Research Project: Development of Management Strategies for Livestock Grazing, Disturbance and Climate Variation for the Northern Plains

Location: Livestock and Range Research Laboratory

2020 Annual Report

Objectives
Objective 1: Develop management strategies to improve rangeland cattle production and ecological stability through effective use of rangeland forage and supplementation. Subobjective 1A: Determine effects of dormant rangeland forage utilization on heifer development, young cow productivity, plant productivity, and species composition. Subobjective 1B: Determine effects of seasonal rangeland forage utilization by steers and heifers during backgrounding on estimates of respiration gas. Subobjective 1C: Determine timing of grazing season and grazing intensity effects on plant productivity, community composition and cattle diet quality. Subobjective 1D: Enhance the accuracy of DNA metabarcoding to assess diet composition. Subobjective 1E: Evaluate factors regulating calf growth on rangelands. Objective 2: Develop management techniques to improve stock water quality in reservoirs by manipulating plant and microbiota abundance. Objective 3: Develop management strategies to restore degraded rangelands and prevent weed invasions. Subobjective 3A: Develop bacterial management strategies to reduce invasive bromes. Subobjective 3B: Improve vegetation outcomes on Conservation Reserve Program lands. Subobjective 3C: Design seed mixes to more consistently meet plant establishment goals during rangeland restoration. Subobjective 3D: Identify seasonal grazing effects on revegetation following Russian olive removal. Objective 4: Identify cool-season perennial grass seed rates that are high enough to prevent weed invasions and low enough to allow establishment of diverse plant communities on disturbed rangelands. Subobjective 4A: Identify cool-season grass seed rates needed to prevent weed invasions and allow seeded shrub establishment during rangeland restoration. Objective 5: Determine the effect of subsurface soil calcium carbonate on available phosphorus, plant biomass, root traits, and mycorrhizal responsiveness. Objective 6: Develop fire management strategies to maintain and improve rangeland stability and livestock production. Subobjective 6A: Determine perennial grass response to timing of fire relative to plant phenology. Subobjective 6B: Quantify drought and post-drought fire effects on plant community composition and productivity. Subobjective 6C: Determine how seasonal timing of fire affects forage quality and cattle grazing preference.

Approach
Sustainability of rangeland production hinges on the ability of plant communities to resist change and quickly recover from disturbance (stability) because changes in species composition, forage production, and forage quality fundamentally affect the animal community. Primary forces of change in rangelands are weather, grazing, alien plants, fire and their interactions. This project is designed to improve ecological sustainability and rangeland production by addressing opportunities for increased efficiency of livestock nutrient conversion, mechanisms affecting restoration success and weed control, and interacting effects of management with weather. Improved efficiency of nutrient conversion from dormant rangeland forages is among the most viable options for increasing animal production and minimizing effects on plant communities. We will address this proposition through a series of experiments evaluating plant and animal responses to dormant-season utilization and supplementation strategies. Rangeland restoration methods will be evaluated for direct weed control and mechanisms controlling successful establishment of desirable species. Water manipulations and historical weather data will be included in experiments to determine weather and long-term climate effects on plants and livestock because precipitation is the primary controlling factor for plant productivity and community composition. Fire research will focus on timing of fire (seasonal and phenological) to facilitate development of fire prescriptions that reduce weedy species, promote desirable species, and increase availability of quality forage. Scientists will be integrated across objectives to determine interacting effects of precipitation, grazing, weeds, and fire on soil and plant communities (production, species composition, diversity, propagation, survival) and cattle (weight gain, reproductive performance, diet quality, diet selection). Understanding mechanisms that control rangeland stability and animal responses to alterations in plant communities will assist land managers and livestock producers in improving rangeland integrity (diverse communities dominated by native species) and efficiency of livestock production. Results will also provide scientists greater understanding of the complex interacting forces on rangelands.

