The case for sagebrush habitat as the iconic landscape of the American West is a fairly one easy to make.
USGS EROS Work Informs Sagebrush Ecosystem Efforts
Sandy, rolling swaths of patchy shrubs and native grasses spread across hilly drylands and burst quickly to colorful life with wildflowers after a rainfall. Unique fauna like the greater sage-grouse, Brewer’s sparrow, and Pygmy rabbit scratch, sing and scurry through the brush. These landscapes evoke the whistling cowboys and hardscrabble ranchers whose stories have captivated the American imagination for generations.
The image of rugged durability inspired by sagebrush country stands in contrast to reality, however. Changing land use, invasive species, and wildfires have emerged as potent threats to sagebrush areas like the Great Basin of Nevada, Oregon and Utah.
More than 350 plant and animal species are “sagebrush obligates,” meaning they need a healthy sagebrush ecosystem to survive. Accordingly, questions of ecosystem protection, restoration, and management have become the subject of continuous discussion and evaluation in recent decades.
As an apolitical scientific arm of the federal government, the role of the U.S. Geological Survey (USGS) in those discussions is both straightforward in concept and complex in operation: To understand and inform those discussions with sound science.
The USGS studies sagebrush habitats to understand the extent and causes of change and to identify and characterize impending threats from wildfires, human disturbances, and invasive species. The results can guide management decisions that best balance the interests and obligations of the stakeholders. The more solid the science, the better those decisions can be.
The contributions of USGS Earth Resources Observation and Science (EROS) to mapping and monitoring change were highlighted recently in the “U.S. Geological Survey Sage-Grouse and Sagebrush Ecosystem Research Annual Report for 2018.”
The full report outlines the work of the USGS program of the same name, led by the USGS National Center’s Ecosystems Mission Area and involving researchers across 10 states.
“USGS science has provided a foundation for major land and resource management decisions in the sagebrush ecosystem including actions that precluded the need to list the greater sage-grouse under the Endangered Species Act,” the report notes.
The expertise offered by USGS EROS has helped build a foundational understanding of the landscape for both the agencies that manage the land and the scientists who study it, according to Steve Hanser, the USGS Sagebrush Ecosystem Specialist who leads the program and edited the report.
“The innovative science and data products developed by EROS scientists move beyond traditional land cover mapping to provide timely measures of vegetation cover and height,” Hanser said. “This information can help inform decision-making at the federal, state, tribal, and local agencies across the sagebrush biome and support other USGS scientists as they develop actionable science to address wildlife, fire, and invasive species management questions.”
Classifying sagebrush country at 30-meter resolution
USGS EROS leans on the deep Landsat archive and a heritage of remote-sensing excellence to offer that insight to stakeholders in sagebrush country, with seven projects noted in the pages of the 76-page circular.
Detailing land cover in sagebrush ecosystems at a wide scale is at the center of the contributions from USGS EROS’ Collin Homer, Director of the National Land Cover Database (NLCD). Shrubland mapping piqued his interest shortly after he began with the project in 2002, he said.
“I realized by about 2005 that we could improve both shrub and sagebrush characterization,” said Homer.
NLCD 2016, scheduled for release in Spring 2019, will include new Western U.S. shrubland data products, some of which are already available through the Multi-Resolution Land Characteristics Consortium.
Landsat is the basis for those fractional land cover characterization products, which break shrublands into their component parts–key details that can be used to monitor ecosystem health on a wide scale and to predict habitat needs.
High-resolution data from Worldview satellites was collected over sample sites as crews collected field data in the same locations. The 2-meter resolution data were then scaled up by integrating 30-meter Landsat images, and the resulting wall-to-wall landscape predictions were subject to three levels of validation for accuracy.
In the end, each 30-meter cell defines the proportion of shrub, sagebrush, herbaceous, annual herbaceous, litter, and bare ground at 1-percent intervals, and the height of shrubs and sagebrush in centimeters.
“It basically gives land managers building blocks they can use for a variety of different applications,” Homer said. “Going forward with it, our goal is to reproduce it on an annual basis.”
They are currently producing annual change products that reach back to 1984.
The shrubland characterization work offers critical insight that informs research to build trendlines over time, work that aims to apply state-and-transition models (STMs) to grazing management decisions, and endeavors to understand the drivers of change to rangeland vegetation.
“It’s not enough just to characterize your environment and see what trends are going on,” Homer said. “Our ultimate objective is prediction: Where’s the landscape going?”
Watching invasive species from above
The work of USGS EROS scientist Bruce Wylie and EROS contractor Stephen Boyte also appears in the report. Wylie and Boyte have tackled shrubland performance anomalies, studied grassland dynamics, and created products for rapid identification of cheatgrass, an invasive annual that grows early in the Spring.
Cheatgrass is particularly nefarious in places like the semi-arid Great Basin, where its rapid green-up and die-off has contributed to an increase in fire size and severity. Browned, fast-burning cheatgrass can carry a blaze between patches of slow-burning sagebrush to produce intense and dramatic fires.
“You have this standing, dead fuel that increases the probability of fire. A lighting strike or cigarette butt there can start it,” Wylie said. “In a drought, these things may be dry as a bone, but (sagebrush) has volatile oils. So when you see these flames, they can be as tall as a telephone pole and burn even the roots below ground.”
The USGS has three goals for its invasive species work: To address prevention, eradication and control measures; to determine the factors that influence their spread and distribution; and to develop maps for early detection and control.
USGS EROS’ cheatgrass work can contribute to all three goals.
The path to the near-real-time monitoring of invasives was marked by earlier research on shrubland anomalies in the Owyhee Uplands region, which began around nine years ago for the Bureau of Land Management (BLM).
The first step was to create historical shrub cover maps using remotely-sensed data, which could in turn be used to predict how vegetation should behave within a healthy ecosystem. Identifying the anomalies - areas where sagebrush and bitter brush growth didn’t match expectations - caught the attention of the USGS partners at Bureau of Land Management (BLM).
The BLM had noticed areas where invasive cheatgrass would die off and not return, but the reasons were unclear. If USGS EROS researchers could identify anomalies for shrubland, the BLM wondered, could the same approach be used to spot cheatgrass die off?
The answer was yes, and the resulting die-off research in 2015 sparked still more interest.
“Our collaborator thought it would be nice if we could do this in near-real-time,” Wylie said. “We thought about it, put our heads together and came up with a plan.”
Field data from Homer’s detailed shrubland characterization products, which offer an annual look at the ecosystem, were used to help train a near-real-time model at 250-meter spatial resolution. That model generates annual maps that can be used to plan fire suppression activities during the year.
USGS EROS researchers are currently developing a 30-meter near-real-time product, which will further aid efforts to deal with immediate land management challenges, especially in areas where the cheatgrass has yet to gain a foothold.
With tools such as those produced at USGS EROS, the Sage-Grouse and Sagebrush Ecosystem Research Program can continue to offer the kind of science needed to manage and protect the ecosystem of the American West and the species who thrive there.