Roger: 0:02

Talking Trees with Lily and Jad. Welcome to Talking Trees. In today's episode, we're exploring innovative, non-invasive methods for studying tree root systems in urban environments. We'll dive into techniques like GPR, ert, eim and sonic tomography, which help map roots without causing damage during construction. Sonic tomography, which help map roots without causing damage during construction. We'll also look at studies on sonic detectors for root detection and acoustic imaging for assessing root health. Let's get started.

Jad: 0:37

Welcome to the Deep Dive. Today we're diving into something a lot of you have been asking about ground-penetrating radar. We'll be talking about how GPR can change the game when it comes to your work as an arborist, and I'm really excited to dig into this with our expert. No pun intended.

Lilly: 0:54

Well, you know, as arborists, we're always trying to get a better understanding of the trees that we're caring for, and of course we can see what's going on with the trunk and the branches. But what's happening below the surface? That's important too, and I think, especially when we're working in those urban environments.

Jad: 1:08

Yeah, absolutely. You think about all the stuff that could be going on underground. You've got utility lines, maybe some buried debris Plus all the construction and compacting of soil can impact those root systems.

Lilly: 1:20

It really is a challenge that we're always facing. We need to figure out how healthy and stable the trees are without causing a bunch of disruption, especially in areas that are sensitive. That's where GPR can really come in handy. It's kind of like we're seeing through the soil, getting a look at what's happening underground.

Jad: 1:35

Okay, so let's break down the basics of GPR. How does it actually work?

Lilly: 1:45

kind of like echolocation, but instead of sound waves we're using electromagnetic waves. So the GPR unit has an antenna that sends those waves into the ground and when those waves hit something like a root they bounce back up to a receiver.

Jad: 1:53

So is it kind of like taking an x-ray of the soil?

Lilly: 1:56

Yeah, in a way it is. Those reflected waves create a visual representation of what's buried down there. We call this a radargram. It shows us the depth, location and even the shape of the roots.

Jad: 2:07

So you can actually see each individual root on this radar gram.

Lilly: 2:10

You can, especially the larger roots and roots with more water content. They show up as these distinct hyperbolic shapes. It's almost like a signature, and you know what's really cool is we can actually use those radar grams to estimate things like root diameter and volume. That can give us a lot of insight into the overall health and stability of the tree.

Jad: 2:28

That's amazing, but I imagine there's some skill involved in interpreting those radar grams. You can't just point the GPR at the ground and get a perfect picture, can you?

Lilly: 2:35

You're absolutely right. There are some nuances. When it comes to data acquisition and interpretation, for example, choosing the right antenna frequency is really important. Lower frequencies they'll penetrate deeper into the soil. That's great for finding those big structural roots that might be causing trouble, but the resolution is lower. Now. Higher frequencies those will give you a much sharper image, but they won't penetrate as deep.

Jad: 2:58

So it's a trade-off between depth and detail.

Lilly: 3:00

Exactly, and that's where experience and knowing the limitations of the tech comes in. You also have to consider the soil conditions Clay soils, for example. They tend to hold more moisture and that moisture can actually scatter the GPR signal, making it harder to get a clear image.

Jad: 3:16

So in those situations would you have to change up your approach?

Lilly: 3:20

We might need to use a different antenna frequency, adjust the scanning pattern or even combine GPR with some other methods like electrical resistivity tomography or ERT. That can be really helpful when you're working with clay soil.

Jad: 3:33

So it's not a one-size-fits-all tool. You've got to adapt and use the right technique for each situation.

Lilly: 3:39

You got it and even with the best equipment and expertise, there's always going to be some limitations. Like GPR is really good at detecting the larger roots, the ones over two centimeters in diameter, but the fine hair-like roots, those can be tough to see and those are crucial for water and nutrient uptake. It's just another tool we can use and, like any tool, it's most effective when you know how to use it well and you combine it with other methods.

Jad: 4:04

Okay, so we've talked about how GPR works and some things that can impact the data and how we interpret it, but let's get down to it. How accurate is this technology? We're talking about electromagnetic waves bouncing off roots underground.

Lilly: 4:19

It's kind of hard to imagine getting precise measurements from that. It's a valid question, and research has actually shown that GPR can be pretty darn accurate, especially when it comes to figuring out root location. Some studies have shown that we can often determine the root position down to about five centimeters.

Jad: 4:32

Wow, that's pretty impressive. I mean you could use that to make sure you don't hit a major root during excavation.

Lilly: 4:37

Exactly, and that's just one way GPR can help us make better decisions about how we care for trees. There are also studies that looked at how accurate GPR is in estimating root diameter and volume, and those results have been positive. Of course, how accurate the results are can vary Soil conditions, the characteristics of the roots and how experienced the operator is All these things can play a role.

Jad: 5:00

So it's not a perfect science, but it's a valuable tool.

Lilly: 5:03

I would definitely agree with that, and it's a tool that's becoming more accessible and more affordable for arborists. So, like I was saying, there is more to using GPR effectively than just aiming that antenna at the ground. We've got different scanning patterns, and knowing how to use those can really impact the quality of the data you're getting.

