Location: Great Basin Rangelands Research2011 Annual Report
1a. Objectives (from AD-416)
Objective 1. Conduct foreign exploration and biological evaluation for biological control agents of weeds of western rangelands such as the annual grass medusahead rye and perennial pepperweed. Sub-objective 1.1: Conduct foreign exploration for natural enemies of medusahead rye and perennial pepperweed. Sub-objective 1.2: Conduct host-specificity testing and impact evaluation to assess biological control candidates of target weeds for risk to non-target organisms. Objective 2. Understand the ecology, biology and genetic variation of invasive weeds such as saltcedar, perennial pepperweed, and medusahead rye, and their natural enemies. Sub-objective 2.1: Conduct ecological studies of seed predators and other natural enemies of medusahead rye in the native and invaded ranges. Sub-objective 2.2: Characterize genetic variation of Lepidium latifolium (perennial pepperweed) in its native and invaded ranges. Objective 3. Determine the effects of integrated weed suppression (particularly saltcedar) and woody plant removal (pinyon and juniper) on ecosystem processes such as water and carbon cycling, and on long-term successional processes (including plants and wildlife), insect impacts on invasion, and restoration processes to facilitate science-based rehabilitation and restoration of lands invaded by these weeds. Sub-objective 3.1: Long-term monitoring of the effects of Diorhabda carinulata (northern Tamarisk beetle) on ecosystem functions, tree mortality and wildlife populations in areas affected by saltcedar biological control. Sub-objective 3.2: Determine guidelines for secondary control methods and restoration planning. Sub-objective 3.3: Determine the effects of two pinyon and juniper removal treatments on the hydrologic budget, particularly soil moisture, as well as understory composition. Objective 4. Develop restoration methodologies to prevent the invasion of annual grasses (such as cheatgrass, medusahead rye, and/or red brome) following destructive events (such as fire) in rangeland ecosystems.
1b. Approach (from AD-416)
Over the next five years we will conduct research to develop appropriate strategies to control exotic weeds and encroaching native species in western rangelands and riparian areas. Control measures will focus on using classical biological control to find insect enemies of exotic weeds, as well as other control measures, such as mechanical treatments. Genetic analyses of exotic weed species will determine the diversity of populations in the invaded range and identify similar populations in the native range to improve our ability to select effective control agents. There is little research on the ecosystem impacts of control measures; we will determine the impacts of control measures on ecosystem functions including carbon and water cycling, plant community composition and small animal diversity. We will also conduct research to determine appropriate restoration strategies for these ecosystems, by testing planting techniques and novel seed mixtures. These investigations will include basic and applied studies using hypothesis-driven experiments conducted in the laboratory, greenhouse, and field.
3. Progress Report
We continued to measure the ecosystem effects of saltcedar biological control by the northern tamarisk beetle. We measured tree mortality, bird and small mammal diversity, changes in saltcedar leaf area, beetle density, understory vegetation composition and carbon and water fluxes. We monitored faunal diversity in native riparian habitats and in saltcedar habitats as indicators of the effects of saltcedar invasion and subsequent biocontrol effort. We expanded bird and small mammal studies to one more site (a total of four sites) and added invertebrate sampling to three of these sites. Wildlife monitoring was mandated as part of the APHIS permit for the release of the beetle, and is essential to future efforts to continue the saltcedar biological control program, which has currently been discontinued by the US Fish and Wildlife Service due to concerns about the endangered southwestern willow flycatcher. A manuscript was submitted on 10 years of wildlife monitoring in saltcedar and native riparian habitats. Sites were selected in beetle affected saltcedar areas for restoration. Installation was initiated for a large common garden experiment designed to test appropriate seeding mixes for sagebrush restoration efforts in areas where medusahead and cheatgrass are present in the seedbank. Sites were selected on clay soil and sandy loam soils and the required field soil and seeds were collected. We completed the first year of a two year field experiment at Keystone Canyon on the impact of cheatgrass invasion on the persistence of native annual species. In preparation for determining the impacts of pinyon-juniper removal methods on the water balance, a site was instrumented with soil moisture probes in plots where the trees will be cut and burned and in control plots that will not be harvested. In addition to foreign exploration for natural enemies of target weeds in their native ranges and subsequent testing for host-specificity and impact (done in collaboration with colleagues in Europe, Agreement No. 5325-22000-023-05S), natural enemies of target weeds have been collected, identified, and studied here in the invaded range. A white rust fungus was collected from two perennial pepperweed populations in Nevada. Similar collections were made by collaborators at California Department of Food and Agriculture and samples were provided to us for laboratory study. Species identification was performed in collaboration with Nevada Department of Agriculture for these four isolates and greenhouse experiments of the host-specificity of the two Nevada isolates were conducted. On single-leaf pinyon pine, a species in the "pinyon-juniper" complex of invasive trees, larvae of the sawfly Neodiprion edulicolis were collected from an outbreak in central Nevada and are being studied in the laboratory. Studies of the ecology and insect diversity are ongoing in Great Basin invasions of both medusahead and saltcedar. Molecular genetic studies of perennial pepperweed and cheatgrass are continuing while molecular biology studies were initiated on medusahead as well as tamarisk beetles, which were released as biological control agents against saltcedar.
