Location: Livestock and Range Research Laboratory2018 Annual Report
Objective 1: Develop management strategies to improve rangeland cattle production and ecological stability in the northern Great Plains through effective use of rangeland forage resources, precision supplementation, and livestock with greater adaptability to climatic, physiological, and nutritional stress. Sub-objective 1.1 Determine effects of dormant rangeland forage utilization on heifer development, plant productivity, and species composition. Sub-objective 1.2 Develop nutritional management for post-weaning heifer development to complement annual and weather-driven fluctuations in forage availability and quality. Sub-objective 1.3 Estimate effects of vegetation, climate, and environmental variables on cattle growth. Sub-objective 1.4 Develop mineral supplement and water amendment strategies to ameliorate weather-induced changes in naturally occurring rangeland stock water quality. Sub-objective 1.5 Develop a molecular barcode system for northern mixed-grass prairie plant species that will enable future description of plants consumed by livestock on rangelands. Objective 2: Develop management strategies integrating grazing, fire, and chemical practices to restore rangelands degraded by weeds and prevent weed invasions in the northern Great Plains. Sub-objective 2.1 Develop fire and herbicide treatment combinations to reduce annual brome abundance in rangelands. Sub-objective 2.2 Develop effective practices to rehabilitate rangeland riverine sites that have been mechanically and chemically treated to eradicate Russian olive. Sub-objective 2.3 Identify and develop effective reclamation strategies for converting coal mining lands back to livestock grazing lands. Sub-objective 2.4 Determine physiological traits allowing perennial seedlings to use dormancy to survive unfavorable environmental conditions. Objective 3: Develop adaptive strategies for managing the interacting effects of livestock grazing, fire, and climatic variation on northern Great Plains rangelands to increase the stability of livestock production while maintaining ecosystem health. Sub-objective 3.1 Quantify grazing season and intensity effects on plant community composition and productivity. Sub-objective 3.2 Quantify interacting effects of climate with defoliation timing and intensity on rangeland stability. Sub-objective 3.3 Determine rangeland community response to autumn defoliation intensity. Sub-objective 3.4 Determine post-fire weather effects on plant community response to summer fire. Sub-objective 3.5 Determine the effect of mycorrhizal fungi and different levels of simulated grazing on plant community composition and measures of soil health. Sub-objective 3.6 Determine plant and soil community response to fire return interval and seasonality.
Sustainability of rangeland production hinges on the stability of plant communities because changes in species composition, forage production, and forage quality fundamentally affect the animal community. The primary forces of change in rangelands are weather, grazing, alien plants, and fire. 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 interacting effects of disturbances with weather and climate. We propose 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 will be included in multiple experiments to determine weather and long-term climate effects because precipitation is the primary controlling factor for plant productivity and community composition. Experiments 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 the mechanisms that control rangeland stability and animal responses to alterations in plant communities will assist land managers and livestock producers in improving rangeland integrity and efficiency of livestock production. Results will also provide scientists greater understanding of the complex interacting forces on rangelands.
Research for the 5-year period supported National Program 215 Component I (Improved Rangeland Management for Enhanced Livestock Production, Conservation, and Ecological Services) by addressing Action Plan Objective A.1 (Develop sustainable rangeland livestock production systems that are economically viable, conserve natural resources, and are adaptable to changing environmental conditions); Objective B.1 (Develop strategies and practices for conserving healthy rangelands and restoring degraded lands under changing environmental conditions to meet a variety of ecosystem services objectives); and Objective C.1 (Improve understanding of the fundamental relationships among management practices, ecological processes, and climatic variability to improve rangeland production, conservation and restoration). Under A.1 we quantified water temperature effects on cattle and the variability in water quality in space and time. Limitations of applying National Research Council cattle nutrition requirements for protein and energy to rangeland systems were identified. Substantial progress was made describing temperature and precipitation effects on cattle production and behavior. Progress was made in developing a molecular barcoding system for northern mixed prairie that will allow calculation of cattle diet composition. Digestion experiments have been completed and DNA has been extracted for 311 plant species. Under B.1, we developed grazing, herbicide and fire management tools for controlling weed species and promoting desirable plants. Techniques were developed to sterilize seeds of weedy annual grasses (Japanese brome, cheatgrass, medusahead, and ventenata) with low herbicide doses. Assessment of numerous long-term restoration projects helped identify successful restoration techniques and driving variables for restoration failures. Progress has been made in strategically combining species with different seed or seedling traits to increase chances of achieving adequate plant establishment during ecological restoration. Reducing grass seeding rates is showing promise in increasing shrub establishment without diminishing success of grass stands. We established that fire can be used to selectively control weeds and pest grasshopper species, providing potential for less impact on non-target species than chemical treatments. Fire reduced the unpalatable species, purple threeawn, and increased forage quality to levels comparable to more preferred species so surviving plants are more likely grazed. Results are being applied by Bureau of Land Management. Under C.1, we established that northern mixed prairie can be grazed the first growing season following fire without detriment to the rangeland. Before this work, federal agencies required 1-3 years of rest following fire. We determined that soil aggregate stability is an uncertain predictor of infiltration and forage production in northern mixed prairie and that rangeland health assessment systems require validation. We determined that plant species in the Northern Plains are less responsive to mycorrhizal fungi than expected based on work from the Central Plains, that plants are limited by phosphorus, and areas where phosphorus is likely limited have lower levels of mycorrhizal fungi. We have observed a strong relationship between spring precipitation and vegetation production, but in contrast to shortgrass and tallgrass prairies, northern mixed prairie biomass was not responsive to extreme rainfall events. Significant progress was made in examining numerous fundamental relationships of fire with soil nutrients, axillary bud production, and soil microbes. Buds of dominant grass species were determined to be responsive to seasonal timing of fire, in some cases, within 24 hours. This continuing work is providing a mechanistic understanding of how fire affects species and species composition.
