Tree Species Selection for Green Infrastructure

In this Wednesday episode of Talking Trees, we explore how thoughtful tree species selection is essential for building resilient green infrastructure in cities facing climate change, soil limitations, and urban stressors.

We discuss:

• Why tree selection should be based on site-specific conditions, including soil compaction, heat exposure, and rooting space
• Tools and frameworks for choosing species, including guides that rate trees by drought tolerance, flood resilience, and ecosystem service potential
• The importance of species diversity to reduce vulnerability to pests, diseases, and environmental extremes
• Lessons from trees thriving in natural habitats and how they can inform urban planting strategies
• How properly chosen trees can enhance urban cooling, air quality, stormwater management, and long-term canopy cover

Species selection isn't just a design decision—it's a foundational step in ensuring that urban trees survive, thrive, and serve.

Background information:

• Sjoman Thesis_608183940.pdf
• tdag_treespeciesguidev1.3.pdf

Chapters

• 0:00 Introduction to Talking Trees
• 1:10 Urban Tree Selection Challenges
• 4:16 Strategic Diversity in Tree Selection
• 5:13 TDAG Guide's Practical Approach
• 6:57 Sustainable Drainage and City Forests
• 9:35 Future of Urban Forestry
• 10:45 Episode Conclusion

Transcript

Introduction to Talking Trees

Roger 0:02

Talking Trees with Lillian Jad. Welcome to Talking Trees, your daily journey into the art and science of urban forestry. In today's episode, we explore the critical process of selecting trees for city environments. Onesource Huemin's thesis delves into innovative methods for identifying new species and genotypes that can thrive on the challenging paved surfaces of northern European cities, emphasizing the need to diversify urban canopies. Meanwhile, the TDAG manual offers a practical guide for choosing trees to enhance green infrastructure across the British Isles. It provides detailed species profiles and evaluates environmental tolerances and functional traits to boost ecosystem services in urban settings. Together, these insights offer a multifaceted view on how to sustainably integrate trees into our urban landscapes, each with its unique geographic focus and analytical depth. Join us as we uncover strategies for building greener, more resilient cities.

Jad 1:10

Hey everybody, welcome back to another Deep Dive. You know, as arborists, we're always thinking about the future, right, picking the right trees for the long haul. But climate change really throws a wrench in the works, doesn't it? I mean, who knows what our cities will look like in 30, 50 years?

Lilly 1:24

It's a huge challenge. It really makes you rethink how we approach tree selection, you know, trying to predict what conditions those trees will be facing.

Jad 1:32

Right Like? Are we planting for a future that's going to be more like, I don't know, the Mediterranean or something even more extreme? We're tackling those questions head on today, looking at a couple of fascinating sources.

Lilly 1:41

Sounds good.

Jad 1:45

First up, we've got Henrik Schoeman's thesis Trees for Tough Urban Sites Learning from Nature.

Lilly 1:47

Ah yes, Schoeman, he's got a really unique approach.

Jad 1:51

Oh yeah.

Lilly 1:51

Instead of focusing on trees that thrive in, say, a nice cushy park.

Jad 1:55

Right right.

Lilly 1:56

He looked at trees that are already dealing with really stressful conditions.

Jad 2:00

So the trees that are basically like surviving boot camp.

Lilly 2:04

Exactly. He studied places like the Quinling Mountains in China oh wow and parts of Romania and Moldavia, where it's naturally hotter and drier.

Jad 2:12

So he's looking at trees that are already adapted to a tougher climate. Smart.

Lilly 2:16

Yeah. His thinking was that by looking at how those trees thrive, we might get some clues about what species are best suited to handle the urban heat islands of the future.

Jad 2:26

Makes sense Survival of the fittest Tree edition. But I'm guessing his thesis is pretty dense, scientifically speaking.

Lilly 2:32

It is Definitely some heavy stuff.

Jad 2:34

So to help us translate all that, we're also looking at the Tree Species Selection for Green Infrastructure Guide.

Lilly 2:39

Right From TDAC, the Trees and Design Action Group.

Jad 2:42

Yeah, the TDAC guide. They take a more practical approach, focusing on the British Isles.

Lilly 2:46

It's a great resource for arborists. For sure, it gives you a framework for putting those scientific insights into action.

Jad 2:52

Okay, before we get lost in the weeds here, sure, maybe a quick reminder. Why does all this even matter? I mean, we all know trees are good for cities. Of course, but with climate change lo.

Lilly 3:06

Well, think about it. Our cities are getting hotter, we've got the urban sheet island effect Right and we're seeing more extreme weather events like droughts. Trees can help mitigate all of that. They cool things down.

