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The Adventure of Keeping Our Forests Healthy

August 13, 2021

A conversation with Dr. Todd Dawson, professor of plant ecology and physiology in the Departments of Integrative Biology and Environmental Science, Policy & Management at UC Berkeley.

Elena Bouldin: Thank you for agreeing to speak with me, and thank you for sending me that video of yours ahead of time. It helped a lot, in preparing for this interview, to get a taste of what you do in the field. I found the video fascinating for two reasons. One, because to see you and your group out there having so much fun and working in a beautiful environment is really cool and it made me want to be there too! The other reason is that it was very interesting to see how current technology is helping you do your work better. As I understand, you've been working in the Whitakers Forest for nine years. Could you explain what you and your team do there?

Giant Sequoia in the Sierra Nevada Source: Save the Redwoods League

Dr. Todd Dawson: Yes, of course. In the broader picture of my research program, I've been involved in Redwood research for twenty five years, and so it's been a long term research program and passion that not only I've been involved in, but many people in my research group as well, mostly graduate students, but also some postdoctoral researchers. As you may know, there's two redwood species here in California. There's the Coastal Redwood, which, of course, is right here in our front yards and backyards in coastal California. And then, there's the Giant Sequoia that lives up in the central and southern Sierra.

The work that we've been doing in the Sierra, both at the Whitaker Forest and outside the Whitaker Forest, has really been focused on trying to understand the physiology of these trees in relation to the natural environmental variation that's out there, and trying to take that understanding of physiology and then place it in an ecological context of what's happening to these trees when they're faced with hotter days, or drier days, or drier winters where the snow doesn't recharge the groundwater, etcetera.

The environmental setting is very important, because we want to place the physiology and the ecology of the trees into that environmental context with a longer term idea that, if we understand their physiology and their ecology, we might be able to better manage the forest, better protect not only the trees, but all of the other biodiversity that depends on the redwood forest, which is a very stable forest. These trees live for a long, long time. And, of course, everything comes to really depend on that stability in the forest that they compose. So, what we've been focused on, is trying to really understand the biology of the trees with the goal of better understanding, not just the trees, but the entire forest.

Elena Bouldin: How exactly do you go about doing that? What is your day-to-day out in the field, out in the forest?

Dr. Todd Dawson: As you can appreciate, these are the biggest organisms on the planet. Nothing has ever been bigger. Not even dinosaurs come close to the size of a redwood tree. And so therein lies a big challenge. How do you study something that is so big? Meeting that challenge has required us to adopt a bunch of tools, different kinds of tools. Some of those are the tools that have been around for a long time, like climbing into the trees with ropes and getting up into the canopy so that we can actually make physical measurements on the leaves and on the branches, map what the crown looks like so we can understand the complexities of how the tree is basically put together. And so that's a set of tools that we use: simply climbing into the trees and then just using simple measurement techniques to try to understand how the tree is built. But then, on the flip side, are all the new technologies that we want and need to apply.

Many of those technologies have to do with using new cameras and other kinds of sensors that we actually mount onto drones. Drones, of course, are basically very small robots - helicopters that allow us to take the cameras — the regular cameras that you use for video, but also different kinds of cameras, called multispectral cameras, that can see wavelengths of light that our eyes actually can't really see very well. These multispectral cameras allow us to look at the reflection of light off of the trees and the forest in ways that give us hints about forest health.

Drone flying over trees Source: Change Started

Dr. Todd Dawson: We've brought this technology into our research because we can't do what drones do. Climbing a single tree, and mapping it, and making measurements can take a team of three or four people all day (or more). The drone technology allows us to scale that up. We can use hundreds of photographs, and then our calibration of that information from within the trees to basically take a single tree measurement, the pictures from the drone, and then merge these together so we can scale that up to the entire forest because the drone sees the forest and the trees. It sees much more than we can see by just studying in a single tree. So the technology has been really a very important step for our research.

Elena Bouldin: How has this changed your research given that you're able to look at the forest in a much broader way, in a better way, I assume.

Dr. Todd Dawson: Absolutely better, yes, great question. How it's changed? It's allowed us, not to sound trite, to see the forest and not just the trees. We can really step back. It's almost like becoming a bird. You get a view from above the forest, and you start to appreciate that two trees may be standing right next to each other, but one will have a spectral signature from the camera that shows that it's stressed, while the tree right next to it is not stressed.

