Roger: 0:02

Talking Trees with Lillian Jad. Welcome to this episode of Talking Trees. Today, we'll be diving into the works of Francis Howell, focusing on the architecture and growth dynamics of tropical trees. We'll explore various growth models, from monopodial to sympodial, and analyze the impact of factors such as rhythmic growth, plagiotropism and orthotropism on the overall tree structure. These studies cover a wide range of species and discuss the relationship between tree architecture, its life cycle and the surrounding environment. In conclusion, we'll examine how these findings can be applied to the broader forest vegetation. Let's dive into this fascinating exploration of tropical tree growth.

Jad: 0:52

Welcome to another Deep Dive. We're going to be exploring tree architecture today.

Lilly: 0:56

A fascinating topic, especially for arborists.

Jad: 0:59

Absolutely, and something that arborists deal with every single day. In particular, today we're going to be looking at the work of Francis Halley. Now. He was a botanist who really revolutionized the way that we think about the shapes of trees.

Lilly: 1:12

And what's particularly relevant about Halley's work for arborists is that it really provides a framework for understanding. You know how trees actually grow and develop, and that can impact all sorts of things, from pruning decisions to even risk assessments when you're looking at trees.

Jad: 1:28

Okay, so let's break that down a little bit Now. I know, as an arborist, I mean, I'm constantly looking at trees and, you know, assessing their health and thinking about decisions about how to care for them but I'll be honest, I've never really thought about it in terms of architecture before.

Lilly: 1:43

Yeah, it's understandable. I think you know, when most people look at a tree, they see a trunk, they see branches, they see leaves. But Hallé, he saw something more. He saw that there was like an underlying order to the way that trees grow, almost like a blueprint, and he called this tree architecture and he dedicated his life to studying and classifying these patterns.

Jad: 2:04

So it's not just random chance that determines what a tree looks like. There are actual rules that govern how they grow.

Lilly: 2:10

Yeah, exactly, it really comes down to genetics. Just like our own DNA determines, you know, our height or our eye color, a tree's genes determine its growth pattern as well. And Halle, along with his colleague Oldeman identified 23 distinct architectural models.

Jad: 2:28

That trees actually follow 23 different models, wow, that's a lot. I mean, I'm already starting to see how this could get really complicated, but I'm definitely intrigued. I mean, like I said, you know, as an arborist, I deal with trees all the time. So if there is a system for understanding how they grow, I want to know about it about it Absolutely.

Lilly: 2:41

And the great thing about Halle's work is that it's not just theoretical, you know, it has very real world applications for arborists. And to kind of make it a little easier to grasp, I think we should maybe focus on two models today that are particularly relevant. We'll look at Massart's model and Auburville's model.

Jad: 3:01

Sounds good.

Lilly: 3:02

So, before we dive into those models, can you just give me an idea of like the basics? I mean, what kind of things was Holly looking at, like what are the basic elements that he used to classify trees? Yeah, for sure what were the things that were important to him. You know, as he looked at trees.

Jad: 3:15

Yeah, so one of the fundamental distinctions that he made was between what he called monoaxial and polyaxial growth.

Lilly: 3:22

Okay.

Jad: 3:23

So monoaxial trees have a single dominant trunk, so think about like a pine tree or something like that, right? While polyaxial trees have multiple stems that arise from the base, almost like a shrub or something like that Okay.

Lilly: 3:36

So you're thinking about kind of the difference between having, like you know, one strong central leader versus a clump of shoots, all kind of vying for dominance?

Jad: 3:46

Yeah, exactly, okay, exactly, and that's something that, as an arborist, I see all the time. So that number of trunks is one way to start classifying these trees.

Lilly: 3:53

Okay, great, so what else was he looking at?

Jad: 3:56

So another thing he considered was whether a tree exhibits what's called rhythmic or continuous growth.

Lilly: 4:03

Okay, if it's what's called rhythmic or continuous growth.