Jad: 5:21

Okay, I'm listening. What kind of scanning patterns are we talking about here?

Lilly: 5:24

Well, the most common ones are grid patterns and circular patterns. With a grid pattern, you're basically moving the antenna back and forth over the area you're interested in, like if you were mowing a lawn. This creates a grid of data points, all nice and systematic. Then we can use that to create a 3D map of the root system pretty detailed too.

Jad: 5:45

So it's like taking a bunch of slices through the soil to build up a full picture.

Lilly: 5:49

You got it, and this is really helpful when you want to see how far a root system extends, say before any construction starts near a tree. Now, circular patterns we often use those when we're focused on a specific area, like the root zone around the base of a tree trunk.

Jad: 6:04

I see. So if you were worried about root damage from something like soil compaction or trenching, you'd use a circular potter.

Lilly: 6:11

Exactly. You scan in a circle around the tree and that gives you a good idea of how the roots are spread out and how dense they are in that important zone.

Jad: 6:17

That makes sense, but I bet all this data collection takes a while, especially if you're working with a large area or a lot of trees.

Lilly: 6:24

It can be time consuming. Yeah, that's why they came up with software that can automatically identify roots. That's been a game-changer. Before that, we had to look at each radar gram ourselves, tracing out the roots and making interpretations based on our experience. It was a lot of work.

Jad: 6:40

That sounds tedious.

Lilly: 6:41

It really was. But now we've got these software programs, we can just feed the data from the GPR into the computer and the software finds the roots for us. It can even classify them.

Jad: 6:51

Wow, that's incredible. It's like having another set of eyes, or maybe a whole team of root experts, looking at your data for you.

Lilly: 6:58

That's a great way to put it, and it not only saves us a ton of time, it also helps to cut down on the chance of making mistakes when we're interpreting the data.

Jad: 7:05

That's a huge plus, yeah, but how accurate are these software programs? Can they really match up to what an experienced arborist can do?

Lilly: 7:13

That's a good question and, like any technology, how accurate these programs are can vary. The good news is they're always working on them, making them better, and the latest software out there is actually pretty impressive. It can tell the difference between roots and other stuff in the soil, like rocks or pipes, and it can even identify different types of roots, like structural roots versus those fine feeder roots.

Jad: 7:39

So it's not just finding the roots, it's about understanding what they do and how they fit into the whole root system.

Lilly: 7:44

Exactly, and that level of detail is super helpful when you're making decisions about how to care for trees and whether they need to be preserved.

Jad: 7:51

All this is really impressive, but I'm also wondering about the limitations of GPR, even with all the advances in software. I mean, no technology is perfect, right? What are some of the things GPR might miss or have trouble with?

Lilly: 8:05

You're right, it's important to know the limitations. One of the toughest things for us is telling apart roots that are overlapping, especially when trees are growing close together.

Jad: 8:13

It's like trying to untangle a big bowl of spaghetti underground.

Lilly: 8:17

Exactly. The GPR signal can get mixed up when roots from different trees cross or get tangled. That makes it hard to really figure out how far each root system goes.

Jad: 8:27

So in those cases, would you need to use other methods along with the GPR data?

Lilly: 8:32

We might have to. Sometimes, just looking at the site can give us clues about how the roots are connected, and in some cases we might use other techniques, like air excavation. That way we can carefully expose the roots in a small area and map them out.

Jad: 8:46

So you're using the right tool for the job and you're aware of the pros and cons of each approach.

Lilly: 8:50

You got it. Another thing to remember is that GPR signals can get weaker as they travel through the soil. We call that attenuation. What it means is, the deeper you go, the less clear the image gets.

Jad: 9:01

So it's easier to get a good look at the shallower roots than the deeper ones.

Lilly: 9:04

Yeah, generally, and the type of soil can make a difference too. Remember how we talked about clay soils holding more moisture. Well, that moisture can scatter the GPR signal, making it tougher to get a clear image.

Jad: 9:16

So would you use a lower frequency antenna in those cases To get deeper penetration?

Lilly: 9:20

We might, but even with a lower frequency the resolution won't be as good, and there are some soils, like those with a lot of clay or metallic debris, where GPR just might not be the best method.

Jad: 9:32

So it's not a magic solution. It has its limits.

Lilly: 9:35

It does, but even with those limits it's a really helpful tool for us arborists. It lets us gather information about roots in a way that wouldn't be possible otherwise, without digging up a huge area.

Jad: 9:46

That's a big advantage. It seems like GPR is really changing the way we think about assessing trees and taking care of them.

Lilly: 9:52

I think so too, and as our urban forests face more challenges from development and environmental stress, it's going to be even more important.

Jad: 10:00

Well, this has been fascinating. I'm definitely going to look into using GPR in my work, but before we wrap things up, I'm curious about those other methods you mentioned, like ERT and sonic tomography. What can you tell us about them?

