Episode 544 Why Trees in Cities?

Hashem Ackbari is an engineering professor at Concordia U who studies heat islands. John Stone was chair of a committee in the IPCC. Eric Davies collects seeds of big ancient trees and grows saplings from them. We discuss ways of using trees in cities to insulate buildings and reduce heating and cooling costs. It is more expensive to raise trees in cities than in natural forests, but their survival is greater where people are around to look after them. Many alien trees species are taking over and replacing native trees, with detrimental effects for the ecological niche, including for the soil and the animals living in that habitat; Norway maples are especially harmful, and have taken over Toronto’s ravines. For the video, audio podcast, transcript and public comments: https://tosavetheworld.ca/episode-544-why-trees-in-cities.


Hashem Ackbari

John Stone

Eric Davies


trees, plant, cities, cooling, people, urban forestry, forest, Toronto, solutions, increasing, urban, benefits, air conditioning, ravines, years, ecosystem, heat, building


Robin Collins, Hashem Akbari, Metta Spencer, Eric Davies, John Stone


       The discussion revolves around the impact of heat islands in cities and how trees can help mitigate their effects. Hashem Akbari notes that the lack of vegetation in cities and their darker surfaces are the two main causes of heat islands. Trees can reduce community temperature by 1-2 degrees Fahrenheit by shading buildings, transpiring, and absorbing dust particles. They also provide shade for pedestrians, clean the air, and absorb ozone.

       Additionally, trees affect wind patterns, making evergreen trees particularly effective in reducing heating energy during the winter. However, there are costs associated with maintaining trees, including root damage to building foundations and the need for eventual removal. The decision to plant trees should be made on a case-by-case basis, taking into account the benefits and costs in each specific environment.

       Robin Collins refers to a 2021 paper authored by Ronnie Drever and 36 other researchers on natural climate solutions, which includes a section on urban forests. The paper promotes an increase of 50% in urban canopy, which currently covers 24% of urban landscapes. The potential benefits of increased tree cover include a reduction in electricity use for cooling and heating, resulting in reduced carbon dioxide emissions. Decisions always must be made on a case-by-case evaluation of the benefits of planting trees, as planting trees in certain areas may actually hinder cooling due to the albedo effect.

       The panelists also touch on the potential co2 sequestration benefits of trees but note that any co2 that is sequestered will eventually be released as the tree decays. They emphasize the need for conservation of old-growth forests, and the clear planning of urban forest projects to optimize benefits while minimizing costs.

       The cost of maintaining a tree in an urban environment is 100 times more than in forestry, and therefore, the promotion of trees should be based on overall quality of living in an urban setting, including providing pedestrians with a friendly environment and minimizing energy use. Some trees absorb ozone. Cities are darker than suburban areas, because of all the dark pavements. There are two immediate solutions: using lighter color roofs and pavements, and at the same time using vegetation to improve the urban living quality.

       There are many benefits of planting trees in urban area, so long as one selects the right species of trees and plants them in areas where they can be maintained by people. But of course there are costs. Trees need constant maintenance. There are issues with fire. Tree roots can damage the foundation of the buildings, and trees have limited lifetime, after which they have to be removed. Each area has different sets of costs. Canada has plenty of water, but in California, having a little bit of green area costs an arm and a leg.  On the other hand, the transpiration of trees cools the area, especially in dry climates. Hashem has also calculated the air conditioning savings from shade trees. You can have an air conditioner but use it only a couple of days per year if you have shade trees.

       Trees can be great sources of community involvement in planting and maintenance, including having environmental courses in schools to encourage students to take responsibility for planting and caring for the trees in their neighborhoods.

       in a forest, when a tree is harvested it would bring in close to $2000 to $3,000 per tree. In an urban setting, harvesting the same tree is worth zero, because it would take $10,000 for particular equipment to come in to safely remove it. So harvest the trees in most urban environments would not be economical. Instead, the trees are desirable for their effect on the overall quality of living.

       The urban benefits can include the mitigation of other climate change risks such as flooding, as well as carbon sequestration, cooling, and promoting biodiversity.

       Eric Davies cautions against planting non-native species, which can harm ecosystems. He emphasizes the importance of big trees as the number one ecological asset that provides genetic biodiversity. Davies maps the oldest and most glorious healthy trees in Toronto, and grows their seeds as part of the rewilding process. The University of Toronto Forestry maps around 1000 trees every year and records their seed production with binoculars. Onewhite oak in Oakville is a rare species that produces seeds between 10-15 years, making it an epicenter for ecological restoration, education, and social reconciliation. The Toronto French School is integrating ecology, inventory, restoration, and management into their curriculum for over 1000 students.

       Hashem Akbari agrees with Metta Spencer that trees can have a better life expectancy if planted where there are human beings to water them and maintain them. In California, when they are harvesting an area, they replace every tree with about 10 seedlings. Each seedling costs only a few cents for them to plant, and if nine out of 10 die, and only one grows to the maturity, they can sustain that forest indefinitely.

       However, policies for changing the entire ecosystem requires a larger level of policy, funding, and long-term impact. John Stone complains that citizens generally seem reluctant to increase tree coverage in cities. The canopy is less where he lives now than when he moved in forty years ago, because people don’t seem to care about replanting trees; they don’t understand the benefits that will accrue from it.      

       But Hashem notes that in a typical city, about 75% of the land is owned by private citizens, who are responsible and maintaining the trees. The other 25% is owned by the city government, which is financed by the same people. So urban forestry has to be providing rather immediate or mid-term solutions to the needs of the people.