Jad: 4:04

Now, rhythmic growth means that the tree has kind of bursts of growth followed by periods of rest, and that's common in like temperate climates.

Lilly: 4:12

Yeah.

Jad: 4:12

So we see that a lot here. Continuous growth on the other hand, means the tree is growing pretty much steadily throughout the year, and you might see that in some tropical species. So you probably noticed working with trees, some trees just kind of they put on a growth spurt in spring and then they kind of slow down. Well, other trees just they just keep going and going and going.

Lilly: 4:31

Shugging along. Yeah Right, exactly.

Jad: 4:33

And then one more element that I think is really important for arborists to understand is the position. And Now, flowers.

Lilly: 4:43

I mean, why would flowers matter so much to the architecture of a tree? I mean, they're pretty, but I wouldn't have thought that they would play such a key role in how the tree actually grows.

Jad: 4:54

Yeah Well, think about what happens when a flower turns into a fruit.

Lilly: 4:57

Okay.

Jad: 4:57

If that flower is located at the tip of the branch, that branch tip essentially stops growing, right.

Lilly: 5:03

Yeah.

Jad: 5:03

Because it's turned into a fruit, right right yeah, because it's turned into a fruit Right right. But if the flower grows along the sides of the branch, then that tip can keep growing outwards, even as the tree is producing fruit.

Lilly: 5:13

Ah, I see. So the position of the flowers can actually determine whether a branch keeps growing or not.

Jad: 5:18

Exactly, that's fascinating, yeah, and that has a huge impact on the overall shape and the spread of the tree.

Lilly: 5:23

Okay, yeah, and that has a huge impact on the overall shape and the spread of the tree. Okay, so now that we've got that kind of basic understanding, I think it's time to take a closer look at Massart's model. Are you ready?

Jad: 5:30

Absolutely. Let's dive in.

Lilly: 5:31

All right, so Massart's model Picture like a conifer, like an erycheria.

Jad: 5:37

Okay.

Lilly: 5:38

Tall majestic. You know those branches that grow out in those distinct tiers. Yeah, that's a classic example of Massart's model. So a single central trunk, rhythmic growth and those tiered horizontally growing branches.

Jad: 5:51

Okay, I can picture that. You know I've worked with plenty of conifers that fit that description. But how does actually knowing about this model help me when I'm out in the field? Like what difference does it actually make?

Lilly: 6:04

Yeah, that's a great question. So think about pruning. For example, you're pruning a young conifer that you know follows this model. Knowing about those tiered branches can help you decide where to make your cuts. You want to maintain that natural structure of the tree, so you'd prune back to a lateral branch within a tier, rather than just chopping off the branch tip randomly. You know what I mean.

Jad: 6:27

Yeah, yeah, it's like you're working with the grain of the wood, so to speak.

Lilly: 6:29

Exactly exactly. And then when you're assessing a veteran tree, you know that follows Massort's model. Understanding its structure is even more crucial for safety reasons. Right, those long horizontal branches can get incredibly heavy, especially as the tree ages, and the points where they attach to the trunk, those are like potential weak spots.

Jad: 6:49

Oh, OK. So I'd be paying close attention to those attachment points, looking for any signs of decay or cracks or anything that that might make the branch more likely to fail.

Lilly: 6:59

Exactly, yeah. And here's where things get a little bit interesting Some trees that conform to Massart's model. They actually start their lives as lianas.

Jad: 7:08

Lianas. Wait, those are those woody vines that climb up other trees in the rainforest right, right, I don't really see how that relates to a conifer, but it really shows you how adaptable nature is.

Lilly: 7:22

So there's this tropical species. Pycnanthus dinklagei, for example, starts with a flexible trunk so it can climb like a vine, and then, as it gets older, the trunk gets more rigid and it transitions into a more typical tree form and eventually it displays the classic tiered structure of Massart's model.

Jad: 7:40

So it actually changes its growth pattern.

