Severe Pruning and Ecoservices

Subscriber-only episode

In this Wednesday episode of Talking Trees, we take a critical look at how severe pruning—especially topping—affects urban trees and their ability to provide ecosystem services. Drawing from the latest scientific research, we explore how pruning practices shape tree physiology, carbon capture, and microclimate regulation.

We discuss:

• Findings from Comin et al. (2024), showing that topping significantly reduces a tree's capacity for cooling and carbon assimilation, despite some short-term physiological responses
• Insights from Muscas et al. (2024), revealing that frequent, moderate pruning can better maintain trees’ long-term ability to sequester carbon and capture particulate matter (PM10)
• How pruning waste management plays a role in the overall carbon balance of urban forestry
• The tension between visual/aesthetic goals and functional performance in tree management
• Why evidence-based pruning strategies are essential for sustaining the ecosystem services trees provide in cities

This episode urges arborists and municipalities to rethink the long-term impact of pruning practices on urban climate and air quality.

Background information:

• Comin et al. 2024. Effects of severe pruning on the microclimate amelioration capacity and on the physiology of two urban tree species.pdf
• Muscas et al. 2024. Effects of urban tree pruning on ecosystem services performance.pdf

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Chapters

• 0:02 Welcome to Talking Trees
• 1:10 Research on Pruning Scenarios
• 2:48 PM10 Capture and Carbon Storage
• 4:58 Thermal Comfort Under Pruned Trees
• 6:22 Disposal Methods and Carbon Impact
• 10:31 Arborists as Environmental Educators

Transcript

Roger: 0:02

Talking Trees with Lily and Jad. Welcome to Talking Trees. In today's episode, we dive into the art and science of tree pruning in the city. Two recent studies shed light on how different pruning practices influence the ecosystem services that urban trees provide. Common and colleagues, 2024, focused on the impacts of heavy crown pruning, revealing that intense trimming can significantly reduce a tree's cooling capacity and disrupt its natural growth. In contrast, muscus and co-researchers, 2024, evaluated various pruning scenarios across the life cycle of 12 tree species. Pruning scenarios across the life cycle of 12 tree species. Their findings suggest that less intensive but more frequent pruning may optimize the tree's ability to capture PM10, airborne dust and enhance carbon storage, ultimately preserving tree health and maximizing their benefits to our urban environments. Join us as we unravel these insights and explore the delicate balance between maintenance and nature's resilience.

Jad: 1:10

Hey everyone, welcome back. You know we're always thinking about how to best care for our trees as arborists, but lately I've been looking at some research, oh yeah yeah, and it's got me thinking about pruning in a whole new way, you know. Interesting it's not just about aesthetics or safety anymore. It's about how pruning can actually impact those crucial ecosystem services our trees provide.

Lilly: 1:32

Yeah, you're absolutely right. There's more and more research comes out that's putting numbers to those impacts.

Jad: 1:36

Exactly, and that's giving us some real data to think about when we're deciding how to prune.

Lilly: 1:39

For sure.

Jad: 1:40

So, ok, I found this study from Italy from 2024, and they really dove deep into this. They compared three different pruning scenarios. They call them combined pruning, ordinary pruning and then extraordinary pruning.

Lilly: 1:53

Okay.

Jad: 1:54

And they looked at these scenarios across 12 common tree species.

Lilly: 1:57

Interesting.

Jad: 1:58

What I thought was really cool is that they based these scenarios on what municipalities are actually doing out there. That's a good point, so it's really relevant to what we're doing, you know, out in the field.

Lilly: 2:08

Yeah, that's key Having research that's based on what's actually happening, you know, real world practices. It makes the findings so much more useful to us.

Jad: 2:16

Exactly so. You know, this study gets really into the details.

Lilly: 2:19

Oh yeah.

Jad: 2:20

Like they actually weighed the branches.

Lilly: 2:22

Really.

Jad: 2:22

To see how pruning affects how much CO2 the trees store. Wow, that's attention to detail. And then they even look at how different ways of getting rid of those branches, like composting or sending them to the landfill, how all that plays into the carbon. You know the whole carbon thing.

Lilly: 2:38

Yeah, it's a really important part of the equation that often gets missed.

