Location: Great Basin Rangelands Research2013 Annual Report
1a. Objectives (from AD-416):
The Integrated Invasive Species Control, Revegetation, and Assessment of Great Basin Rangelands project has two objectives: 1) Identify and characterize biotic and abiotic conditions and processes that affect plant community factors and ecosystem dynamics on healthy and degraded rangelands to improve the ability to predict how rangelands will respond to changing environmental conditions and alternative management practices and 2) Devise management guidelines, technologies, and practices for conserving and restoring Great Basin rangelands.
1b. Approach (from AD-416):
The research project is organized into four complementary components: (1) ecology and control of invasive plants, (2) revegetation of degraded rangelands, (3) maintaining and/or enhancing healthy rangelands, and (4) quantifying economic and environmental impacts of management practices at the landscape scale. Experiments will be conducted to understand the seed and seedbed ecology of several native and non-native grasses and shrubs. Herbicides and tillage will be used to vary content of competing vegetation as it affects shrub establishment. Research will be conducted to document ecological processes which control expansion of Western Juniper. Levels of genetic variation of selected plants will be compared between high and low quality ecological conditions sites to determine effects of disturbance on genetic diversity. Rainfall simulators will be used to characterize runoff and soil erosion processes at the scale of a plant community under different manipulative treatments (altered grazing practices, burning, and brush removal) to quantify the hydrologic impact of the conservation practices. The SWAT model will be utilize to evaluate which alternative management scenarios (i.e., a change in vegetation state as represented by changes in canopy and ground cover or vegetation composition by life form) are the most cost effective in achieving the desired environmental benefit. Formerly 5325-11220-006-00D (June, 2011).
3. Progress Report:
This is the final report for this project which has been replaced by new project 5370-13610-001-00D, "Invasive Species Assessment and Control to Enhance Sustainability of Great Basin Rangelands". The Great Basin Rangelands Research Unit (GBRRU) in Reno, Nevada, has developed new herbicidal techniques and seed mixtures to increase the variety and density of desirable native and introduced species to rehabilitate degraded Great Basin rangelands. In one study, ARS researchers were able to establish 3.9 perennial grasses ft-² in areas where cheatgrass had died-off from natural causes compared to 0.6 ft-² outside of the die-off zone. We found that by disking sites that were still dominated by cheatgrass prior to seeding, the resulting action buried the majority of cheatgrass seeds and prevented the cheatgrass seeds from germinating. This resulted in an 83% decrease in cheatgrass densities and a corresponding increase of 244% establishment of desirable seeded species. The combination of these results was sufficient to decrease fuel loads and significantly reduced the risk of wildfire and provides a variety of treatments for reducing the impact of cheatgrass. GBRRU has investigated passive approaches to rangeland restoration. Results of a successful field experiment using “diversionary seeds” to enhance seedling recruitment of Indian ricegrass from seeds cached by small mammals were published. Research on animal seed-dispersal vectors of expanding populations of western juniper was conducted comparing germination rates of seeds dispersed by birds, by small mammals, and by neither of these seed dispersers. Cumulative results clearly indicated that a two-phase dispersal system yields the best seedling recruitment in which birds consume fruits, defecate the seeds, and small mammals then harvest and cache the seeds from the bird droppings. GBRRU has completed studies to document how the exotic annual grass, cheatgrass, alters biogeochemical cycling and nutrient availability and basic understanding of the competitive nature of the plant. Currently, physical-based overland flow erosion models for rangeland applications do not separate disturbed and undisturbed conditions in modeling concentrated flow and total sediment yield. Therefore, it is difficult to estimate benefits of conservation practices. GBRRU found that burning increases erosion by amplifying the power of overland flow because wildfire removes obstacles and changes soil properties affecting erodibility itself. GBRRU observed concentrated flow erodibility had a high value at overland flow initiation and then started to decline with time due to reduction of sediment availability from the scoured soil surface. We developed new empirical functions to predict erodibility variation within a runoff event as a function of cumulative unit discharge. Empirical equations were also developed to predict erodibility variation with time postdisturbance as a function of readily available vegetation cover and surface soil texture data. This will provide ARS the means of predicting impact of conservation by correlating increases in cover attributed to the conservation action with decreases in soil erosion.
1. Cheatgrass is the most successful weed in the Great Basin. Exotic annual grass invasion into the Great Basin over the last 100 years has resulted in more environmental change than has occurred in the last 10,000 years. Scientists in the Great Basin Rangelands Research Unit in Reno, Nevada, tested the hypothesis that cheatgrass alters or “engineers” the soil to favor its own invasiveness. Research indicates that cheatgrass increases the availability of soil nitrogen and phosphorus relative to native species. In a multi-state field study on cheatgrass-invaded areas the team found that nitrate-nitrogen levels at depths of 1-2 meters were extremely high compared to controls. The team predicts that declining nitrogen availability in surface soils will hinder the growth of cheatgrass in the long-term and favor growth of perennial grasses, which can exploit deep reserves of nitrogen and lead to rehabilitation of degraded western rangelands.
