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Research Project: Integrating Ecological Process Knowledge into Effective Management of Invasive Plants in Great Basin Rangelands

Location: Great Basin Rangelands Research

2019 Annual Report

At more than 50 million hectares, the Great Basin is the largest North American desert but also the most threatened. Great Basin ecosystems have been significantly altered by invasive annual grasses and expanding native conifer populations. This has resulted in altered fire cycles, wildlife habitat loss, and massive expenditures on rehabilitation. Over the next five years, we will conduct research to further elucidate mechanisms of invasion and develop new and evaluate current control strategies for exotic grasses and encroaching woody species in Great Basin rangelands. Objective 1: Develop new strategies to improve the control of invasive annual grasses, especially cheatgrass and medusahead grass, in Great Basin ecosystems based on using an improved understanding of the ecology, biology, and genetic variation of these weeds and the native plant communities they are invading. Subobjective 1A: Describe and analyze the genetic structure of invasive annual grass populations. Subobjective 1B: Identify ecological associations relevant to the proliferation, impact, and control of invasive annual grasses. Subobjective 1C: Determine the effectiveness of seeding strategies on reducing invasive annual grasses and fire frequency. Subobjective 1D: Elucidate invasive-native plant associations across climatic gradients and determine native species mixes resistant to invasive annual grasses under future climate. Objective 2: Identify and quantify the effects of integrated weed control for invasive woody plants (including pinyon, juniper, and saltcedar) on ecosystem processes, such as water cycling and seed ecology, to improve restoration and management of Great Basin ecosystems under variable climatic conditions. Subobjective 2A: Quantify the long-term effects of Diorhabda carinulata (northern tamarisk beetle) on water and carbon cycling, tree mortality, and wildlife populations in areas affected by saltcedar biological control. Subobjective 2B: Investigate adapted foundational plant materials suitable for restoration strategies in woody plant invasions to prevent secondary weed invasions. Subobjective 2C: Investigate effects of post-invasion mechanical tree control in established pinyon and juniper stands on ecohydrology and sagebrush steppe community recovery and determine the effects of native seed eating insects in reducing juniper seed viability as a pre-establishment control strategy.

Over the next 5 years, we will embark on a research program that will enhance the ability to manage invasive weeds in riparian and rangeland environments. Sagebrush habitats are at risk due to downslope expansions of woody native trees and upslope expansion of invasive annual grasses. The studies will address factors that influence the resistance and resilience of sagebrush ecosystems, that allow them to either be resistant to invasion or to recover from disturbance. We will accomplish this by integrating innovative approaches to weed control, increasing our understanding of relevant ecological processes, and providing guidelines for rehabilitation of damaged ecosystems. Specifically, we will initiate new research to describe genetic variation and the population structure of invasive annual grass species, explore biological control strategies for these grasses, and evaluate how post-fire seeding treatments affect invasive annual grass populations and wildfire frequency and severity. We will build on existing saltcedar biological control studies to promote the return of key native species and prevent secondary weed invasion, expand our mechanistic studies of pinyon- and juniper-encroached sagebrush ecosystems and of the effects of tree control treatments on these systems, and begin investigating the role of climate change in weed invasion and native species survival. If data are not available, suitable field sites cannot be found, permissions to work are not granted, or if suitablie biological candidates cannot be found, then we will modify our plans and experimental procedures as necessary.

