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Eyes on Earth Episode 64 - Colorado Bark Beetles

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Detailed Description

Outbreaks of native bark beetles can lead to conspicuous changes in a forest landscape. They’ve been present for thousands of years with occasional outbreaks, but there’s a lot we don’t yet understand about them. Exactly when and where have outbreaks occurred? How severe were they? What happened to the forest afterward? How will a warming climate influence outbreaks? On this episode of Eyes on Earth, we hear from researchers Dr. Sarah Hart and Dr. Kyle Rogers, who use Landsat to help find answers to those questions. A recent study led by Dr. Rodman used Landsat to identify the locations and severity of bark beetle outbreaks in the southern Rocky Mountains. The researchers were surprised to find smaller areas of severe mortality than they expected. Landsat can even be used to help predict patterns of future outbreaks. Dr. Zhiliang Zhu, a USGS researcher, adds his perspective of the effects of forest disturbance as well.

Details

Episode:
64
Length:
00:13:59

Sources/Usage

Public Domain.

Transcript



KYLE RODMAN:

Being a person that studies the impacts of climate change on ecosystems, It's really easy to get caught up in these depressing findings where it's sort of like, you know, everything's changing, and humans may or may not be able to do much about it. This is one of those things where things changed less than we expected. You know, that's a positive sign in my mind.

JANE LAWSON:

Hello everyone. And welcome to another episode of Eyes on Earth. Our podcast focuses on our ever-changing planet and on the people at EROS and across the globe, who use remote sensing to monitor the health of Earth. My name is Jane Lawson and I'll be hosting today's episode. Where we're talking about the use of Landsat to study bark beetle outbreaks in Rocky Mountain forests. Outbreaks some bark beetles like mountain pine beetles and spruce beetles can lead to conspicuous changes in a forest landscape. When the large trees under attack die and lose their needles. These native beetle species have been tunneling under the bark of specific trees like lodgepole pines and Engelmann spruce for thousands of years. They're often continually present at low levels until conditions favor an outbreak, a warmer drier future could lead to more frequent outbreaks, but there are a lot of unknowns, especially in remote areas about exactly when and where outbreaks have occurred. How severe they were and what happened to the forest there afterward. Enter Landsat whose scale and nearly 50-year archive can help provide some of these answers to researchers and even help to predict future outbreak patterns. Our guests today are here to talk about how their recent research use Landsat data to identify and map bark beetle outbreaks and their severity in the Southern Rocky Mountains. Dr. Sarah HART is a forest ecologist at Colorado State University. And Dr. Kyle Rodman is a research scientist at Northern Arizona University's Ecological Restoration Institute, who previously worked with Dr. Hart as a post-doc. Dr. Zhiliang Zhu will add insight later in the podcast as well. He has used Landsat extensively in his forest and wildfire research. His current research involves biologic carbon sequestration. Dr. Hart, Dr. Rodman, welcome to Eyes on Earth.

SARAH HART:

Thanks for having us. It's great to talk about our research.

RODMAN:

Thank you, Jane. It's exciting to be here.

LAWSON:

First of all, what do you think makes bark beetles interesting to study Dr. Hart? Would you like to start?

HART:

Sure. I think one of the things that's fascinating about bark beetles is the fact that there are these small little insects. And that they're only capable of causing broad-scale tree mortality during certain periods

LAWSON:

Dr. Rodman, what do you think makes them interesting?

RODMAN:

I grew up in Colorado, and in Colorado over the past couple of decades, we've had some pretty severe outbreaks that have really changed the way that forest look in the state. And this is kind of echoing things that we've seen in broader scales across the Western U.S. and Western Canada. For me, something that made me really interested in studying these dynamics is growing up around these, these processes as they unfolded. My mom and I went skiing a lot when I was a kid, because my parents were divorced when I was younger and that was kind of our activity together, the thing that we did pretty regularly to spend time together. And I can remember going to, you know, summit county areas up around Vail and Breckenridge. And seeing the same trees from year to year look very different, right? And that was for me a pretty formative experience and spawned a lot of interest in this.

LAWSON:

So, what makes the bark beetles important to study? Why do we need to know what happens in the forest during and after outbreaks?