       Robin Collins recommends that cities inform citizens about the benefits of planting trees and bushes, such as electricity savings and winter windbreaks. Stone also mentions the usefulness of ivy on the walls outside, which doesn’t damage brick walls. However, planting trees on balconies in a 23-story building could have some cooling effects, but the long-term impact and weight of the tree need to be considered.


This transcript has been machine generated using “otter.ai.” Prior to using information from the transcript, please watch the video to catch any obvious errors.

Metta Spencer  00:00

Hi, I’m Metta Spencer. Today we’re going to talk some more about urban trees. We’ve been having several conversations about forests in through, in cities, in the past couple of months. And so we’re going to continue this today. And it is part of the Pugwash series that you may have been watching.  Pugwash has been good enough to cooperate with project save the world and having some serious conversations about several different global solutions to global threats. And one of them is, of course, all of them that we’re dealing with have to do with global warming. But we want to talk about the possibility of using trees in cities to keep us a little cooler than we’re going to be otherwise in the years to come. So I have a stellar lineup of people who are interested in in trees and know various things about global warming and trees. Let me start with Professor Hashem Akbari, who is a civil engineering professor at Concordia University in Montreal. And then John Stone, who is a retired person is an expert, who has served as the vice chair of working group one and two of the IPCC, which stands for Oh, my goodness, International Panel on Climate Change. Is that the right word for it, John?

John Stone  01:28

That’s correct.

Metta Spencer  01:30

We’re used to calling it IPCC and I think we’ve forgotten sometimes what it means. Anyway, welcome. And a former graduate student I knew a few years ago who’s who was in forestry, here in in Toronto, and that is Eric Davies. Now he has a, I think, a business. I’m not quite sure what you do in terms of trees, but maybe you’ll have a chance to tell us I know what your avocation is, Eric, which I love. Eric goes around collecting the seeds of stupendously wonderful old trees, especially in Toronto in the ravines and other public places. And, and collects them and he gets people to to raise new trees from his superlative seeds. So this is a good thing. Good thing.  In Ottawa is Robin Collins, who is very active in the Pugwash group, and also Bill Bhaneja also in Ottawa. They are two longtime members and very active members of the Pugwash community. And they will be mostly helping me interrogate these fine gentleman about trees today. So I know that Hashem I think I recruited you because I came across your name as somebody who has was a real expert on heat islands, to give us some notion about the importance and the impact of heat islands, that is areas in cities that are hotter than they would be because of the concrete and other other things. So what we can do about it?

Hashem Akbari  03:14

The majority of my effort has been forecast on how to provide solutions to mitigate heat islands. And being a environmentalist, I’m mostly interested in the solutions that are available solutions that people can do immediately. Cities are warmer than suburban areas during the summer and some and most of the time also during the winter. During the winter, this warms up the cities are a small assets because they reduce heating energy demand, but during the summer, there are significant penalties for that, increasing cooling energy use, increasing the severity of urban pollution as increasing the effect of the heater soars mortality, morbidity, and you name it. So, the focus has been what are the solutions to reduce the heat islands and there are two obvious solutions that one would see that the cities are different than the suburban areas in most cities in northern latitude. There are in an environment that the surrounding area are typically greener than the city itself. Therefore the lack of vegetation so somehow would effect the effect the heat island and also the cities are darker than suburban areas, that is because of all dark who have gone dark pavements. So that poses itself to two immediate solutions, the solutions of using cool or lighter color roofs on pavements, and at the same time using the vegetations in order to, in order to improve the urban (inaudible) living quality. So, looking at trees, there are a list of benefits that trees would provide. During the summer, they shade the buildings that will effect the cooling energy use, they also (inaudible) transpire and that would create some cooling. There are plenty of trees in an urban area in your community that can reduce the community temperature by one or two degrees Fahrenheit. And then the leaves of the trees have the capability of absorbing dust particle or sticking to dust particles and when the rain falls down, they wash them out. So they had to clean the cities they provide, they provide shade alongside the streets. So they improve the comfort for the pedestrians walking. And also they are some trees would absorb the ozone, which is an air pollutant through dry (inaudible) by the leaves. Then, in addition to that, trees also would affect the wind pattern to other cities. And in a place like Canada, which mostly is dominated by heating energy use, we find out that urban forestry is particularly the evergreen trees, a strategically placed place around the buildings can reduce the wind and therefore they would impact the cooling, the heating energy during the winter. Reducing the breeze throughout the throughout the building. So having said…

Metta Spencer  07:22

Excuse me, let me, let me ask you a little about that. Because right now my I live in a condo and our board is planning relandscaping and I and one of the things we’re talking about is is planting more trees around. Now are you did you say that the conifers do a better job of insulating in that regard should be we should we be thinking in terms of planting conifers around close to the perimeter of the walls?

Hashem Akbari  07:52

Yeah, the the solution may not be as simple as one would think.

Metta Spencer  07:58


Hashem Akbari  07:58

The obviously to have evergreen trees would reduce the wind speed. And therefore that would help reduce the heating energy during the winter forget that, like any planning elements for the city’s buildings, individual calls, there are costs associated. And one should also look at the costs. Trees need constant maintenance. And one has to pay for that either by his or her own labor or hire professionals to do that. Trees create issues with the fire storms, one has to be careful about that. Tree roots and can create significant damages to the foundation of the buildings, one has to be worried about. And typically have limited lifetime. And during that lifetime, they eventually die then have to be removed. And one has to be thinking about the costs of those. So there is a series of benefits associated with trees. And there are series of costs associated with the with the trees that the largest scale, one has to do it. One of the beauties of the trees are that individuals because of the comfort and visual comfort that it is creating their own their own neighborhood. They love to have it. So one has to really ride on that on that boat and try to make it happen the way that the other issues would be minimized.

