Project : USDA ARS

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Research Project: Development of Ecological Strategies for Invasive Plant Management and Rehabilitation of Western Rangelands

Location: Great Basin Rangelands Research

2025 Annual Report

Objectives
The Great Basin covers approximately 54 million hectares of the western United States with ranching, mining, and recreation as the primary economic activities. Invasive annual grasses and expanding native conifer populations have significantly altered ecosystems on over 20% of the Great Basin. Changes in plant type and cover, together with climate variability, drought, and land conversion have resulted in dramatic reductions in available forage and wildlife habitat, while increasing the frequency and intensity of wildfires. Public awareness of the impacts of invasive weeds has produced conflicts regarding proper rangeland management strategies. The research proposed here will produce critical data regarding the development of complementary control strategies to address 1) biological, chemical, and cultural control of the most important invasive annual grass species: cheatgrass (Anisantha tectorum), red brome (A. rubens), and medusahead (Taeniatherum caput-medusae); and 2) the effects of woodland encroachment on water resource availability. Research will focus on the discovery and evaluation of arthropods as biological control agents against invasive annual grasses; development of methods to revegetate rangelands degraded by wildfire with plant species that can prevent reinvasion of annual grasses and other noxious weeds, while enhancing biological diversity and forage for grazing animals; and assessment of water use by native conifer populations that are replacing grazable range. Resulting management guidelines and tools will facilitate sustainable delivery of goods and services from Great Basin ecosystems to agricultural producers and land managers, while mitigating the deleterious effects of weeds and wildfires. Objective 1: Discover and evaluate new biological control candidates for invasive annual grasses i.e., medusahead, cheatgrass, and red brome to develop new biological control strategies. [NP304, C2, PS2B] · Sub-objective 1A: Conduct field surveys to discover, identify, and collect natural enemies of medusahead, cheatgrass, and red brome. · Sub-objective 1B: Evaluate candidate biological control agents of medusahead, cheatgrass, and red brome for their suitability for release in the Great Basin and adjacent invaded regions. Objective 2: Analyze the distribution of limited resources critical for plant growth between native and invasive plants, soil properties, and hydrologic processes on degraded rangelands to improve rangeland conservation and rehabilitation strategies. [NP304, C2, PS2B] · Sub-objective 2A: Assess the effects of pre- and post-emergent herbicides on invasive cheatgrass populations and on the rehabilitation of ecosystems after wildfire. · Sub-objective 2B: Investigate and quantify critical water resources of rangelands, including water use of pinyon and juniper and hydrologic responses of a meadow to tree control.

Approach
Foreign surveys for natural enemies of medusahead, red brome and cheatgrass in their native ranges will be conducted by a team of collaborators led by ARS-Reno, in coordination with European and other ARS partners. Efforts will be made to visit each surveyed target weed population at least once in all seasons over the course of the project in order to observe all plant phenological stages and their associated natural enemies. New natural enemies of targeted annual grass species that are discovered in the course of these surveys will be prepared for evaluation as candidate biocontrol agents (CBCAs), including testing of host-range and the potential for each CBCA to reduce target weed populations. Target weed populations will also be surveyed in the Great Basin to determine if native-range natural enemies are already present. Genetic markers will be used to reveal precise relationships between geographically separated populations of CBCAs. The efficacy of three soil-active pre-emergent herbicides, Imazapic (Plateau), Sulfometuron methyl-Chlorsulfuron (Landmark XP), and Indaziflam (Esplanade), to reduce cheatgrass and its associated seed bank will be tested. Herbicides will be applied in the fall on two recently-burned Wyoming-sagebrush sites, as well as on adjacent unburned areas infested with cheatgrass. Seed mixes (native and introduced species) will also be evaluated for their ability re-establish persistent, desirable plant communities. A weather will be established station at each research site to record amount and time of precipitation events. Plant and soil attributes will be measured bi-monthly over the entire year. Foliar cover, seedling emergence, mortality, persistence, and density of all test plant species, as well as cheatgrass seed bank density, will be estimated and species diversity and richness will be calculated. Effects of herbicides and seeding treatments on native plants, invasive species, biological soil crust, and soil properties will be evaluated. Pinyon and juniper trees will be instrumented with heat dissipation probes to measure transpiration at Porter Canyon Experimental Watershed (PCEW) in plant communities dominated by pinyon-juniper, sagebrush steppe, and meadows (where groundwater springs occur). Locations will include a valley bottom site and east- and west-facing hill slopes. Additional trees will be instrumented with variable depth probes to control for reductions in flow with depth of xylem area. Stems will be collected from trees to extract xylem water to determine the source of transpiration water from these trees using stable isotopic analyses of hydrogen and oxygen in plant xylem water. In addition, the effects of mechanical tree removal on a downslope meadow system will be quantified by measuring changes in ephemeral flow and groundwater levels relative to eight years of baseline data. Vegetation transects will be measured annually to quantify tree removal treatments on groundwater depth, soil, moisture, meadow community composition, and peak of seasonal greenness