Lilly: 10:13

Yeah, those are some cool methods. They can give us a different view of what's going on underground and sometimes, using them along with GPR can give us a really complete picture of the root system.

Jad: 10:23

Okay, so let's start with electrical resistivity tomography, ERT, right? What's the basic idea behind it?

Lilly: 10:29

Well, egrt is all about how easily electricity can flow through soil. We basically put electrodes into the ground and send a little bit of current between them low vertige, of course and how that current travels. It depends on what the soil is made of, how much moisture is in it and you guessed it whether there are roots in the way.

Jad: 10:48

So the roots are kind of like electrical pathways.

Lilly: 10:50

You could think of it that way Roots, especially the bigger structural roots, they tend to have lower electrical resistivity than the soil around them. So when that current hits a root it's going to take a different path and we can measure that change in resistivity.

Jad: 11:06

That's pretty neat. So how do you turn that information into an image of the root system? That makes sense.

Lilly: 11:11

So the ERT equipment. It takes a bunch of readings at different depths and spaces and then all that data goes into some software that creates a 3D map of what's underground. The map shows areas of high and low resistivity. And those low resistivity areas those often line up with where the roots are.

Jad: 11:29

So it's like a heat map of the soil, where the hot spots are the roots.

Lilly: 11:32

Yeah, that's a good way to think about it and, just like with GPR, ert can be really helpful for finding those big structural roots that could be a problem for buildings or other structures.

Jad: 11:42

But I'm sure it has some limitations too, right?

Lilly: 11:44

Oh, of course, One of the biggest drawbacks with ear tea is that it's not so good at picking up those really fine hair-like roots, the ones that are super important for water and nutrients. They're just not big enough to really change the electrical resistivity of the soil.

Jad: 11:59

So ear might be great for finding those problem roots, the big ones, but it could miss some of the smaller roots, even though they're important too.

Lilly: 12:06

Exactly, and another thing is that you need to actually touch the soil with the electrodes, which can be a problem in areas with pavement or if the tree has a lot of surface roots.

Jad: 12:16

Okay, so ear tea has its good points and bad points. Now, what about sonic tomography? That one sounds pretty interesting.

Lilly: 12:23

It is. Sonic tomography uses sound waves to get a picture of what's underground, kind of like when you knock on a wall to see if there's a stud behind it.

Jad: 12:30

So you're listening for how the sound changes as it travels through the soil and roots.

Lilly: 12:34

Right. We put sensors around the tree and they send out and receive sound waves. How fast those waves travel depends on how dense and rigid the material is and roots. They're denser than the surrounding soil, so sound travels through them faster.

Jad: 12:49

So by looking at the patterns in those sound waves you can make a map of where the roots are.

Lilly: 12:54

Exactly and, like air, sonic tomography can be good at detecting those larger structural roots.

Jad: 13:00

But I bet it has limitations too, huh larger structural roots.

Lilly: 13:05

But I bet it has limitations too. Huh, it does. A big one is that sonic tomography mainly shows you root density, not individual roots. So it can tell you if there's a bunch of roots in an area, but it can't really pinpoint exactly where each root is.

Jad: 13:15

So it might not be the best tool if you're trying to avoid hitting a specific root while you're digging.

Lilly: 13:20

That's right and, just like with ear, you need direct contact with the soil, which can be tricky sometimes.

Jad: 13:25

Okay, so we've got three pretty powerful tools here GPR, ERT and sonic tomography. Each one has its strengths and weaknesses, Sounds like. The main takeaway is that there's no one perfect solution for every situation.

Lilly: 13:38

Absolutely. The best way to go is often to use a combination of these methods. That way you get a more complete picture of the root system. For example, you could use GPR to get a detailed map of how the roots are spread out and then use ERT or sonic tomography to double check if there are any large roots in specific areas.

Jad: 13:55

It's like having a whole toolbox full of different instruments, each one for a special job.

Lilly: 14:00

Exactly. The more tools we have to work with, the better we can make decisions about how to take care of trees and whether to preserve them.

Jad: 14:08

Well, this has been a really amazing deep dive into how we can assess tree roots. I feel like I have a whole new understanding of how complex and important root systems are.

Lilly: 14:17

I think so too, and I hope our listeners are excited to learn more about these technologies and maybe even start using them in their own work.

Jad: 14:24

I hope so too. You know, a healthy tree starts with a healthy root system, and with all these new advances we're in a much better position to protect and preserve our urban forests.

Lilly: 14:35

Well said, and I'm sure, as these technologies keep getting better, we'll learn even more about that amazing world beneath our feet. Thanks for listening. We'll learn even more about that amazing world beneath our feet.

Jad: 14:43

Thanks for listening.

Roger: 14:46

Thank you for tuning in to Talking Trees. Today we explored innovative non-invasive techniques for studying tree root systems, from GPR to sonic imaging. We hope these insights help inspire better ways to protect our urban forests during construction. Stay with us for more episodes where science and nature intersect. Until next time, keep digging deeper into the world of trees.