Eyes on Earth Episode 42 – Rangelands of the U.S.

JOHN HULT: 

Hello everyone, and welcome to this episode of Eyes on Earth. We're a podcast that focuses on our ever-changing planet and on the people here at EROS and across the globe that use remote sensing to monitor and study the health of Earth. I'm your host, John Hult. The Bureau of Land Management administers more than 244 million acres of land in the United States. More than any other Federal agency. The vast majority of that land, more than 99% of it, in fact, is spread across 11 western states. On today's episode we are talking with a scientist from EROS who's spent years working to develop satellite-derived mapping products that can help land managers both in and outside government agencies find patterns and manage resources across the Western U.S. Matt Rigge is a research physical scientist who's helped develop a 30-plus year Back In Time product that breaks down rangelands into their component parts, like sagebrush, bare ground and litter. Matt, welcome to Eyes on Earth.

RIGGE: 

Thanks John. Happy to be here.

HULT: 

Matt, why don't you tell us why it is important to understand changes to rangelands. What is it about rangelands that we need to know and what kinds of changes have the biggest impact on the lives of people and the environment?

RIGGE: 

Rangelands are a really spatially extensive land cover type worldwide. In the United States as well, especially in the Western US. They support a lot of different ecosystem goods and services, like wildlife habitat, forage for livestock, erosion control, and recreational resources. Not to mention they serve as a backdrop for lots of western movies. At the same time, rangelands are under pressure from climate change, alterations to the historical fire regime. A lot of areas are getting burned more and more frequently now than they have in the past, and some locations getting burned less often than they have in the past. Fire regime alteration is related to invasion by exotic grasses like cheatgrass. There's also pressure from oil and gas exploration, mining, coal mining and recreation, off road vehicle usage, etc. All of those changes have kind of come together to lead to a decline in rangeland-obligate species, like the sage grouse.

HULT: 

When you say sage grouse or sagebrush obligates, you're talking about animals that need a particular kind of environment to live in, like they need the sage brush to survive. Is that right?

RIGGE: 

Exactly. So sagebrush is one of the important shrubs in range lands in the western US. And the sage grouse, the population of that bird has been dramatically declining over the last several decades. Like you said, yeah, it needs sagebrush to survive.

HULT: 

My understanding is that sagebrush doesn't just pop right back. So it a fire moves through, you were talking about fire regimes, if a fire moves through and burns a bunch of sagebrush, what typically happens?

RIGGE: 

In some cases, the sagebrush does recover, but it takes quite a while to get back to the pre-fire condition-30, 40 years in some cases, maybe more. In a lot of cases more recently those sites get invaded by cheatgrass, which further accelerates the fire cycle. It really has a negative impact on sagebrush populations. More on the wetter end, there is encroachment from Pinyon-Juniper forest from the higher elevations. It's sort of getting squeezed from both ends.

HULT: 

Right. The native habitat is disturbed in some way, whether that is by fire, development or recreation and what comes back is not necessarily the natural vegetation. That can have an impact on down the line.

RIGGE: 

Exactly. And not only that but it fragments the landscape. A lot of animals in rangeland areas require a really extensive undisturbed habitat. So fragmenting the landscape up into smaller chunks of area, even if those areas are quote/unquote "pristine," it still provides less value than larger chunks of landscape.

HULT: 

Tell us just really basically how satellites are used to track land change to begin with. We are talking big changes, changes like land cover, not changes in the season. How do you use satellites to track changes to the landscape?

RIGGE: 

Land cover change, we can pick that up. For example, going from a grassland to a shrubland or visa versa. But more important is the within-state changes-changes in the quality of a grassland or changes in the quality of a shrubland through time that would be too subtle of a change typically to result in a land cover change yet have ecological importance. A shrub patch increases in density through time. These sort of changes are still really important to capture, but they would be entirely missed with classifying the landscape as just shrubland, grassland or barren which is sort of the traditional land cover classifications types used in rangelands. 