Lilly: 7:41

It does.

Jad: 7:42

As it matures. Wow, nature is matures. Wow, nature is so cool. Okay, so we've got Massart's model. Now what about Oberville's model? How is that different?

Lilly: 7:50

Yeah, so Oberville's model also a single trunk, rhythmic growth. But here's the key difference the flowers grow laterally along the branches, not at the tips.

Jad: 8:02

Oh, OK, right, so that goes back to what we were talking about before, about the position of the flower Exactly, if it's at the tip, the branch stops growing there. If it's on the side, it can keep growing outward.

Lilly: 8:13

Exactly, and that's what gives trees that follow Oberville's model their distinctive, spreading, often slightly drooping appearance. Think of the iconic pagoda tree.

Jad: 8:23

Okay.

Lilly: 8:23

You know, terminilia catappa. Yeah, this beautiful spreading branch, hallmark of this model.

Jad: 8:28

Okay, I'm starting to see the difference. So, massart's model you get those distinct tiers of branches.

Lilly: 8:33

Yeah.

Jad: 8:33

While with Obervilles they tend to spread out more horizontally.

Lilly: 8:36

Exactly, exactly, and that difference. It has implications for how we approach things like pruning and assessment. So if you've got a young tree that's following Obervilles' model, you have more flexibility with pruning because you can remove the tips of the branches and it's not going to stop them from growing. They'll just keep extending outwards because of those lateral flowers.

Jad: 8:56

Oh, ok. So it's a little bit more forgiving than massarts, where you really have to be careful not to disrupt that tiered structure.

Lilly: 9:03

Right, exactly. But then, when it comes to assessing a veteran tree that follows Oberville's model, you have to keep those long horizontal branches in mind, because they can become a concern, especially if they start to droop significantly. So you're thinking about things like cabling or bracing.

Jad: 9:22

Right right. To support those heavy limbs and prevent them from you know, breaking yeah, you don't want to lose a major branch on a tree that's been growing for you know, who knows how long Could be decades Exactly.

Lilly: 9:34

And another interesting thing about Opereville's model it includes some of the most massive trees in the world, like Terminalia superba, this African rainforest giant. It can get up to 45 meters tall.

Jad: 9:47

That's incredible. So these models can describe everything from like a small ornamental tree to a giant of the rainforest.

Lilly: 9:55

Yeah, exactly, it really shows you how powerful these models are.

Jad: 9:58

Right.

Lilly: 9:59

They provide a framework for understanding this huge diversity of tree forms. But we also have to remember that trees are living organisms and they don't always follow the blueprint perfectly. They have to adapt to their environment.

Jad: 10:13

Yeah.

Lilly: 10:13

And that's where the concept of reiteration comes in.

Jad: 10:15

Oh right, okay, Remind me what reiteration is all about.

Lilly: 10:18

Yeah, so essentially, reiteration is the tree's way of hitting the reset button. It's the process where a tree recreates its architectural model, but in a new location on the tree. So let's say a tree loses its main stem due to some damage or disease. In some cases it can reiterate by producing new trunks from lower branches, so it's forming like a bayonet junction.

Jad: 10:40

Oh, okay.

Lilly: 10:40

So it's a pretty remarkable adaptation that allows trees to survive even when things go wrong.

Jad: 10:45

So reiteration is like the tree's backup plan.

Lilly: 10:47

Exactly and understanding. Reiteration is so valuable for arborists.

Jad: 10:52

Yeah, I can see how that would be really helpful. If I'm pruning a tree, I need to know how it's going to respond Is it going to just sprout a bunch of weak shoots, or is it going to actually reiterate and create a strong new branch structure?

Lilly: 11:04

Exactly, and by understanding the reiteration potential of different species you can make more informed decisions about pruning. You know wound care, even tree selection, yeah, so you're kind of one step ahead.

Jad: 11:17

This is all starting to make a lot of sense to me. I mean, I've always observed these patterns in trees, but I've never had like a framework for understanding them.

