EP 10: The Science of Trees in Cities
We enter a better kind of urban jungle on this episode all about the science and economics of trees in cities -- way more interesting than you might think at first. Yep, there's a big economic argument for more trees in our cityscapes. Our guests here apply scientifically backed dollars-and-cents appraisals to the trees that line our streets or green our downtowns. And they discuss tools you can access to tally such values where you live. And, yes, we also discuss the much-harder-to-quantify relationship that humans and trees have shared since the dawn of man -- and what that means for city neighborhoods lacking in greenery. A lot to think about -- and surely a few surprises -- in the episode. Show notes: Greg McPherson - http://www.fs.fed.us/psw/programs/uesd/staff/gmcpherson/ Report, "Structure, function and value of street trees in California, USA" -http://www.fs.fed.us/psw/publications/mcpherson/psw_2016_mcpherson004.pdf David Nowak - http://www.nrs.fs.fed.us/people/dnowak iTree - http://www.itreetools.org Adam Dale - https://adamgdale.org Report, "Forecasting the Effects of Heat and Pests on Urban Trees: Impervious Surface Thresholds and the 'Pace-to-Plant' Technique" - http://ecoipm.org/wp-content/uploads/2016/05/Dale_2016_Arb.pdf Jill Jonnes, "Urban Forests: A Natural History of Trees and People in the American Cityscape" - http://jilljonnes.com UPI story, "Tree growth slows as cities heat up" - http://www.upi.com/Science_News/2016/10/05/Tree-growth-slows-as-cities-heat-up/2081475676027/ Report, "Urban warming reduces aboveground carbon storage" -http://rspb.royalsocietypublishing.org/content/283/1840/20161574 OpenTreeMap - https://www.opentreemap.org City of Raleigh Urban Forestry Division - http://www.raleighnc.gov/community/content/ParksRec/Articles/Programs/UrbanForestry/UFDivision.html NEWS AND REPORTS SINCE THIS EPISODE'S AIRING: New report, 11/16, "Selecting Trees to Grow in Cities" - http://www.srs.fs.usda.gov/compass/ CityLab article, "The Big Green Payoff From Bigger Urban Forests" -http://www.citylab.com/design/2016/10/the-big-green-payoff-from-bigger-urban-forests/505913/ Smithsonian.com, "Why Public Health Researchers Are Looking to Urban Trees" - http://www.smithsonianmag.com/science-nature/why-public-health-researchers-are-looking-urban-trees-180960985/?no-ist Governing article, "Phoenix's Ambitious Plan to Beat the Desert Heat" -http://www.governing.com/topics/transportation-infrastructure/gov-phoenix-shade.html
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Transcript
On this episode, Municipal Equation.
Why is it that we are attracted to trees and, you know, feel good when we're around trees in some way we don't really know. The bottom line is that, you know, trees, for every dollar spent maintaining these street trees, they're producing about $5.82
in benefits every year. The science of trees in cities. It's not just aesthetics. My name is Ben Brown, and this is Municipal Equation from the North Carolina League of Municipalities. Episode 10. I work in Raleigh, North Carolina. Its nickname is the City Of Oaks. And if you come to visit, it's fairly apparent why. According to visitraleigh.com, the nickname came from the city's founding fathers, who wanted to maintain the wooded nature of the area. And today, it's still a big point of pride. A number of local companies have incorporated the city of Oaks nickname into their own names and logos. Raleigh's city government gets it too with an in house urban forestry division. Its website says, Raleigh is the city of oaks. Let's keep it that way. So we've got the word urban in front of forestry there. Urban forestry. It's its own science. Related, yeah, but separate from the undeveloped world. There are entirely different considerations for trees and cities. And as I said at the top of this episode, the stakes are a lot higher than just plain old scenery. So what else? Mental health seems like an obvious benefit that we can derive from trees in a cityscape? Yeah. Trees make us feel good, especially when they give us a break from the asphalt and the office buildings and the red traffic lights that we sit in front of. And we don't necessarily have to go to science to break that down for us, but when we do get into the science of trees within cities, urban forestry becomes a lot more interesting than some of us might think at first. The bottom line is trees can really add up for the quality and future of a city or town.
So it's a big field of study for urban planners and scientists alike. Environmental services. How do the trees provide that? You can use green infrastructure or urban forest, whatever you wanna call it, it, to reengineer cities. The question is if you understand what they do, you can do a better job and how they do it. You have on this That was David Nowak. He works with the US Forest Service. That was during a talk he was giving in Dublin, Ireland. Beginning, just so we're on the same page. Just try to answer one question. If I could only plant one tree in the city, in Dublin, what would I plant and where would I plant it? And now also when would I plant it, if you take in the time series. And that's what we're trying to answer. And that question becomes in the context of what do you care about in Dublin. So what to plant and where to plant it depends on what problems you have and where you exist. So if I'm worried about air quality, I might plant over here and do this species. If I'm worried about water, it might be over here.