We never really imagined that two neighbors living within feet of each other could be so different in their stress physiology, their growth, and things like that. So this kind of information allows us then to go in and ask the question that you're probably going to ask, which is, why? Why would two trees sitting right next to each other be so different? And this allows us then to make a whole bunch of additional measurements to actually try to answer that question.

Why? Maybe one tree is rooted in a funny little place. It doesn't get the same amount of water than the one that's just 50 feet away. By measuring just a few of the trees on the ground you can't really see how different neighboring trees may differ. The sensors on the drone allow us to have new eyes, if you will. We see things in ways that we simply can't see with our own eyes, and that allows us to make new measurements, target our measurements to particular parts of the forest, or particular trees in the forest, to come up with a more comprehensive understanding about what the forest is doing, what the trees are doing, which ones are stressed, which ones are not stressed, etcetera, etcetera. So this is where this technology really has helped open the door, because we're seeing the trees now in a whole new way that we never were able to see before.

Elena Bouldin: That is fascinating! I was actually going to ask, because one thing I find really interesting is tree communication. There's been multiple studies about their mycorrhizal networks and all of that. You just said two trees that are right next to each other might have very different responses to stress, but I would have thought it'd be the opposite because of how they're supposed to be communicating by sending signals alerting the rest of the trees of potential stressors. For example, I read how, if one tree gets attacked by some pest, it will start producing its own insecticide and alert trees nearby to start creating their own insecticide. But you just said that's not always the case, that's not always how it works out. What other patterns are you seeing?

Dr. Todd Dawson: I think you raise a very important issue. There are some cases where the evidence shows that there can be some type of communication, if you will. I don't really like to call it communication because it's not communicating like you and I are communicating, right? It's really chemical signaling. We know that plants can emit signals that they've been attacked by a pest, as you pointed out. That emission of a signal created by plant hormones is sensed by their neighbors, and their neighbors may respond. If they were human they might say, "hey, wait a minute, this tree is getting attacked by insects. Maybe I should up regulate the sorts of chemicals I can produce to help me defend myself from the pest that may be attacking me soon." I know that is anthropomorphizing things, but it makes the point that plants can have their own flavor of communication too.

So, it is communication, in a sense, but it is what we call hormonal communication. It is linked to different chemical compounds that all plants can produce at high levels or low levels to communicate with the other members in the area where they are living. So it's a different kind of communication, they're not calling each other up saying "hey, here come the beetles, watch out." It's a very different way of communicating, but indeed, it is communication.

The same thing can happen below ground. As you said, the mycorrhizal or the fungal networks that are associated with the roots of different trees can be involved in helping move resources back and forth between neighboring trees. But as you might imagine, it's imperfect. It's never going to be a perfect thing that every tree is going to be connected to each other, that a healthy tree might be helping, say, an unhealthy tree out. That may, or may not, be something that can happen. There's a lot of uncertainty out there, just as there is uncertainty in our human society. Not everybody benefits the same way, has accessibility to the same resources. And that plays out in the forest, too. So it's imperfect as we might expect. Nothing that happens in nature is always going to be a perfect solution. Some things succeed, some things don't. And the hope is that they succeed more than they fail. But it's certainly an imperfect process.

Elena Bouldin: I understand. Going back to the Whitaker Forest, what changes have you seen over the past nine years that you've spent working there?

Dr. Todd Dawson: When that film I sent you was taken, we had been working in the Whitaker Forest for nine years, but we've actually been working there for more than nine years. We've gone in and out of the forest site for about 15 years, but really it has been since the last drought hit California, which was, as you probably know, from 2012 to 2016. Over 130 million trees, particularly in the Sierra Nevada, died because of these four years of drought. During two of those years, we had no snowpack. And of course, the snowpack is what sustains a lot of the Sierra Nevada forest. It's almost like an IV bag human use when they are in the hospital. There's this slow drip of water that comes from the melting of the snowpack. And that snowpack recharges the water in the soil and in the deeper subsoil that these trees that live in the Sierra Nevada depend on. That's what helps sustain them through the otherwise dry, warm summers.