that's hard, given that we're also burning more and we're doing all sorts of things that release carbon. But it's not like we have to double the amount of carbon in forests. We just have to increase it by a couple of percent. And that actually would wipe out like a third or so of the climate change we're causing by burning fossil fuels. And the other two thirds we can easily also fix and save money in the process by actually investing in alternative renewable energy: solar, wind, geothermal and the like. And so, we actually already have all of the tools, you know, even though we sometimes talk about climate change as being a trade-off between the economics and the environment. It's actually the reverse. They're going to go together now. We need to save climate change in order to save the economy and vice versa. And we have all the tools. So, it's really just figuring out how to make this happen at governmental, corporate and individual levels. And we're going to be better off economically, as well as in terms of our nature if we do so. And so, I'm optimistic because those two things now align. It's not like you're making a choice between one or the other. And the sooner that becomes part of everyone's understanding, it wouldn't be political anymore because, basically, you're doing good for both at the same time. And so, I'm optimistic that both our positive nature of humans to do the right thing and our need to make money will align in a way that will help us to stop climate change. Now, are we going to do it as fast as you or I would like? No. But I think it will happen in 20 or 30 years from now. People will look back and say, "What the heck were they doing in 2017 and 2022 and 2012 before we get around to actually making this happen globally?"

David Fair: Well, I'd like to end on notes of optimism. So, that's where we're going to have to stop today. But obviously, the work you've been doing is the work that will continue. And with the knowledge gained, the more we will learn and the more advancement we will make and the optimism will grow. So, thank you very much for the time and the conversation today, Dr. Reich.

Dr. Peter Reich: Well, I thank you for inviting me in and for thinking that this is something important to share with your listeners.

David Fair: That is Dr. Peter Reich. He is director of the Institute for Global Change Biology at the University of Michigan School for Environment and Sustainability. He led a five-year experiment as part of a larger study to better understand what's going to happen to northern forests in the United States, Canada, and around the world as the climate continues to change. It was recently published in the journal Nature, and you'll find more information and links at our website at WEMU dot org. Issues of the Environment is produced in partnership with the office of the Washtenaw County Water Resources Commissioner, and we bring it to you each Wednesday. I'm David Fair, and this is your community NPR station, 89 one WEMU FM, Ypsilanti.

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