His focus as a research forester is investigating urban vegetation and what actual measurable or immeasurable services it all provides to us. And he helped develop a series of tools that allows users to learn the actual quantified value of the trees we see around us when we're strolling down a city block. More on that in a bit. But first, let's check-in with a recent study done by the office of doctor Greg McPherson, who's also a research forester with the forest service in the Pacific Southwest. The study came out earlier this year and reported actual dollars and cents values of city street trees. The study was done in California, but McPherson thinks that it, or at least the approach to the research, definitely has an application across the country.
But for California specifically The bottom line is that, you know, trees, for every dollar spent maintaining these street trees, they're producing about $5.82
in benefits every year. And that was figured up by looking at the available data on close to a million street trees, which tallied up to a value of $1,000,000,000 or more than $110 per tree for the more than 9,000,000 street trees in California. And so, for example, if we
find that a tree in the west side of a home saves 100 kilowatt hours in air conditioning costs and it costs 10¢ a kilowatt hour, that translates into $10 a year in air conditioning savings produced by that tree in the West side of a house. And trees have other ways of influencing temperatures in cities.
They also reduce stormwater. They can impact air pollution, carbon dioxide uptake, and then economic stuff like their impact on property value.
So there's there's no doubting the fact that trees are a cost, but we need to be aware of the fact that they're working, you know, twenty four hours a day, three hundred sixty five days a year to improve our environment, improve our health. And having, you know, a dollar value attached to that, I think, is probably the bottom line. McPherson also found plenty of unused street space, vacant sites, meaning a lot of potential for planting.
His work on this occasion was more environmentally focused.
But There is a growing body of research that shows well tree commercial areas. You know, people tend to shop longer and spend more money and pay more for parking than in commercial areas without trees, for example. And I think there is kind of a growing awareness that trees, healthy trees really kind of add to the ambiance and to the attractiveness and to the feel of a community and they give it a special quality that makes people want to be there. And that has value whether from a business perspective, the whole aspect of neighborhood people coming together and planting and stewarding trees and kind of the community cohesion that comes from people getting out and being together and doing something to improve the environment in their local neighborhood. So I think more and more awareness about the value of trees and the value of, how that investment pays back over the long run.
Back to David Nowak, who you heard in Dublin a few minutes ago. He was part of the development and is really the voice of a great online resource called I Tree at itreetools.org, which allows you or me to input information about our immediate locale. I Tree will, for one, tell us what the economic value of the trees are in local services, similar to what we talked about, like energy savings and carbon storage, which is measurable and does have a dollar amount. So you can find out what your city has going for it, dollar wise, with trees, public and private. Nowak said it's been available for about ten years.
And it came about through research that we had done originally starting in Oakland, California and then Chicago, and we were doing assessments of various cities and the ecosystem services. So around the late nineties, mid nineties, we decided to automate the process and build codes that would do this so anybody can collect data on trees and forests and understand their services and values.
Alright. I'm going to itreetools.org right now. And, it gives you a few different options, a few different tools to click on. I'm going to click on the I Tree Landscape tool because it says you can calculate values for entire cities that way. Okay. So it's up now and there's a Google map in front of me and, it allows you to draw a box over the map, over a geographic area. And, I'm gonna select an area that is pretty much the entirety of Raleigh, Give or take, if I'm doing this right. I actually might be going outside of the city limits a little bit. Okay. So, it's giving me some results and I'm clicking over to where it says tree benefits for the area that I selected. And for that area, it looks like more than $8,000,000 a year in value in carbon sequestration, which means carbon dioxide is removed from the atmosphere. And it's also giving me some other figures related to, air pollution removal and hydrology. And for the area, the tree service is worth almost $5,000,000 a year in avoided runoff. Every year $5,000,000 in avoided runoff.