Lilly: 11:25

Yeah, and that's the beauty of Halley's work, you know.

Jad: 11:28

Yeah.

Lilly: 11:28

He gives us this language, this system for kind of decoding the complexity of tree growth. Yeah, but he goes beyond just modern trees.

Jad: 11:36

Okay.

Lilly: 11:37

He was also fascinated by the architecture of ancient trees.

Jad: 11:40

Ancient trees, extinct trees, these remnants of like prehistoric forests.

Lilly: 11:45

So he was actually looking at fossils. He was particularly intrigued by these calamites, extinct tree-like plants. They grew up to 30 meters tall during the Carboniferous period.

Jad: 11:56

Wow, that's massive.

Lilly: 11:57

Over 300 million years ago. Trees that big over 300 million years ago that's mind-boggling. Yeah, and so he studied these fossilized remains very meticulously, analyzed their branching patterns, the arrangement of their leaves.

Jad: 12:12

Wow.

Lilly: 12:12

Even the structure of their internal tissues.

Jad: 12:15

That's amazing. So did these calamites fit into any of his 23 architectural models?

Lilly: 12:20

Yeah, he discovered that their growth pattern closely aligned with what he called the Adams model, which is characterized by continuous growth and branches that develop from predetermined positions on the trunk. So it's a model that's relatively rare in modern trees, but it was clearly a successful strategy for these ancient giants.

Jad: 12:36

It's fascinating to think that even trees that lived millions of years ago followed these like fundamental architectural principles.

Lilly: 12:43

Yeah, it really speaks to the enduring power of these models.

Jad: 12:46

Right.

Lilly: 12:47

And Halley even suggested that these calamites, with their unique growth pattern and the swampy environments that they inhabited, he thought they might have actually resembled modern mangrove trees.

Jad: 12:58

Mangrove trees, those trees that grow in saltwater, along tropical coastlines.

Lilly: 13:02

Exactly.

Jad: 13:02

That's a strange connection.

Lilly: 13:04

It might seem strange, but it highlights this remarkable convergence of form in nature, right.

Jad: 13:11

Yeah.

Lilly: 13:11

Similar environments lead to similar adaptations, even across vast spans of time.

Jad: 13:17

So studying these ancient trees can actually inform our understanding of modern trees.

Lilly: 13:21

Absolutely.

Jad: 13:22

Yeah, it's like looking back in time to see how these architectural models have evolved and adapted over millions of years.

Lilly: 13:27

Exactly. And speaking of looking back in time, there's another fascinating aspect of Halley's work that I want to share with you, and it's this concept of model conforming trees.

Jad: 13:37

Model conforming trees Okay.

Lilly: 13:38

So these are trees that like stick to their architectural model like glue, throughout their entire lifespan. They're like the, like, the textbook examples. So no matter what challenges they face, they maintain that same basic growth pattern.

Jad: 13:51

Yeah and Hallie found that these model conforming trees they tend to have certain characteristics in common often have a relatively long lifespan, delayed onset of sexual maturity. They produce a limited number of like large seeds. It's like they're putting all their energy into growing tall and strong before they even think about reproducing.

Lilly: 14:12

So they're like the marathon runners of the tree world slow and steady, focused on longevity.

Jad: 14:17

That's a great analogy, yeah, and while most trees exhibit some degree of flexibility in their growth patterns, these model conforming trees provide valuable insights into the strategies that have allowed certain species to thrive over really long periods.

Lilly: 14:32

I see how that would be valuable information for arborists, Like if we're trying to select trees for a particular site, knowing which species are more likely to stick to their blueprint, even in tough conditions. That could be really helpful. It's all about understanding those trade-offs that trees make and choosing species that are well-suited to the environment where they're going to be planted.

Jad: 14:52

This is amazing stuff. Yeah, it's like Hal has given us a whole new language for understanding trees.

