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.

Nomenclature: Glyphosate; common velvetgrass, Holcus lanatus L.

Management Implications: This study was designed to evaluate short-term effects of a single application of chemical and mechanical control techniques on Holcus lanatus L. (common velvetgrass) cover and nontarget plant cover and species richness. Our results showed that various glyphosate concentrations were equally effective at reducing cover of common velvetgrass, and that there were no statistically significant effects of treatments on nontarget cover and species richness. A one-time spot spray application was effective at reducing common velvetgrass in the post-treatment year 1, but not longer. These spot-spray herbicide treatments, even at the highest concentrations, did not have detrimental effects on nontarget species. This is particularly important where land management objectives are not just to control invasive plant infestations but also to support native species, special status plants, or traditionally used plants (i.e., plants species that are important in ongoing American Indian traditional cultural practices such as those involving ceremony, subsistence and artistry). Despite the lack of herbicide impacts to nontarget species at any of the concentrations evaluated, the lowest concentration (0.5%) would be recommended because higher concentrations were no more effective at controlling velvetgrass. Despite the statistically significant reduction in common velvetgrass cover during posttreatment year 1, 6.3% common velvetgrass cover still remained, and the reduced cover effect was gone by posttreatment year 2. This study suggests that glyphosate treatments could be an option to control common velvetgrass, but one application will not maintain control after the first year. In order to gain long-term control, managers could experiment with glyphosate treatments repeated annually or even multiple times per year to control infestations. Hand pulling common velvetgrass at these densities for only one year was ineffective at controlling common velvetgrass. Moreover, studies have suggested

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.

Nomenclature: Aminocyclopyrachlor; quinclorac; leafy spurge, Euphorbia esula L.; western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles).

Management Implications: The Sheyenne National Grassland (SNG) is a native tall grass and mixed grass prairie located in southeastern North Dakota that has been invaded by leafy spurge (Euphorbia esula L.). Most herbicides commonly used for leafy spurge control cannot be used on the SNG due to very sandy soils (> 80%) and shallow groundwater. Previous control programs had utilized picloram which subsequently was found in a stock well on the grassland. The widely successful biological control agent Aphthona spp. has not established in a high enough population to noticeably reduce leafy spurge. At the time of the study, 2,4-D was the single herbicide option that could be used on the SNG, but only provided short-term (< 3 mo) top-growth control. A new noxious weed management plan was adopted which included aminocyclopyrachlor and quinclorac as possible options for leafy spurge control. However, the potential for leaching into the groundwater was a concern. Movement of quinclorac and aminocyclopyrachlor was evaluated in soil columns that replicated field conditions from five ecological sites on the SNG. Precipitation was applied to the 70 cm long soil columns as either the average annual precipitation of 51 cm applied over 9 wk or the largest recorded heavy rain event of 15 cm water over 48 h. Quinclorac leached to a depth of approximately 45 cm following the 48 h heavy rain event while movement did not exceed 65 cm following the average annual precipitation regardless of soil type. Aminocyclopyrachlor leaching was greater than quinclorac and moved through the column into the leachate in all soil types following both precipitation events. 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. Only quinclorac was considered suitable for use on the SNG to control leafy spurge and has the added benefit of not harming the western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles), a federally listed threatened plant found throughout the SN

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.

Nomenclature: Aminocyclopyrachlor; dicamba; diflufenzopyr; picloram; yellow toadflax, Linaria vulgaris P. Mill.

Management Implications: Yellow toadflax (Linaria vulgaris P. Mill.) rapidly increased in North Dakota from approximately 20 ha in 1997 to over 6,000 ha by 2011. At the time, the only herbicide labeled for control of this weed was picloram at 1.1 kg ha⁻¹, which only provided short-term reduction and had limited application potential because it is a restricted-use pesticide. Biological control of yellow toadflax was considered an ideal solution but no successful agent was available. To develop a stop-gap management plan to reduce yellow toadflax spread, a series of experiments were conducted with a goal to discover a more effective herbicide control program with minimal impact on nontarget species. The addition of diflufenzopyr to picloram increased yellow toadflax control from < 50% 2 yr after treatment to > 90% and allowed for reduced application rates. Diflufenzopyr is only available in combination with dicamba and in a three-way mixture with picloram provided long-term control when applied throughout the growing season from June through September. Aminocyclopyrachlor applied at various rates provided an average of 85% yellow toadflax control when applied in June but control gradually declined to 50% or less when the treatments were applied in September. Land managers now have at least two options for yellow toadflax control. Picloram plus dicamba plus diflufenzopyr can be applied throughout the growing season to control yellow toadflax, which would allow for well-timed application to co-occurring invasive species such as Canada thistle (Cirsium arvense L.) or leafy spurge (Euphorbia esula L.) because this herbicide combination is effective on all three species. Aminocyclopyrachlor is also effective on these species, but the optimum application window would be early in the season (June) for optimum yellow toadflax control. Both picloram and aminocyclopyrachlor can injure desirable forbs. To alleviate a portion of forb damage, the application of picloram plus dicamba plus diflufenzopyr could be timed for when a desired forb species would be least affected, such as after seed-set. With several available options, managers

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.

