Kentucky bluegrass was introduced into the present-day United States in the 1600s. Since that time, Kentucky bluegrass has spread throughout the United States and Canada becoming prolific in some areas. In the past century, Kentucky bluegrass has been a presence and often a dominant species in some prairies in the Northern Great Plains. Sometime within the past few decades, Kentucky bluegrass has become the most-common species on the untilled, native prairie sites of much of North and South Dakota. In this article, we hypothesize how Kentucky bluegrass has come to dominate one of the most endangered ecosystems in North America—the prairie—through a historical, ecological, and climatological lens. We urge others to start addressing the invasion of Kentucky bluegrass with both new research and management strategies.

One of the highest priority invasive species at both Yosemite and Sequoia and Kings Canyon national parks is Holcus lanatus L. (common velvetgrass), a perennial bunchgrass that invades mid-elevation montane meadows. Despite velvetgrass being a high priority species, there is little information available on control techniques. The goal of this project was to evaluate the short-term response of a single application of common chemical and manual velvetgrass control techniques. The study was conducted at three montane sites in Yosemite National Park. Glyphosate spot-spray treatments were applied at 0.5, 1.0, 1.5, and 2.0% concentrations, and compared with hand pulling to evaluate effects on cover of common velvetgrass, cover of other plant species, and community species richness. Posttreatment year 1 cover of common velvetgrass was 12.1% ± 1.6 in control plots, 6.3% ± 1.5 averaged over the four chemical treatments (all chemical treatments performed similarly), and 13.6% ± 1.7 for handpulled plots. This represents an approximately 50% reduction in common velvetgrass cover in chemically- treated plots recoded posttreatment year 1 and no statistically significant reduction in hand pulled plots compared with controls. However, there was no treatment effect in posttreatment year 2, and all herbicide application rates performed similarly. In addition, there were no significant treatment effects on nontarget species or species richness. These results suggest that for this level of infestation and habitat type, (1) one year of hand pulling is not an effective control method and (2) glyphosate provides some level of control in the short-term without impact to nontarget plant species, but the effect is temporary as a single year of glyphosate treatment is ineffective over a two-year period.

The Sheyenne National Grassland (SNG) is a native tall grass and mixed grass prairie located in southeastern North Dakota. Approximately half of the SNG has been invaded by leafy spurge (Euphorbia esula L.) and control methods have been limited. Many herbicides cannot be utilized at the SNG due to sandy soils (> 80%) and shallow groundwater, nor can they be applied near the western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles), a federally listed threatened plant found on the SNG. Quinclorac and aminocyclopyrachlor were considered for use on the SNG but potential to enter the groundwater was unclear. Movement of quinclorac and aminocyclopyrachlor was evaluated in 70 cm soil columns that simulated field conditions from five ecological sites. Quinclorac leached further following the heavy rainfall event of 15 cm in 48 h compared to the annual precipitation of 51 cm applied over 9 wk. Quinclorac leached approximately 45 cm into the soil profile averaged over all soil types and both precipitation events but never exceeded 65 cm regardless of soil type. Aminocyclopyrachlor leaching was greater than quinclorac and moved through all soil types into the leachate following both watering regimes. Desorption of both herbicides was incomplete. Approximately 10 and 32% of applied aminocyclopyrachlor and quinclorac, respectively, remained in the top 5 cm of soil regardless of soil type or watering regime. Quinclorac but not aminocyclopyrachlor was considered suitable for use at the SNG to control leafy spurge and has the added benefit of not harming the western prairie fringed orchid.

Yellow toadflax (Linaria vulgaris P. Mill.) infestations in North Dakota increased 300-fold from 1997 to 2011, when the plant was added to the state noxious weed list. Long-term control of other invasive species had included biological control agents, but no effective agents for yellow toadflax had been identified, so a control program using herbicides was needed. The objective was to shift from short-term control with picloram applied in the fall at maximum allowed rates to long-term management with minimal nontarget species impact with an adaptive management approach. Yellow toadflax control was increased from an average of 64% with picloram at 1,120 g ha−1 alone 12 mo after treatment (MAT) to over 90% when applied with diflufenzopyr while the picloram rate was reduced 50%. Yellow toadflax control with aminocyclopyrachlor applied at 140 g ha−1 ranged from 91 to 49% 12 MAT when applied in June or September, respectively. In contrast, yellow toadflax control with picloram plus dicamba plus diflufenzopyr averaged > 90% regardless of application date during the growing season. Land managers now have at least two options for long-term yellow toadflax control with a wide window of application timing. The goal of replacing a single high-use–rate herbicide treatment was met but both picloram and aminocyclopyrachlor can injure many desirable forbs. However, application timing can now be adjusted to have the least impact on nontarget species. The adaptive development program led to a 58% reduction in yellow toadflax infestations in North Dakota by 2014.