Metta Spencer  09:48

Okay, so it sounds like you’d have to get a computer out and figure out the cost benefit analysis. Is that right or is there a handy rule of thumb that you can give us that will give us a enable us to make that kind of estimation in our heads?

Hashem Akbari  10:07

I think that there are, there are cities such as City of Toronto or city of Los Angeles, many other cities throughout the world that considering urban forestry is one of their plans. And in each environment, the solution may be different. In Canada, we are blessed with having plenty of water and water not be an issue. In California, having a little bit of green area costs an arm and a leg. So, one has to be really careful about this, there is no rule of thumb.

Metta Spencer  10:45

I see.

Hashem Akbari  10:46

However, this is the point that I would make. If an individual is making the decision, one has to make sure or help that individual to make the right decisions. For instance, selecting trees that would be, would be less costly throughout their life and having recommendation where to plant those trees, and so on so forth.

Metta Spencer  11:13

Thank you, okay. Okay, I’m gonna ask Robin to take over because I know you have some questions that aren’t you’re just burning to put to somebody here. So…

Robin Collins  11:23

I’ve been looking at Ronnie Drever and authored by, I think 36 other people, a paper that came out 2021 on the natural climate solutions. A very significant paper, but I think it used it look mostly at the Canadian scenario or scenarios and try to assess the relative significance of various carbon sequestration and climate change amelioration efforts. The, without going through the list of what are the highest priorities, which would include grasslands, and bogs and so on. There is a section on urban forests. And there’s a supplementary research material for the for the paper that most people read. And that’s why I was looking down here I’m skimming through the supplementary to find out what the references were to urban trees. So, it would appear that what they’re recommending is an increase of 50% of the scale of urban canopies, which they, which they see as as reasonable. And just to put that into perspective. They figure 24% overall of urban landscapes have canopy. But that depends on whether you’re looking at the parks or the street scapes or the industrial areas and so on. And they’re suggesting a go from 24 to 36% within, you know, a few decades, let’s say. So, I actually haven’t got the number, the percentage of improvement they anticipate, the Urban Canopy Growth will will result in. And maybe maybe some others here have some ideas about, you know, what’s the bang for the buck here by increasing the Urban Canopy? I think, yeah, Jim, you you quite well laid out what the attributes are, which is not so much sequestration of carbon, but the secondary, which is the cooling effect in the summer and the warming effect in the winter in Canadian landscapes by tree growth, which results in lower electricity use, and thereby less carbon dioxide. So does anybody have any of the numbers of you know, what we can expect in terms of, of the total problem? What this what urban trees might be able to resolve?

Eric Davies  14:22

I’ve got to I’ve read a lot about how about the numbers they’ve used for at the global scale. And from what I gather, you know, a lot of this has come about just over the past few years and some of the numbers you know, the initial numbers were, if we planted trillion more trees in the world, because the world can fit approximate a trillion more trees that would sequester up to 30% of the carbon problem. But then there are a lot of issues almost like with Hashem said with the, with the cooling he sometimes he can plant trees, for instance, in grasslands and it can actually hinder it because To the albedo effect. And so I think like, what Hashem is saying is it really does require kind of a case by case evaluation. And if you if we just try to plant a trillion trees using the same approach everywhere, it, it could actually be definitely not as, as effective as it might be.

Robin Collins  15:21

I think that’s the, that’s the focus of the Drever study as well. I mean, this is the natural climate solutions project, right. And what is meant by natural climate is that, you know, non human technology is kind of implied or, you know, human planting is probably not the way to go in many of these things, but it’s natural succession. But there are some areas where humans can do things, such as in cities, and where trees can be planted and having this, you know, advantage of cooling and heating. So…

John Stone  16:01

I wouldn’t be too worried personally about getting the numbers correct. Because I think we’re, there’s so many processes that we still don’t understand. And that there were so many benefits that Hashem mentioned, that are result of planting poor trees. But there’s a there’s several issues here, which I think was easy to get them confused. What is the whole question of urban heat sinks, urban heat islands, which are real, real concern, and this concern for health reasons.  Because the, we’re going to see, as we already have started to see, an increase in extreme heat events, as climate gets warmer. And with we’re seeing, in fact, just generally speaking, with climate change, this increase of extreme events delivers greater severity, increased frequent frequency. So we have to be conscious of superior health effects that we have to do what we can to make sure we don’t make the heat island effect any worse. One of the ways to prove things is to take account of the fact that what why have we got a heat island well that’s because of the amount of concrete there is in cities, and with the tarmac that there is on roads, and we can start to surface over those things. But it’s, it’s actually we said, The other possibility is strategies to plant trees,  or at least have increased tree cover where it’s possible. And there’s no doubt  from the science we have that increasing tree cover will benefit, climate change in reduced emissions and concentrations of greenhouse gases in the atmosphere. And, but as a sort of talking, you can see there are so many different processes involved, which we don’t actually totally understand. But that shouldn’t stop us actually going ahead and enacting because we know enough already.