1. Seeding and herbicides establish native plants in downy brome-invaded landscapes. Managers are struggling to restore native plants to degraded rangelands invaded by downy brome and other invasive weeds with the end goal of increasing livestock forage production and improving wildlife habitat. ARS scientists in Miles City, Montana collaborating with Montana Department of Environmental Quality and the coal mining industry seeded native grasses, forbs and shrubs after using herbicides to control downy brome in former coal mining fields that became dominated by downy brome after initial seeding efforts failed. The herbicide glyphosate applied in fall just after downy brome emerged substantially reduced downy brome cover and promoted native grass and forb establishment. Additionally, this same glyphosate treatment allowed establishment of big sage, among the most difficult and important species to restore to western U.S. rangelands.
2. Fire and grazing effects are independent of grazing history. Removal of livestock is often suggested to help recover degraded rangelands. Removal of large grazers from rangelands that evolved with significant grazing pressure can alter natural processes and may change the magnitude or direction of community responses to other disturbances that follow. ARS scientists in Miles City, Montana applied six levels of disturbance with combinations of fire (fall fire or no fire) and grazing utilization (0, 50, or 75% biomass removal) to moderately grazed pastures and paired areas that had livestock excluded for 15 years to determine grazing history effects on rangeland response to disturbance. Livestock exclusion increased cool-season perennial grass 26% and forb biomass 179% and reduced warm-season perennial grass 80% with no effect on total current-year biomass. Diversity was greater in grazed pasture than exclosures. Every biomass, cover and diversity measure was affected by fire, grazing utilization, or both except sub-shrub biomass. Contrary to expectations and despite numerous treatment effects, grazing history only impacted fire effects for old standing dead material and effects on grazing utilization were limited to old dead, bare ground, richness and dominance. Fire reduced annual grass 53%, forbs 37% and diversity with no differences in total current-year biomass. Grazing to 75% utilization reduced total current-year biomass 11%. Limited interaction among disturbances indicates effects of livestock exclusion were not sufficient to alter change in biomass or diversity in response to fire or grazing utilization. Grazing history affected starting points for most variables, but changes caused by grazing utilization or fire were similar between pastures and exclosures, indicating management decisions can be made based on independent knowledge of grazing or fire effects.
3. Successfull rangeland restorations following disturbance depends on the presence of helpful soil biology (mycorrhizas=root fungi). Some believe invasive alien plants are less dependent on mycorrhizal associations than native plants and that weak mycorrhizal responsiveness may be a general mechanism of plant invasion. ARS scientists in Miles City, Montana determined from experiments on 68 grassland species from the Northern Plains and 95 species from the Central Plains that mycorrhizas increased the biomass of 19% and 61% of species, respectively. However, plants from the Northern Plains tended to have varied responses to mycorrhizas, suggesting varied resource allocation strategies when roots are colonized by mycorrhizal fungi. Findings indicate that many plant species may have difficulty establishing into areas with degraded soil biology. Some plants for the Northern Plains region appeared to be less dependent on mycorrhizas, suggesting they may be more likely to establish into areas with degraded soil biology. Invasive grassland plants had a wide range of interactions with mycorrhizas and some are likely to degrade the quality of a site's soil biology. There was no evidence that invasive species respond differently to mycorrhizas than native species. Results will facilitate restoration efforts by informing managers of circumstances when soil management actions are beneficial to their desired species mix.
4. Wet and dry years naturally occurring livestock water quality. Water quality consumed by livestock reflects both the mineral content of the surface soil, subface soil and rock and bedrock. Precipitation events may accelerate solubilization of those minerals or concentrate them through evaporation. To minimize losses due to mortality or reduced production, water sources need to be rapidly tested prior to livestock turn out into fresh pastures. Existing technology was applied to test water quality instantaneously with hand-held meters. University Extension agents, NRCS range conservationists, ranchers and nutritionists have adopted rapid testing technology developed by ARS scientists in Miles City, Montana to test water quality in real time to avoid the consequences of cattle consuming water of poor quality.
5. Massive seed banks limit Russian olive control. Land managers throughout the West are having difficulty controlling Russian olive trees and reinvading seedlings. ARS researchers from Sidney and Miles City, Montana with NRCS (Miles City and Bridger Montana) determined successful practices for controlling invasive Russian olive populations and returning native species to these degraded areas, finding that using a tree shear and immediate herbicide application to the cut stump resulted in 96% Russian olive mortality. Because Russian olive is a nitrogen fixer, we expected high weed abundance to limit the success of planted native species in this N- and P-limited ecosystem. However, revegetation was successful: almost all planted species established. Although revegetation increased native species diversity and cover, there was no evidence that the plantings served to competitively exclude weeds in this five-year study. Exponential variation in newly-emerged Russian olive seedlings (approximately 50-5000 seedlings per acre) in the removal area every year of the study indicates that understanding seed banks of this species is critical to its control.
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