HULT: 

So we're looking at components that make up rangeland as observed throughout the Landsat satellite archive. Where did the idea to go sort of beyond land cover itself or the thematic land cover and look at these components, where did that come from? And why is it important to look at those components?

RIGGE: 

Yes, so these products, we call them the Back In Time or BIT for short. They have been in development for the better part of the last decade. The primary goal of this was to improve the National Land Cover Database, the NLCD classification of rangelands, and then to better understand the change missed by thematic land cover maps-NLCD would be one of those. We are looking at 30-meter resolution maps with fractional cover of components. When I say fractional, I mean 0 to 100% cover shrub, herbaceous, litter and bare ground. Rangelands can be comprised of a varying fraction of each of those four components. A pixel could be called 10% shrub, 20% herb, 20% litter, and 50% bare ground. I actually did the math on that, and there's 94 million possible combinations of those 4 components. We actually take that a couple steps further. We map the cover of sage brush, as well. We are also measuring annual herbaceous, cheatgrass, medusahead, these invasive annual grasses that are strongly related to the fire regime.

HULT: 

So what we are looking at here, instead of something like National Land Cover Database, where you would see a 30 meter pixel, you know about the size of a baseball infield, and it would say, "this is shrubland, this is barren ground," whatever. Your product will look at that same pixel and say this % is litter, this % is sagebrush, this % is bare ground etc. How is that useful? How would you use that as a land manager?

RIGGE: 

It is really foundational. They need to know how the landscape is comprised from a vegetation standpoint. This information allows them to set management specific targets and track changes thru time. A pixel could go from 20% shrub to 30% shrub. That is ecologically meaningful for sage grouse, but it would be entirely hidden within the shrubland land cover classification. If you want to look at long-term changes in rangeland, you need to have these sort of data.

HULT: 

You're one of the authors of a really recent paper, where you used a decade of field observations and Landsat data in Wyoming to see how well these satellite products could track the impacts of climate change and land management decisions. Tell us a little bit about that work. I mean, why do need to have field observations when you have the satellite, for one thing? Second off, how did you do that for a decade? Did you fly to Wyoming twice a year for 10 years, or did you hire a kid on a moped to go out and check? How did you accomplish that? There is a lot to unpack there, I know. Get into that what did you learn?

RIGGE: 

Well, unfortunately we did not hire any local kids or fly there twice a year. These plots were measured consistently by the same observer, which is a really important thing. There is an observer bias between different observers. Someone might have a bias to say this site is more shrub or this site is less shrub, etc. These plots were set up at two monitoring sites about 15 miles from each other. They really had divergent stories through those 10 years. One was in a really pristine, sagebrush-dominated rangeland with only a small amount of change observed. But the other site had a lot of change, mostly related to energy development. A number of sites got bulldozed to build oil pads on that second site. The take-home story in this analysis was that the Back In Time was able to capture those changes in both sites.

HULT: 

Tell us a bit about the collaboration between your group at EROS and the group that does the annual cheatgrass monitoring. You guys combined those products to build a tool for the Western Governor's Association. Tell us a little bit about that.

RIGGE: 

Sure. So there is another group at EROS that is taking a slightly different approach than ours. Focusing on cheatgrass and other invasive grasses across the west. We are only using a couple images per year, where they are using multiple images per year to track the subtle differences in phenology between these invasive grasses and the native grasses.

HULT: 

So something like a cheatgrass, if the rain falls, it gets green really fast, it gets brown really fast. If you can see that change happening in real time, you go "oh, that's cheatgrass." Is that kind of what they are doing?

RIGGE: 

Yes. Pretty much. It would have a slightly different phenological signal. That difference would allow you to separate those areas invaded out from those areas that have not been invaded.

HULT: 

So there is that product and then your product which goes back in time, and you just crunched them together like Rock 'Em Sock 'Em Robots and handed it over to the Western Governor's Association. How did putting those two things together help? What did you make for them?