Progress Report
Project 2060-22000-024-00D addresses Problem Statements 2B2 (Modeling and monitoring weed invasions/outbreaks in natural ecosystems, including effects of global warming, wildfires, and changes in human activities) and 2B3 (Systems approach to environmentally sound weed management in natural ecosystems) of the NP304 Action Plan. Progress continued toward Sub-objective 1A, as our efforts to compare cheatgrass populations from the plant’s native range (in Eurasia) to populations in the invaded range (the Great Basin and surrounding regions) advanced despite a molecular biology support scientist vacancy. Cheatgrass plants become highly flammable after they dry down in summer and they remain on the landscape, contributing to increased severity and frequency of catastrophic wildfires in the western U.S., and the extirpation of native plant communities, including the sagebrush steppe. By genetically matching invasive cheatgrass populations with their Old World progenitors, we will be able to focus our searches for cheatgrass biocontrol agents in native range regions with the most closely related cheatgrass populations to those in the Great Basin. Significant progress was made toward Sub-objective 1B, thanks in large part to continued support from the Bureau of Land Management, which allowed one ARS scientist at Reno, Nevada, to carry out field research in Bulgaria and Greece in spring 2019 to collect and study natural enemies of cheatgrass and medusahead, in collaboration with researchers at Plovdiv, Bulgaria and Rome, Italy. Medusahead is another flammable annual grass invading the western U.S., but it is also highly unpalatable to livestock due to its ability to sequester high levels of silica within its vegetative tissues. Promising insects were collected. In addition to this field work, taxonomic research continued, in collaboration with researchers in Belgrade, Serbia, to describe and name a new species of mite that was discovered on cheatgrass in Bulgaria by our team in 2017. Preliminary research to understand the host-range of another new mite species, Aculodes altamurgiensis, that was discovered by our team on medusahead in Italy in 2014 (and later found on medusahead in several other countries) indicated high host-specificity on medusahead (with wheat, barley, oat, maize, and other grasses included in the test but not attacked); this test also found that the Italian strain of A. altamurgiensis showed variable performance on five different medusahead populations, including two from Italy and three others from California, Idaho, and Nevada. This result is consequential as it indicates that tests of other A. altamurgiensis strains (e.g. from Bulgaria or Serbia) will be necessary as we search for a strain with damaging performance on all invasive medusahead populations. In another important finding, A. altamurgiensis was collected by an ARS researcher at Reno, Nevada, from a medusahead population in northeastern California in autumn 2018. Research on the life cycle of A. altamurgiensis by our international team also determined that when medusahead plants dry, mites sequester themselves in cavities between the seed and seed coat. As such, it is likely that progenitors of the A. altamurgiensis found in California arrived in seeds from a mite-infested medusahead population originating somewhere in the native range. In spring and summer 2019 we have intensively searched medusahead populations in California, Idaho, Nevada, and Oregon for additional A. altamurgiensis populations, in collaboration with ARS researchers in Albany, California. In addition, basic research on the biology of a model species of mite (Aceria tosichella), in collaboration with researchers in Poznan, Poland, supported Sub-objective 1B by streamlining mite-rearing protocols in the laboratory and improving our understanding of their dispersal behavior; rearing and dispersal are key components of a biocontrol program. Wildfires burn large areas of western North American forest ecosystems in most years and their frequency is expected to increase with climate change. However, few studies assess vegetation recovery and fuel dynamics more than 10 years following a fire. In support of Sub-objective 1C, an ARS scientist from Reno, Nevada, measured plant species composition, conifer seedling regeneration, fuel loads, and ground cover at 15 wildfire sites that burned 9-15 years earlier. Studies took place in five vegetation types distributed across eight western states, including Alaska. The 15 fires were selected for having been previously sampled immediately post-fire and re-sampled one year later, thus providing an opportunity to extend the analysis to long-term vegetation recovery. A key goal of post-fire rehabilitation is to reduce fine, continuously distributed fuels, such as senesced cheatgrass and other dried annual grass plants. However, little is known about the effects of rehabilitation on the reduction of cheatgrass invasion across landscapes. Progress toward meeting Sub-objective 1C also included analysis of the effects of 84 environmental, rehabilitation, fire history, and plant species variables on cheatgrass cover and density in Wyoming-sagebrush steppe communities. Cheatgrass cover and density were greatest at low and mid-elevation sites, decreasing above 1,400 meters. Cheatgrass cover generally decreased as bottlebrush squirrel tail cover or Sandberg’s bluegrass density increased. Cheatgrass cover decreased as the number of rehabilitation treatments or time since rehabilitation increased. The results suggest that post-fire rehabilitation strategies that include a diverse mixture of native bunchgrass species can be an effective means of suppressing cheatgrass after a fire. Progress was made toward Sub-objective 1D with the establishment of a rehabilitation-climate experiment on the site of the Monroe fire near Winnemucca, Nevada. ARS researchers at Reno, Nevada, established 30 macro-plots with three replicates per treatment. Treatments within the macro-plots include: 1) herbicide/no herbicide, and 2) five precipitation variables; ambient, spring addition, spring reduction, summer addition, and summer reduction. In each macro-plot, we established nine subplots with the following forb treatments: 1) no forbs, 2) annual forbs, or 3) perennial forbs (with three replicates per treatment). Plots were raked, hand-broadcasted, and pressed with a mini imprinter. Percent cover and seedling counts were made on all subplots. Preliminary results suggest that only herbicide affects cheatgrass cover; altered precipitation has no effect on cheatgrass. The final results will assist managers in determining optimal post-fire rehabilitation practices. Work by an ARS scientist at Reno, Nevada, to measure ecosystem effects of salt cedar biological control by the northern tamarisk beetle was conducted in support of Sub-objective 2A. This research identifies and quantifies the effects of integrated weed control for the invasive woody plant salt cedar on ecosystem processes, such as water cycling and restoration potential of desirable Great Basin ecosystems. Water and carbon dioxide exchanges were measured with an eddy-covariance system over a stand of salt cedar to complete the last year of a 12-year data set. In addition to the measurements of water and carbon dioxide, every three weeks during the growing season surveys of the densities of northern tamarisk beetle and changes in leaf area index of salt cedar were conducted. This work is essential to understanding the effects of the salt cedar biological control program, which has currently been suspended by the U.S. Fish and Wildlife Service due to concerns about unintended effects to the endangered southwestern willow flycatcher. Progress toward Sub-objective 2C was made via a ninth consecutive year of data collection by an ARS scientist at Reno, Nevada, in the Porter Canyon Experimental Watershed (PCEW) in the Desatoya Mountain Range of central Nevada. This instrumented watershed quantifies the effects of tree management strategies on ecosystem processes and plant community composition. Analysis of plant phenology photographs and environmental sensors in PCEW were completed this year. Also in support of Sub-objective 2C, ARS researchers at Reno, Nevada, collected and dissected berries from California juniper trees in order to compare the insects infesting berries of this juniper species to those previously found within berries of Utah and western juniper. Preliminary results show that while some niches of California juniper berries (e.g. seed, pulp, resin cells) are occupied by the same species found in the respective niches of Utah and western juniper berries, other berry niches of the three juniper species are occupied by different but closely related insect species. Further comparison in the literature to juniper species in the eastern U.S., and Eurasia revealed a similar phenomenon, suggesting evidence of parallel evolution among these insect species, adapting to various changes encountered as the host juniper species diverged and radiated.