Robin Collins  18:19

John, I know you you’d said in an email that, you know, your own house planning of Ivys, for instance, has resulted in a cooling of your house in the summer. And, and I mean, I’ve noticed that to our house, there’s lots of trees, we don’t use air conditioning, there’s only a couple of days in a year where air conditioning is really would have been nice, but we still don’t have it. But you know, eliminating air conditioning in certain parts of the world could have a massive impact on reduction in electricity usage. Hashem you had said, you thought there was maybe a one to two degree was that Fahrenheit or centigrade reduction? I’ve seen numbers higher than that like in you know 10 To 10 to 20% cooling impacts. Do you have any more on that than?

Hashem Akbari  19:18

Sure? I guess that you mentioned couple of things that I had to clarify. The air conditioning energy savings that we have calculated and measured because of the shade trees. These are the trees that are directly shading the buildings, depends on the existing load, cooling load of the building.  In moderate climates, as you mentioned, the that the cooling season is very short, and the outdoor is only few degrees. warmer in fewer hours than then the comfort range having several trees on the west and south side of the building, building during the summer would eliminate the need for air conditioning altogether. So, this is so the impact of the trees in terms of the percentage savings on single family coolings would increase to about 100% in very, very moderate, or what I call it transitional climates, that having a tree or a cool roof, or a combination of them would eliminate the need for air conditioning. Then, in addition to that, trees, because of the process of evapotranspiration would cool the communities. This particularly happens in the in the dry climates, that in literature, typically they are being referred to as “golf course effect’. When you pass in an area that has a large golf course, you would find out that it is a few degrees cooler, so that one or two degrees or three degrees cooler can definitely happen depending on the location, that would create an additional neighborhood level cooling of about another 25% to what you have saved from the direct savings. So from the direct savings, if you say you save $100 a year on cooling roof, this neighborhood cooling perhaps would improve your cooling reduction, your cooling by another 25%. So, I also wanted to comment a little bit on the co2 sequestration, we got to understand that we are talking about the cycle. And any kilogram of co2 that it is being sequestered from the atmosphere, it is going to into three, three components, leafs, branches, and a stem and roots. The leaves typically are cyclical and they are releasing their co2 on an annual basis. And that’s why you’re seeing you’re seeing that sinusoidal effect in the killing plants. And on the trees themselves carbon stored on the body of the tree as biomass and the roots. Eventually, it comes a time that these biomass would die. So if they die a replacement tree would keep that level of, of co2 on the earth rather than the on the atmosphere. So it would be another plateau that one would achieve. If one would find out solutions that integrate the biomass in other aspects of the energy utilization within the society in a form of renewable, then you do have a process that you can think about a longer process of stability toward the lower threshold of co2 concentration in the atmosphere. But at this time, if you plan to billion trees 100 years from now, these trees are going to grow, and then they’re going to, some of them are going to die, you have to constantly replace them. And at that level, you have a new level of co2 concentration in the atmosphere. So trees would not sequester as there are most trees would not sequester as their co2 for for 10s of 1000s of years. You know, the longest trees that I have ever seen lived are sequoias that you know live for about 3000 years.

Metta Spencer  24:09

I see, Robert, a few more follow up that I’ve got another question.

Robin Collins  24:19

Yeah, so I was gonna ask you about that short term, long term phenomenon. Part of the projects that we are looking at are they’re, they’re biased to a certain extent by a desire to see benefits within a short period of time. So there were five years. And there are some things that can clearly be advantaged within that short timeframe. But there’s also the fact that, you know, larger trees can take 30 years to grow and become really good especially in the trunk and branches, carbon sinks. Do you do any of you have any thoughts on the I mean, without saying we have to do both? Any thoughts on how, how this should be prioritized? I mean, in terms of policy you know, what, what are the what are the things that should be done right away? And what are those things that should be done with expectation of result, significantly later?

John Stone  25:33

Things that you can do right away, it makes sense to stop chopping down trees.

Robin Collins  25:37

Right. So there’s a conservation side of this.

John Stone  25:40


Robin Collins  25:40

Including old growth. But I mean, we do have plantations, where, you know, trees are designed, or they are kind of factories for tree production, where there’s a cycle, to put them up, take them down, put them up, take them down, to provide wood for construction, and furniture, and so on. So those aren’t the ones you’re talking about. John, I’m assuming you’re talking about the the old growth. And some, some of the ones that had been torn down that shouldn’t have been down, been taken down and need to be replanted?

John Stone  26:20

Yes,  I agree with you.

Hashem Akbari  26:22

Let me let me comment on that one. I think that when it comes to urban forestry, we have to accept that we are living in a capitalistic society. And no matter in how we are worrying, we have limited resources. So the issue in here would be clear planning, that would minimize the cost or optimize the benefits of any projects that we are trying to pursue throughout the city, including the including the trees. And also I should mention this, this point that having the best type of tree that in a forest, when it is being harvested would bring in close to $2000 to $3,000 per tree. In an urban setting, it’s worth zero, because it would take $10,000 for particular equipment to comie in to safely remove that tree from the environment. So in terms of the dollar and cents, trying to harvest the trees in an urban, in most urban environments would not be an economical approach rather than doing the data manage manage forestry. So, trees should be promoted and should be planned based on the overall quality of living in an urban setting, setting, including that it is coming, promoting pedestrians in a friendly environment, promoting minimizing energy use either being good because of the because of the transportation or energy or anything like that. So one should really pursue it in that direction.