Jad: 2:42

Yeah.

Lilly: 2:42

You know, most people don't think about what happens to the branches after they're cut. But it all has an impact.

Jad: 2:47

Okay, now let's talk about PM10 capture.

Lilly: 2:49

Okay.

Jad: 2:53

This is where things got really interesting. For me, it turns out all three of those pruning scenarios actually reduced PM10 capture, but ordinary pruning had the smallest impact.

Lilly: 3:00

Well, yeah, that makes sense, if you think about it.

Jad: 3:02

Right.

Lilly: 3:02

Leaves are like the main filters for PM10. So whenever you're taking them away, no matter how you're pruning, it's going to reduce that surface.

Jad: 3:09

Right.

Lilly: 3:09

I think it really shows how important it is to try and keep as many leaves as we can whenever we're pruning.

Jad: 3:15

Yeah, so you might think that cutting branches off automatically means less CO2 storage, right?

Lilly: 3:20

Yeah, you would think that.

Jad: 3:29

But it's not always the case. It really depends on what happens to those branches after you cut them, right, if that wood is stored or reused in the right way it can actually become a carbon sink Interesting, and it can even make up for the CO2 that's lost when the tree starts growing back.

Lilly: 3:36

So it's not a simple equation.

Jad: 3:38

Not at all. The study actually uses the linden tree as an example.

Lilly: 3:41

Linden tree okay.

Jad: 3:42

Heliacordata.

Lilly: 3:43

Right.

Jad: 3:43

And they found that if the branches are disposed of correctly, the crown could actually store 65% more carbon.

Lilly: 3:50

Wow 65%.

Jad: 3:52

Over its entire lifetime.

Lilly: 3:53

That's incredible.

Jad: 3:55

Isn't that amazing. Imagine as you could tell your clients that.

Lilly: 3:57

Yeah.

Jad: 3:57

Suddenly you're not just talking about, you know, keeping the tree healthy.

Lilly: 4:00

Right.

Jad: 4:01

You're talking about real environmental benefits.

Lilly: 4:03

Exactly. Having this kind of data gives us so much more to talk about with clients Totally and it can really help us push for better disposal practices in our communities.

Jad: 4:12

I like that. Now, this Italian study. They also looked at something pretty cool. What's that Human thermal comfort? Okay, they use these things called the apparent temperature index and the humidex to measure how comfortable it felt to stand under trees that had been pruned, and their findings are really relevant to the work we do in cities and towns.

Lilly: 4:31

I bet.

Jad: 4:32

So both of those indices consistently showed that it was a lot less comfortable to stand under trees that had been topped Really, especially during those hot summer months.

Lilly: 4:40

That makes sense. I mean when you think about it.

Jad: 4:42

Now here's the crazy part being near a topped tree was often no better than just standing out in open grassy field. Wow, it's all about shade density. Topped trees Just don't have enough leaves to block the sun.

Lilly: 4:54

Right.

Jad: 4:55

So more of that solar radiation is hitting the ground.

Lilly: 4:57

Yeah.

Jad: 4:58

And that can actually make it hotter under a topped tree than in a spot with no trees at all.

Lilly: 5:03

It's kind of counterintuitive, isn't it?

Jad: 5:05

It really is. It's a perfect example of how our printing decisions can have these unintended consequences.

Lilly: 5:12

Yeah.

Jad: 5:12

They don't just affect the tree's health, they affect the whole environment around it. So we've seen some pretty strong arguments against topping from this Italian study.

Lilly: 5:19

We have.

Jad: 5:20

But there's another study from 2024 that adds even more evidence to the case. This one focused specifically on the negative effects of topping Okay and it really highlighted those long-term risks. Like what Well you know those big cuts you make when you're top of tree.

Lilly: 5:33

Right.

Jad: 5:34

They're basically like open wounds.

Lilly: 5:35

Yeah.

Jad: 5:36

Disease can get in easily and that weakens the tree and shortens its life.

Lilly: 5:39

That's a big problem.

Jad: 5:40

It is especially in urban areas.

Lilly: 5:42

Yeah, for.

Jad: 5:43

And that's not even considering the liability issues If a tree that's been poorly pruned ends up falling.

Lilly: 5:48

You're right.

