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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.


Aerial photograph of the Sierra Nevada Source: NASA

Dr. Todd Dawson: Well, during that drought that occurred, the recharge of those water resources didn't happen. And because of that, many trees died. Not many of the giant Sequoia died, but many of the other trees did, like the White fir, and the Ponderosa pine, and the Sugar pine, and even some of the Incense cedar, which are all part of the forest up in the Sierra Nevada. They suffered massive water deficits, and were killed either outright by the drought, or they were weakened, and insects or pathogens came in and attacked them. That really weakened them and ended up killing them. So, to your question, what we saw in the Whitaker Forest was really rapid mortality, a real turnover in the forest, a lot of trees basically dying within that forest. And this was brought about by this very, very severe drought, the drought that, by some estimates, was the worst drought that had occurred in California in over six hundred, maybe seven hundred years. So this is an amazingly dry situation for many of the trees.

Elena Bouldin: Yeah, last week I visited Muir Woods. I hadn't been there in a while, and I was actually shocked because it's very dry now. The little creek that passes through the forest is barely a few drops, and the whole undergrowth is covered in dust. I had heard your interview with Ira Flatow on Science Friday about the redwoods and the fog, and there you talked about how the fog is very important to the redwoods because it keeps the air around them moist, but also brings them nutrients, such as nitrogen, during the dry season. There is still fog in the Bay Area, so I'm wondering, is it normal to have a dusty Muir Wood? I had never seen it that way before. Are you concerned about that?


Reedwood trees at Muir Woods

Dr. Todd Dawson: I definitely am concerned about it. I think you raise a number of really good points about the changes that we're seeing here in coastal California to the environment that sustains the coastal redwoods. As you said, one of the things that, of course, is fascinating about the Coastal redwoods, and about Muir Woods itself, is that, often, during the summer time, when we don't have any rainfall here in California, we still get really wet fogs that penetrate the forest every night, often with a lot of fog drip that goes into the soil. And it is basically feeding the forest with water and even nutrients. Not only the trees, but also all the other organisms that inhabit the redwood forest, the understory plants, and many of the animals that come to depend on those very moist, cool conditions that occur when the coastal fogs ooze into the forest at night. And this is what we're used to but that's also been changing over the last 50, 60 years. The fog is going down now. Some of the work that we've done has shown that fog has changed a great deal; declined by up to 30, maybe up to 40 percent in any given year. And that means that there is a lot less water input from the fog banks that normally would come in during the summertime.

So your own experience in Muir Woods is borne out by this new information, it's saying that summers are now also drier, so not only winters are drier because we're getting less rainfall, but the summers are drier because we're getting less fog. So overall, the water resources both in the wintertime as rain and the summertime as fog are declining. And of course, that has really negative impacts on the redwood forest, and everything that depends on that redwood forest.

Elena Bouldin: Have you seen this pattern in other areas that you've studied?

Dr. Todd Dawson: Yes, we've got sites in the Sierra Nevada, that are focused on the Giant Sequoia, but we've also got a lot of sites up and down the coast that are focused on the Coastal Redwood. Some of those sites are in northern California, some are kind of here in Central, in the Santa Cruz Mountains, and then all the way down to the southern end of where the Redwood Forest, the Coastal Redwood Forest lives, and that's near southern Big Sur. That's where some of the impacts are the most severe. We've seen that many of the trees, particularly the larger trees that are growing up out of the canyons, are being severely impacted by having less rainfall, less fog, and warmer, longer summers. And so, if you go down to Big Sur and you hike into some of the canyons along the Big Sur coast, you'll see that many of the trees are either dying or they're losing a lot of their leaf area. We're used to having Redwood trees be these beautiful, tall trees with all this wonderful green leaf area, but that leaf area now is thinning. The trees are stressed, and so they're basically dropping a lot of their needles. I'm sure you've seen this as you drive around, for example, here in central California: if you look at Redwood trees near the freeway, you'll see that they look very thin and they don't look very healthy. Well, those kinds of trees are also what we're seeing in the southern part of the Redwood Range. Not a great picture. I think the southern end of the Redwoods eventually will probably end up dying, and the range of the Redwoods is likely to contract, become a smaller overall area that supports Coast Redwood as we go into the future.