Composting is a common practice for management of herbaceous yard materials and other decomposable materials. Although composting is promoted by state agencies for many materials, a notable exception is invasive plants due to concerns about spreading propagules with the finished product. To address this issue, we measured the viability of garlic mustard and common buckthorn seeds exposed to turned or static composting methods. Piles were built in 2012 and 2013, and seeds from both species were inserted and monitored for viability. Seed viability was reduced rapidly regardless of year, composting method, or species. Viability of seeds was zero within 7 and 15 d of composting for garlic mustard and common buckthorn, respectively, in both years. Results indicate that composting facilities are able to render the seeds of these invasive plants nonviable using either composting method because inactivation is within the composting timeframes typically practiced by the industry. This includes the process to further reduce pathogens (PFRP) with thresholds of 55 C for 15 d for the compost management process used for this trial.

Introducing exotic forages in the attempt to enhance livestock and wildlife forage has been practiced widely for over a century. These forage species are selected for traits conferring persistence under stress, potentially yielding invaders that transform native plant communities. Using standardized systematic review guidelines and meta-analytical techniques we quantified effects of exotic forage invasion on change of native plant community structure, and compared the magnitude and direction of change across exotic forage species, plant functional groups, and structure of plant communities. Our study of 13 exotic forage species in North America (six C4 grasses, three C3 grasses, and four legumes) yielded 35 papers with quantitative data from 64 case studies. Nine of the 13 species met our inclusion criteria for meta-analysis. The overall effect of exotic forage invasion on native plant communities was negative (Ē̄ = −0.74; 95% confidence interval [CI]: −0.29 to −0.25). The effect size was most negative for two C4 grasses, Lehmann lovegrass and Old World bluestems. A negative effect was also expressed by C3 and C4 grass functional groups, and these effects were stronger than for legumes. Effect size differed among measures of plant community structure, with the greatest negative effect on native plant biomass and the least negative effect on species evenness. Weighted fail-safe numbers indicated publication bias was not an issue. Exotic forage species are important for agricultural production but may threaten complex multi-functioning landscapes and should be considered as a subset of potentially invasive exotic species. Characteristics making exotic forages different from other exotic plants hinge on pathways of selection and dispersion: selection is based on persistence mechanisms similar to characteristics of invasive plants; dispersion by humans is intentional across expansive geographic regions. Exotic forages present a complex socio-ecological problem exacerbated by disconnected scientific disciplines, competing interests between policy and science, and organized efforts to increase food production.

The rate of transportation, introduction, dissemination, and spread of nonnative species is increasing despite growing global awareness of the extent and impact of biological invasions. Effective policies are needed to prevent an increase in the significant negative environmental and economic impacts caused by invasive species. Here we explore this issue in the context of the history of invasion and subsequent regulation of cacti introduced to South Africa. We consider seven approaches to restricting trade by banning the following: (1) species already invasive in the region, (2) species invasive anywhere in the world, (3) species invasive anywhere in the world with a climate similar to the target region, (4) genera containing invasive species, (5) growth forms associated with invasiveness, (6) cacti with seed characteristics associated with invasiveness, and (7) the whole family. We evaluate each approach on the basis of the availability and complexity of information required for implementation, including the cost of the research needed to acquire such information, the likely numbers of false positives and false negatives, the likely degree of public acceptance, and the costs of implementation. Following a consultative process, we provide recommendations for how to regulate nonnative cacti in South Africa. The simplest option would be to ban all cacti, but available evidence suggests that most species pose negligible risk of becoming invasive, making this option unreasonable. The other extreme—reactively regulating species once they are invasive—would incur significant control costs, likely result in significant environmental and economic impacts, and limit management goals (e.g., eradication might be unfeasible). We recommended an intermediate option—the banning of all genera containing invasive species. This recommendation has been partly incorporated in South African regulations. Our study emphasizes the importance of scientific research, a legal framework, and participation of stakeholders in assessments. This approach builds awareness, trust, and support, and ensures that all interests are reflected in final regulations, making them easier to implement and enforce.