Jad 3:17

Their root systems help manage stormwater runoff.

Lilly 3:19

Exactly. Plus, we can't forget the social and ecological benefits.

Jad 3:23

Oh, totally. I mean. Trees bring so much to the table. They clean the air, they provide habitats for wildlife and, let's be honest, they just make cities more pleasant places to live.

Lilly 3:33

It's about creating a more livable, sustainable urban environment.

Jad 3:37

Absolutely, and a big part of that is choosing the right mix of trees. Both Shoman and TDAG talk a lot about diversity.

Lilly 3:43

Yes, strategic diversity is essential.

Jad 3:46

OK, but what makes it strategic? Is it more than just planting lots of different types of trees?

Lilly 3:51

Think of it like this you don't want to put all your eggs in one basket, right?

Jad 3:54

Aha no.

Lilly 3:55

Same goes for trees. If we rely on just a handful of species and then a pest or disease comes along, it could wipe out a huge chunk of the urban forest.

Jad 4:06

That makes sense. Diversity is like an insurance policy.

Lilly 4:08

Exactly.

Jad 4:16

And the strategic part comes in when you start thinking about the specific benefits and resilience of each species. You want trees that can handle the heat, the drought the pollution, all the challenges of urban life. It's like we're assembling a team of superhero trees.

Lilly 4:24

It really is. And you know, what's fascinating is that Droman identified 27 tree species that seemed to have that superhero potential. But here's the thing.

Jad 4:33

What's that?

Lilly 4:34

Only four of them are commonly used in Northern Europe right now.

Jad 4:37

Wow. So there's this whole untapped world of tree possibilities out there, like a secret garden of resilient species just waiting to be discovered.

Lilly 4:46

That's a great way to put it, and that's where the TDAC guide comes in. Yeah, it helps us figure out how to actually use those underused species, you know, taking into account practical considerations like space, soil conditions, making sure they're compatible with urban infrastructure.

Jad 5:00

Okay, so we've got Shoman pointing us towards exciting new options and the TDAG guide showing us how to make it all work in the real world. Sounds like a winning combination, I think so. All right, let's crack open that TDAG guide and see what gems we can uncover.

Lilly 5:13

You know, one thing I really like about the TDAG guide it's realistic. It doesn't pretend that urban environments are these ideal places to plant trees.

Jad 5:22

Right, because they're not, are they? It's tough out there for a tree in the city.

Lilly 5:26

Exactly so. The guide actually has a whole section on constraints.

Jad 5:29

Constraints OK.

Lilly 5:30

Things like limited space, sure, compacted soil. You've got buildings, casting shade, maybe overhead power lines to worry about, and don't forget about all that underground infrastructure.

Jad 5:41

Oh yeah, the pipes, the cables, all that stuff can really mess with root growth, can't?

Lilly 5:45

it Definitely. And then there's pollution, of course.

Jad 5:47

Right, it's like a minefield out there.

Lilly 5:49

It is, but that's where this constraint section is so helpful. It walks you through how to assess a site, pinpoint potential problems OK and then ultimately, how to choose trees that are most likely to actually thrive in that environment.

Jad 6:02

So it's like a problem solving guide for urban arborists. Love it. What else makes this guide stand out?

Lilly 6:08

Well, for one thing, it's really user-friendly. They use symbols to quickly convey key information about each species.

Jad 6:15

Oh, that's nice.

Lilly 6:16

You know like crown form, mature size, tolerance for things like drought or pollution.

Jad 6:21

So you can get a quick snapshot of the tree's characteristics without having to read a whole paragraph.

Lilly 6:25

Exactly, saves you a lot of time. But if you do want to dive deeper, they've got those detailed tree profiles. Oh, okay, they cover everything from flowering times and fruiting habits to potential drawbacks Like maybe the tree produces a lot of messy fruit litter.

Jad 6:41

Oh right, or maybe it's known to trigger allergies. That's a good point. We don't want to create a beautiful urban forest only to have people complaining about like sticky sidewalks or sneezing fits.

Lilly 6:50

Exactly. It's all about finding the right balance, creating a space that benefits both people and the environment.

Jad 6:57

Absolutely. And speaking of benefits, the guy also mentioned something called.

Lilly 7:00

BREEAM.

Jad 7:01

Yeah, breeam assessments. I've heard the term but honestly I'm not totally sure what it means. Can you break it down for us?

Lilly 7:06

Sure, breeam is basically a sustainability assessment method that's often used in building construction and urban planning, and the idea is to encourage more sustainable design practices, including how we choose and plant our trees.

