Research provides first-ever analysis of vegetation trends on BLM lands across West

Remote sensing technology highlights challenges and opportunities for BLM-managed rangelands

Recently published science shows the power of new remote-sensing tools for monitoring rangelands and developing effective strategies for adaptive management and conservation, especially in the American West that falls under a mix of private, federal, tribal, and state management.

Remote sensing technology offers a cost-efficient and spatially diverse method of analyzing vegetation trends on western rangelands, including the more than 233 million acres managed by the Bureau of Land Management.

The new research, led by Andrew Kleinhesselink, a WLFW-affiliated researcher with the University of Montana, utilized the Rangelands Analysis Platform to conduct an unprecedented assessment of trends in vegetation cover and production for all BLM rangelands from 1991 – 2020.

The team’s analysis covered more than 21,000 BLM grazing allotments totaling 233 million acres across 11 western states (excluding BLM lands in Alaska). They evaluated trends at a variety of spatial scales, including eight different ecoregions, dozens of BLM field offices, 21,000+ individual grazing allotments, and 30-meter x 30-meter pixels, providing land managers a full accounting of 30 years’ worth of vegetation trends across western BLM rangelands for the first time. Of note, this research did not evaluate grazing by livestock or the BLM’s grazing management.

The team found widespread increases in cover and production of annual grasses and forbs, declines in herbaceous perennial cover, and expansion of trees. Cover and production of annual plants, primarily annual invasive grasses like cheatgrass, now exceed that of perennial plants on nearly 52 million acres of BLM rangeland, marking a fundamental shift in the ecology of these public lands.

Additionally, tree cover increased in half of the ecoregions affecting some 108 million acres and underscoring the threat of woodland expansion for western rangelands.

This research highlights the power of remote sensing, while also recognizing that traditional, in-field vegetation monitoring has played a critical role in ensuring remotely sensed data is accurate and valid.

The Rangeland Analysis Platform, used in this analysis, was trained and validated by two standardized, in-field vegetation monitoring programs, the BLM’s Assessment, Inventory, and Monitoring program (in place since 2011) and the NRCS’ National Resources Inventory (in place annually since 2000). Together, these programs have provided data for more than 80,000 locations across public and private lands in the Western U.S., which helps ensure remote sensing tools, like RAP, are accurate and trustworthy.

The vegetation changes identified in this research – more invasive annual grasses and more woodland expansion – threaten the ecological function and habitat value of millions of acres of public lands. These findings provide unprecedented opportunities to partner with other public, tribal, and private entities to strategically target and scale-up rangeland restoration actions.

Instead of investing limited resources into areas that have already been highly invaded by trees or exotic annuals, an effective approach may be in prioritizing conservation of the most intact areas of rangeland and then expanding outward through restoration, an approach coined “Defend the Core.”

This approach would align with Working Lands for Wildlife’s Framework for Conservation Action in the Sagebrush Biome. It also mirrors the approach outlined in the recently released Sagebrush Conservation Design, which highlights that three-quarters of the threats facing intact sagebrush rangelands are problems of ecosystem function, such as invasion by exotic annuals and tree expansion.

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Long-Term Trends in Vegetation on Bureau of Land Management Rangelands in the Western United States

Abstract: The US Bureau of Land Management (BLM) manages nearly 1 million km² of public lands that support recreation, livestock production, and wildlife habitat. Monitoring the condition of vegetation on these lands is crucial for sound management but has historically been difficult to do at scale. Here we used newly developed remote-sensing tools to conduct an unprecedented assessment of trends in vegetation cover and production for all BLM rangelands from 1991 to 2020. We found widespread increases in cover and production of annual grasses and forbs, declines in herbaceous perennial cover, and expansion of trees. Cover and production of annual plants now exceed that of perennials on > 21 million ha of BLM rangeland, marking a fundamental shift in the ecology of these lands. This trend was most dramatic in the Western Cold Desert of Nevada and parts of surrounding states where aboveground production of annuals has more than tripled. Trends in annuals were negatively correlated with trends in bare ground but not with trends in perennials, suggesting that annuals are filling in bare ground rather than displacing perennials. Tree cover increased in half of ecoregions affecting some 44 million ha and underscoring the threat of woodland expansion for western rangelands. A multiscale variance partitioning analysis found that trends often varied the most at the finest spatial scale. This result reinforces the need to combine plot-level field data with moderate-resolution remote sensing to accurately quantify vegetation changes in heterogeneous rangelands. The long-term changes in vegetation on public rangelands argue for a more hands-on approach to management, emphasizing preventative treatment and restoration to preserve rangeland habitat and functioning. Our work shows the power of new remote-sensing tools for monitoring public rangelands and developing effective strategies for adaptive management and conservation.

Citation: Andrew R. Kleinhesselink, Emily J. Kachergis, Sarah E. McCord, Justin Shirley, Nicole R. Hupp, Jennifer Walker, John C. Carlson, Scott L. Morford, Matthew O. Jones, Joseph T. Smith, Brady W. Allred, David E. Naugle. Long-Term Trends in Vegetation on Bureau of Land Management Rangelands in the Western United States. Rangeland Ecology & Management, Volume 87, 2023, Pages 1-12, ISSN 1550-7424.

Permanent URL: https://doi.org/10.1016/j.rama.2022.11.004

Acknowledgments: Funding for this project was provided by the Montana-Dakotas State Office of the Bureau of Land Management. We thank the Intermountain West Joint Venture, part of the United States Fish and Wildlife Service, for its contracting expertise. Working Lands for Wildlife, part of the USDA’s Natural Resources Conservation Service, supported David Naugle during this effort.