Progress Report
Objective 1A: Data were collected on individual supplement intake, animal productivity, plant productivity and species composition. Modifications based on the previous year trials proved effective in recording more animals at the feeders. Objective 1B: Additional training was attempted to get better use of the feeder and more data from the respiration gas instruments. Those attempts were unsuccessful for a second year. Objective 1C: Vegetation samples were collected and growing season grazing treatments and diet samples were completed. Data have been analyzed for the initial experiment. Objective 1D: Lab time has been limited by COVID-19-related restrictions, which has delayed PCR analyses. Objective 1E: We completed our analysis of factors regulating calf growth. Due to forage quality dynamics, calves weaned at 180 days of age weigh 1 lb. less for each day later they are born in spring. Objective 2: The water quality study was reassigned following the retirement of the lead scientist. The field project was redirected because sulfate concentrations shifted in the high sulfate reservoir. The revised study grows plants on a floating island in a stock tank filled with high sulfate water from another reservoir to compare sulfate concentrations (mg of sulfur per g of biomass) and stocks (g sulfur per plant) of nine plant species. Objective 3A: The weed-suppressive bacteria study on annual bromes is complete. Objective 3B: Twelve fields were enrolled in the Conservation Reserve Program project and all data collection was completed for those fields. Objective 3C: The fourth and final year of seeding was completed to identify more consistently effective seed mixes for rangeland restoration and all 2020 data were collected. Objective 3D: Russian olive tree removal started in spring 2020, and seeds from mature trees will be collected this fall for seeding the plots. Objective 4: Two replications were seeded and vegetation was sampled on all plots to begin pinpointing optimal grass seed rates for allowing shrub establishment. Objective 5: Initial mycorrhizal trap cultures yielded mycorrhizal morphotypes for only half of the focal plant species. A second set of modified trap cultures has been started. This has delayed the start of the experiment to determine effects of soil calcium carbonate on available phosphorus, plant production, and mycorrhizal responsiveness. Objective 6A: Growth trials were initiated at the Mandan location, but treatments were not applied because it was not yet possible to synchronize growth stages of the 6 species. If phenological stages cannot be synchronized with the next trial, fire treatments will be applied as each stage occurs for each species. Objective 6B: Drought treatments were applied and plots are prepared for fire treatments. The project is being extended 1 year because last year was very atypical in that there were record levels of sweetclover throughout the region and on the research site in particular. Objective 6C: Sites were prepared for fire treatments this summer. As with 6B, the project was delayed after the reporting period last year due to abundant sweetclover in the plots and resulting alterations in fuel structure. The project is proceeding 1 season off-schedule.

Accomplishments
1. Fall water effects on soil moisture and plant productivity. Understanding fall precipitation effects on rangelands can improve forage production forecasting and inform predictions of potential climate change effects. ARS researchers at Miles City, Montana, used a rainout shelter and water addition to test the effects of seasonal precipitation on soil water and production of cool-season perennial grasses, warm-season perennial grasses, annual grasses, and forbs. Treatments created conditions ranking among the driest and wettest September-October periods on record. Fall water effects on shallow (15 and 30 cm) soil water were not detectable by May. Effects persisted into July at depths below the primary root zone. The greatest effect of added fall water was increased weedy annual grass production. Even record high levels of fall water had minor effects on total biomass, functional group composition and soil water that were short-lived and overwhelmed by the influence of spring precipitation. Movement of fall water to deep soil before the growing season suggests plants that would most benefit from fall precipitation are those that could utilize it during fall (winter annuals), or deep-rooted species (shrubs).

2. Mowing is not a substitute for fire. Mowing is a common management technique sometimes considered a safer alternative to fire. To determine whether mowing can substitute for fire in rangeland, ARS researchers at Miles City, Montana, compared effects on plant biomass, composition, cover, soil nutrients, and forage quality. Production was similar among control, mowed and burned treatments, but mowing reduced cool-season perennial grasses 12% and increased forbs 8%. Non-native species were a larger component of mowed (12%) than control (6%) or burned plots (4%). Plant-available soil nitrogen and sulfur more than doubled with fire and there was a trend for more phosphorus in burned plots. Mowing affected 42% of the forage quality variables with a 2% average improvement across all variables and fire affected 84% of the variables, with a 12% average improvement. Mowing increased forage phosphorus and potassium, whereas fire increased forage concentrations of nitrogen, potassium, phosphorus, sulfur, magnesium, iron, manganese and copper. Digestibility increased 2.2% with mowing and 6.7% with fire. Although mowing can be a useful management tool, it is not a substitute for the ecological effects of rangeland fire.

