Location: Great Basin Rangelands Research2017 Annual Report
The Great Basin is the largest North American desert covering more than 50 million hectares. Major vegetation types in the Great Basin include: salt desert shadscale/greasewood, sagebrush/bunchgrass and mountain shrublands, pinyon/juniper woodlands, subalpine forests, and alpine tundra. The region has extremely variable climate both spatially and temporally and a complex mixture of public and private land ownership. Ranching, mining, and recreation form the basis of rural economies. Over 20% of Great Basin ecosystems have been significantly altered by invasive plants. This land conversion has resulted in dramatic reductions in forage availability, wildlife habitat, and biodiversity, has increased wildfire frequency and intensity, and altered the hydrologic cycle. Critical research needs addressed in this project are: (1) ecology and control of invasive weeds, (2) rehabilitation of degraded rangelands, (3) maintaining/enhancing healthy rangelands, and (4) quantifying the impact of management practices. Objective 1. Assess and quantify ecological conditions and biotic processes that maintain healthy rangelands, improve forage production, and enhance recovery of degraded sagebrush, and pinyon/juniper woodlands under uncertain climatic conditions in the Great Basin. • Sub-objective 1.1: Expand the ‘genetic toolbox’ to allow us to determine how the reproductive ecology of invasive annuals affects the structure and function of selected Great Basin ecosystems. • Sub-objective 1.2: Determine mechanisms underlying the expansion of native western juniper (Juniperus occidentalis) woodlands. Objective 2. Assess and quantify interactions between annual grasses and fire on watershed processes and ecosystem services under uncertain climatic conditions. Objective 3. Develop and transfer innovative management approaches and technology for conserving and rehabilitating sagebrush, pinyon/juniper woodlands, and salt desert shrublands to meet natural resource and agricultural production goals. • Sub-objective 3.1: Mechanistically understand how intact perennial grass communities resist invasion by annual grasses, especially cheatgrass. • Sub-objective 3.2: Provide management guidelines and transferable technologies to our stakeholders for establishing and enhancing native and introduced grasses, forbs, and shrubs in Great Basin ecosystems. Objective 4. Develop decision support tools for USDA to assess impact of type, location and number of management practices required to meet conservation and agricultural production goals nationwide. • Sub-objective 4.1: Enhance RHEM, KINEROS2, APEX, and SWAT models for assessing hydrology and erosion responses associated with management of disturbed vegetation states and transitions occurring on sagebrush-steppe ecological sites. • Sub-objective 4.2: As part of a national assessment, quantify soil loss on western rangelands.
Objective 1.1: Determine how the reproductive ecology of invasive annuals affects the structure and function of selected Great Basin ecosystems. Hypothesis: Occasional outcrossing facilitates expansion of cheatgrass across the intermountain west by selecting for new genotypes adapted to drier and more alkaline sites. IonTorrent® platform will be utilized to identify new single-nucleotide polymorphisms (SNPs) in cheatgrass to document if outcrossing is occuring. Objective 1.2: Determine mechanisms underlying the expansion of native western juniper woodlands. Hypothesis: Quantify rodent preferences to either juniper berries hand-collected or passed through the gut of a Robin and determine percent germination and seedling establishment between treatments. Objective 2: Assess and quantify interactions between annual grasses and fire on watershed processes and ecosystem services. Hypothesis: Conversion of Wyoming sagebrush community to cheatgrass, as a result of wildfire, will negatively alter runoff and erosion. Rainfall simulation will be used to quantify soil erosion in intact sagebrush and ecosystems converted to annual grass dominance and predict soil erosion with the Rangeland Hydrology and Erosion Model (RHEM). Objective 3.1: Mechanistically understand how intact perennial grass communities resist invasion by cheatgrass. Hypothesis: Healthy, robust, and intact perennial grass communities facilitate resistance to invasion by cheatgrass. Growth of cheatgrass will be contrasted in soil occupied by established perennial grasses and in unoccupied soil in greenhouse and field studies. Objective 3.2: Provide management guidelines and transferable technologies to our stakeholders for establishing and enhancing Great Basin ecosystems. Hypothesis: Combined application of appropriate soil-active herbicides and optimal plant materials will enhance revegetation/restoration success on cheatgrass-infested rangelands. Objective 4: Enhance ARS natural resource models (e.g. RHEM) for assessing hydrology and erosion responses associated with management of disturbed vegetation states and transitions occurring on sagebrush-steppe ecological sites. Hypothesis: Runoff and soil erosion will increase when either pinyon/juniper or annual grasses invade sagebrush-steppe ecosystems. An instrumented watershed, Porter Canyon in central Nevada, will be used to evaluate the impact of cheatgrass invasion and pinyon/juniper woodlands on surface runoff, soil loss and sediment yield. Data will be used to evaluate model performance and measure utility of model to assess conservation practices.