2. Estimating rate of spread of invasive weeds. Invasions by exotic species are generally described using a logistic growth curve divided into three phases: introduction, expansion, and saturation. ARS researchers in Reno, Nevada, used five datasets ranging from 41 to 86 years in length at five sites in four western states to estimate the expansion of seven exotic species. A greater variety of curve shapes was documented by long-term datasets than those published based on herbaria sampling. Many of the species evaluated were characterized by sporadic spikes and crashes in populations indicating that invasion and rapid expansion of exotic plants is not inevitable. The general lack of fit with current theory is the result of the complex interactions between climate, land management, and succession that drive vegetation change in rangeland environments and provides hope that we can restore degraded rangelands by identifying when invasive species are vulnerable to revegetation efforts.
3. Targeting conservation saves time, money, and land. It is estimated that soil loss costs the United States between $6 and $16 billion dollars every year. ARS researchers in Reno, Nevada, in collaboration with ARS researchers in Boise, Idaho, and Tucson, Arizona, have designed a system to model soil erosion based on quantitative data from Natural Resources Conservation Service-Natural Resources Inventory (NRI). This modeling approach can be used to predict the effectiveness of alternative management actions and support cost–benefit analyses to optimize return on investments in conservation. This allows for rapid determination of regional needs and identification of where conservation may be most cost-effective in arresting land degradation and enhancing ecosystem services. This same concept can be used to inform policy and to provide a quantitative mechanism to justify targeting to meet specific goals.
4. New ways to estimate precipitation in remote areas of the west. Traditionally, weather stations are often located in cities and not across the vast expanse of open and uninhabited western rangelands making it difficult to forecast drought or develop mitigation plans. Scientists in the Great Basin Rangelands Research Unit in Reno, Nevada, modified wildlife guzzlers (wildlife water developments) as a cost-effective means of improving estimates of climatic parameters in remote Nevada catchments. Field results indicated that water levels in the wildlife guzzler tank measured by pressure transducers corresponded well with measured precipitation events. This study’s results demonstrate that guzzler sites can be augmented with climatic instrumentation at a relatively low cost to improve the quality and density of climate observations, benefitting hydrologists, climatologists, and livestock and wildlife managers.
5. Estimating impacts of drought. ARS researchers in Reno, Nevada, evaluated the spatial variability in green leaf cover of a semi-arid shrub dominated rangeland by comparing field measurements to aerial and satellite imagery. Results indicate that sampling schemes can be defined to reduce sample variance and require fewer sampling locations to achieve a given level of accuracy using satellite imagery before reaching the field site. This would increase cost–effectiveness of individual sample sites and allow more area to be sampled for a fix cost. This technique provides a quantitative means of documenting the health of rangelands and the impact of drought on forage production in western shrub-dominated landscapes.
6. USDA reviews the benefits of conservation on rangelands. USDA spends millions of dollars on conservation each year and has been challenged to define the net benefit of conservation. ARS researchers in Reno, Nevada, in conjunction with University faculty and Natural Resources Conservation Service staff evaluated the conservation benefits of rangeland practices. Together they determined that minimal investment had been made by the rangeland profession in formally assessing conservation practice effectiveness at the appropriate scale and over appropriate time spans. Consequently, conservation practices have seldom been monitored to obtain the ecological and socioeconomic data necessary for a thorough assessment of conservation practice outcomes. This research indicates that new paradigms in the development and support of rangeland monitoring programs must be designed and implemented if Congress desires to increase accountability and cost-effectiveness of conservation programs.
7. Native Animals can assist in rehabilitating western rangelands. Seed harvesting, consumption, and dispersal through caching by granivorous (i.e., seed-eating) desert rodents have profound impacts on specific plant species and on species composition of arid plant communities. Scientists in the Great Basin Rangelands Research Unit in Reno, Nevada, assessed the feasibility of utilizing the seed dispersal services of native animals as a passive restoration strategy. This was successfully tested on a field scale for the first time by broadcasting millet as a “diversionary seed”. The rodents cached and preferentially recovered the diversionary seeds before beginning to consume the less desirable target seeds used in rehabilitation. This passive restoration approach can be used cost-effectively to restore degraded rangelands where traditional approach cannot be applied due to site conditions.
8. Degraded Great Basin rangelands can be rehabilitated with herbicides. Rangelands of the Great Basin are difficult to rehabilitate due to invasive species competition and extreme aridity. In cooperation with stakeholders, including the livestock industry and the mining industry, ARS scientists in the Great Basin Rangelands Research Unit in Reno, Nevada, tested cheatgrass control methods, plant material testing, and post-rehabilitation practices to provide resource managers and private land owners the technologies to rehabilitate rangelands. Our techniques have resulted in 98% control of cheatgrass on our research plots. Moreover, such control has increased the establishment of desirable plant species benefitting forage value, wildlife habitat, and plant community structure. The Nevada Department of Wildlife has documented a 400% increase in the local mule deer populations in these study areas.
Al-Hamdan, O.Z., Pierson Jr, F.B., Nearing, M.A., Williams, C.J., Stone, J.J., Kormos, P.R., Boll, J., Weltz, M.A. 2013. Risk assessment of erosion from concentrated flow on rangelands using overland flow distribution and shear stress partitioning. Transactions of the ASABE. 56(2):539-548.