Barb goatgrass is an invasive annual grass from the Mediterranean region that negatively affects both native plant biodiversity and the forage quality of grasslands. Prescribed burning may be the best landscape-level tool available to manage invasive species like barb goatgrass while also enhancing biodiversity, but few studies have quantified the long-term effects of fire on goatgrass and the rest of the plant community. We assessed the effects of fire on an invading front of barb goatgrass on a private ranch in Sacramento County, CA. We established burned and unburned treatment plots within the goatgrass-infested area and used prescribed fire to burn the treatment plots in June 2005. We monitored plant-community composition before burning and for 7 consecutive yr following the burn. Additionally, we tested the viability of goatgrass seeds in both burned and unburned plots. One year after the burn, goatgrass cover in burned plots was 3% compared with 21% in unburned plots. This reduction in goatgrass cover was still strong 2 yr after the burn (burned, 6%; unburned, 27%) and weaker but still statistically significant for 4 of the next 5 yr. The burn also reduced germination of goatgrass seed by 99% as indicated by seed-viability tests conducted in the laboratory. The native plant community responded positively to the burn treatment in the first year following the burn with an increase in native diversity in burned plots vs. unburned plots, but the effect was not detectable in subsequent years. Nonnative annual forb species cover also increased in the first year following the burn. Our study shows that a single springtime burn can result in a short-term boost in native species diversity, reduced seed germination of barb goatgrass to near zero, and reduced cover of barb goatgrass for at least 7 yr after the burn.

Concern raised against using highly competitive, exotic, large-statured, perennial grasses with fast growth rates as bioenergy crops has led to calls for risk assessment before widespread cultivation. Weed risk assessments (WRAs) are decision support tools commonly used throughout the world to determine the invasion risk of new plant taxa—primarily used as a pre-entry screen. Here, we compare the common Australian (A-WRA) and newer U.S. (US-WRA) models to evaluate the invasion risk of 16 candidate bioenergy crops and to compare their WRA scores to 14 important agronomic crops and 10 invasive species with an agronomic origin. Of the 40 species assessed, the A-WRA and US-WRA ranked 34 and 28 species, respectively, as high risk, including the major crops alfalfa, rice, canola, and barley. Surprisingly, in several cases, both models failed to effectively parse weeds from crops. For example, cereal rye received scores above (US-WRA) or comparable to (A-WRA) kudzu, a widespread damaging invader of the Southeastern United States introduced as forage. Our results indicate that these models are unable to accurately address broad, intraspecific variation and that species introduced for agronomic purposes pose special limitations to WRAs. This further supports other calls for postborder evaluation (e.g., field testing) following WRA screening. We should be cautious of the role of WRAs in setting policy, as illustrated by this relative evaluation of novel crops.

Annual bromes (downy brome and Japanese brome) have been shown to decrease perennial grass forage production and alter ecosystem functions in northern Great Plains rangelands. Large-scale chemical control might be a method for increasing rangeland forage production. Although fall application has been shown to be the most effective and least likely to impact co-occurring native species, spring germination of downy brome may reduce the efficacy of fall-only herbicide application. We assessed the impact of a low glyphosate dose rate (210 g ha−1) applied to rangelands in fall or in fall and spring on nontarget species and on annual brome abundance at two sites in eastern Montana over 2 yr. We tested the following hypotheses: (1) nontarget effects are greater with spring herbicide application, (2) fall and spring herbicide application are necessary for effective downy brome control, and (3) fall herbicide application is sufficient to control Japanese brome. Few nontarget effects occurred; two dicotyledonous species exhibited small increases in response to herbicide. We found that that a single fall application reduced downy brome cover and seed bank density, but after the second fall application in the following year, downy brome did not continue to show a response to herbicide. After 2 yr of fall herbicide application, Japanese brome had denser seed banks in plots where herbicide had been applied. Blanket glyphosate application on rangelands is an unreliable method for controlling annual brome invasions in the northern Great Plains.

