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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

2020 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
This is the final report for project 2060-22000-024-00D, "Integrating Ecological Process Knowledge into Effective Management of Invasive Plants in Great Basin Rangelands." The new project is currently going through the Office of Scientific Quality Review. Despite the vacancy of a Molecular Biologist since early in the project, progress was made on Sub-objective 1A. In addition to the vacancy, rapid advances in technology substantially decreased the cost of DNA sequencing, thus obviating the original methodology described in the Plan. To achieve our objectives, we pursued two separate alternative strategies to the original methodology. The first was to order a Genotyping by Sequencing (GBS) study from a commercial laboratory, which revealed genetic sequence differences (SNPs) between 40 cheatgrass populations collected from the native and invaded ranges by ARS researchers from Reno, Nevada, and their international collaborators. This data is being analyzed in collaboration with researchers familiar with the appropriate software pipelines. The GBS data, comprising a large amount of small DNA sequences from the 40 populations, has also been used to assemble a complete chloroplast genome sequence for cheatgrass, which does not yet exist in the literature. SNPs within the chloroplast genome from among the 40 populations are under analysis to produce polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLPs) to enable efficient, inexpensive characterization of cheatgrass populations. Similar tools are planned from data of the entire cheatgrass genome following complete analysis of the GBS data. The second alternative strategy has been to pursue sequencing of the entire cheatgrass genome in collaboration with ARS in Stoneville, Mississippi, and Penn State University in State College, Pennsylvania. The cheatgrass genome is large enough that this would have been an impractical goal five years ago. Whole genome sequences, combined with the existing GBS data, will accelerate the analysis of differences and similarities between cheatgrass populations in its native and invaded ranges, will enable genetic studies of traits associated with cheatgrass invasiveness, and will facilitate similar studies of its weedy relative, red brome. Research in support of Sub-objective 1B focused on ecological associations relevant to the invasion of the annual grasses cheatgrass, medusahead, and red brome into the Great Basin, as well as to their native-range natural enemies, particularly eriophyid mites, that might prove useful as biological control agents. In a collaboration between ARS scientists in Reno, Nevada, and Peoria, Illinois, fungal endophytes were identified from the native and invaded ranges of medusahead, first by culturing them on media and later using a metagenomic protocol developed in Peoria. Using fungus-specific PCR primers, over 400 different fungal DNA sequences were detected from medusahead specimens, most without matches to known species in online databases. Cataloging this unexpected diversity of fungal endophyte species continues. In 2016, an ARS scientist from Reno, Nevada, was awarded the first ARS-European Biological Control Laboratroy (EBCL) sabbatical, which entailed spending 6-7 months each year (2016-2018) in the field, based at ARS-EBCL in Montpellier, France. This led to an increased emphasis on the discovery of candidate biocontrol agents of the targeted grass species in their native ranges in support of Sub-objective 1B, following the aforementioned critical vacancy that adversely affected research in support of Sub-objective 1A. During these field surveys in support of Sub-objective 1B, as well as in 2019, four new species of arthropods were discovered that are now under evaluation for their suitability as candidate biological control agents. These include two eriophyid mites, one on cheatgrass and one on medusahead, as well as a midge and a weevil on cheatgrass. Eventual release of any of these candidate agents would represent the first biocontrol agents released on an annual grass targets in the 150+ year history of this practice, which can take 5-20 years of research to obtain approvals for agent release on private, state, and federal lands. In addition, surveys in the Great Basin revealed the presence of the medusahead mite in North Eastern California, providing evidence that it has been passively introduced at some time in the past. This has stimulated intensive surveys of medusahead populations throughout the Great Basin to determine if the mite is present in other states. Currently, approximately 50% of the sagebrush steppe has been lost in the western Great Basin as a result of land use change, plant invasions, and altered fire regimes associated with cheatgrass, which warrant rehabilitation treatments in order to maintain native plant communities. In support of Sub-objective 1C, the effects of rehabilitation treatment and fire history on native plant communities were studied using a combination of field work and spatial analysis to examine the effect of fire history, rehabilitation history, and environmental variables on plant community assembly, cheatgrass invasion, and changes in fire regime characteristics. In addition, plant species composition was sampled following 15 wildfires that burned 9-15 years prior, providing a unique opportunity to examine long-term vegetation recovery. Plant community recovery depended on the presence of invasive plants, burn severity, and precipitation, and fuel-reduction treatments reduced burn severity resulting in fewer invasive species. Native species richness increased with elevation, but nonnative species richness did not. Cheatgrass cover and density decreased as the number of rehabilitation treatments or time since treatment increased and were inhibited by diverse native bunchgrass communities. Fire regimes were influenced by site moisture with more xeric sites burning more frequently, particularly in the last twenty years. Sites that were aerially seeded prior to a fire had shorter fire return intervals and more frequent fires than drill-seeded sites. Drill seeding with diverse bunchgrasses rather than monocultures of nonnative bunchgrasses further inhibited cheatgrass and resulted in fewer, less frequent fires with longer fire return intervals. In support of Sub-objective 2A, scientists from Reno, Nevada, monitored tamarisk ecosystem responses to the northern tamarisk leaf beetle (NTLB), a biological control agent released across the western United States in the early 2000s. Twelve years of data were collected on small mammal diversity, stand-level carbon dioxide exchange and evapotranspiration rates, understory plant community response, leaf area index, and NTLB density. This is the longest dataset on carbon and water fluxes in a tamarisk invaded site in North America. Our results indicated that for this site along the Truckee River effects on carbon dioxide and water fluxes were transient and recovered as NTLB populations declined. Furthermore, the Great Basin site and several other sites in southwestern deserts that had large initial NTLB outbreak conditions produced dramatic mid-season canopy dieback of tamarisk in response to NTLB herbivory. In 2010, due to concerns about habitat for the federally funded endangered southewestern willow flycatcher, the Animal and Plant Health Inspection Service (APHIS) officially discontinued this program. Porter Canyon Experimental Watershed (PCEW) was established in 2009 to understand the influence of pinyon and juniper (PJ) woodland expansion on the hydrologic cycle of central Nevada rangelands. Research at PCEW, which is representative of ~ 1m acres of central Nevada watersheds, has continued in support of Sub-objective 2C of this project plan. Significant expansion of PJ cover has been observed at lower elevations, as well as increased PJ population densities at upper elevations, reducing the extent and productivity of the historical sagebrush steppe communities with negative ecological impacts, e.g. on sage grouse. USDA-BLM initiated large-scale woodland thinning treatments at PCEW in 2016 to reduce fuel loads and improve wildlife habitat. In concert, ARS researchers from Reno, Nevada, measured the ecological and hydrologic responses of these treatments. A coupled ground-water/surface-water flow model (GS-FLOW) for the entire watershed was created in collaboration with Desert Research Institute, Reno, Nevada, along with studies on the influence of PJ interception, surface runoff, and soil erosion processes, and the use of remote cameras to monitor plant communities. The project will continue to monitor the impacts of PJ encroachment and PJ removal on water balance, as well as the efficacy of treatments to restore sagebrush and meadow plant communities. Sixty trees were instrumented with sap flow sensors in a novel, automated process to convert raw voltages into data on tree water use. Also, in support of Sub-objective 2C, ARS researchers in Reno, Nevada, conducted extensive research on insects that infest berries of juniper species whose populations are expanding into sagebrush and rangeland ecosystems. Berries were sampled from three species of juniper (western, Utah, and California juniper) in the Great Basin and adjacent areas of southern California and dissected in the laboratory. In addition, adults were collected in the lab after emerging from boxes full of intact berries. More than 40 insect species and one mite species were identified, at least seven are seed predators that render seeds inviable. This research will determine if arthropod damage to juniper seeds is primarily accomplished by one or a few species or is attributable to a greater variety of species. This is an essential first step for potential biological control applications, and it has immediate utility for parameterizing models of juniper expansion. This work resulted in three peer-reviewed journal articles.