Metta Spencer  28:47

Now, let me let me make sure I understand you because that’s very interesting. Are you suggesting that the cost of maintaining or planning and keeping a tree in the city is less than it would be in the country, or  in the forest?

Hashem Akbari  29:04

It is the other way around. It is the cost of maintaining the tree in an urban city, in urban environment typically, is 100 times more than what it is in forestry. In an urban environment. If you have, if you have professional to come in to cut the branches of the tree you’re talking a project in the order of about 1000 to $2,000 every five years.

Metta Spencer  29:40

Okay, so that’s the reason why it would make no sense whatsoever to try to plant trees in the city with the idea of getting of harvesting them you do not want to do that you want to do

Hashem Akbari  29:53

We don’t want to do that.

Metta Spencer  29:54

Only ones that you hope you can keep alive.  And one of the things that interests me is that that, you know, trees, as I understand it, you know, they’re they the mortality rates pretty high when, when they’re first planted, they may or may not live, and a lot of them don’t, and probably, in many cases, the majority don’t. So, if we planted trees out in the boonies where nobody can go, and just left them, the mortality rate is going to be pretty high. But if we planted trees where a long roads, a country roads, for example, which is, by the way, considered part of urban forestry, is that the highways and the and the roads out in the country, but you know, along the farmlands, That if we planted trees along there, there, it’s accessible, so that people can go and water them and and if need be prune them, or whatever they have to do. So it would seem to me that the, the fate of a tree is much more promising if you plant planted where there are people that can look after them, then in in a forest where they may or may not survive because of natural events. Am I, am I goofy, or is that reasonable?

Hashem Akbari  31:10

You are, you’re absolutely correct. In that respect. I add to that, that when in urban forest environment, say in California, they are harvesting an area, they replace every tree with about 10 seedlings, each seedling cost about the cost about few cents for them to plant it. And if nine out of 10 die, and one grows to the maturity, they have been able to sustain that, that forest and forest production to forever. So it is a, it is not the percentage of the survival is the cost of what it would take to keep that sustainability going. And, again, I have to repeat this thing. trees are about one of the most expensive three maintenance element of the residential neighborhood, particularly if it has to be dealt with professionals. So that’s the point that I’m trying to make.

Metta Spencer  32:31

One of the things that I hope we will do is not only plant lots of trees in Toronto, or in Canadian cities in general, but also encourage neighbors to get out there and plant them themselves. Not only in their own property, but we should have parties where they you know, bring a sandwich and a spade, and Saturday morning, meet me at such and such a corner and we will have some trees for you, and some fertilizer or whatever you you need. And let’s all get together and have a good time. And then each person will be responsible for whatever tree he planted. And we’ll all come and give him good watering and take the weeds up every now and then. I think that would be a wonderful community building project. Do you agree? Has anybody here had any experience along those lines?

Hashem Akbari  33:28

I have to fully agree with that on you have been promoting the idea of having environmental course in in high schools, where students will be on their say, at ninth grade or eighth grade will be given a project of planting and maintaining a tree or several trees in their own neighborhood for the next four years that they are in the in the high school number that way. There are some studies, social studies that have done that by having a sense of community ownership, these are students would grow totally in the adolescence in a different way, in a kind of social way, in a responsible way. There have been again, some studies done by the sociologists find out that that’s a much better way to raise a teenager in our communities. So,  We have. The sense of ownership makes a lot of proud to these students.

Metta Spencer  34:46

And Eric Davies has had some experience doing that, haven’t you Eric? With kids.

Eric Davies  34:52

Yeah, yeah, I the things are number one scale thinking at the level of the ecosystem, not the tree. Number two native eco systems instead of just anything. And and I think that’s a really neat point, I want to touch on the the harvesting of the Urban Wood. I’m just wondering if I can share my screen with you to show you a couple slides? Can I could I do that? Okay, let me you know, this is a sketch from the United Nations, this is the decade of ecosystem restoration. And I think this is a really important place to start in terms of scales is that we need to not only plant trees, but we need to restore ecosystems. And you can see the kind of vision there. Can you see that toggle back and forth?

Metta Spencer  35:35

Yeah, yeah.

Eric Davies  35:37

So when you restore an ecosystem, you’re doing a lot more than planting trees, you’re restoring forests and streams and how those ecosystems are all integrated. Is is a really important thing. And I think, if we start at the level of thinking about trees, without getting to the forest, we run into a lot of problems. You know, these are kind of important words, but a tree, native trees, host biodiversity, non native trees don’t right? Native trees form ecosystems. And as you can see that middle panel, the trees are the foundation for the biodiversity above it. And it’s the ecosystems that provide ecosystem services, which can be everything from carbon sequestration, to cooling. And rather than going at things individually, like heat, or this or that, when you restore the health of ecosystems, not only to get all those ecosystem services, but in there, you’ll see these cultural ones, right. And this can be anything from general health to success in school. And, you know, the problem if I just go through here is now most of our urban areas are not native trees. So they’re not providing ecosystem functions. And I guess that so even in Toronto right now, but the Canada 2 billion tree program, if you look at it, they want to plant 2 billion trees and 50% of the species are non native species, including Norway maple, which is extremely toxic species that kills the fungi in the soil, thereby preventing the communication of trees and, and a whole bunch of other important processes and also is toxic to insects. So then causes a complete collapse and the ability of the ecosystem to sustain biodiversity. And because of

Metta Spencer  37:23

That’s one thing we definitely should include in our recommendations. If Pugwash thinks about that, you better send us some evidence, because that sounds, you know, like we ought to mention that no, don’t plant Norway maples.