Jad: 5:48

This study really emphasizes how important it is to think about those long-term consequences when we're making pruning choices.

Lilly: 5:57

Yeah, we have a responsibility to be making good decisions.

Jad: 5:59

Absolutely.

Lilly: 6:00

Decisions that will keep our trees healthy and help them live long life For sure. Especially the trees we're caring for in our cities and town.

Jad: 6:06

Right.

Lilly: 6:06

You know, it's interesting how these studies are connecting topping with all kinds of problems like diseases and even changes in the local climate.

Jad: 6:13

Right.

Lilly: 6:13

It really shows that we need to be thinking about pruning more holistically, you know.

Jad: 6:17

Yeah, it's about seeing the bigger picture and understanding those long-term impacts.

Lilly: 6:21

Exactly.

Jad: 6:22

Now, speaking of long-term impacts, there's another study from 2024 that I found really fascinating. Oh, yeah, yeah, this one also looked at those three pruning scenarios Okay, combined ordinary and extraordinary.

Lilly: 6:33

Right.

Jad: 6:34

But they looked at them from a different angle. They wanted to see how each scenario affected a tree's ability to capture PM10 and store carbon over its entire lifespan.

Lilly: 6:44

Oh, wow.

Jad: 6:45

Which they defined as 70 years 70 years Okay. Yeah, so that's a pretty long time.

Lilly: 6:49

It is. It really helps us for those cumulative effects.

Jad: 6:52

Right. So when it came to PM10 capture, it probably won't surprise you that any kind of pruning had an impact.

Lilly: 6:58

Right.

Jad: 6:58

I mean, we are removing leaves and those are like tiny air purifiers.

Lilly: 7:02

They are.

Jad: 7:03

But the interesting thing is that ordinary pruning consistently had the smallest reduction in PM10 capture.

Lilly: 7:10

Interesting. So less aggressive pruning is better for air quality.

Jad: 7:13

In the long run, yeah.

Lilly: 7:14

In the long run.

Jad: 7:15

Now, when we look at carbon storage things got a little more complex. Oh yeah, how long run. Now when we look at carbon storage things got a little more complex.

Lilly: 7:19

Oh yeah, how so?

Jad: 7:20

Well, this study calculated something called the total carbon balance of the tree, which takes into account the CO2 stored in the tree itself.

Lilly: 7:31

But also the emissions from getting rid of the pruned material. So it's kind of like a full accounting of the carbon Exactly.

Jad: 7:34

Remember how we talked about how even a pile of wood chips has a carbon footprint, I do. Well, this study took all of that into account.

Lilly: 7:43

Interesting.

Jad: 7:43

And here's the thing.

Lilly: 7:44

Yeah.

Jad: 7:45

There wasn't a huge difference in total carbon balance between the three pruning scenarios.

Lilly: 7:49

Really.

Jad: 7:50

It suggests that how often you prune and how much you prune might not be the biggest factors when it comes to carbon storage.

Lilly: 7:57

Huh, so what is?

Jad: 7:59

Well, it seems like the species of the tree, and what you do with those pruned ranches.

Lilly: 8:03

Right.

Jad: 8:03

Those have a bigger impact on the overall carbon picture.

Lilly: 8:06

So it's not as easy as saying this pruning method is better for carbon.

Jad: 8:10

Not at all. It's about those nuances you know, and making informed decisions based on the specific situation.

Lilly: 8:16

Absolutely, and that's where we, as arborists, really come in.

Jad: 8:19

Right.

Lilly: 8:19

We can use this knowledge to talk to clients and help them understand.

Jad: 8:23

And we can encourage those disposal practices that are good for the tree and the environment.

Lilly: 8:26

Exactly.

Jad: 8:27

Okay, so let's talk about those disposal methods for a minute. Okay, this study looked at four options. Okay, anaerobic digestion, composting, open dumping and landfill.

Lilly: 8:36

So the main ones.

Jad: 8:37

Yeah, and they even figured out the greenhouse gas emissions for each method.

Lilly: 8:41

Huh, I'm curious to see what they found.

Jad: 8:43

Well, get this anaerobic digestion and industrial composting.

Lilly: 8:46

Which we think of as being eco-friendly.