So there's different tools for different users. Landscape uses landscape scale maps. And from that data, we derive from the measurements you put in, in essence, of carbon storage or sequestration, and then we apply a value. The value is based in this in terms of carbon is based on the social cost of carbon from the US government. And so we multiply the the amount of kilograms or or pounds stored in the tree times this multiplier based on the estimated effect of the value from The US report of of value per ton. And it's important to know as many things that are important to know in this one is it's not just the carbon because these trees will provide multiple services that would provide pollution removal that affect water flows will affect temperature energy use. So one is important to know is what are these multiple benefits that are being received and possible trade offs? Because sometimes when we design, we might enhance one benefit but lose another depending on the situation. And sometimes there's there's costs associated with it. So trying to understand all the aspects about the trees in terms of the services. And then what's the secondary, which is what we're often asked is what's the value of that? So we use different means to estimate the value. Carbon, we use the social cost of carbon. For air pollution, we looked at human health costs and the impact of trees on human health. And that's often what city managers want to know is the common denominator is not necessarily tons, but it might be dollars.
David, there are more ways to apply this data than I can imagine. What are some real ways that you've seen people make good use of this tool? And and you mentioned city managers. Could could you maybe tell us how, for instance, a local government might make use of I Tree?
Yeah. People have it's it's interesting to watch because people who use it use it in many different ways to to to try and hopefully better their their environment. Some people have used it to enhance integrate trees within the city system. So the city of Oakville, John McNeil was very progressive, Oakville just outside Toronto in integrating forestry within the whole management system. And so many of the people are trying to do that is trying to link green infrastructure within the management of all the gray infrastructures and linking it that way. Some people have used it for climate change action plans. Some people have used it for, creating new positions, showing that there is a value to the forest, that we need to manage it. So then new positions were created because trees, in essence, are public good. So investing public dollars to enhance this public good, could be a wise investment. And many people, not necessarily from the city side, but from the the user side, have been advocates to trying to promote this information to the politicians or to the city system where they use the information for advocacy. So people have put price tags on trees outside capitals to show the value of the trees, to try to take this information and make it more prominent, I guess, to the to the politicians and the city managers about the values of trees. And it had very, very innovative ways to do so do so. Some cities have done, billboard campaigns. Milwaukee did that about the values of their forest, that are provided.
So in communicating the monetary values, I'm I'm seeing some different tools on the site, like the landscape tool. And among the different tools, if I wanted to make a case for the economic value of trees in my neighborhood, for instance, can I Tree produce a report that I could print out and give to other people
yes it there are different ways to attack it most pretty much all tools will give you a standard report of information from what you put in there And there's a suite of tools? But if you went from aerial, you can go top down, which means if you're going large scale areas, you would use either I Tree Canopy, which you can photo interpret area. And from that, so you want to do a neighborhood, you would just sample your neighborhood from Google from the canopy cover. And that would produce a report on carbon storage and pollution removal for that area. And we'll produce a report on that. You can also go to landscape, which is preloaded with national land cover maps and go from the block groups upward to get estimates for your area. So doesn't involve you going into the field. You're either interpreting or using preloaded satellite maps. The other is either through canopy, where you go to your house and and collect the data, or through eco, where you would do some sampling inventories and do a bottom up approach where you're measuring trees and let the computer calculate the benefits. So there are different ways to go. And I think if you're if you're just starting, I'd start from top down, either canopy or landscape, to get an idea. To get more accurate measures, I would go to eco or canopy where you're actually measuring trees.
Well, David, what what else? What what didn't I ask about with regard to I Tree or just about the hidden value of trees in a city environment?
I I think two things are important. One is first understanding what you have locally and the value of the resource. That's what I Tree is trying to do. And I think more important, what we're trying to get to is what's the next step that we have to do to make our environment better? And that's a locally derived decision. So what we're trying to answer in I Tree is based on what the local conditions are, what are the risks? I'm in a certain city. It might be air pollution. It might be UV radiation. It might be water quality. What do we have to do to our forests now to create a healthier and more sustainable forest in the future? So I try to get at the answer of what species should we plant? Where should they be located? Trying to optimize the designs to make a better tomorrow. So first step is knowing what you have. Next step is what how do you take that information and move it forward to create a better environment?
When it comes to smart management of a city tree population, there's a lot of study and a lot left to learn. Just a few months ago, a team from the University of Florida led by assistant entomology professor Adam Dale published a study that could be a lot of help to municipalities when it comes to planting trees or designing landscapes with, for instance, downtown revitalization projects. Dale looked at red maple trees, pest infestations, survivability, and how the urban environment is impacting all of that, versus how the tree would perform in a natural environment.
We've shown that certain insect tests outbreak on urban red maples, but not on maples and nature. And this is because they directly benefit from the warmer temperatures in cities, drought stress common on urban trees, and all of these things reduce tree condition, which means they aren't providing those services that we talked about. And those trees have to be managed more intensively or replaced.