Beetle-killed Giant Sequoias, Sequoia National Park (2015) Source: National Park Service

Elena Bouldin: What are your primary concerns with that?

Dr. Todd Dawson: Well, one of the key concerns is not only are we losing the forest and what that forest supports in terms of the other biodiversity, that depends on it: the insects, the birds, the bats, the salmon that go up into the streams that are in the Redwood Forest. Those are all part of what the Redwood Forest basically is helping to sustain in terms of other biodiversity here in California. So we'll be losing that. That's one of my concerns, the loss of biodiversity that will be linked to the losses of the forest. The loss of the water cycle, we're losing the trees, which are really the straws in the earth, that are taking that water out of the earth and transpiring it back, and recycling it. And if we lose the forest, we lose basically the recycling power of the forests themselves, not just here in California, but around the world, wherever we lose forest, whether that's from droughts or human cutting of forests, or things like that. And then, of course, the other thing that I know you will appreciate, is that, as we dry the forest out, one of the big concerns is: what does it mean for wildfires? Wildfires sweep into these areas, as we saw last year. Big Basin, one of our most beautiful Redwood forest close to the Bay Area, saw terrible wildfires last year. We lost a big part of the Redwood forest in the Big Basin State Park. And that is largely due to the fact that we've changed the hydrologic balance, we've warmed up the climate. So we've basically dried things out and we've made those forests that would otherwise not be as susceptible to devastating wildfires much more susceptible now to wildfires.

Look at this summer. Look at these giant fires that are burning all around the western United States, not just in California, but throughout Idaho, and Montana, and Colorado, and New Mexico, and Arizona. The entire western part of North America is really seeing an increase in the number of wildfires. That's all related to this warmer, drier world that we are now experiencing.


Caldor Fire burns through trees on Mormom Emigrant Trail east of Sly Park, Calif. (August 2021) Source: SF Chronicle


Elena Bouldin: Do you think it's also because of our forest management practices? In the past one hundred years, the directive has been to suppress all fires, but that actually weakens the forest, and, when fires happen, they're greater.

Dr. Todd Dawson: Yes, I think all of the evidence points to that. This is a very good point that you make here. In the past, and for a long time, many of the agencies —whether it was the Forest Service, the Bureau of Land Management, the Park Service, or the State Parks— really had a very hands off attitude about natural areas that they may have been responsible for managing. And because of that, the fire suppression policies were not very well thought out. They allowed fuels to build up because they didn't allow small fires to get rid of some of those fuels. And because of that, you get these big loads of fuels. Then, on top of that, you get warmer and drier climates. And then, when you get a fire, it's a devastating fire. So you're absolutely right, the fire suppression efforts really have to change, and the fire management efforts really have to change. If we want to keep our forests healthy, we're going to have to get in there and use fire as a tool. Don't let the fuels build up, get in there and make sure that we allow fire to become part of a natural cycle, not a devastating cycle where it basically kills all the trees, but a cycle that burns up some of the understory wood. It gets rid of it and it lessens the overall susceptibility to these massive and very severe wildfires that we're seeing, not just here in California, but around the world.

Look at what is happening in Greece right now, they've had wildfires really devastate a big part of the country. And part of it is because it's so dry and the forests are not being managed very well. So, we humans have to play a better role, a very important role. And we have to play that role now in a more active way and in making sure that we don't allow these things to happen going forward.

Elena Bouldin: Agree! Going back to your work. Obviously you don't just do field work. You collect data and then you analyze it, I suppose. Could you explain how exactly you go about doing that?

Dr. Todd Dawson: Yes. We have a team of people that often go out into the forest. Of course, we need to work in teams because these trees are so big that it takes quite a crew to get up there and make all the kinds of measurements we need to make. And, of course, there's also safety reasons. We need to have people so that, if someone gets stuck into a tree, or there's a problem such as a failure of some equipment, we have other people there that can help rescue or help whoever needs it.