Nonnative, invasive plants are becoming increasingly widespread and abundant throughout the southwestern United States, leading to altered fire regimes and negative effects on native plant communities. Models of potential invasion are pertinent tools for informing regional management. However, most modeling studies have relied on occurrence data, which predict the potential for nonnative establishment only and can overestimate potential risk. We compiled locations of presence and high abundance for two problematic, invasive plants across the southwestern United States: red brome (Bromus rubens L.) and African mustard (Brassica tournefortii Gouan). Using an ensemble of five climate projections and two types of distribution model (MaxEnt and Bioclim), we modeled current and future climatic suitability for establishment of both species. We also used point locations of abundant infestations to model current and future climatic suitability for abundance (i.e., impact niche) of both species. Because interpretations of future ensemble models depend on the threshold used to delineate climatically suitable from unsuitable areas, we applied a low threshold (1 model of 10) and a high threshold (6 or more models of 10). Using the more-conservative high threshold, suitability for Bromus rubens presence expands by 12%, but high abundance contracts by 42%, whereas suitability for Brassica tournefortii presence and high abundance contract by 34% and 56%, respectively. Based on the low threshold (worst-case scenario), suitability for Bromus rubens presence and high abundance are projected to expand by 65% and 64%, respectively, whereas suitability for Brassica tournefortii presence and high abundance expand by 29% and 28%, respectively. The difference between results obtained from the high and low thresholds is indicative of the variability in climate models for this region but can serve as indicators of best- and worst-case scenarios.

Urban riparian plant communities exist at the interface between terrestrial and aquatic habitats, and they are rich sources of species biodiversity and ecosystem services. The periodic floods that promote species diversity in riparian plant communities also increase their vulnerability to nonnative plant invasions. Plant invasions are constrained by seed and suitable habitat availability. However, how seed dispersal and establishment limitations interact to shape nonnative plant invasions in riparian communities is poorly understood. We use Stream Visual Assessment Protocol data to evaluate the hydrological and geomorphological parameters that influence the seeding and establishment of six common nonnative species in urban riparian habitats: garlic mustard, purple loosestrife, reed canarygrass, common reed, Japanese knotweed, and multiflora rose. To address this objective, we analyzed stream reach data collected during a basin-wide environmental assessment of the extensively urbanized upper Niagara River watershed. We found limited support for our prediction that propagule limitation constrains the distribution of nonnative riparian species, likely because these species are well established in the study area. Instead, we found that opportune stream reach characteristics better predict the distribution of the common invasive riparian species—most notably open tree canopy. Given that there is widespread investment in urban riparian forest restoration to improve water quality, increase stream-bank stability, enhance wildlife habitat and promote recreation, our data suggest that riparian forests may provide the additional benefit of reducing the abundance of some, but not all, invasive plants.

Curtis Prairie is an 80-yr-old restored prairie that, despite its diverse vegetation and dense cover, was invaded by Phalaris arundinacea (reed canarygrass) during the 1980s. Our search for a method to eradicate Phalaris involved field tests of a grass-specific herbicide (sethoxydim as Vantage®). To reduce Phalaris growth and favor native vegetation, we used an adaptive approach that began in 2005 by testing sethoxydim application with and without adding a seed mix of 32 native plants. Sethoxydim reduced flowering but not cover of Phalaris; we therefore reapplied sethoxydim to all the 2005 plots in 2006 and again in 2007. We began a second experiment in 2006 that combined late-May burning followed by late-June sethoxydim application. This combination reduced Phalaris cover the most of all treatments. In a third experiment in 2007 we repeated the late-May burn + late-June sethoxydim treatment but did not find a reduction in Phalaris cover. We attribute differences in burning + herbicide effects to year effects. Because the Phalaris canopy remained dense even where we applied sethoxydim for 3 yr (first experiment, 2005), we were not surprised that our 2005 seeding of 32 native forbs and graminoids (but not grasses) barely increased native species presence. Six years after seeding, however, we found 12 of the seeded species along with 21 unseeded natives. The adaptive approach of designing new experiments based on prior results led to a promising approach in 2006 (burning before applying sethoxydim to the resprouting Phalaris). Repeating that combination in 2007 indicated a year effect and that no single approach would eradicate this clonal grass.