1. Long-term monitoring makes a difference. Many biological control projects have not been monitored for long periods of time; therefore, their effectiveness cannot be accurately assessed. Two ARS scientists at Reno, Nevada, continued to monitor tamarisk ecosystem responses to the biological control agent, the northern tamarisk leaf beetle. This has produced 12 years of data on small mammal diversity, stand-level carbon dioxide exchange and evapotranspiration rates, and understory plant community response. Ecosystem responses of carbon and water cycling showed a very different pattern in the last three years than the previous nine years. This work has resulted in several publications, a book chapter, invitations to national meetings, and technical advice for other USDA researchers.

2. Discovery of two new insects attacking cheatgrass. Cheatgrass is a widespread invasive grass in the western U.S. that becomes highly flammable after drying down in summer, remaining on the landscape and contributing to increased severity and frequency of catastrophic wildfires. Following the collection in Spring 2018 of a fly feeding on cheatgrass in Greece by an ARS scientist at Reno, Nevada, an ARS collaborator in Beltsville, Maryland, determined that it is a new species. As a result of this discovery, the ARS scientist returned to Greece (as well as Bulgaria) in Spring 2019, along with collaborators from Bulgaria and Italy, with the goal of finding additional populations of the new fly species in order to establish laboratory colonies for evaluation of the fly as a potential biocontrol agent of cheatgrass. In addition to finding new populations of the fly, this team also discovered the first beetle species to be recorded feeding on cheatgrass in the field. Taxonomic identification of the beetle is still underway. Discovery of a new species of insect attacking a biological control target, is particularly significant as it indicates that the likelihood of the new insect being highly specific to its host plant is high, which is critical for a biological control agent.

