EROS Rangeland Tools Aid Western U.S. Land Managers

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The extensive rangelands across the Western United States are threatened by invasive grasses, climate change, and altered fire regimes that can disturb the landscape. The largely semi-arid lands are also important for the survival of species that need undisturbed sagebrush ecosystems to thrive.

color photo of USGS EROS scientist Matthew Rigge

USGS EROS Research Physical Scientist Matthew Rigge

But most satellite-based land cover datasets don’t offer the kind of detail needed to track the small but ecologically meaningful shifts in vegetation that can alter fire regimes and improve habitats.

Research Physical Scientist Matt Rigge recently took a turn in the guest’s chair for the EROS podcast Eyes on Earth to talk about how new EROS data products help fill in that gap. Rigge talked about a 30-plus year Back In Time (BIT) product that breaks down rangelands into their component parts, like sagebrush, bare ground and litter. He also touched on an EROS partnership with the Western Governors Association that leans on those BIT data, EROS-produced cheatgrass data, and data from the University of Montana to help land managers be proactive sin handling rangelands.

Here are some highlights from the show.

JOHN 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 U.S. 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 in 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:

My understanding is that sagebrush doesn’t just pop right back. So 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 in the higher elevations. It’s sort of getting squeezed from both ends.

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

HULT:

Right. So the native habitat is disturbed in some way, whether that’s 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:

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 sorts 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 are sort of the traditional land cover classification types used in rangelands.

HULT:

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?

Animation of Shrubland coverage over time

Animation of change in shrub component coverage, created using the Multi-Resolution Land Characteristics Consortium's Rangeland Viewer tool. 

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 (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.

HULT:

So instead of something like National Land Cover Database, where you would see a 30 meter pixel and it would say, “this is shrubland, this is barren ground.” Your product will look at that same pixel and say this percent is litter, this percent is sagebrush, this percent 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 through 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.

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 Governors 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 … We combined our annual herbaceous product with the 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.

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