The mission of our research unit is to undertake basic and applied research to improve the health and sustainability of Great Basin rangelands. After an extended drought, the fall and winter of 2016-2017 brought exceptionally high precipitation. The Sierra Nevada Range had 200 percent and the Northern Great Basin received 130-200 percent of normal precipitation. Most of the Northern Great Basin had very high cheatgrass densities that suppressed growth of native grasses and later season forbs. Higher than normal precipitation encouraged early season forbs, shrub flowering, and seed production, which has benefitted mule deer populations and other wildlife. Growth of weedy fine fuel species, such as cheatgrass, has facilitated over 28 wildfires in Northern Nevada with over 800,000 acres burned. A major consequence of cheatgrass-fueled wildfires is the loss of sagebrush habitat for the greater sage-grouse. Our research unit conducts research to rehabilitate cheatgrass-degraded rangelands, including re-introduction of sagebrush to enhance habitat for the endangered sage-grouse and other wildlife. Besides the loss of vegetation for livestock and wildlife, wildfires increase the risk of post-fire soil erosion from wind and water. The potential magnitude of post-fire wind and water erosion on rangelands is also under investigation. Progress was made on all four objectives and their sub-objectives under National Program 215, Component I, Improved Rangeland Management for Enhanced Livestock Production, Conservation, and Ecological Services. Our research falls under: 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 service objectives. Objective B.2. Develop decision support tools usable at multiple scales including landscape levels for inventorying and assessing rangelands; and, for selecting, implementing, and monitoring conservation and restoration practices. Objective C.1. Improve understanding of the fundamental relationships among management practices, ecological processes, and climatic variability to improve rangeland production, conservation and restoration. Objective 1: We acquired DNASTAR Lasergene SeqNinja software and initiated bioinformatic analyses to determine genetic variation using markers known as single nucleotide polymorphisms (SNP) among numerous cheatgrass populations collected throughout the Great Basin and Mohave regions of Nevada in 2016. Completion of these analyses will allow us to identify hundreds of SNP and single sequence repeat (SSR) markers. Using analyses conducted to date, we initiated comparisons of SSR and SNP variation. Additional cheatgrass populations and several red brome populations were sampled in 2017 to expand the geographic coverage of our genetic studies of invasive annual grasses. Seed caching trials were completed with western juniper seeds at three field sites in Northeastern California. Several fruit-eating bird species (e.g., American robins, Townsend’s solitaires) consume berries and defecate the seeds, and seed-caching small mammals (e.g, yellow pine chipmunks, California kangaroo rats) are secondary dispersers of juniper seeds defecated by birds. Germination experiments with western juniper seeds were completed and demonstrated that germination is enhanced in seeds defecated by birds and buried or cached by small mammals. Utah juniper berries are not consumed by birds, but are husked and cached directly by seed-caching small mammals, bypassing a step in the dispersal system of western juniper. Objective 2: Sustainability of the soil resources is difficult due to repeated wildfires that expose the site to accelerated soil erosion. These findings are being used to develop new Ecological Site Descriptions (ESDs) in partnership with Natural Resources Conservation Service (NCRS) that incorporate hydrologic information for the first time. ARS scientists in Reno, Nevada, Tucson, Arizona, and Boise, Idaho, are using this new information to develop technical guides to enable resource managers to determine which sites should be revegetated first to maximize overall sustainability of Great Basin rangelands. Fire not only affects water erosion and associated watershed processes, but also affects wind erosion due to exposed soil for several months after fire. Little is known about the extent of soil loss due to wind erosion. Partnering with other ARS scientists, NRCS, Bureau of Land Management (BLM), U.S. Geological Service, Department of Defense, and The Nature Conservancy, we have developed the National Wind Erosion Network (NWERN), which currently has 13 sites across U.S. rangelands. The NWERN will provide standardized data to support the understanding of wind erosion processes across land use, land cover types, and different management strategies; support the development of open-access technologies to assess wind erosion and dust emission that integrate new data sources and complement existing monitoring programs; and encourage collaboration among scientists, resource managers, and policymakers to develop opportunities for enhancing wind erosion monitoring and assessment for scientific and land management applications. Establishing protocols to measure soils and vegetation after fires and soil monitoring will allow managers to assess their goals of soil