Talking Trees

Alex Shigo

Arboricultural Academy Season 2025 Episode 118

Use Left/Right to seek, Home/End to jump to start or end. Hold shift to jump forward or backward.

0:00 | 9:01

In this episode of Talking Trees, we pay tribute to Dr. Alex Shigo, the father of modern arboriculture. His groundbreaking research on tree biology, particularly the CODIT model (Compartmentalization of Decay in Trees), revolutionized how arborists understand and care for trees.

We discuss:

  • His pioneering work at the U.S. Forest Service
  • The shift from wound "healing" to compartmentalization
  • How his discoveries redefined pruning practices and tree risk assessment
  • His famous motto: “Touch trees.”
  • The lasting global influence of his teachings on arboriculture

Dr. Shigo didn’t just change how we cut trees—he changed how we think about them. His legacy continues to guide arborists, urban foresters, and tree lovers worldwide.

Background information:

  • Alex Shigo - Wikipedia
  • An Introduction To Alex Shigo And His Pruning Techniques - TreesUK
  • CODIT & MICROS by Dr. Alex Shigo


Send us Fan Mail

Support the show

Buzzsprout


HeroHero



Arboricultural academy


Podcast is created using AI tools.

Introduction to Dr. Alex Shigo

Roger

Talking Trees with Lillian Jadd. Welcome to Talking Trees. Today we explore the life and work of Dr Alex Shigo, the pioneer of modern arboriculture. Shigo revolutionized tree care with his concept of CODIT Compartmentalization of Decay in Trees shifting how we approach tree biology and management. We'll dive into his biography, his contributions to the field and insights from a video where Shigo himself discusses Cotted and Tree Biology. Get ready to learn about Shigo's lasting impact on arboriculture.

Jad

All right, let's jump into our deep dive today, and you know, I think, we're going to explore the work of a true legend in our field, dr Alex Shigo.

Lilly

Yes.

Jad

Now as a professional arborist, you know. I'm sure you've heard the name.

Lilly

Of course.

Jad

You're familiar with some of his revolutionary ideas about tree care.

Lilly

Absolutely.

Jad

He's often called the father of modern arboriculture.

Lilly

He is.

Jad

And for good reason. His research completely transformed the way we approach tree care.

Lilly

Yeah.

Jad

We're talking about a time when pruning practices were more about aesthetics than tree health. Right, and the invention of the one-man chainsaw oh yeah, gave Shigo a new tool for understanding trees.

Lilly

That's right. Before Shigo, a lot of our knowledge about tree decay came from studying cross sections of wood. Yeah, but with the chainsaw he could create these incredible longitudinal sections, like slicing a loaf of bread lengthwise. Suddenly, you could see the pathways of decay in 3D tracing how it spreads within the tree.

Jad

And that's where his groundbreaking discovery of Cody comes in.

Lilly

Yes.

Jad

Compartmentalization of decay in trees.

Lilly

Compartmentalization of decay in trees.

Jad

He realized that trees don't heal wounds in the same way our skin does.

Lilly

Right.

Jad

They don't regenerate tissue, nope, they compartmentalize.

Lilly

Think of it as the tree building internal walls to seal off the decay, preventing it from spreading further.

Jad

Okay.

Lilly

And each wall has a specific function in this defense mechanism.

Jad

So let's break down these walls, because this is where it gets really interesting for us arborists.

Lilly

Yes, it is.

Jad

Wall one, the strongest forms right after injury, plugging the vascular system above and below the wound.

Lilly

Right.

Jad

What's so cool is that this wall prevents the vertical spread of decay.

Lilly

That's right.

Jad

Then you've got wall two, which runs perpendicular to the grain.

Lilly

Yep.

Jad

Slowing the inward spread.

Lilly

It's like the tree is reinforcing its defenses, building a fortress against the invading decay.

Jad

Wall three is fascinating because it's formed by the growth rings limiting the lateral spread. Right it's like the tree is creating a time capsule of the injury. Yeah, Limiting the lateral spread Right. It's like the tree is creating a time capsule of the injury. Yeah, and finally, wall four the barrier zone forms as new wood grows around the wound, completely isolating the damaged tissue.

Lilly

Shigo's CODIT model showed us that trees are incredibly resilient, capable of fighting off decay and continuing to thrive even with significant internal damage.

Roger

Yeah.

Lilly

And his findings had huge implications for how we approach pruning.

Jad

You can't talk about Shigo without talking about his famous phrase touch trees. Oh, yeah, he wasn't just talking about the physical act of touching a tree. It was about connecting with trees on a deeper level.

Lilly

Right.

Jad

Understanding their biology and respecting their natural defenses.

"Touch Trees" Philosophy

Lilly

He believed that by truly understanding how trees work, we could provide better care and make more informed decisions about pruning, tree selection and even planting. He encouraged people to see trees as complex living beings, not just static objects in the landscape.

Jad

It's like he was saying hey, if you're going to work with trees, you need to speak their language.

Lilly

Absolutely.

Jad

And Kodut was his way of translating that language for us.