Dale said the impervious surfaces are the primary reason why the landscapes are warmer, the trees are drought stressed, and they're more susceptible to pests. So the study team came up with some guidelines regarding urban tree planting sites.
And so your guidelines are in the form of impervious surface thresholds or points at which the amount of impervious surface around a tree becomes damaging to that tree. And so these will help people preventively reduce pest populations, tree stress, and the damage they cause.
They came up with a pretty simple way to record how much impervious surface is around a planting site, and it doesn't involve any computers or surveying equipment. And so basically all a person has to do is walk an x of 100 steps through a planting site,
Count those steps that land on impervious surface, and that number is the percentage of impervious surface around that planting site. People can learn more about this and other related work by looking at my lab's website at adamgdale.0rg. I've also got a Twitter account that I try to keep updated regularly at adamgdale. And more of this work and similar work is also at my collaborators, Steve Frank's website, ecoipm.0rg.
So we've heard a lot on the science, academic, and economic side. But there's also that human connection, the human value with tree lined streets or parks in the middle of cities or historic oak trees and so on. Just as I was lining up interviews for this episode, I came across a book that had just come out. It was getting rave reviews and a lot of media attention, and its title happened to be Urban Forests. The subtitle is A Natural History of Trees and People in the American Cityscape. The author is Jill Jones, and I'm proud to say that I got her for an interview right before she went on to be featured on The Diane Rehm Show. Jones observes a strong relationship between humans and trees, going back to the earliest days of man.
And so I think that there is a deep bond that is extremely intuitive between people and trees. And one of the kind of wonderful things about, living in an era of science and technology is that this is now getting documented. So I think trees are really essential to human health. And, the first really groundbreaking study of this is by a man named Roger Ullrich, who's actually a landscape architect. And he was able to find a situation where you had a hospital where gallbladder patients, everything about them was the same, except some of them were did their recovery in rooms where they could see trees and some where they were looking at a brick wall. And the ones that could see trees, required less medication, got out of the hospital faster, and also healed faster. So, actually, hospitals now design themselves differently because they realize that when people, can see greenery and trees, they just do better. And there have been a number of recent studies where they fit people up with, I guess, I don't know, various medical monitors, and they're actually able to see that your cortisol levels, which is means, you know, you're the thing that sort of this marker for stress, as you are looking at trees and especially as you're out and about, you know, with trees, that those things are coming down. So why is it that we are attracted to trees and, you know, feel good when we're around trees? In some way that we don't really know, they're just calming us. And, you know, trees are really complex. And I think there's something about the way, you know, feeling of well-being that is very instinctively, understood.
Jones has no doubt the municipalities should consider trees as part of a local infrastructure.
I think a lot of cities are going to have to be retrofitted with nature. So it's not just that you would have a street tree or a park tree or whatever. You would those trees would be embedded in sort of larger green infrastructure projects that do things like address stormwater or address urban heat islands that just create a much richer, more textured, but actually very practical and serving many purposes, green infrastructure. So if you have good healthy trees, they can bring the temperature down, so that saves you energy. They can mitigate stormwater that saves, you know, the cost of all your sewers and so forth. And just aesthetically, what you find with trees is that where you have trees, you've got more economic development, more business, higher home prices. I mean, with all this new technology, there's all this mapping technology. I mean, I'm sure you're familiar with cities that have, basically created urban tree canopy maps, and you can see what the percentages are. And not surprisingly, people who can afford it put themselves into places where they're surrounded by trees. And they may or not may not be, again, consciously aware of the fact that, oh, we have chosen this neighborhood. It happens to have a 47% tree canopy. Oh, people who can't afford to live wherever they want, they're living in a place with a 6% tree canopy. So, one of the upshots of these tree mapping tools is this emergence that there's really this environmental injustice. If we know, as we do, that trees deliver a lot of benefits that are both practical, like, you know, you're not in an urban heat island, you're not having big stormwater problems, it's all that shade brings out the neighbors and that makes for a safer environment. And literally, we also know from studies that women who live near trees, pregnant women, they have better birth outcomes. One of our mottos or, you know, beliefs at the Baltimore Tree Trust is that everyone deserves to live on a tree lined street. And one of the things you notice if you start looking in, you know, poor minority neighborhoods is that's often where the trees are not.