Jad: 8:48

Exactly those actually had the highest greenhouse gas emissions per kilogram of wood.

Lilly: 8:54

Really.

Jad: 8:55

Yeah, it was surprising to me too at first.

Lilly: 8:57

Yeah.

Jad: 8:57

But it all comes down to how they did the calculations.

Lilly: 9:00

Okay.

Jad: 9:00

They assumed a much higher moisture content for the wood in those two methods compared to dumping and landfill.

Lilly: 9:07

So that skewed the results.

Jad: 9:08

Exactly. It just goes to show that those models are helpful.

Lilly: 9:11

We need to understand the whole picture.

Jad: 9:13

Right, we can't jump to conclusions.

Lilly: 9:14

Yeah, open dumping and landfill had the lowest emissions.

Jad: 9:17

In this study.

Lilly: 9:18

But obviously those come with a whole other set of environmental problems.

Jad: 9:21

Exactly. It's not just about greenhouse gases. There's potential for contaminating the soil and water.

Lilly: 9:26

Visual pollution too.

Jad: 9:27

Right and we're wasting valuable resources.

Lilly: 9:30

Absolutely so. This research really shows us that we need to be thinking about responsible disposal.

Jad: 9:35

Yeah.

Lilly: 9:35

But it also reminds us to look at the whole picture Right To consider the overall environmental impact. It's complicated.

Jad: 9:42

It is. There are no easy answers, nope. Every study we look at just shows how complex tree care really is.

Lilly: 9:48

It does.

Jad: 9:49

There are so many factors to consider.

Lilly: 9:50

So many, and as we learn more, our role as arborists becomes even more important.

Jad: 9:55

Yeah.

Lilly: 9:56

We need to be the ones guiding these sustainable urban forestry practices.

Jad: 10:00

We've covered a lot of ground here.

Lilly: 10:01

We have.

Jad: 10:02

From how pruning affects CO2 storage and PM10 capture, right To those surprising findings about thermal comfort.

Lilly: 10:08

Yeah.

Jad: 10:08

And the complexities of carbon accounting.

Lilly: 10:10

Definitely.

Jad: 10:11

But the question is how can we actually use all of this information?

Lilly: 10:15

That's the key question, isn't it?

Jad: 10:16

As arborists, how can we use it to make decisions and have better conversations with clients?

Lilly: 10:20

Well, I think it comes down to education.

Jad: 10:22

Okay.

Lilly: 10:22

First, we need to make sure we understand all of this ourselves Right the nuances, the limitations, the whole picture.

Jad: 10:27

Yeah.

Lilly: 10:28

And then we can use that knowledge to educate our clients.

Jad: 10:30

I love that.

Lilly: 10:31

To have those real conversations about different pruning methods and what they mean in the long run.

Jad: 10:35

Arborists as educators.

Lilly: 10:37

Exactly. It's not just about telling clients that topping is bad.

Jad: 10:41

It's about showing them the data helping them see how their choices affect everything From carbon sequestration to the microclimate around their property. Exactly, it's about empowering them to make decisions that match their values.

Lilly: 10:53

Yes.

Jad: 10:54

So, as we wrap up this look at pruning and ecosystem services, I want to leave our listeners with a thought. As arborists, we have this amazing opportunity to be champions for trees, to advocate for them, to show people how important they are.

Lilly: 11:08

How vital they are.

Jad: 11:09

For our lives and community.

Lilly: 11:10

Let's use everything we know, our skills, our passion.

Jad: 11:13

To make sure that urban forests can thrive.

Lilly: 11:15

And provide those benefits for generations to come.

Jad: 11:17

Couldn't have said it better myself and to all our fellow arborists out there.

Lilly: 11:21

Yeah.

Jad: 11:21

Keep up the great work. You're making a real difference, one tree at a time.

Roger: 11:27

Thank you for joining us on this episode of Talking Trees. Today we explored the nuanced effects of urban pruning practices on tree health and the ecosystem services they provide. We learned that heavy crown pruning can disrupt a tree's cooling ability and growth, while less intensive, more frequent trimming may enhance dust capture and carbon storage. May these insights inspire us to care for our urban forests with a balanced approach. Until next time, keep nurturing the green in your city. You.