Eric Davies  37:36

Yeah well, so here’s there’s 73 native trees in Toronto. And when you look at the trees, almost 50% are gone of the native ones. And if you look at this is all the cities in North America, the black circles are the native trees that are gone, you can see that most of the native species are gone. So you know, if we wanted to really restore the health like I’ll just maybe just show you this one last thing to give you an idea of how serious it is. But this is the Toronto ravines we conducted the studies 40 years apart. And originally was all native trees, Toronto ravines has 27,000 acres, that’s historical. This is 1977, the red is just the Norway maple. And in 2015, it was almost 50%. And this is what’s happening to the ravines. So one last neat point. And that is it. If you look at this Toronto ravines there’s 27,000 acres. And I’ve calculated the Norway maple, it’s 186 million board feet of timber. And really, what we should be doing is harvesting that timber, sequestering that carbon and buildings, and then allowing that ecosystem to get restored to have 100 times more potential for not only the ecological health, but the ability of people to use that ecosystem. And in in a weird way, I wonder if that’s the problem is that we don’t treat our urban forests as a resource that we can harvest. It’s just this kind of like, you know, Hashem said plant a tree, it’ll die plant, another one without stewarding that resource to become something valuable in the future. So,

Metta Spencer  39:14

Okay. A question occurs to me is, is it economically reasonable to go out there and be selected, go through the forest and say, This is a tree we want to take out. And here’s another one over there. But but you know, that’s quite different from the way most of the I don’t know, plantations of  trees work with a it’s a monoculture. They put them in rows and all take them clear, cut them down and so on. It’s obviously cheaper to clear cut, but it doesn’t make sense or is there an efficient way of taking out trees that should be removed, but with without disturbing the rest of the trees in the forest?

Eric Davies  39:55

Yeah, very, very easy.

Robin Collins  39:57

Eric just, before you answer that, let me can I just add a detail to it. The difference between urban forest here and plantation forests, I’m assuming those are two different categories. And I mean, you mentioned the ravines and then city where there are, you know, large woods, let’s say woods, I wasn’t considered that those would be harvested. But I mean, you’re making an interesting point that they might be. But there is a distinction, I think Metta between, you know, removing the individual trees in an urban setting, versus what you would do in the natural setting out way beyond the cities where you wouldn’t remove individual trees. But it just the scale is just this is not sensible to do it that way. So, so you, you need to do the natural process. I mean, it’s it’s part of the biodiversity aspect of it. But there’s natural processes for forest to maintain themselves. And you want, you want the any replacement to enhance that process, so that, so that you don’t have to have human intervention.

Metta Spencer  41:10

Okay, there’s a secret fight going on here between Robin and me.

Robin Collins  41:15

No, I don’t…

Metta Spencer  41:18

I think like you say, you’re trying to make an argument for clear cutting and making an argument for a trying to find a way to avoid clear cutting. I think that’s what this is really a

Robin Collins  41:29

No, no it’s not actually because the clear cutting of, of where there are tree plantations where they’re managed forests that are managed for the purpose of producing wood, those are clear, those are clear cut. Yes, that but I’m not talking about natural forests. I’m talking about regions in which you have trees that are planted specifically for human use, and replant.

Metta Spencer  41:58

But natural forests are sometimes clear cut for him.

Robin Collins  42:02

That’s a different that’s a different argument, though.

Metta Spencer  42:05

Okay, but let Eric replied to me. Is it possible and economically realistic to go through and pick out a few trees here and there to remove without destroying the rest of a natural forest?

Eric Davies  42:21

100% in the hardwoods, you know, kind of like Robin said, if you’re most of the forestry operations in Canada happened on what’s called the area undertaking which are mixed woods, on the Canadian Shield and above. And in the further you go, when you get up into the boreal, the lifecycle of those trees is dominated by disturbance, fire disturbance. And so landscape scale disturbances like clear cutting, when done properly, can maximize the productivity of that for wood. And if that wood is used in a way that sequestered then there, there is some logic to doing that, right. And but in the urban areas, single tree selection is great. And I think the neat thing that Hashem mentioned is that if you if you’re if you if you think about harvesting a tree in an urban area strictly for the value of the wood, it would not be economical. But if you look at Toronto, there are emergency meetings happening almost on a monthly basis about the flood risk. The Toronto ravines was created in the 50s as a mitigation for Hurricane Hazel. And, the idea is those ravines help infiltrate the water and control it. Now 50% of the ravines are invaded by non native species, and they’re increasing the flood risk. So if that flood risk is billions of dollars a year, over a decade, whatever the cost of managing your forests is not just for the wood, it’s also for mitigating against these climate change risks and kind of like the paper actually, that Robin brought up at the beginning. If you look at the abstract of that, again, as they call it, co-benefits. So the question carbon is one, but natural based Climate Solutions is about you know, reducing flood risk and urban Island heat effect and all these things and, and so, I hope that we view our urban areas in a different way, you know, we have to kind of incorporate the forestry perspective from up north with that Co-benefit approach of the cities and hopefully we can bring those together and yeah, create a healthier ecosystem that would be all around enriching for all those services.