So we go with the team, and we collect a lot of the data that's actually in the trees themselves. Many times we'll install instruments in the trees that will help us measure the water status of the tree. We'll measure some of the micro climate variation in the canopies, the light, humidity, temperature, things like that. And we'll measure it within the crown itself, because within the crown there's often a very different microclimate than outside of the trees, and, of course, we need to measure the microclimate because that's the climate that's in contact with the tree itself, and has a local influence on the way the tree behaves in terms of its physiology.


Measuring a trunk's diameter Source: Open Oregon


Dr. Todd Dawson: So we collect all of that information, usually in campaigns that go for a week, maybe two weeks at a time, and then we bring all of that information back to the laboratory, where we analyze the data gathered and ask the question, "what was the tree's water use behavior during this period when maybe it was warm or maybe it was foggy, et cetera, et cetera". Then we can start asking the question "when there was variation in the microclimate, what was the variation in the physiology that the trees expressed in relation to those micro climatic variation?" Many times it takes quite a few days to work all that data because we are collecting it using computerized data loggers. So we're collecting data every 15 minutes, and you can imagine you get thousands of data points. It takes a while to download the data, make sure there's no errors in them, et cetera. And then we begin to plot the data up and try to look at how the trees are responding to the environmental variation that we were also measuring on that site.

Sometimes we'll also collect samples from the trees themselves, like pieces of the leaves, and analyze them for chemical composition, et cetera. Sometimes we'll collect soil, or water from the groundwater or from the streams, and then from the plants too that allows us to then connect the water resources in the environment to the water in the actual plants themselves. So there's a whole bunch of different kinds of samples that we end up collecting, and that takes a long time for a team to work up this wide diversity of data.

We do that several times during the year so that we can also get a picture, not only for how they may have behaved this month, but the month before, and then during the winter months, and the year before, when it was wetter, or drier. In this way, we begin to get a longer term picture of how the trees are behaving, not just in a single year, but over decades. We also start seeing what the trends look like in different places where we're actually doing our investigations.


Elena Bouldin: How can these observations and predictions of plants' physiological adaptations to environmental changes help us? I'm thinking in terms of our ability to mitigate the negative consequences of climate change on redwoods, in this case, or forests in general.

Dr. Todd Dawson: Great question. I think we can't begin to reshape our policies, or even our models about what we will be predicting the future forest to look like, until we understand what the present forests are doing. Based on that information, and, as I was saying a few minutes ago, the year-to-year variation, how does the tree respond to three or four years of drought compared to times when there was no drought? Just like you and I show variation: one year we might get sick and we might not feel very well, but other years we feel better. That's another piece of how we come to understand our own health.

For the trees we do that over different seasons and different places, with different sized trees. And all of that information then becomes a database that then can be used to inform our predictive models. For example, if we go into a warmer and a continually drier world, what would we predict would happen to redwood trees based on that prior knowledge that we gathered from all these other years of studying the trees in their natural environments? It is the validation of the parameters that we use to build a model.

Example of a model, displaying projected changes for a given global mean temperature (GMT) threshold Source: Climate Science Special Report

Dr. Todd Dawson: A model is only as good as the things (data) we put into it, so we really need to understand the behavior of the trees in relation to climatic variation to refine and build a really good predictive model. Once we have that, then we can look forward into the future and we can run different scenarios.

Let's run a scenario where the temperature increases two degrees. All right. Let's run the scenario where it increases two degrees and rainfall decreases by 20 percent. What will we expect the trees to do under that scenario? And so the model can run different kinds of scenarios' forecasting into the future. And based on those scenarios, then we can have a prediction of what we think the trees will do in relation to those new scenarios. But we can't do that without information about the trees in the real forest themselves. And so that's kind of the interplay; between collecting data in the field, understanding what the trees are doing, and then using that in a modeling context to then look forward and say "in the next 20 years, the next 50 years, the next one hundred years, when we expect the environment to change, what do we expect the trees to do in relation to that change?"

Elena Bouldin: So I'm guessing you also complement your data with, for example, the IPCC report that came out on Monday, or other people's data to make your model better?