1. Four new candidate biological control agents of invasive annual grasses were discovered. Invasive annual grasses disrupt the ecology of western rangelands, both in competition with native plant species and, when dry, producing highly flammable tinder to spark and carry wildfires to larger fuel sources, causing social, economic, and environmental damages. Cheatgrass and medusahead are grasses of Eurasian origin that were introduced in the 19th century and have become widespread across the West, often in dense populations much too large to manage using herbicides or other weed control methods. A biological control program to combat invasive annual grasses was established by an ARS researcher in Reno, Nevada, in collaboration with cooperators from several European countries. They have discovered four candidate biocontrol agents, including a new species of mite that attacks medusahead and new species of mite, midge and weevil that attack cheatgrass. These four species are currently under evaluation for their host-specificity and damage potential in order to determine if they are suitable for importation and release in the West to control these destructive invasive grass species. Release of any of these weed-killers would represent the first ever release of an agent to control an annual grass in the 150+ year history of weed biological control.

2. Long-term ecological effects of a released biocontrol agent were assessed. As an example of ARS’s well-known commitment to long-term research, two ARS researchers from Reno, Nevada, monitored saltcedar ecosystem responses to the introduction of the northern tamarisk leaf beetle, a biological control agent of saltcedar. This has produced twelve 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 pattern of plant recovery in the last three years relative to the previous nine years. This work has resulted in 11 peer-reviewed publications, a book chapter, invitations to national meetings, and technical advice for a data call to ONP.

3. Post-wildfire rehabilitation strategies were assessed. On average, $35 million/year is spent on post-fire rehabilitation treatments by the USDA, Bureau of Land Management (BLM) to reduce annual grass invasion and re-establish native communities that are resilient to future wildfire. Using a combination of field work and spatial analysis, an ARS scientist from Reno, Nevada, examined the effects of fire, rehabilitation, and environmental variables on plant communities, cheatgrass invasion, and changes in fire regimes. Both elevation and aridity influenced cheatgrass invasion and future wildfire. Aerial seeding tended to increase future fire compared to drill seeding and diverse bunchgrass communities after wildfire and rehabilitation were most successful in reducing cheatgrass invasion. These results provide valuable information to land managers and suggest post-fire rehabilitation treatments should focus on using a diverse assemblage of native grasses to reduce invasion by exotic annual grass species. These techniques are being used by USDA, BLM on over 70,000 acres at the 2018 Martin Fire site with demonstrated success in establishing desired species and reducing cheatgrass density.

Review Publications
Karpicka-Ignatowska, K., Laska, A., Kuczynski, L., Rector, B.G., Lewandowski, M., Puchalska, E., Skoracka, A. 2019. A novel experimental approach for studying life-history traits of phytophagous arthropods utilizing an artificial culture medium. Scientific Reports. 9.
Snyder, K.A., Scott, R.L. 2019. Longer term effects of biological control on tamarisk evapotranspiration and carbon dioxide exchange. Hydrological Processes. 34(2):223-236.
Cristofaro, M., Roselli, G., Marini, F., de Lillo, E., Petanovic, R., Vidovic, B., Auge, M., Rector, B.G. 2020. Open field evaluation of Aculodes altamurgensis, a recently described eriophyid species associated with medusahead (Taeniatherum caput-medusae). Biological Control. 30(4):339-350.