Location: Great Basin Rangelands Research2012 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:
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 through Agreement No. 5370-22000-023-01S), natural enemies of target weeds have been collected, identified, and studied here in the invaded range. A weevil was collected from two perennial pepperweed (Lepidium latifolium, PPW) populations in Nevada (Elko and Reno). Species identification was performed and greenhouse experiments on the impact of the weevil damage on PPW growth were also conducted. On single-leaf pinyon pine (Pinus monophylla), a species in the "pinyon-juniper" complex of invasive trees, laboratory studies of the sawfly Neodiprion edulicolis were continued. Studies of the ecology and insect diversity are ongoing in medusahead (Taeniatherum caput-medusae), juniper (Juniperus spp.) and saltcedar (Tamarix ramosissima). Molecular genetic studies of medusahead and cheatgrass (Bromus tectorum) are also continuing. In continued work to measure ecosystem effects of saltcedar biological control by the northern tamarisk beetle, Diorhabda carinulata, we measured ecosystem exchanges of carbon dioxide and water, tree mortality and monitored small mammal diversity in response to ongoing herbivory at sites where beetles have been established for multiple years. Annual monitoring of small mammal populations at saltcedar sites undergoing biological control was conducted at 4 sites, 3 of which have been monitored since before the beetles were released. At most of these sites, a paired location with native vegetation was also monitored for comparison with saltcedar. We continued to examine different restoration strategies for saltcedar invaded sites. We mowed salt cedar plots for the second year of replication in a restoration experiment and applied herbicide treatments to mowed plots. Additionally, we seeded the desired native species into the treated plots. We expanded instrumentation in a pinyon and juniper encroached watershed in central Nevada. We installed a full array of soil moisture probes and instrumentation to monitor the water use of individual trees. Additionally, we are conducting detailed studies on which water sources these trees use and the ability of these trees to redistribute rainfall. We continued to measure the interaction between native annual species and cheatgrass at the level of the individual and the population. A component was added to a current field study and consists of a water addition treatment to assess how the outcome of the interactions might change under different climate scenarios. The first year of a common garden experiment was completed and pots were reseeded as necessary for the second year of the experiment. A complementary greenhouse experiment was completed examining the competitive interactions of cheatgrass and medusahead. We are in the process of selecting additional field sites for another year of research and setting up the common garden experiment for planting in the fall.
1. Effects of saltcedar invasion and biological control of saltcedar on wildlife. In the first major effort to document effects of saltcedar invasion on vertebrate populations other than birds, ARS researchers in Reno, Nevada, continued to monitor small mammal populations in native riparian habitats and in saltcedar habitats and summarized an 11 year dataset. 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 were found to occur exclusively in native habitats, thus implying that these species would respond favorably to saltcedar control. This work fulfills post release monitoring requirements of wildlife required by the APHIS permit. The results justify continuation of the saltcedar biological control program, which is currently postponed due to concerns about effects of saltcedar control on wildlife populations.
2. Effects of saltcedar invasion and biological control of saltcedar on carbon and water cycling. Biological control of saltcedar with Diorhabda carinulata (the northern tamarisk beetle) is currently underway in several western states in the U.S. through historical releases and the natural migration of this insect. Given the widespread dispersal of this biological control agent and its many unknown consequences, ARS researchers in Reno, Nevada, examined a variety of ecohydrological effects of the beetle on a saltcedar invaded ecosystem in the Great Basin Desert, Nevada. Nearly four years of ecosystem carbon dioxide (CO2) and evapotranspiration (ET) fluxes measured with an eddy covariance system were analyzed. After three and a half years of beetle herbivory these data showed that the resulting defoliation events produced short-term decreases in ET and CO2 uptake. However, total ET and CO2 fluxes over the growing seasons were not affected in a clear directional trajectory of reduced ET loss and reduced CO2 uptake, perhaps due to variability in beetle density. This research provides important information on the ecosystem-level effects of biological control and the ability of this system to provide valued ecosystem services, specifically water availability and carbon sequestration potential.
3. Development of genetic markers for medusahead. The invasive weed medusahead is closely related to wheat. SSR markers from wheat that were developed for use in the genome of the invasive weed medusahead were screened in six medusahead populations from the western Great Basin by scientists in the Great Basin Rangelands Research Unit in Reno, Nevada. Differences in the genetic fingerprints produced by these SSR markers indicate varying levels of relatedness between these six populations, suggesting that multiple introductions of medusahead have contributed to this weed invasion. This understanding of the relatedness of different populations will aid in selecting potential control strategies for this invasive weed.
4. Biological control of pinyon pine by native sawflys. Biocontrol is a viable option to control invasive weeds. Based on field observations of severe defoliation of pinyon pine over large areas by epizootics of the pinyon sawfly (Neodiprion edulicolis), it was hypothesized that inundative biological control releases (i.e. releasing large numbers of lab-reared sawflies into areas lacking natural populations) might aid the removal of pinyon trees in areas where they are not desired. Scientists in the Great Basin Rangelands Research Unit in Reno, Nevada, tested the feasibility of this strategy by studying the life-cycle and biology of N. edulicolis in laboratory experiments. The results of the studies indicate that the main challenges to large-scale sawfly rearing are the difficulty in obtaining live pinyon trees for rearing in the greenhouse and the high rate of parasitism in field-collected source populations of sawfly larvae. Otherwise, the sawfly was amenable to laboratory culture and has potential as an inundative biocontrol agent.
Snyder, K.A., Scott, R.L., Mcgwire, K. 2012. Multiple year effects of a biological control agent (Diorhabda carinulata) on Tamarix (saltcedar) ecosystem exchanges of carbon dioxide and water. Agricultural and Forest Meteorology. 164:161-169.