So are there cities that have really tried to, make an initiative out of planting trees to,
turn things around economically and socially? Oh, yeah. I mean, so if you look at New York City, which, again, you know, I write about this in my book. I mean, they under mayor Bloomberg, and he was driven by receiving all of this new tree data about the value of trees and all the perform all the services that they perform for energy and stormwater and aesthetics and so forth, he quadrupled the city's forestry budget and launched million Trees NYC. So they have a typical city might plant anywhere from 5,000 to 10,000 trees a year. Mhmm. So New York just planted more than a 100,000 trees a year. Now it's true. A lot of those are whips, you know, little trees that get planted in parks. But, I mean, they planted more than 200,000 street trees, which is phenomenal. And they started they, you know, they did all this mapping so they could look and see what the tree canopy was in different neighborhoods, and they started in six neighborhoods where the tree canopy was really low. And literally there were just blocks with no trees. I mean, I see that here in Baltimore. I mean, much of Baltimore has a very beautiful tree canopy. But if you go to East Baltimore, I mean, I can tell you because that's where we plant trees. There are you can literally have situations where there are three straight blocks, and there might be two or three trees, three trees in those blocks total. So, yeah. And I don't think that that is unusual. I think if you start to look in cities, in kind of tough, difficult neighborhoods, or, you know, places that have been have seen a lot of, you know, people leaving, so you've got a fair amount of abandonment. I mean, you will see there are not a lot of trees.
Yeah. And it seems like, you know, the the benefit arises in a city branding or promoting itself not just by the architecture, not just by the culture or the job opportunities, but also by the vegetation. And it seems like that's something that we, as a whole, are becoming more, conscious of, and maybe I'm imagining that. But I feel like over the past ten years, at least where I live, there's been more of a vocalized interest in green spaces and parks in the context of a city. And I also feel like that's impacted the kind of staffing or priorities that some city governments have. Is that something you've seen as well? Yes. So it's really interesting because, as I say, I've been working on this book a long time,
and it's like the zeitgeist has really changed, and I that has to do with a few things. One, millennials wanna live in cities. Millennials are much more outdoorsy, I think, than many of their, you know, the baby boomers were. Mhmm. They aren't planning to find their green in the suburbs. So, if there's gonna be green, it needs to be where they are. They don't really wanna get in a car and go a long distance importance of trees because of this science and, you know, the technology that makes that science so easily available. Mhmm. So I I really do think that that is true. And I have to honestly say I wrote this book to advance that cause. I mean, I I mean, the the very title, urban forest, is kind of an oxymoron as far as most people are concerned. Sure. Yeah. Yeah. So it's it's literally and, again, it's just not something that people are consciously thinking about. And I there there is a, you know, an urban forestry movement. Many cities have got tree groups, but it's pretty tiny, and the money that's available to it is pretty tiny. And I I would love to see my book, you know, really make people aware of this and aware that this is really something we can do about climate change that will improve everyone's everyday life because most of us live in cities. Mhmm. And, you know, if if you would really increase, city urban forestry budgets and, again, you know, we're not talking major money here in terms of what gets spent on urban forestry or what you'd need to spend to
do it
right.
More info about Jill Jones and her book at jill jones dot com. Jones is spelled with two n's. Urban Forests is widely available on Viking Press. I'll have links to all kinds of material referenced in this show and the show notes at soundcloud.com/municipalequation. One piece that we didn't really get into actually circles back to Raleigh, which was the date line of a UPI story from October 5. A research team at North Carolina State University found that urban warming has a curbing effect on tree growth and on photosynthesis. This kind of relates to what Adam Dale talked about. This research group found greater amounts of pests on trees in these warmer urban sites, but the pests weren't the bottom line. The study found that urban warming was associated with an estimated 12% loss of carbon sequestration, which again involved removing carbon dioxide from the atmosphere. I'll link to that in the show notes. I'll also include some material about another service called Open Tree Map. It's at opentreemap.org. And a lot of big cities are using it to map out or do an inventory of local trees. It's designed to be easy and usable on your iPhone or iPad, what have you, so you can do inventory work from the field. And it actually links up with I Tree and helps the user, whether it's a city or a tree group or just a lone gun, find the quantified benefits of trees around them. But you can use OpenTreeMap for management, promotion of tree programs and so on. So check out our SoundCloud page for more information about
that.
I really wanna hear your feedback about this episode. Your stories about urban forestry, city trees, the value that you see, or don't see. You can email me at bbrown@nclm.org, or find me on Twitter. Handle is at muniequation. That's at m u n I equation. Municipal Equation is made possible by the North Carolina League of Municipalities online at nclm.0rg. Also, the league has its annual conference coming right up with plenty of material for cities and towns of all sizes, and I'll report back with some of the highlights and new ideas to share. If you have any ideas for this podcast, a future episode maybe, please let me know. In the meantime, thanks for listening. This is Ben Brown. Keep in touch.