HART:

It's important to understand what's going on with bark beetle outbreaks, because they can lead to extensive tree mortality across really broad landscapes and even across continents. These outbreaks have important consequences for a lot of ecosystem services. Whether it's aesthetics, like Kyle was talking about skiing, or it's carbon cycling, like we'll hear about later. They have impacts on water supply wildlife habitat, lots of different attributes of the forest ecosystem are shaped by bark beetle outbreaks

RODMAN:

I agree with everything you said. And I, you know, I won't add much to it except to say that a lot of the planning that we do when we think about the way forests look and the things that we use them for, whether that's for lumber or the value that they provide to wildlife or the recreational or aesthetic values that they give to us. A lot of the time, when we think about those values, we think of them as fairly static, right? Like sort of fixed in time, but something like a bark beetle outbreak or a wildfire, it can rapidly change the way and ecosystem looks and the value it provides the humans, the value it provides to wildlife. A whole host of things. Beyond that it can also affect how disturbances operate in the future. So, if we have a severe bark beetle outbreak today, two, three decades from now, we're unlikely to have another one in that same place because of these feedback mechanisms that happen with bark beetles in particular.

LAWSON:

So, we're talking, like you said about tiny insects. About the size of cooked rice, right? Dr. Hart, how does a satellite in space, particularly Landsat, offer advantages to studying those tiny insects that you wouldn't have on the ground?

HART:

One of the things that makes studying any disturbance hard is that they tend to happen infrequently in time and things like bark beetle outbreaks can unfold across these broad landscapes. Having data from Landsat with its relatively fine spatial grain as well as kind of this long record really allows us to figure out how these outbreaks are spreading across landscapes and where they're initiating that we couldn't get at with just going out and trying to walk around in the woods and look for the outbreak. Oftentimes we don't know the trees are being attacked until they are already dead. And so Landsat really provides us with this great temporal record. That's critical to understanding the dynamics.

LAWSON:

Because you can see the trees that are dead from a Landsat scene or image?

HART:

Correct. Yeah. So as the bark beetles attack the trees, you can imagine what a dead tree looks like. The needles start to turn a red color and eventually the needles fall off. And so, we can use Landsat to tell where once there was green, healthy trees, and now there are red and dying trees. 

LAWSON:

Dr. ZHU, do you want to add a little about the use of Landsat from your perspective, with the USSG and from working at EROS, home of Landsat?

ZHU:

The benefit would be for people who manage forests. And also, communities that live in the areas. Obviously, folks living in Colorado or New Mexico, they know much better than we do because they experience it. They look at their backyard, the trees dying and they can see the movement gradually coming up to their backyard. Or they see the changing climate has driven more infestation, and that also has negative feedback. What used to be green forests, they kind of absorb more CO2 and have a cooling effect for the atmosphere. You've lost the needles. Ground is more barren than before. You no longer have the carbon sequestration capability, and also the mountains getting hotter. So, it's a, it's a kind of a feedback that you don't want to see. So, I think the work that the Landsat provides makes the decision making by land managers and citizens more timely and more accurate. Ultimately, it's about how they can make an informed decision using Landsat derived products.

LAWSON:

You mentioned carbon. So, let's talk a little bit about the ramifications of outbreaks like this on the carbon stocks in the forests.

ZHU:

The issue is that whenever the forests experience insects or wildfire two consequences occur. One is that they stopped sequestering new carbon. So, they no longer help cooling the climate by absorbing CO2. Second is that they take a longer time to recover, to regenerate. And because the climate has changed summer rainfall is much less frequent and sometimes it's heavy rainfall that washes away soil. That also does not help regeneration. The longer the trees are not recovering. Obviously, the longer carbon is in danger of losing it. The trees are not recovering. Obviously, the longer carbon is in danger of losing it.

LAWSON:

Dr. Rodman, tell me a little about what you've learned about bark beetles in your recent study.

RODMAN:

We spent a lot of time on this recent paper that you mentioned. Trying to think about how we could accurately portray what was going on across this landscape of the Southern Rocky Mountains. And when I talk about the Southern Rockies, I'm talking about sort of the core mountains of Colorado, Southern Wyoming and Northern New Mexico. This contiguous region that has some high elevation forest. We were looking primarily at these set Alpine forests. Which are sort of the upper half of the elevational bands of forest ecosystems in this region, a huge area, right? Because when we talk about this region, we're talking about roughly 50% of it's covered in forest, roughly 50% of that is subalpine forest. So, these are, you know, the headwaters of major watersheds, like the Colorado river or the Rio Grande, the Arkansas. All-important water sources in different areas. We were using field records that a bunch of people that we collaborate with as well as Sarah and I had gone out and collected to essentially ground truth what we were seeing in the imagery to be able to say, and this particular site on the landscape, we see 50% of the trees that were there in the nineties have died in the last few decades. Or a 90% or 10%. So, we had pretty extensive ground-truthing in this study and we use that information to then model the severity of outbreaks across the region. We found that roughly 40% of the area that we were looking at, which was over 10,000 square kilometers, a huge extent in this region has been affected to some extent by three species of native bark beetles. In that area. What we've noticed is that there are some places that have been really hard hit. Where the majority of trees have died because of these bark beetle attacks. But what I found pretty interesting and sort of surprising is that the places that we saw near total mortality were pretty uncommon actually. These places where we had, you know, 90 plus percent of the trees dying in a given site. That's not as common as you would expect from seeing photos or driving through areas that have been hard hit.

