Location: Great Basin Rangelands Research
2022 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
Research in support of Objective 1 continued but was delayed due to COVID-19, with the inability of ARS scientists and foreign collaborators to conduct essential international travel in the Eurasian native ranges of the targeted weeds species. Substantial progress was made on Sub-objective 1A by in-country collaborators in the weeds’ native ranges, but still much less than under normal circumstances. Establishment of laboratory colonies of recently discovered biocontrol candidates of cheatgrass and medusahead, a key goal of most other planned fiscal year (FY) 2021 research in Objective 1, was impossible due to travel restrictions, but we hope to resume work in Spring 2023. 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 relates to Objective 1 because it 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. Collections of targeted invasive weeds were made in California and Nevada, in order to monitor the presence and extent of 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 and is currently under development.
Progress was made in support of Sub-objective 2A, where repeated years of herbicide and seeding applications were performed to test three separate pre-emergent herbicides for their efficacy on cheatgrass control and success in allowing targeted seeded species to germinate and grow following the herbicide applications. Soil samples continued to be collected and soil health continued to be monitored to measure available soil resources, such as available nitrogen and soil moisture. Bioassay samples were collected to record cheatgrass seed bank densities and seeded species densities was also recorded to monitor initial survivability of native and introduced perennial grasses. Although the region is experiencing drought conditions, more favorable precipitation resulted in adequate initial seedling emergence and survivability. Adequate establishment of perennial grasses should result in a decrease of cheatgrass densities and associated fuels. Effective weed control treatments should reduce wildfire threats, increase sustainable grazing resources and improve wildlife habitats. Preliminary data was presented at an international meeting as well as a stakeholder field tour. 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.
In additional support of Sub-objective 2A, we 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, we applied two herbicide treatments, three native seeding treatments at two seeding rates. Unburned plots were also established outside the fire perimeter as a control. Plant cover, plant height, gap intercept, and biological soil crust cover were measured at the peak growing season. To characterize the physical environment of the soil, we installed soil moisture and temperature probes, and measured soil stability and soil surface roughness. The methods portion of the manuscript has been written. Preliminary analyses showed wildfire reduced total biotic cover from 25 to 5% but was not affected by glyphosate. Cheatgrass was higher in burned areas than unburned areas and glyphosate initially reduced cheatgrass cover but only from 8 to 5%. Seeding rate had no effect on total biotic or seeded species cover. Soil stability was substantially lower in burned plots but was not affected by glyphosate or seeding. Soil microrelief was not affected by wildfire, glyphosate, or seeding.
Progress was made on Sub-objective 2B and subordinate project #2060-22000-025-06I: 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. This reduces herbaceous forage, alters wildlife habitat, accelerates surface runoff and soil erosion, increases woody fuel loads, and increases risk of catastrophic wildfires, with significant loss of ecosystem services. Of great concern to land managers in arid environments is the amount of water used by plant species. Eight years of data were collected from both pinyon and juniper trees instrumented with heat dissipation probes to measure tree sap flow velocity and the total volume of water used by these species. These data are now fully cleaned and processed. Initial results were summarized and presented in an outreach meeting to stakeholders. This project is synthesizing data sets of plant water use, stomatal conductance, soil moisture and weather data from multiple locations. Two manuscripts are being prepared with these data that look at: 1) contrasts between co-occurring pinyon and juniper trees in response to drought and heat waves, and 2) relationships between plant water use strategies and time lags between stomatal sensitivity to vapor pressure deficit and heat events.
Progress was made on subordinate projects #2060-22000-025-07I and #2060-22000-025-08A. These projects address the decline of North America’s sagebrush biome, which has been at an alarming rate due to exotic annual grasses promoting large-scale catastrophic wildfires, which not only burn the degraded areas where the fires initiate but spread into native plant communities, which creates more disturbed areas for exotic annual grasses to colonize. Effective methods for seeding native vegetation back into degraded sagebrush systems is needed to prevent weed invasion and arrest this invasive plant-fire cycle. Unfortunately, success rates for reestablishing native plants from seed in disturbed sagebrush systems is less than desirable, and seeding success is predicted to further decline with climate change increasing aridity and more erratic precipitation. To sustain the ecological integrity and economic vitality of the sagebrush biome it is of upmost importance that new technologies be developed that can improve arid land seeding success. Our collaborator at Brigham Young University successfully installed and monitored plots seeded with native species and coated with different seed coatings over two growing seasons. Some of these plots were located within the Martin Fire in Nevada. These seed coatings are to hopefully increase the germination and emergence of native species in areas that have recently experienced catastrophic fire. Fungicide seed coatings increased seedling emergence 73% of the time across all the study sites and sampling years. Overall, these results indicate that fungicide seed coatings have the potential to improve dryland restoration efforts.
Accomplishments
1. Diversity of seed-feeding insects in juniper species associated with severe wildfires reveals global evolutionary trend. Populations of juniper species in the western United States have increased in density and geographical distribution in recent decades, encroaching on productive range and contributing to increases in the intensity and size of wildfires. ARS researchers in Reno, Nevada, collected and identified more than 60 species of insects, plus one new mite species, from berries of California, western, and Utah junipers. Many of these insects, as well as the mite, are damaging to seeds and thus affect density and spread of these tree populations. Comparison of insects collected from these three juniper species with insects reported in the literature from Virginia juniper (from eastern North America) and two Mediterranean juniper species revealed remarkable parallel evolution of related insects occupying the same berry niches in the six far-flung juniper species. This was a significant finding in the field of evolutionary ecology, in addition to having important real-world applications. Given the growing role of junipers in western wildfires, this new knowledge could lead to new management strategies for reducing viability of juniper seeds and limiting spread of these trees.
Review Publications
Clements, D.D., Harmon, D.N., Blank, R.R. 2022. Seed mix performance and cheatgrass suppression on arid rangelands. Rangelands. 44(2):129-135. https://doi.org/10.1016/j.rala.2022.02.003.
Newingham, B.A., Kachergis, E., Ganguli, A.C., Foster, B., Price, L., McCord, S.E. 2021. Lessons given and learned from rangeland monitoring courses. Rangelands. 44(1):29-38. https://doi.org/10.1016/j.rala.2021.08.003.
Haddad, M., Strohmeier, S.M., Nouwakpo, S.K., Rimawi, O., Weltz, M.A., Sterk, G. 2022. Rangeland restoration in Jordan: Restoring vegetation cover by water harvesting measures. International Soil and Water Conservation Research. https://doi.org/10.1016/j.iswcr.2022.03.001.
Pyke, D.A., Schaff, S.C., Chambers, J.C., Schupp, E.W., Newingham, B.A., Gray, M.L., Ellsworth, L.M. 2022. Ten-year ecological responses to fuel treatments within semiarid Wyoming big sagebrush ecosystems. Ecosphere. 13(7). Article e4176. https://doi.org/10.1002/ecs2.4176.
