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An unprecedented collaboration between USGS and University of Montana researchers to produce a data layer showing where invasive grasses threaten rangelands in the West is playing a critical role in a new management “toolkit” launched by the Western Governors’ Association (WGA).

color map of annual herbaceous land cover
A map depicting the amount of annual herbaceous cover (primarily cheatgrass) across the Western U.S. Data are based on the weighted average of USGS Back in Time, fractional component time-series; USGS Harmonized Landsat-Sentinel data; and the University of Montana Rangeland Analysis Platform products—all from 2016-2018.

Teams from the Earth Resources Observation and Science (EROS) Center, led by retired Scientist Collin Homer and Research Physical Scientist Bruce Wylie, blended their invasive grass mapping products with one developed by the University of Montana to provide the most comprehensive look yet at where western rangelands and sagebrush ecosystems may be endangered.

The new collaborative base layer will help state officials and land managers identify opportunities for projects and conservation efforts meant to stop the advance of annual herbaceous plants such as cheatgrass, which fuel wildfires and can overwhelm sagebrush landscapes.

“It is a cliche, but it is so true; a map like this is worth a thousand words,” said Lindy Garner, the Sagebrush Ecosystem Invasive Species coordinator for the U.S. Fish and Wildlife Service. “The invasive annual grasses are a significant threat to the West, to our livelihoods, to our conservation efforts, to our communities. In terms of prioritizing our efforts and our dollars, we think this (project) was the right thing to do.”

‘A Remarkable Experience’

WGA Senior Policy Advisor Bill Whitacre called work on the collaborative effort “a remarkable experience.”

“The data layer developed by EROS and the University of Montana, as well as the contributions of our other partners on this project, will be extremely useful for land managers working to address the spread of invasive annual grasses,” Whitacre said.

The one thing that makes this data layer so promising and unique is the joint work that went into it, Garner said. None of the stakeholders fighting the presence and advance of invasive grasses—the Federal government, the states, and private groups—have enough funding or capacity to deal with it themselves, and never will, she said.

“But with the new toolkit, land managers can better identify where we can be most cost effective, most successful, and get the highest return on our investment,” Garner said. “That’s what this type of information will help us do.”

That such an annual herbaceous data layer came together at all — and in just a few months — caught even those contributing to it by surprise. In the world of remote sensing science, it’s not unusual for teams serving various interests to produce similar products, said Matt Rigge, an ASRC Federal contractor at EROS who works with Homer’s team. But with limited financial resources, teams are motivated to deliver products superior to their closest competitors whenever possible, he said.

And that, Rigge added, can lead to “this sort of arms race that you have ... the survival of the fittest in some cases. That’s why, from my perspective, I think what we did here is relatively unprecedented.”

Wylie, whose team received National Land Imaging funding three years ago to use harmonized data from Landsat and the European Space Agency’s Sentinel-2 system to produce cheatgrass maps at 30 meters, said potential users of those maps know there are a variety of options out there and want to know how they differ or are better than the others. “It’s kind of like, ‘Which one do we trust, and which one do we use?’ ” Wylie said.

A Shared Stewardship Memorandum

WGA and the U.S. Department of Agriculture (USDA) signed a Shared Stewardship Memorandum of Understanding in December 2018. Under that agreement, WGA and USDA have been collaborating on efforts to meaningfully address the large-scale infestation of invasive annual grasses on western forests and rangelands. The new toolkit and data layer were the results of that effort. Development of the toolkit was aided by the Western Invasive Species Council, a Western Governors-appointed advisory group created in 2019.

color photo of fire on rangeland
Photo captured during a wildfire driven by locally abundant cheatgrass cover in sagebrush steppe in the foothills northeast of Boise, ID.

Neal Pastick, a research physical scientist with KBR and contractor to the USGS who works with Wylie’s team, created the algorithm that blended the work of the three groups into the single base layer that estimated the percent cover of invasive grasses at 0 to 100 percent at a per-pixel level, or roughly 30 meters by 30 meters.

The University of Montana brought to the table what it calls the Rangeland Analysis Platform (RAP) tool, which covers everything west of the borders of Minnesota down to Louisiana. Homer’s product starts in western North Dakota, follows a line down to western Texas, and maps areas west of that. And Wylie’s team is working on near real-time mapping of invasive herbaceous plants in Wyoming and the Great Basin.

The integrated product combined average annual estimates from 2016 through 2018, Pastick said. While the areas covered by the three products don’t always overlap, “we do have a convergence of evidence of the three within the most problematic areas historically,” he said.

Thealgorithm arrives at an estimate of invasive grasses through what Pastick calls a “weighted mean.” If two of the products show similar estimates, and the other one differs quite a bit, the latter is given a very low weight.

For example, let’s say you asked three students what four plus three is, Pastick said. One may say “eight,” another “six,” and the third comes back with “one.” In that case, the weight of the outlier, “one,” would be so low that it would essentially be cast out and the other two averaged, he said.

“The thing is, we didn’t go into this saying one product is better than the others,” Wylie said. “It’s kind of like saying, ‘In this pixel, these two agree. And over here, these other two agree.’ I think it has really brought home the fact that there wasn’t one best approach, and that the best approach may be this convergence of evidence kind of logic.”

Room for Improvement

Because this effort came together so quickly, there are ways to improve it, Pastick said. With additional funding, the next step would involve better quantifying uncertainties in the integrated products and/or calibrating them (e.g. determining weights) with actual field data.

In addition to releasing the toolkit, all parties will emphasize the importance of being proactive, Garner said. “We’re trying to promote from the invasive species management standpoint that, if we truly want to remove this invasive species threat to the West, we have to stop the bleeding.”

That means preventing cheatgrass and other invasives from getting established and spreading by using the tool to identify where the first tell-tale signs of annual herbaceous plants are starting to show up in areas that haven’t been invaded yet, Garner said.

“We need to try to defend those core areas that are not yet invaded, and we need to put resources and capacity to that,” she said. “Then in those transitional areas between areas that are not invaded and areas that are highly invaded ... we need to do aggressive management and defend those cores so it doesn’t keep moving across into those areas.”

This tool can help accomplish that, Garner said. And by working with the bipartisan WGA, “we’re hopeful that some state programs or even some organizations will be more open or more willing to get on board,” she said.

While the Federal government is trying hard to provide funding, information, and science to get at the problem of invasive grasses, success will most certainly come about because of collaborations like this data layer, Garner said.

“We have to have the governors, the states, and the private landowners understand this problem,” she said. “This tool helps with that understanding. I don’t think I’m misstating it here when I say that everybody is really happy with what this provides.”

For more information:,-115.9897&z=6&lc=pfgc&year=2019&mask=apply&tab=1&Annual%20herbaceous%20cover_v=true


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