3. Improving plant competition research. Models of plant-plant interactions underpin our understanding of species coexistence, invasive plant impacts, and plant community responses to climate change. In recent studies, models of competitive interactions failed predictive tests, thereby casting doubt on results of many past studies. We believe model failures are caused by variation in unobserved factors (e.g., nutrients, soil pathogens) that influence plants. Such heterogeneity is ubiquitous, and models that ignore it will suffer omitted variable bias. ARS scientists at Miles City, Montana, used instrumental variables analysis to test for and correct omitted variable bias in studies that followed common protocols for measuring plant competition. In an observational study, omitted variables caused competition to seem like weed and non-weed species benefitted from their interaction. In an experiment that partially controlled competitor abundances with seeding, omitted variables caused competition to seem about 35% weaker than it really was. Our research identified effective experimental and analytical methods for studying plant competition.

Review Publications
Vermeire, L.T., Strong, D.J., Gates, E.A., Marlow, C.B., Waterman, R.C. 2019. Can mowing substitute for fire in semiarid grassland. Rangeland Ecology and Management. 73(1):97-103. https://doi.org/10.1016/j.rama.2019.08.006.
Vermeire, L.T., Rinella, M.J. 2020. Fall water effects on growing season soil water content and plant productivity. Rangeland Ecology and Management. 73(2):252-258. https://doi.org/10.1016/j.rama.2019.11.006.
Rinella, M.J., Knudsen, A., Jacobs, J.S., Mangold, J.M. 2019. Seeding causes long-term increases in grass forage production in invaded rangelands. Rangeland Ecology and Management. 73(2):329-333. https://doi.org/10.1016/j.rama.2019.10.008.
Metier, E.P., Lehnhoff, E., Mangold, J., Rinella, M.J., Rew, L. 2019. Control of downy brome (Bromus tectorum) and Japanese brome (Bromus japonicus) using glyphosate and four graminicides: effects of herbicide rate, plant size, species, and accession. Weed Technology. 34(2):284-291. https://doi.org/10.1017/wet.2019.112.
Reinhart, K.O., Rinella, M.J., Waterman, R.C., Petersen, M.K., Vermeire, L.T. 2018. Testing rangeland health theory in the Northern Great Plains. Journal of Applied Ecology. 56:319-329. https://doi.org/10.1111/1365-2664.13273.
Rinella, M.J., Reinhart, K.O. 2019. Toward more robust plant-soil feedback research: reply. Ecology. 100(9):e02810. https://doi.org/10.1002/ecy.2810.
Rinella, M.J., Strong, D.J., Vermeire, L.T. 2020. Omitted variable bias in studies of plant interactions. Ecology. 101(6):e03020. https://doi.org/10.1002/ecy.3020.
Smart, A.J., Harmoney, K., Scasta, J.D., Stephenson, M.B., Volesky, J.D., Vermeire, L.T., Mosely, J., Sedivec, K., Meehan, M., Haigh, T., Derner, J.D., McClaran, M.P. 2019. Forum: Critical decision dates for drought management in central and northern Great Plains rangelands. Rangeland Ecology and Management. 1-10. https://doi.org/10.1016/j.rama.2019.09.005.
Stotz, G.C., Cahill Jr, J.F., Bennett, J.A., Carlyle, C.N., Bork, E.W., Askarizadeh, D., Bartha, S., Beierkuhnlein, C., Boldgiv, B., Brown, L., Cabido, M., Campetella, G., Chelli, S., Cohen, O., Diaz, S., Enrico, L., Ensing, D., Erdenetsetseg, B., Fidelis, A., Garris, H.W., Henry, H.A., Jentsch, A., Jouri, M.H., Koorem, K., Manning, P., Mitchell, R., Moora, M., Overbeck, G.E., Pither, J., Reinhart, K.O., Sternberg, M., Tungalag, R., Undrakhbold, S., van Rooyen, M., Wellstein, C., Zobel, M., Fraser, L.H. 2019. Not a melting pot: Plant species aggregate in their non-native range. Global Ecology and Biogeorgraphy. 29:482-490. https://doi.org/10.1111/geb.13046.
James, J.J., Sheley, R.L., Leger, E.A., Adler, P.B., Hardegree, S.P., Gornish, E.S., Rinella, M.J. 2019. Increased soil temperature and decreased precipitation during early life stages constrain grass seedling recruitment in cold desert restoration. Journal of Applied Ecology. 56(12):2609-2619. https://doi.org/10.1111/1365-2664.13508.