Lilly

Absolutely, and he wasn't afraid to challenge the status quo. Oh yeah, shiga was very vocal about his criticisms of common pruning practices.

Jad

Yeah.

Lilly

Like flush cuts that removed the branch collar. Uh-huh. He argued that these practices actually weakened trees.

Jad

Yeah.

Lilly

And made them more susceptible to decay.

Jad

Remember that quote where he said scant attention is given to pruning as it affects the health of trees, while great attention has been given to pruning as it affects the desires of man.

Lilly

He really hit a nerve with that one.

Challenging Tree Care Conventions

Jad

He did. Shigo was a champion for trees, advocating for practices that prioritize their long-term health and well-being.

Lilly

Yes.

Jad

Even if it meant clashing with conventional wisdom or aesthetic preferences.

Lilly

Right.

Jad

His work really sparked a revolution in the arboriculture world it did, leading to the development of new pruning standards and techniques that are still used today.

Lilly

It's amazing to think about how much our understanding of tree care has evolved thanks to Shigo's research.

Roger

Yeah.

Lilly

He really laid the foundation for modern arboriculture.

Jad

He did. Yeah, his influence goes beyond just pruning. Yeah, shigo really opened our eyes up to the incredible complexity of trees as living organisms.

Lilly

Absolutely.

Jad

He talked about trees as generating systems Right, constantly growing and adapting to their environment.

Lilly

It's a fascinating concept. He compared trees to the human body, always replacing old cells with new ones, constantly regenerating and renewing itself, and this understanding is crucial for us as arborists.

Jad

Right, because it changes the way we think about wounds and decay.

Lilly

Exactly.

Jad

It's not just about removing the damaged parts. It's about understanding how the tree responds to those injuries and how we can support its natural defenses.

Lilly

He was adamant that we stop seeing trees as static objects and start recognizing them as dynamic living systems constantly interacting with their surroundings, and this shift in perspective has had a profound impact on how we approach tree care.

Jad

He even challenged the traditional view of heartwood.

Lilly

He did.

Jad

Which was often dismissed as just dead tissue Right. But Shigo argued that heartwood plays a crucial role in the tree's defense system.

Lilly

He pointed out that heartwood is incredibly strong and resistant to decay. It provides structural support and acts as a barrier against further spread of decay. He even called it protection wood, emphasizing its vital function in the tree's overall health.

Jad

I remember when I first learned about Shigo's ideas about heartwood.

Lilly

Yeah.

Jad

It was like a light bulb went off Right. Suddenly I realized we've been underestimating the complexity and resilience of trees for far too long.

Lilly

Absolutely.

Jad

And he debunked a lot of misconceptions about heart rot.

Lilly

He did.

Jad

He showed that the presence of decay in the heartwood doesn't necessarily mean the tree is doomed.

Lilly

Right.

Jad

In fact, trees have evolved to compartmentalize decay and continue thriving even with significant heartwood loss. That's right. He encouraged us to look beyond the visible symptoms and understand the tree's internal mechanisms for dealing with decay. He wanted us to see the bigger picture and appreciate the incredible adaptability of trees.

Dr. Shigo's Enduring Legacy

Lilly

Shigo's work was groundbreaking, not just for its scientific rigor, but also for his ability to communicate complex ideas in a way that was accessible and engaging. He didn't just publish his findings in academic journals he wrote books, gave lectures and traveled the world sharing his passion for trees with anyone who would listen.

Jad

He was a true advocate for trees, always pushing for better understanding and more informed tree care practices, and his legacy continues to inspire arborists around the world.

Lilly

What's remarkable is that Shigo didn't just present his findings as absolute truths. He encouraged critical thinking and further research, urging others to build upon his work and continue exploring the mysteries of trees.

Jad

He often said that we should never stop learning, that the world of trees is full of wonder and complexity, and that there's always something new to discover. He saw himself not as the final authority, but as a guide, inviting others to join him on this journey of discovery.

Lilly

Yeah, and he gave us the tools to do just that. You know his coded model, his research on pruning, his insights into tree biology. His legacy is a call to action for all of us in the arboric culture field.

Jad

It is.

Lilly

It's a reminder to keep learning, keep asking questions and keep pushing the boundaries of our understanding of trees.

Jad

So the next time you're out in the field working with trees, remember Dr Chigot and his message. Touch those trees, feel their energy and appreciate their complexity. Use his insights to make informed decisions and provide the best possible care for these magnificent living beings. For these magnificent living beings.

Roger

Thank you for joining us on this episode of Talking Trees. Today we celebrated the groundbreaking contributions of Dr Alex Shigo his revolutionary cottage concept, his hands-on approach to understanding wood decay and his challenge to traditional arboricultural practices. We hope his legacy inspires you to look deeper into the science and art of tree care. Until next time, keep touching the roots of nature.

Podcasts we love

Check out these other fine podcasts recommended by us, not an algorithm.

Arboristika aktuálně Artwork

Arboristika aktuálně

ČSOP - Arboristická akademie
ArboChat Artwork

ArboChat

ČSOP - Arboristická Akademie