RIGGE: 

We combined our annual herbaceous product with this cheatgrass mapping project at EROS, and also we tied in some data from the University of Montana. They have a tool called the Rangeland Analysis Platform. It is sort of easy to see that these could be competitive products. But we kind of all work together to share data and put it into a single weighted average. Looking at the average across those three products, the error rates are much, much lower than any of our three respective products individually. The overall goal of combining these three data sets was to define the areas that have already been extensively invaded by annual grasses, those that have been uninvaded or are in still pretty pristine condition, and to sort of flip the paradigm of management. Management has been pretty reactive to annual grass invasion, trying to stop it from spreading. We are thinking about defending the core areas of pristine habitat and trying to extend those pristine areas where possible.

HULT: 

Where else do you see this going in the future? What is this going to be useful for?

RIGGE: 

Researchers looking for suitable habitat for sage grouse, antelope etc., a number of different species. They have been using them to evaluate trends and habitat conditions. And even to define what is potentially suitable habitat. What I think we will probably see more of in the future is more emphasis placed on how the component cover values respond to changes in the climate condition. Another big push we would like is to get these data into the hands of private ranchers. They are being used largely by public land managers-BLM, forest service, state agencies etc.-but I think the private landowners and managers would find them incredibly useful as well.

HULT: 

It sounds like really what you are trying to do is use these data as a starting point. Here is what we know and here is how we can use that to plan for the future. That kind of information is something that a private land manager would find useful, as well. I mean you manage thousands and thousands of acres you kind of want to know what is going to happen, I suppose?

RIGGE: 

Exactly. And you may have looked at those sites every year for the last 20 years, but it is hard to put it into context and quantify what you are seeing. 

HULT: 

What is the next step here? Do you continue to produce Back In Time products or is this a one and done? Do you update them every year? What's the next step? And also, where do you go to find this stuff?

RIGGE: 

We are currently in the midst of a major reprocessing of our Back In Time data so we are going to extend the time series thru 2020. Currently it is only going through 2018.

HULT: 

And then every year on a certain date? Or whenever you update these products, people go where? MRLC.gov?

RIGGE: 

Yes. It is on MRLC.gov. Also on sciencebase.gov. On MRLC, we have a data visualization tool that allows users to interact with the data and download custom extents. If they don't want to download the entire Western U.S., which are huge data files, this allows users to dynamically interact with the data. Download smaller pieces that they may be interested in. Those would be available hopefully on an annual basis, updated data for the previous year say by early spring of the following year. I've got to give a lot of credit to the talented group of folks we have here at EROS who are toiling away, mostly behind the scenes getting these data sets created. So a big thank you to the EROS team and the BLM for funding this work. We also have a number of peer-reviewed scientific papers describing the methods used to produce the data. For those who would like to know how the sausage is made, so to speak. The papers present some interesting case studies on how our fractional cover data could be applied as well.

HULT: 

Matt, any closing thoughts? Anything you would like to add?

RIGGE: 

Rangelands are important, and monitoring rangelands is important as well. To better manage the resources we have we have to first understand the current spatial patterns. Area X is in better condition than Area Y. Then the important thing is to extend this knowledge through time to see how or if certain areas are moving away from or towards the desired conditions from a management perspective. 

HULT: 

We have been talking to Research Physical Scientist Matt Rigge about how satellite data can be used to better understand the Rangelands of the Western United States. Thanks for joining us, Matt.

RIGGE: 

It was nice to talk to you today, John. I appreciate your time.

HULT:

We hope you come back for the next episode of Eyes on Earth. Until then, visit usgs.gov/eros, that's usgs-dot-gov slash e-r-o-s to find every episode. You can also subscribe to us on Apple Podcasts or Google Podcasts. This podcast is a product of the U.S. Geological Survey, Department of Interior.