Invasive Species
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In 2006, we initiated fuel reduction treatments (prescribed fire, mowing, and herbicide applications [tebuthiuron and imazapic]) in six Artemisia tridentata ssp. wyomingensis communities. We evaluated long-term effects of these fuel treatments on: (1) magnitude and longevity of fuel reduction; (2) Greater sage-grouse habitat characteristics; and (3) ecological resilience and resistance to invasive annual grasses. Responses were analyzed using repeated-measures linear mixed models. Response variables included plant biomass, cover, density and height, distances between perennial plants, and exposed soil cover. Prescribed fire produced the greatest reduction in woody fuel over time. Mowing initially reduced woody biomass, which recovered by year 10. Tebuthiuron did not significantly reduce woody biomass compared to controls. All woody fuel treatments reduced sagebrush cover to below 15% (recommended minimum for Greater Sage-grouse habitat), but only prescribed fire reduced cover to below controls. Median mowed sagebrush height remained above the recommended 30 cm. Cheatgrass (Bromus tectorum) cover increased to above the recommended maximum of 10% across all treatments and controls. Ecological resilience to woody fuel treatments was lowest with fire and greatest with mowing. Low resilience over the 10 posttreatment years was identified by: (1) poor perennial plant recovery posttreatment with sustained reductions in cover and density of some perennial plant species; (2) sustained reductions in lichen and moss cover; and (3) increases in cheatgrass cover. Although 10 years is insufficient to conclusively describe final ecological responses to fuel treatments, mowing woody fuels has the greatest potential to reduce woody fuel, minimize shrub mortality and soil disturbance, maintain lichens and mosses, and minimize long-term negative impacts on greater sage-grouse habitat. However, maintaining ecological resilience and resistance to invasion may be threatened by increases in cheatgrass cover, which are occurring regionally.
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Invasive annual grasses, wildfire, and climate change are changing ecosystem processes in the sagebrush biome at a pace and scale requiring an assessment of where processes can be saved, where they can be regained, and where they are lost. Confronting these threats is the primary focus of restoration and management efforts, guiding policy creation, project prioritization, and action on the ground. The new Defend the Core framework helps land managers, landowners, and policy makers to use the tools or management actions most likely to improve conditions.
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Four case studies shared at the 2020 Invasive Annual Grass workshop provide lessons learned and opportunities to advance future management efforts to inform the direction for new science. Tackling the complex problem of invasive annual grass management will require an expansion of science-based case studies of real-world management efforts, strong science and management partnerships, and a platform for continuous learning and communication, such as a comprehensive database to document management outcomes along with Open Access journals that allow publishing of negative and null outcomes.
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This article provides a broad overview of sagebrush plant community ecology, how that ecology has varied through time, the role of invasive annual grasses in influencing sagebrush plant community ecology, and thoughts on a productive path forward.
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The cool wet spring across much of the northwestern US has created a sea of cheatgrass that has improved fuelbed continuity and fuel loading, often exceeding 200 percent of normal. As a result we expect the potential for grass driven wildfires, especially in the Snake River Plain, eastern Washington, northwestern Nevada and northeastern California to be at least average to considerably above average.
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This study propose a trait-based framework for understanding how invasive plants afect native fauna, which draws on community assembly, niche, and trait theories to define the mechanisms by which invasive plants alter ecological conditions relevant to native animals. This approach moves beyond prior frameworks by explicitly accounting for the context dependency that defines most ecological interactions and invasion outcomes.
Short- vs medium-term effects of pre-emergent herbicides on target and non-target species after fire
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While short-term effects of chemical herbicides that target exotic annual grasses were relatively consistent and predictable, longer-term effects were specific to the herbicide and plant community. The “spray-and-release” strategy may confer resistance to re-invasion by exotic annual grasses if herbicides prevent re-invasion for an extended period.
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This study documented a 30% increase in ventenata cover and 55% increase in frequency on the PNB over the past 15 yr, including areas that were not disturbed by fire or cattle grazing. We found only weak evidence that cattle grazing increased ventenata standing crop when compared with cattle-excluded paddocks, something that could be related to timing of use. There was no evidence that prescribed burning impacted the response of ventenata on its own. However, we found some evidence of interactions between cattle grazing and prescribed fire that suggests prescribed burning could help reduce the abundance of ventenata in areas grazed by livestock. These studies reinforce the important differences between ventenata and other invasive winter annuals in grasslands and clarify a need for research that focuses primarily on the dynamics between this relatively new exotic species in grasslands and the many ecosystems it now inhabits.
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Sampling seven taxa from the same sites allowed us to ask how trait–environment–performance associations differ among taxa and whether natural selection favors similar traits across multiple taxa and functional groups. All taxa showed trait–environment associations consistent with local adaptation, and both environment of origin and phenotypes predicted survival in competitive restoration settings, with some commonalities among taxa. Notably, rapid emergence and larger seeds increased survival for multiple taxa. Environmental factors at collection sites, including lower slopes (especially for grasses), greater mean annual temperatures (especially for shrubs and forbs), and greater precipitation seasonality were frequently associated with increased survival. We noted one collection site with high seedling survival across all seven taxa, suggesting that conditions within some sites may result in selection for traits that increase establishment for multiple species. Thus, choosing native plant sources with the most adaptive traits, along with matching climates, will likely improve the restoration of invaded communities.
We compared moderate grazing during the off season with not grazing in five Wyoming big sagebrush−bunchgrass communities in the northern Great Basin. Treatments were applied annually for 10 yr (2009−2010 through 2018−2019). Plant community characteristics were measured after treatments had been applied from 6 to 10 yr. Off-season grazing reduced exotic annual grass density and cover. After a decade, annual grass cover was twofold greater in ungrazed areas. Sandberg bluegrass density increased with off-season grazing, but large bunchgrass density was similar between off-season grazed and ungrazed areas. Perennial and annual forb density and cover were similar between off-season grazed and ungrazed treatments. Biological soil crust cover was also similar between off-season grazed and ungrazed areas.