Metta Spencer  44:26

Okay, now that you’re you’re on screen, I want to follow up with what I originally asked you, you I know I’ve had lunch with you a long time ago, in which you were talking about taking this children’s classes of grade school kids out to the ravines and pointing out to them the magnificent old, old trees that you particularly map.  You keep a map of all of the oldest and most glorious old healthy trees in Toronto, and you show the kids how to how to collect seeds and and they raise them in coffee pot.

Eric Davies  44:59

If you want to save the world, really, if you want to get really down to the practical stuff, the number one thing are big trees. They’re the number one ecological assets that are the last source of genetic biodiversity. And if you can see, for instance, like this old idea of rewilding by starting with the trees, you know, Aldo Leopold in the 18’s says that, you know, we need you know, a lot of the rewilding is about animals. You know, they have a huge effect, like wolves in Yellowstone. But rewilding trees is something that is really important. So I would go around Toronto, we’ve got about 1000 trees mapped. This is through University of Toronto forestry, we get students every year that to look through binoculars at the seed production. This is a white oak in Oakville. It’s the longest interval between seed crops at any tree in North America between 10 and 15 years. And this is regarded as one of the best species, Oaks and the best genus to trees for biodiversity in the world. So

Metta Spencer  45:55

So you think, every 10 or 15 years, they produce seeds?

Eric Davies  46:01

Yeah, and they think it’s actually getting longer. So red oak is a common native oak, and it produces acorns about every two to five years. But the white oak, very long lived tree and it produces only, you know, seven to 15 years, and it’s getting more variable. So we’re mapping these trees. And we’re growing them. This is a photo of me from the mid 90s doing this. And the idea is these trees can be Epi Centers. And not only for ecological restoration, but for social, like education for reconciliation, for because, you know, I that was actually my interest in really always talking with you Metta. And because it’s, it’s the chicken and the egg question. Like, I’m interested in ecology and making ecosystems better for nature as well as people. But if people are happier and more peaceful, then they’re better stewards of the land. And so the big tree idea is really, so much of the hope is also to facilitate them as epicenters of education. And so I am working. currently, I’m working at Toronto, French school is the place I’ve been spending a lot of my time at over the past couple of years. And they’ve got a large chunk of ravines and they’re really interested in, we’re trying to integrate the curriculum, integrate ecology, inventory, restoration and management into their curriculum. And it’s pretty incredible when you look at 1000 students in a school, and if you give them the tools to go map biodiversity, and start doing their own projects and thinking on it, it’s it’s, it’s pretty powerful, what you know, if people can start doing this, so that’s

Metta Spencer  47:43

My son went to Toronto French school and graduated, and I wish you had been there for him. Okay, thank you so much. Yeah. Okay.

Hashem Akbari  47:54

I would like to bring a little bit closer attention and forecast to urban forestry. We should remember that, in a typical city, about 75% of the land is owned by private citizens, they are the people responsible and maintaining the trees. And the other 25% is owned by the city government, that it is being financed by the same people throughout the city. So the issue of the urban forestry is, from one point of view is very simple, it has to be providing rather meet immediate or mid term solutions to the needs of the people. The issue of changing the entire ecosystem, it’s typically out of the scope of an individual in an urban setting is a policy issue being taught out at a larger level and it’s impact is going to be very, very long term. And I dare to guess, based on the history, that many of these long term plans have been stopped in one way or the other. So it is nice to have a dream. But our dream at this time should be forecast of how to improve the quality of life in the urban setting five years from now. So heat a storm is coming. So what are we going to do? And also making sure that’s economical. So the urban trees should we look really in that scale? Who is paying for it? Who is maintaining it? What is benefit?

Metta Spencer  50:00

Go on Robin, sorry.

Robin Collins  50:01

Let me let me pass this on to John, too, because in terms of incentives, and government policy, what’s your experience, John, on, on, on on what’s the best way of getting governments to support this kind of thing at the, it is really at the local level, not so much the national level, but there could be leadership at the national level level?

John Stone  50:26

Well, it’s interesting that you bring up this question of incentives, because I was just about to make the point. I’ve been living in this house for at least 40 years, it was a new development when I moved in. And over the years, we’ve had a number of trees planted and growing. But recently, we’ve lost so many, losses because of the directional, the tornado, because of diseases and everything else. So the tree canopy, we’re roughly where I live now, is less than it used to be when we moved in. And you in idealistic fashion, you would hope that the residents would want to actually replant those trees and increase the the canopy of trees, but it’s not happening. It’s not happening, because I guess they don’t understand what what they can do and the benefits that will accrue, but also because they don’t see it’s their responsibility. And you know, we just say, well, we’ll do it tomorrow, something. So we’ve we’ve been singularly ineffective in developing policies, which will make sure people see it in their own interest to increase tree cover in cities.

Robin Collins  51:45

I think maybe one of the reasons why people aren’t (inaudible), I have exactly the same problem you’re talking about, we had about 25 trees, and I think it was six or seven have come down over the last 10 years, either by insect infestation, or the (inaudible) or other wind issues. But Hashem maybe you can, you can say something about, you know, ways that the public can be inspired to want to plant I mean, one thing I was thinking about was, you know, cities need to inform their citizens more clearly about the the cool, the electricity benefits of planting trees, and and or bushes and shrubs in for the winter, windbreaks. And what these would, the savings would be.  You know, there’s all sorts of other benefits, I realize, you know, aesthetic and otherwise, but just on just on the reduction of electricity for the carbon footprint. I mean, surely there’s ways cities can measure the impact of trees being grown, and report on them. You know, sort of like maybe a report card every year on which you know, how many trees has gone up and how many have come down, that kind of thing.