Nomenclature: European buckthorn, Rhamnus cathartica L.; garlic mustard, Alliaria petiolata (Bieb.) Cavara & Grande.

Management Implications: Land managers will continue their efforts to control the spread of invasive plants in natural areas. These efforts will generate a volume of plant material that needs to be managed as a waste. This research demonstrates that the use of landfilling for disposal is not the only option available for garlic mustard- and European buckthorn-infested material. Well-managed compost facilities are more than capable of achieving the temperatures necessary to render seeds from these species unviable. Placement of the materials within static managed piles with proper moisture and carbon-to-nitrogen ratios create conditions that are favorable for the destruction of seeds from these species in a short time period. An additional practice that could easily be adopted would be to require placement of infested material in the center of the compost piles and leave them unturned for a period of up to 7 d. This would expose any seeds present to maximum pile temperatures, thus reducing seed viability while still allowing facility operators adequate time to meet the process to further reduce pathogens (PFRP) turning requirements. Other options for waste management include composting materials on site to produce a soil amendment, thus eliminating the cost of transporting and disposal of plants materials as currently practiced.

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 ( =  −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.

Nomenclature: Lehmann lovegrass, Eragrostis lehmanniana (Nees); Old World bluestems, (plains) Bothriochloa ischaemum var. ischaemum (L.) Keng. and (yellow) Bothriochloa ischaemum var. songarica (Rupr. ex Fisch. & C.A. Mey.) Celarier & Harlan.

Management Implications: The breeding, selection, and introduction of exotic forages have led to changes in native terrestrial plant communities in North America. Although not all exotic forages have become invasive, many have become problematic and shown aggressive expansion into areas beyond the initial plantings. Potential changes to the native plant community include reduced species richness, evenness, and diversity, and lower total cover and biomass. These exotic forage species are successful invaders because they are selected for traits conferring persistence under stress such as grazing, repeated haying, and environmental stress. Many of the desirable traits selected for in forage species are similar to traits common in invasive plants such as ease of establishment, high seed production with extensive longevity, vigorous vegetative reproduction, rapid growth rate, competitive resource use, and resistance to removal and predators (insects and disease). Managers should carefully consider invasion potential to guide species selection when exotic forage is proposed in a hay or permanent pasture scenario. Managers may also consider using native seed mixes, especially for restoration of natural areas, but native seed costs are currently prohibitive and exotic seed is typically cheaper. This cost discrepancy continues to constrain reseeding natural areas or planting of Conservation Reserve Program fields with seed mixes to optimize wildlife use. We also suggest that managers monitor areas of exotic forage presence and begin measuring expansion over time into other areas. Our results also suggest that managers consider limiting the establishment of wildlife food plots with exotic forage species that may invade beyond the planted areas. Finally, dialogue between managers and other stakeholders is needed to discuss innovative solutions for exotic forage invasion situations or potential situations.

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.

Management Implications: This article develops a framework for assisting decision-makers in developing effective nonnative species policies.

Using cacti in South Africa as a case study, we consider several general approaches for imposing trade bans and evaluate these on the basis of the complexity of information required for implementation, the likely numbers of false positives and false negatives, the degree of public acceptance, and the costs of research and implementation. Following a consultative process, we provide recommendations that have been partly incorporated in national regulations.

Our study highlights the importance of combining scientific research, stakeholders’ opinions, and legal components in developing new nonnative species policies.

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.

Nomenclature: Barb goatgrass, Aegilops triuncialis L.

Management Implications: We studied the long-term effects of a single, prescribed burn on barb goatgrass control and on native and nonnative species diversity in a grassland community in California. A single, late-spring burn reduced the cover of goatgrass for at least 7 yr following the burn. The burn had short-lived, positive effects on the native plant community with an increase in native plant cover and richness for a single year following the burn. The long-lasting effect of a single burn on the goatgrass was unexpected, given other research, which suggests that 2 consecutive yr of fire treatment are required for significant control. We suspect that this burn was particularly effective because it was conducted during a year with high fuel loads, which allowed ground temperatures to reach levels necessary to effectively kill the goatgrass seeds as they fell to the ground in the inflorescence. Our germination study confirmed that the fire effectively reduced the germination rate of seeds contained within intact, but burned, spikelets to near zero. It is rare for a study to track a management treatment for more than 2 to 3 yr, but our results demonstrate that there is great value in doing so. Prescribed burning is a very costly and risky treatment to implement, so understanding how well it works and how often a site should be burned to control the target species is very useful for decision makers. We were also able to document a distinct trend in goatgrass and native species cover over that period and to evaluate how that trend aligned with climatic data like rainfall. In fact, we believe total rainfall amounts may have affected the goatgrass in two ways: high rainfall in the year of the burn produced above-average biomass, which fed a hotter and more-complete burn, and low rainfall starting 3 yr after the burn may have reduced the cover of goatgrass in both burned and unburned plots, potentially prolonging the fire’s effect.