stabilization. Objective 3: A greenhouse study was completed testing suppression of cheatgrass by established crested wheatgrass. The study measured how distance of sown cheatgrass from crested wheatgrass affected its growth. Relative to cheatgrass sown at 70 centimeters (cm) from crested wheatgrass, cheatgrass sown at 10 cm was suppressed over 99% and a major cause of suppression was reduced soil nitrogen availability. The combined results of several experiments also suggest that suppression of cheatgrass by established perennial grasses is partially the result of allelopathy. Allelopathy is a biological phenomenon where one plant inhibits the growth of another. Field and greenhouse data suggest that established perennial grasses retard nitrification thereby reducing soil nitrate availability. Two common post-fire rehabilitation treatments in areas prone to annual grass invasion include herbicide application and subsequent seeding with perennial species. We established an experiment on the Strawberry fire near Great Basin National Park in collaboration with BLM and ARS National Program Staff to assess the effects of herbicide and seeding treatments. In another study, manuscripts were published on the success of soil-active herbicides and plant materials for Great Basin rangeland restoration/rehabilitation practices. Testing a number of soil-active herbicides on the control of highly competitive cheatgrass was followed by testing plant materials adapted to arid rangelands of Great Basin environments. We continued research on impacts of seed-caching desert rodents on seedling production of Indian ricegrass in arid plant communities. We resampled plots where diversionary seeding experiments with Indian ricegrass seeds were placed (winter 2014), and had a lack of seedling recruitment in 2015 and 2016 due to low winter precipitation. Despite above average precipitation in 2017, we found few Indian ricegrass seedlings on plots this year. This is attributed to lack of seedling recruitment to rodent populations consuming naturally occurring, as well as, diversionary seeds during the past two years of poor seed production. A summary of a successful application of diversionary seeding was included in a review paper submitted to Rangelands. Objective 4: A 4-day Rangeland Ecohydrology class is being developed to provide NRCS employees an understanding of dominant hydrologic and erosion processes on rangelands, equations implemented in the Rangeland Hydrology and Erosion Model (RHEM), and how to access and interpret model predictions for different ecological and climatic conditions. ARS scientists working with collaborators have developed a framework for inclusion of key ecohydrologic feedbacks using the RHEM for inclusion into ESDs and consequently enhancing the utility of ESDs for assessing rangeland sustainability. The use of these concepts will help in guiding development of conservation practices to enhance resilience-based management strategies. Sediment and salt transport processes on western rangelands were assessed and areas of vulnerability for accelerated soil loss and salt loading to perennial rivers in the Upper Colorado River Basin were identified. The RHEM is being modified to estimate salt loading from saline range uplands. Effective runoff, soil erosion, and salt load reduction strategies can be met by increasing vegetation density, thereby, increasing soil deposition and a reduction in salts entering the Colorado River. This research has been transferred to Jordan where it is being used in restoration efforts in the Badia region of Jordan and to Kazakhstan where it is being used to develop a prototype national assessment framework to assess rangeland health and sustainability.
1. Herbicidal control of cheatgrass. A key component to rehabilitate cheatgrass-degraded rangelands is the use of soil-active herbicides. ARS researchers at Reno, Nevada, have tested the herbicides Plateau®, LandMark® and Matrix®. Cheatgrass densities were reduced over 96 percent, which significantly decreased seeded species seedling competition for limited resources. Herbicide plots increased soil moisture by more than 40 percent greatly benefitting the establishment of newly seeded species by more than 600 percent. Increased establishment of seeded species decreased cheatgrass associated fuels by more than 900 percent reducing the potential for catastrophic wildfires and loss of life and property.
2. Spatial and temporal soil nutrient availability following wildfire. Elevated nutrient availability following wildfire in sagebrush ecosystems facilitates invasion by the exotic annual grass, cheatgrass. ARS researchers in Reno, Nevada, have completed an 18-month study quantifying soil nutrient availability over time and by microsite (sagebrush understory and sagebrush interspace). The study confirms previous research that post-fire surface soil, particularly in burned shrub canopies, has long-term elevated nitrogen availability. Surprisingly, wildfire resulted in long-term and large increases in manganese availability, again largely in burned sagebrush canopies. Such increases in manganese availability likely benefits cheatgrass more than native grasses and helps to explain why cheatgrass is so invasive in the western United States.