Lilly: 14:57

Yeah, and that language can help us become better stewards of these incredible living organisms.

Jad: 15:03

That's fantastic. Well, we've covered a lot of ground today we have. Are there any specific species that are known to be really good at reiterating?

Lilly: 15:11

Yeah well, I mean, a lot of trees can reiterate to some extent, but species that naturally grow in disturbed environments like riparian areas or forest edges they tend to be particularly good at it. So you're thinking about things like willows, poplars, sycamores. Those are all good examples.

Jad: 15:26

Okay, so those are some species I might consider if I've got a tough urban site. What else should I be thinking about in terms of tree architecture when I'm planting an urban forest?

Lilly: 15:36

Well, diversity is always key. Just like a diverse portfolio is more stable than one with all your eggs in one basket, a diverse urban forest is going to be more resilient to pests, diseases, even climate change.

Jad: 15:50

Right. So if one species gets hit hard by, you know, a certain pest or disease, the others are less likely to be affected. So the whole forest can kind of withstand those challenges.

Lilly: 16:00

Right, and diversity isn't just about species, it's also about structural diversity. So imagine an urban forest where all the trees have like the same shape and branching pattern, if a big windstorm comes through, they're all vulnerable to the same types of damage.

Jad: 16:15

Oh, but if you've got a mix of trees with different heights, different crown shapes, different branching patterns, then the wind forces will be distributed differently, so the forest as a whole is less likely to be like devastated.

Lilly: 16:25

Exactly, and Hallé's models give us this framework for understanding and for creating that structural diversity.

Roger: 16:31

Right.

Lilly: 16:32

So we can pick trees from different models, different growth habits, different branching patterns to make a more resilient and, frankly, a more visually appealing urban forest.

Jad: 16:40

It's incredible to think that these architectural models that we've been talking about, which can seem a bit, you know, theoretical, they can have such a tangible real world impact.

Lilly: 16:50

Absolutely, and it's not just about resilience either. It's also about aesthetics. I mean an urban forest that's diverse.

Roger: 16:56

Yeah.

Lilly: 16:56

With a mix of tree shapes and sizes, You've got layers of foliage, dappled light coming through the canopy. I mean that's just more beautiful and more engaging for people.

Jad: 17:06

It creates a much richer experience, visually and ecologically.

Lilly: 17:11

Absolutely so. By understanding tree architecture, we can create urban forests that are not just resilient, but they're also these, you know really stunning and really inviting spaces for people to connect with nature. This has been a really really eye-opening deep dive.

Jad: 17:25

Yeah, I feel like I'm looking at trees in a whole new way. I'm glad to hear it and I have a really, really eye-opening deep dive. Yeah, I feel like I'm looking at trees in a whole new way.

Lilly: 17:30

I'm glad to hear it.

Jad: 17:31

And I have a whole new set of tools to use when I'm out there working with them.

Lilly: 17:34

Yeah, and that's the power of Halley's work, you know. He gives us this way to see the underlying order and the beauty in what can sometimes seem like the very chaotic world of trees.

Jad: 17:45

Right right.

Lilly: 17:46

So the next time you're looking at a tree, just remember it's not just some random collection of branches and leaves, you know, it's a masterpiece of natural architecture with a story to tell and a future to shape, and you, as an arborist, have the privilege of being a part of that.

Jad: 18:01

That's a beautiful thought. Thanks for joining us on this deep dive into tree architecture. We hope you learned a lot and we'll see you next time into tree architecture. We hope you learned a lot and we'll see you next time.

Roger: 18:11

Thank you for joining us for this episode of Talking Trees. If you enjoyed today's exploration of Francis Hall's work on tropical tree growth, don't forget to subscribe and stay tuned for more in-depth discussions. Your support helps us continue sharing valuable knowledge. We appreciate your continued interest and we look forward to bringing you more exciting insights next time. Until then, keep exploring the wonders of trees and nature with us.