LAWSON:

What did you think about those results Dr. Hart?

HART:

The work that Kyle did was really informative in thinking about how bark beetle outbreaks really generate this complex landscape. So, all of these patches of severe mortality, but then the patches where you don't have as severe mortality create more complexity in the landscape then I think we knew before Kyle's research.

LAWSON:

Anything else, surprise you or challenge you about this study?

HART:

I think just like Kyle highlighted, it's really easy to drive down I-70 here in Colorado and see lots of dead trees and assume that, you know, trees are dead everywhere, but just recognizing that in many places, there are lots of surviving trees was kind of a positive note for me in thinking about how these forests will develop in the future. It's not all doom and gloom, and we're anticipating that these forests will return to Conifer forest in the near future.

LAWSON:

So how can this study and other bark beetle research, help force managers and people who live in and near the forest in the future, especially in a changing climate?

HART:

You know, understanding kind of the patterns of mortality is important for how we think about managing these systems. First and foremost, if you know where there's lots of tree mortality, that might be locations where you might want to concentrate some of your efforts to reduce the risk of things like tree fall, hazard and campgrounds, and you know, near power lines and people's homes. And then kind of like Kyle was mentioning earlier. Thinking about managing forests. We're increasingly understanding that disturbances are natural drivers of the composition and structure. That's typically what we're trying to manage. And so kind of understanding how bark beetle outbreaks function to shape this structure and composition across broad landscapes is really important for how we move forward with managing force in the context of climate change.

RODMAN:

As you mentioned earlier Jane, this is something that we expect will probably increase in frequency in the future. These, these kinds of outbreaks across broad scales. If we have more and more drought that tends to make trees more susceptible, it accelerates the life cycles of the beetles. It allows these outbreaks to happen more often and potentially it's a smaller and smaller trees. But on the flip side, having outbreaks now means that we're unlikely to have a severe one in the near future. So, when we start thinking about predicting future dynamics or projecting future change, the patterns that are out there today are really critical to being able to predict what's going to happen in two decades, five decades from now because bark beetles are one of these classic disturbances that have negative feedbacks on themselves. When you have an outbreak that kills all the large trees, it takes a long time for trees to get big again. Or bark beetles to be able to attack them again effectively.

LAWSON:

Hopefully Landsat's archive will extend into the future so that people can continue to use it for the large-scale studies like this.

RODMAN:

Yeah, absolutely. And you know, as Sarah mentioned earlier, it really is a valuable tool for the kinds of studies that we are doing here because, you know, with tree rings, we can go back a long way. In particular locations, we can go back a long time. Right. And we can understand the dynamics in particular places. But Landsat is one of the few tools that we have access to that gives us a fairly long temporal record. As well as really extensive information. So, going from that understanding of places on the landscape to actually understanding the entirety of the landscape.

LAWSON:

Any closing thoughts from either of you?

HART:

Landsat is particularly valuable for some of our remote systems that don't get as visited as frequently by people. Some of our wilderness areas that we have here in Colorado or where some of the outbreaks started. And without Landsat we really wouldn't know when they started and how they spread across those landscapes, because they're so infrequently visited.

RODMAN:

You could say similar things about rugged areas in Montana and Idaho and Western Canada, right. Places that just don't see a lot of visitation in general. And aren't a huge management concern because they're so remote, like managers aren't out there walking around the forest every day.

LAWSON:

Thank you all for joining us for this episode of Eyes on Earth. Where we talked about using Landsat to capture bark beetle outbreaks in the Southern Rockies. Check out our EROS, Facebook, and Twitter pages to watch for our newest episodes. You can also subscribe to us on Apple podcasts. This podcast is the product of the US Geological Survey/Department of the Interior.

 

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