Jad 7:21

So it's like a green seal of approval for buildings and landscapes.

Lilly 7:24

Yeah, you could think of it that way. And in the context of urban forestry, BREEAM really pushes us to think long term. Choose trees that are going to provide a wide range of benefits over their entire lifespan.

Jad 7:36

Contributing to a truly sustainable urban forest. That makes a lot of sense, but you know I keep coming back to that statistic from Shoman's research Only four of those 27 resilient species are commonly used in northern Europe. Why do you think that is? It seems like we're missing out on so much potential.

Lilly 7:52

I think part of it might be tradition. We tend to stick with what we know, what's been done before, even if those trees might not be the best choices for a changing climate.

Jad 8:01

So we're kind of stuck at a rut.

Lilly 8:02

You're saying Maybe a little bit, and then there's the issue of aesthetics.

Jad 8:05

Oh yeah.

Lilly 8:06

You know, some of those underused species might not fit our traditional image of what an urban tree should look like.

Jad 8:12

Right, right. So we might need to broaden our horizons a bit, be more open to different shapes, different textures.

Lilly 8:17

I think so. I mean, why can't a city street have the same kind of visual diversity that you see in a botanical garden?

Jad 8:24

Yeah, that's a great point. Shake things up a bit. Speaking of shaking things up, the TDAC Guide also has this whole section on sustainable drainage systems, or EDDS.

Lilly 8:33

Oh yeah, LDS are great. I'm familiar with the basic concept, but for those who aren't, can you give us a quick rundown? Sure, addies are all about mimicking natural drainage patterns.

Jad 8:42

You know, instead of just channeling stormwater runoff straight into the sewer system right we try to slow it down, filter it, let it soak back into the ground, and trees play a huge role in that process oh right, their root systems help absorb water and their canopies help intercept rainfall, so less of it hits the pavement in the first place.

Lilly 9:00

Exactly. It's like there are these natural sponges and umbrellas helping to mitigate flooding, which is becoming a bigger and bigger issue with climate change.

Jad 9:08

Wow, that's really interesting. So it's not just about picking trees that can handle drought.

Lilly 9:12

Right.

Jad 9:12

It's about choosing trees that can actually help us manage stormwater.

Lilly 9:16

It's all connected. You know the trees, the water, the climate, the built environment.

Jad 9:20

It's like this big, complex puzzle and we're trying to figure out how all the pieces fit together.

Lilly 9:25

Exactly. And that actually leads me to a question I wanted to pose to you and our listeners. You know, thinking about all this, all these challenges, all these new ideas.

Jad 9:32

Yeah.

Future of Urban Forestry

Lilly 9:33

It makes me wonder are we kind of at a turning point in urban forestry?

Jad 9:38

Hmm Interesting. What do you mean?

Lilly 9:41

Like, will we have to completely rethink what an urban forest should be?

Jad 9:44

You mean?

Lilly 9:45

Move away from that traditional image. You know, rows of the same tree, all neat and tidy.

Jad 9:50

Oh right, so instead of those like perfectly manicured streetscapes?

Lilly 9:53

Yeah.

Jad 9:54

We might see something more I don't know wild, more diverse.

Lilly 9:57

Exactly More like a natural forest.

Jad 10:00

With different species all mixed together, kind of a patchwork.

Lilly 10:03

And trees chosen not just because they look pretty, but because they can actually handle those tough urban conditions.

Jad 10:09

Right, right. Trees that can take the heat, manage the stormwater, provide all those benefits we've been talking about.

Lilly 10:15

It's about creating these resilient, biodiverse ecosystems right in the heart of our cities.

Jad 10:21

Wow, that's a pretty powerful image, like we're not just planting trees anymore, we're creating these like intricate tapestries of life. Man, this has been such a great deep dive, so inspiring. I feel like I'm walking away with a whole new perspective.

Lilly 10:34

I hope so. It's been great talking with you about all this.

Episode Conclusion

Jad 10:36

To all our listeners out there, thanks for joining us. Keep learning, keep experimenting and keep planting those three. We'll see you next time on the Deep Dive.

Roger 10:47

Thank you for joining us on today's episode of Talking Trees. We've explored two insightful perspectives on selecting trees for urban environments Quamon's innovative approach for diversifying urban canopies on paved northern European surfaces and the TDAG manual's practical guide for choosing resilient species across the British Isles. We hope these insights inspire thoughtful choices for building greener, more sustainable cities. Until next time, keep nurturing the green in your urban landscape.