Dr. Todd Dawson: Absolutely – you nailed it. And in fact, I'm not a modeler. So what I depend on is other people who are building those models. They will contact me just like you did, and say, "hey, Todd, what do you expect the redwoods to do? What kind of physiological, or ecological, or hydrological information can you give me that I can stick into my model to make a forecast or a prediction about what's going to happen to redwoods, whether it's Coast Redwood or Giant Sequoia, or other trees that live here in the state of California. So those modelers are always reaching out to people like me and saying, "hey, we need some of this information so we can make our model better. What can you give us?" And so the information that comes from our field studies, and even some of our controlled studies done in the greenhouse, we give to the modelers, and then the modelers can better refine their models to make the predictions more sound and more robust.

Elena Bouldin: I was going to ask you about what you do with your data once you've analyzed it. I understand you give it to your modelers, but do you give it to anyone else, to government agencies, for example? Once you know what you know, how do you act upon what you know?

Redwood Forest


Dr. Todd Dawson: Again, great question. So the typical thing that we do once we collect data is to try to publish it in peer-reviewed scientific journals where we write a paper, we include the data, the key figures or tables that show what we're learning about the particular forest or tree itself. That information gets published in the peer-reviewed literature.

And then, many times, we will also write up reports that we will give to either the Park Service, or the Forest Service, to let them know what we're learning about from our studies in various locations around California. They really appreciate that because they don't have people that do what we do. They do have people that will go out and try to act to change the management strategies or even the management policies, but they depend on us for the scientific information to help inform their policies and their practices. And so we will hand over the scientific papers, or sometimes we'll just write up a report, and we'll hand it to them and say, "this is what we're learning." And we might even make some recommendations. We might even say, "well, going forward in these areas, we think that you should allow some low-level ground burning, for example, to reduce fuel loads", or "you need to remove some of the dead trees that are in the forest to also reduce the fuel loads, and that may then allow the remaining trees to grow larger and healthier, but also reduce the fire risk in some areas".

So we try as best we can to not only publish this stuff that we're learning in the scientific literature, but make it available to the agencies who are looking for my favorite word, "solutions". This is what we're all about. We got to find solutions and we hope the science can inform us in a way that we can come up with great solutions, sustainable solutions that we can all look to and say, "OK, this is what we've got to do to turn the corner and really allow our forests to be sustainable going forward". And so it's a dance, if you will, between the scientists and what we do, and the agencies that use what we have learned in shaping their policies and their practices going forward.

Elena Bouldin: It’s getting late and I know you need to go, but I want to thank you for your work, because, as you said, science can drive these solutions. Thanks to science, we might be able to preserve these wonderful forests that provide, as you say, so many resources, hydrological resources, biodiversity resources, carbon sequestration, resources and even, to top it off, aesthetic resources.


Dr. Todd Dawson: Absolutely. I mean, let's face it, we can't forget the aesthetics. As you just said, that's so important. It's like a wonderful poem, or a piece of music, or a beautiful painting. It's part of our human condition as well to appreciate nature. It's such an important part of us and our humanity, just like anything else that we come to appreciate.

And so it falls to us to sustain that, to protect it. Despite the climate changes that are happening and a lot of the losses that we're seeing around the world, I remain optimistic that we have people like you, the next generation, that are mindful of this and say, "I care. I want to find a solution. I want to make a difference. And I'm going to be a better steward of our planet and our natural resources because I want to see this in perpetuity". We want you to be able to walk through those forests and love what they are for the rest of your life and for the lives that come after that. And so we have to take an active role in being a participant. We can't be a pedestrian anymore. We are part of this. And we need to make sure that if we want to have forests around, and beautiful streams, and all the birds, and wildlife, and other plants out there, butterflies, you name it, it's going to fall to us. We're the ones that have to be better stewards of our planet.

Elena Bouldin: I completely agree. I also want to thank you for your kind words. You're very kind. And you're incredible. I've learned a lot and I am fascinated by your field. I really appreciate that you took the time to speak with me.


Dr. Todd Dawson: My pleasure Elena – really.

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