Progress Report
This the final report for project 2060-22000-025-000D, “Development of Ecological Strategies for Invasive Plant Management and Rehabilitation of Western Rangelands” which is scheduled to expire in October 2025. A new project titled, “Improving Invasive Plant Control and Rehabilitation Techniques in Western Rangelands” is currently undergoing OSQR review/certification. Progress was made on Objective 1 by in-country collaborators in the weeds’ native ranges despite international travel delays due to COVID-19. Establishment of laboratory colonies of recently discovered biocontrol candidates of cheatgrass and medusahead was impossible due to travel restrictions; however, field collections of targeted invasive weeds in California, Idaho, Nevada, Oregon, and Washington were achieved to discover natural enemy populations of targeted weeds in their invaded ranges in the western United States. A new laboratory protocol for rapidly assessing field-collected weed samples for the presence of insect and mite natural enemies, emulating established environmental DNA (or “eDNA”) protocols from other fields of study was conceived. A significant advancement was made in a subordinate project with the taxonomic description of a mite that was previously collected from cheatgrass in Bulgaria and Serbia as a new species to science. This indicates that this mite has never been recorded as an agricultural pest before; if it had, it would have been described as a species. Therefore, it is unlikely to present an important risk to cereal crops if it is eventually approved for release as a biocontrol agent of cheatgrass. Due to the relocation of the Research Entomologist to a different ARS location, who was responsible for Objective 1, no additional progress was made beyond FY 2022. For Sub-objective 2A1, progress was made on the testing of three separate pre-emergent herbicides, imazapic, sulfometuron-methyl-chlorosulfuron, and indaziflam on their efficacy in controlling the exotic and invasive annual grass, cheatgrass. Pre-emergent herbicides effectively controlled and reduced cheatgrass on treated habitats, on average, by more than 96%. Following pre-emergent herbicide applications, the successful seeding of perennial grasses increased perennial grass densities more than 600%. This increase in perennial grass densities has resulted in effective and continued suppression of cheatgrass through resource competition, resulting in reduced cheatgrass associated fuel loads as well as improved nutritional perennial grass forage. The integrated approach of effective weed control practices and perennial grass establishment reduces wildfire threats associated with cheatgrass invasions, while also improving grazing and wildlife resources. Data was presented at national and regional meetings, field tours, and was highlighted by the Institute for Managing Annual Grasses Invading Natural Ecosystems (IMAGINE) 2025 Workshop. In support of Sub-objective 2A, Experiment 2A2, ARS researchers in Reno, Nevada, evaluated the use of herbicide and seeding treatments after wildfire. Two common post-fire rehabilitation treatments in areas prone to annual grass invasion include herbicide application and subsequent seeding with perennial species. Although this is common practice, we lack knowledge on how these combined treatments affect plant communities and soil properties. ARS researchers established an experiment on the Strawberry fire near Great Basin National Park in collaboration with the Bureau of Land Management and the National Park Service to assess the effects of herbicide and seeding treatments. In a factorial design, they applied two herbicide (glyphosate) treatments and three native seeding treatments at two seeding rates. Unburned plots were also established outside the fire perimeter as a control. Both plant communities and soil physical characteristics were measured for six years to understand long-term responses. First, seeding method and rate had minimal effects on plant cover or perennial plant densities. The pipe harrow seeding method reduced biological soil crust cover and decreased soil stability. Soil stability was dramatically decreased by wildfire and stability remained low over the six years. Herbicide reduced cheatgrass cover in the first three years, but effects were lost in years 4-6. Perennial grass cover was initially not affected by herbicide but increased in herbicide plots in years 4-6. Results were presented at national conferences and were spotlighted in a field tour with the ‘Results Oriented Grazing for Ecological Resilience’ working group along with a fact sheet. Further progress has been achieved on the manuscript for submission. In support of Objective 2, progress was made on Sub-objective 2B: Investigate and quantify critical water resources of rangelands: assess water use of pinyon and juniper, as well as the hydrologic responses of a meadow to tree treatments. Weed challenges in the Great Basin are not limited to exotic or annual species. Since the 1850s, native conifers (juniper and pinyon) have been infilling existing woodlands and expanding into sagebrush steppe. Efforts to reduce woody plant encroachment have been undertaken by multiple land management agencies and private producers, that are concerned with the reduction in forage for domestic grazing, increased wildfire risk, increased soil erosion, and a reduction in water availability for desirable plant communities. Over the lifetime of this project, multiple experiments and long-term instrumentation were used to examine the abiotic and biotic effect of tree control treatments at the Porter Canyon Experimental Watershed. A manuscript was submitted on the water use requirements of pinyon and juniper which utilized five years of continuous data from trees instrumented with sap flow probes. In addition, this information was distilled into a fact sheet to distribute to stakeholders. In prior years of this project, manuscripts were published examining the phenological changes in meadows using phenocams to assess phenology. There was strong agreement between phenocam metrics of greenness and measures of plant production and vigor obtained from satellite-based imagery from the Landsat archive. Furthermore, the effect of soil water availability and different grazing management strategies were discernible in the phenology curves derived from phenocam imagery. Manuscripts were also published on the redistribution of rainfall by sagebrush and the use of rainfall-generated stemflow water by pinyon and juniper.

Accomplishments
1. Improving restoration practices to reduce wildfire threats. Great Basin rangelands are experiencing nearly 70% loss of core big sagebrush plant communities that are being converted to exotic and invasive annual grasses, particularly cheatgrass. The accidental introduction and subsequent invasion of cheatgrass to Great Basin rangelands has increased the chance, rate, spread and season of wildfires. Fighting these wildfires, as well as post-fire restoration, costs nearly $40 million annually. ARS researchers in Reno, Nevada, have been testing pre-emergent herbicides to reduce cheatgrass densities and improve restoration of perennial grasses for long-term suppression of cheatgrass. On average, pre-emergent herbicides effectively reduced cheatgrass densities by 96.4%, allowing for an increase of more than 600% in initial emergence and establishment of desirable perennial grasses on arid Great Basin rangelands. This research has significantly increased perennial grass densities, converted annual grass dominated communities back to a perennial grass state, and significantly reduced cheatgrass fuel loads by more than 93%. A reduction in cheatgrass-associated fuels significantly reduces the risk and severity of wildfires, while substantially improving sustainable grazing and wildlife resources.

U.S. DEPARTMENT OF AGRICULTURE

Great Basin Rangelands Research: Reno, NV