Hashem Akbari  53:10

I would, I would refer to two experiments. One of them was done during the Olympics in I think that 1984 in Los Angeles. That three people managed to plant 1,000,000 trees. And it was mostly an advertisement process, and seedlings were being distributed for free in the local nurseries. And then those million trees were supposedly planted. But at the rate of survival of those, as was mentioned, it’s a kind of was a minimum. The other one was Sacramento Municipal Utility District SMART for short, about two decades ago, embarked on a tree planting program. And these trees were being planted by the professionals. And they manage to have these trees plants, planted either on the private properties or alongside the street at a very, very reasonable costs. And the SMART was promoting primarily for energy efficiency improvement of the energy. The Los Angeles is promoting it for water conservation, because trees are shading the lands that consume a lot more water. So each locality has its own specific issues that one has to be worried about it. And trees for parking lots to shade the cars is another, another program that is being promoted by many cities throughout the, throughout the country. So examples of these are huge, but they are not widespread everywhere. And there are good reasons for that, money, money.

Metta Spencer  55:23

I’d like to go back to John’s mention of having ivy on his walls outside. And I think that’s a it’s not our bailiwick because we’re talking about trees, but it’s relevant. And but I’d heard that Ivy damages brick walls, that as it climbs up there, it kind of interferes with the grout and something. So the question I would have is, could we recommend that people plant ivy on their brick houses? A lot of houses in Toronto or brick? Mostly? And could it could we recommend that? Or would we have to take into account some of the things that Hashem was already mentioned? The cost benefit analysis of, of doing it?

John Stone  56:14

Criticism as well, that attaches to the walls? But from my own observations, that’s not the case.

Metta Spencer  56:23

Oh, good, fine. So you recommend ivy,

John Stone  56:27

Or it’s just there’s so many things we can do on our own if we want to. I mean, for example. I didn’t, I didn’t used to have air conditioning in my house rented until two years ago. Because I feel that if we have screen doors at the front and the back of the house, windows that could be opened and closed just of times that you’re through the day, we could survive with the heat, and humidity. And we didn’t need air conditioning. I changed my mind recently, because I’m getting older. And because the number of extreme heat events are increasing. But just like other people, we mentioned that the air conditioner doesn’t come on more than two or three times during the summer. So there are some things that we shouldn’t do, you can do like opening and closing screen doors. I am, I don’t have a dryer in my house. Because I can dry the clothes indoors in this winter, simply because the image relative humidity is so low. And in the summer, I can put the clothes out to dry outside. And so those sorts of things we can do simply to counteract this climate change impacts. 

Robin Collins  57:56

Yeah, the in the air conditioning box isn’t the problem, it’s turning it on. Right, you can still have air conditioning, but if you don’t use it, you’ve reduced the electricity. So you can still do all these improvements. Even if you’ve got air conditioning. The point is that you’re going to lower the temperature and then you won’t have to use it as much and same with planting bushes and shrubs for the winter. A lot easier to plant bushes and shrubs and the prune them and the plant trees and they have this windbreak capability. I don’t know as much about, Hashem probably knows more about it. But if you plant them, I think it was at least a foot away or something. And there’s a there’s a buffer zone that’s created. And it’s anyway, it’s all laid out. And people don’t know about these things. I think that’s part of the problem. People think,..

Metta Spencer  58:45

I live in a high rise and I have a balcony hadn’t occurred to me. I can plant something in planters of my balcony, does is there any? Let’s assume that in my 23 storey building that all have a balcony, would it? Would it be useful to get people to put trees and planters on their balconies?

Robin Collins  59:07

Well, it would have a minor effect. I mean, the the transpiration alone, you know, the water transfer process would have a cooling effect. I mean, others might have even would be small. But it wouldn’t be zero.

Metta Spencer  59:23

Maybe Hashem can you estimate what it? Is it worth even proposing?

Hashem Akbari  59:28

No. Again, the reason that it is no, is if a person would like to have a small shop or a small plant on their balcony and enjoy it. They should do. But if you are trying to think about planting a tree on the 25th floor of a building, you got to make sure how that tree would be 10 years from now. And if that tree grows and destroy and create an extra weight on the balcony and forces the balcony to fall down. Then, you know, these are all the issues that you have to think about that, you know, it’s one has to be it is the question of dollar and cents fundamentally. And the benefit of that that you get mostly is visual benefit and enjoyment that you are. You’re taking care of a living being to be to be a tree. And that’s, that’s the benefit that you have. We all spend hundreds of dollars every year in gardening. And next year, we do the same thing we never claimed that it would improve our air quality it improves our energy efficiency, but definitely, definitely it improves my quality of life.

Metta Spencer  1:00:50

That was wonderful. Okay, well, I’ve enjoyed the quality of life in our conversation today. I think it’s been good fun. And I’ve learned a lot. So our time is up. And I want to thank everybody for the contributions that you’ve made along these lines. So we’ll see what comes to this and see what we can promote. All right. Thank you all. Bye.  Project save the world produces these shows, and this is episode 544. You can watch them or listen to this audio podcast on our website tosavetheworld.ca People share information there also on six global issues. To find a particular talk show enter its title or episode number in the search bar, or the name of one of the guest speakers. Project save the world also produces a quarterly online publication. Peace magazine, you can subscribe for $20 Canadian per year. Just go to pressreader.com on your browser. And in the search bar, enter the word peace. You’ll see buttons to click to subscribe.


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