thumbnail

Potential Risks of Vegetation Treatments to Introduce and Increase Invasive Annual Grasses in Rangelands of Montana, North Dakota, and South Dakota—A Science Synthesis to Inform National Environmental Policy Act Analyses

Scientific Investigations Report 2025-5058
Prepared in cooperation with the Bureau of Land Management and the U.S. Fish and Wildlife Service
By: , , , , , and 
https://doi.org/10.3133/sir20255058

Links

Abstract

The U.S. Geological Survey is working with Federal land management agencies to develop a series of planned structured science syntheses to support environmental effects analyses that agencies conduct under the National Environmental Policy Act (NEPA). This report synthesizes science information relevant to environmental effects analyses concerned with potential increases in the distribution and abundance of invasive annual grasses (IAGs) from proposed vegetation treatments for habitat restoration. The focal environments for this synthesis are rangelands in the intermontane valleys of Montana and the northern Great Plains of Montana, North Dakota, and South Dakota. The synthesis is organized to align with the standard elements of NEPA analyses and provides information on relevant scientific studies, data availability, analysis methods, and mitigation measures. We found that the likelihood of increasing IAGs from vegetation treatments depends on treatment type and environmental context. In sagebrush ecosystems of the focal region, prescribed fire often reduces or does not increase IAGs. Treatments that cause soil disturbances, such as mechanical removals of sagebrush or firebreak constructions, are more likely to increase IAGs than other treatments. Herbicides applied to reduce sagebrush cover have not increased the proportion of IAGs in the plant community. Temperature and precipitation have been strong factors in determining IAG responses to vegetation treatments in sagebrush ecosystems of the focal region, where more precipitation in spring and summer likely provides a competitive edge to native, perennial grasses more than winter annual grasses like Bromus tectorum L. (cheatgrass). In grasslands, prescribed fire often reduces IAGs, but effects depend on the abundance of native species and are often short lived. Mowing can increase or decrease IAGs in grassland ecosystems. Grassland site conditions, such as southeast-facing slopes, sandier or rockier sites, or lower native species cover or richness affect the likelihood of invasion by annual grasses. Maintaining adequate cover of perennial vegetation creates rangelands that are resistant and resilient to annual grass invasions. Managers can minimize invasion potential by focusing on treatment type, placement, and seasonal timing. Herbicides also can provide effective mitigation, especially in combination with other controls such as prescribed fire or grazing. This report can be incorporated by reference in NEPA documentation, included in a project record, or provide a general reference for understanding and identifying literature about increases in IAGs associated with vegetation treatments in rangelands in this focal region.

Suggested Citation

Johnston, A.N., Wood, D.J.A., Ebenhoch, K.G., Rutherford, T.K., Maxwell, L.M., and Carter, S.K., 2025, Potential risks of vegetation treatments to introduce and increase invasive annual grasses in rangelands of Montana, North Dakota, and South Dakota—A science synthesis to inform National Environmental Policy Act analyses: U.S. Geological Survey Scientific Investigations Report 2025–5058, 36 p., https://doi.org/10.3133/sir20255058.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Executive Summary
  • Purpose of This Report
  • How to Use This Report
  • Caveats to Use of This Report
  • Science Synthesis—The Potential for Vegetation Treatments to Introduce and Increase Invasive Annual Grasses
  • Methods For Developing This Science Synthesis
  • References Cited
  • Glossary
Publication type Report
Publication Subtype USGS Numbered Series
Title Potential risks of vegetation treatments to introduce and increase invasive annual grasses in rangelands of Montana, North Dakota, and South Dakota—A science synthesis to inform National Environmental Policy Act analyses
Series title Scientific Investigations Report
Series number 2025-5058
DOI 10.3133/sir20255058
Publication Date September 29, 2025
Year Published 2025
Language English
Publisher U.S. Geological Survey
Publisher location Reston VA
Contributing office(s) Northern Rocky Mountain Science Center
Description ix, 36 p.
Country United States
State Montana, North Dakota, South Dakota
Online Only (Y/N) Y
Additional publication details