3. New practices to reduce cheatgrass density are successful. The introduced and invasive annual grass, cheatgrass, has increased the chance, rate, spread and season of wildfires resulting in significant loss of native plant communities. ARS scientists at Reno, Nevada, are testing a recently released pre-emergent herbicide, Indaziflam, to aide in cheatgrass control efforts and improve restoration practices to increase diversity and improve ecosystem function. The results of using the pre-emergent herbicide Indaziflam has reduced the first year cheatgrass seed bank density by 98.8 percent, above-ground densities by 99.4 percent, and cheatgrass-associated fuels by more than 98 percent. This significant decrease is essential to the establishment of seeded species to restore degraded rangelands and suppress future cheatgrass densities and associated fuel loads.

4. New practices increase seeding success and reduces cheatgrass dominance. The accidental introduction and subsequent invasion of the annual grass, cheatgrass, has increased the frequency of wildfires from an estimated 60-110 years down to as frequent as every five-10 years in arid Great Basin environments. This increased wildfire frequency threatens life, property and destroys critical habitat. Millions of dollars are spent annually fighting these fires and millions more are spent trying to restore burned habitats. ARS scientists at Reno, Nevada, have been testing pre-emergent herbicides to control cheatgrass and open a window of opportunity to improve restoration success and decrease cheatgrass densities and associated fuels. This research has resulted in an increase of perennial grasses, shrubs and forbs that successfully suppress cheatgrass and associated fuels by more than 96 percent, therefore significantly decreasing the chance, rate, spread, and season of wildfires associated with cheatgrass dominance.

Review Publications
Snyder, K.A., Huntington, J.L., Wehan, B., Morton, C., Stringham, T.K. 2019. Comparison of landsat and land-based phenology camera normalized difference vegetation index (NDVI) for dominant plant communities in the Great Basin. Sensors. 19(5):1139.
Tonkel, K.C., Dimitri, L.A., Rector, B.G., Longland, W.S., Kirchoff, V.S. 2019. Life history and distributional information for three species of Periploca Braun (Lepidoptera: Cosmopterigidae) inhabiting Juniperus spp. (Cupressaceae) berries in the western U.S. Pan-Pacific Entomologist. 95(1):37-46.
Morgan, T.A., Harmon, D.N., Blank, R.R., Clements, D.D. 2018. The benefits of using pre-emergent herbicides in rehabilitating cheatgrass-infested rangelands. The Progressive Rancher. 7:14-15.
Snyder, K.A., Evers, L., Chambers, J., Dunham, J., Bradford, J., Loik, M. 2018. Effects of a changing climate on the hydrological cycle in cold desert ecosystems in the Great Basin and Columbia Plateau. Rangeland Ecology and Management. 72(1):1-12.
Browning, D.M., Snyder, K.A., Herrick, J.E. 2019. Plant phenology: Taking the pulse of rangelands. Rangelands. 41(3):129-134.
Skoracka, A., Rector, B.G., Hein, G. 2018. The interface between wheat and the wheat curl mite, Aceria tosichella, the primary vector of globally important viral diseases. Frontiers in Plant Science. 9:1098.
Smith, A.G., Newingham, B.A., Hudak, A., Bright, B.C. 2019. Got shrubs? Climate mediates long-term shrub and introduced grass dynamics in chaparral communities after fire. Fire Ecology. 15:12.
Clements, D.D., Harmon, D.N. 2019. Survivability of Wyoming big sagebrush transplants. Rangelands. 41(2):88-93.