1. Effects of saltcedar invasion and biological control of saltcedar on wildlife. In the first major effort to document potential effects of saltcedar invasion on vertebrate populations other than birds, ARS researchers in Reno, Nevada continued monitoring small mammal populations in native riparian habitats and in saltcedar habitats. Although there are no systematic differences in the species diversity of communities in these areas as compared with saltcedar, some riparian-obligate small mammal species have been found to occur exclusively in native habitats, thus implying that these species would respond favorably to saltcedar control. Additionally, feeding trials have shown that small mammals, like birds, act as significant predators on the beetles that have been established for saltcedar biological control. A manuscript has been submitted reporting 10 years of the small mammal monitoring efforts and another manuscript was submitted regarding predation on beetles with a collaborator from Arizona State University.
2. Soil type mediates interactions between an invasive plant and its biocontrol agents. ARS researchers in Reno, Nevada demonstrated that abiotic factors (soil type in this case) can change the outcome interactions between multiple biocontrol agents attacking the same weed. Broadly, this study highlights the need to explicitly consider abiotic variability when selecting release sites for new agents – an agent that is minimally effective in one area may be more effective in another. More specifically, the recently approved agent Puccinia jaceae solstitialis has been generally considered a disappointment as a biocontrol agent but this work shows that in areas where starthistle has invaded serpentine soils, it is expected to be more effective and these areas are of special concern because these soils are home to numerous species of endangered and/or endemic plants and insects and reducing starthistle density in such areas would have great conservation efficacy.
3. Developed molecular genetic markers for medusahead from existing SSR markers from wheat. The invasive weed medusahead is closely related to wheat. Scientists in the Great Basin Rangelands Research Unit in Reno, Nevada conducted basic research on the molecular genetics of the invasive annual grass medusahead, producing new genetic markers that will aid in future genetic studies of this weed. Existing markers called SSRs that were developed in wheat breeding studies were adapted for use in medusahead. These PCR-based markers are economical to use and have detected differences between medusahead populations in preliminary studies. These markers will be used to study the relatedness of invasive medusahead populations to each other and to compare them to medusahead populations in the native range in order to determine the source countries of the medusahead invasion in America.
4. Potential bioherbicide of perennial pepperweed in Nevada. Biocontrol is a viable option to control invasive weeds. Scientists in the Great Basin Rangelands Research Unit in Reno, Nevada collected and identified a white rust that is found on perennial pepperweed plants in Nevada and California. The fungal samples were collected as part of a project to assess the importance of natural enemies of perennial pepperweed in the invaded range of the weed. Samples from two white rust populations in Nevada and two more in California were identified as Albugo lepidifolii using morphological and molecular genetic identification methods. This result is promising since A. lepidifolii is currently known to have a narrow host range limited to close relatives of perennial pepperweed. Based on observations of A. lepidifolii on perennial pepperweed in the field in Nevada, infection appears to take place late in the season, after the plant has produced ample foliage and seeds. Further research will focus on whether application of A. lepidifolii early in the season can kill foliage before it can mature.
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