3. Quantifying soil erosion on saline rangelands. Historically, quantifying rill erosion and deposition on rangeland hillslopes has been extremely difficult. ARS scientists in Reno, Nevada, and Tucson, Arizona, in conjunction with collaborators at University of Nevada, Reno, Desert Research Institute and Texas A&M Kingsville, have developed new 3-D imaging software and approaches to define surface roughness before and after rainfall events. This allows land managers to identify where soil erosion and soil deposition is occurring. Having this information, land managers can define conservation practices to efficiently treat only areas that are actively eroding by planting vegetation in concentrated flow paths, disrupting the erosion process, increasing deposition on site, and saving precious top soil and scarce nutrients from entering regional lakes and rivers. This approach drastically reduces the area that needs to be treated thereby saving significant amount of funding required to restore degraded rangelands.
4. New technology available to enhance rangeland Ecological Site Descriptions (ESDs). Historically, hydrologic information on rangelands has not been available within ESDs. ARS scientists in Tucson, Arizona, Boise Idaho, and Reno, Nevada, in association with university collaborators, have developed a new risk assessment technique for assessing sustainability of rangelands. The use of risk assessment techniques on soil erosion from specific return period runoff events provides unique information to assess the sustainability of the site in contrast to a reference site. This information provides land managers with a quantitative method to determine where conservation should be applied in a most cost-effective manner to manage lands for secure food supplies and safe and abundant water.
5. Seed caching by rodents and diversionary seeding to restore rangelands. Previously, ARS researchers in Reno, Nevada, demonstrated that seedling production of Indian ricegrass, a native bunchgrass that supplies an important source of livestock forage on arid grazing lands, is enhanced by the seed caching activities of desert rodents. This finding was then applied by introducing the concept of diversionary seeding, in which inexpensive commercial seeds are broadcast on rangelands to reduce the chance that seed-eating rodents recover and consume their natural caches of Indian ricegrass seeds. Plots on which diversionary seeds were applied had greater production of Indian ricegrass seedlings from rodent caches than did plots without diversionary seeds. The research demonstrated that seed caching, which is central to the diversionary seeding concept, enhances seedling survival of Indian ricegrass. This indicates that diversionary seeding and seedling establishment from natural rodent caches not only enhances the production of Indian ricegrass seedlings, but also increases the longer-term survival of the plants and increase overall health of the plant community.
6. Dual nitrite reduction pathways in bacteria. Denitrification and ammonification are important components of the nitrogen cycle. Denitrification leads to nitrogen loss from soils while ammonification leads to nitrogen retention. Researchers at the Desert Research Institute and ARS scientists in Reno, Nevada, cooperated on basic research to decipher the regulatory mechanisms for denitrification verses ammonification in a bacterial isolate that possess both genetic pathways in the same genome. Intrasporangium calvum, a unique Actinobacteria isolated from nitrate contaminated soils, was grown over a range of carbon to nitrate ratios, nutrient concentrations, and nitrite versus nitrate. We found that irrespective of concentration or ratio, excessive production of nitrite induces the ammonification pathway. These results are important because soil productivity could be enhanced if land management practices aim to promote bacterially-mediated retention of nitrogen using the ammonification pathway over the denitrification pathway.
7. Plant/soil relationship of cheatgrass. ARS researchers in Reno, Nevada, have completed a series of field and greenhouse experiments to determine if and how the exotic annual grass cheatgrass modifies or “engineers” the soil to favor its invasiveness. Overall, the data are conclusive; relative to native vegetation, cheatgrass “engineers” the soil to obtain greater levels of nitrogen and phosphorus necessary for its rapid growth, seed production, and invasiveness. The ability of cheatgrass to obtain access to these nutrients offers an explanation of why it has been able to invade myriad communities including very arid salt deserts to mesic high elevation grasslands once thought unlikely to be invaded by cheatgrass.
8. Flammability of cheatgrass. ARS researchers in Reno, Nevada, in cooperation with scientists at Babes-Bolyai University, Romania, studied the differences in germination, growth, and flammability of cheatgrass from native populations in Europe and invasive populations from the northern Great Basin. We hypothesized that populations from frequently burned regions of the Great Basin would have (1) greater tolerance to fire at seed level, (2) higher relative seedling performance in post-fire environments, and (3) greater flammability than unburned Central European populations that evolved without fire. Great Basin populations and greater growth had enhanced flammability in three out of five measured parameters compared to European populations. These intraspecific differences in fire-related traits contribute to the persistence and invasiveness of the frequently burned North American cheatgrass populations.
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