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.

Nomenclature: Kudzu, Pueraria montana var. lobata (Willd.) Maesen & S.M. Almeida; cereal rye (Secale cereale L.); alfalfa, Medicago sativa L.; barley, Hordeum vulgare L.; canola, Brassica napus L.; rice, Oryza sativa L.

Management Implications: The U.S. bioenergy industry seeks to cultivate dedicated energy crops to meet increasing demands for bio-based energy sources. Many of these potential crops are not native to the United States and are large-statured, perennial species with fast growth rates that effectively compete with resident vegetation—all traits shared by many invasive plants. Therefore, there have been repeated calls to prevent the introduction and wide cultivation of invasive species for bioenergy. One method widely used to identify the invasion risk of new species are weed risk assessments, with the Australian (A-WRA) and United States (US-WRA) versions being the most widely used. To identify the invasion risk of bioenergy crops, we compared their A-WRA and US-WRA scores to those of the 14 of the most-common agronomic crops and 10 invasive species originally introduced for agriculture. This allowed us to compare the biofuels to crops, which we expected to have low WRA scores and to known invaders, which we expected to have high WRA scores. Both WRAs found most species to be high risk, including many crops. The WRAs suffer from many limitations, including being unable to deal with species that include high intraspecific variation, like Sorghum bicolor, which is both a crop and weed. Therefore, WRAs should be used cautiously in setting policy, even when only serving as the first tier of a multistep, risk-assessment process.

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.

Nomenclature: Glyphosate; downy brome, Bromus tectorum L. BROTE; Japanese brome, Bromus japonicus Thunb. ex Murr. BROJA.

Management Implications: Broad-scale low-rate glyphosate application over rangelands infested with annual bromes is an attractive option for increasing forage production of perennial grasses in the northern Great Plains. When we assessed the impact of glyphosate applied in fall or in fall and spring on annual bromes (downy brome and Japanese brome) and nontarget species abundance at two sites over 2 yr, we found that a fall application of 210 g ha⁻¹ reduced downy brome cover and increased Japanese brome seed bank. Negative nontarget effects were not observed. Because Japanese brome and downy brome tend to co-occur in northern Great Plains rangelands and their negative impacts to perennial grass production are similar, broad-scale low-rate glyphosate application is likely not a reliable option for rangeland improvement.

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.

Nomenclature: Red brome, Bromus rubens L.; African mustard, Brassica tournefortii Gouan.

Management Implications: In the arid and semiarid regions of the southwestern United States, two nonnative, invasive plant species, red brome (Bromus rubens L.) and African mustard (Brassica tournefortii Gouan) occur at varying levels of abundance. Within the study region (i.e., the area from which presence and high abundance data were collected), bioclimate envelope models (BEMs) indicate current widespread climatic suitability for the presence of both species. However, central and northwest Arizona, southern Nevada, and Baja California, Mexico, are currently most climatically suitable for high abundance of Bromus rubens. Hot, dry regions of southern California are currently most climatically suitable for high abundance of Brassica tournefortii. Based on a high threshold (6 or more of 10 models project suitability), climatic suitability is projected to increase only for Bromus rubens presence ( 12%), whereas climatic suitability for Brassica tournefortii presence could decrease (−34%). Similarly, climatic suitability for high abundance of Bromus rubens (−42%) and Brassica tournefortii (−56%) could also decrease. For Brassica tournefortii, areas of contraction (i.e., projected loss of climatic suitability) appear in southern Arizona and California, and in Baja California and Sonora, Mexico. For high abundance of Bromus rubens, contraction is projected to occur along the southern edges of climatically suitable area, primarily in Arizona and Nevada. Climatic suitability for Brassica tournefortii is projected to contract mainly in western Nevada, southeastern California, and Baja California, Mexico. Based on an ensemble of future models and a low threshold (any 1 of 10 models projects suitability), climatic suitability

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.

Nomenclature: Garlic mustard, Alliaria petiolata (Bieb.) Cavara & Grande; purple loosestrife, Lythrum salicaria L.; reed canarygrass, Phalaris arundinacea L.; common reed, Phragmites australis (Cav.) Trin. ex Steud.; Japanese knotweed, Polygonum cuspidatum Sieb. & Zucc.; multiflora rose, Rosa multiflora Thunb. ex Murr.

Management Implications: The progression from individual plant invasions to the establishment of widespread exotic communities requires that potential invaders are available and that there is suitable habitat in which they can establish. Nonnative riparian plant communities are widespread, particularly in urban areas, and often share common species. We evaluated the hydrologic and geomorphologic parameters that might influence the urban riparian distributions of six common nonnative riparian species in the urbanized upper Niagara River watershed: garlic mustard, purple loosestrife, reed canarygrass, common reed, Japanese knotweed, and multiflora rose. We found that four of these species are well established in the region so that seed availability did not appear limiting; instead, we found riparian canopy cover the strongest limiting factor on the invasive riparian communities. These data suggest that limiting the distribution of invasive species in urban riparian habitats requires a straightforward approach: restore riparian forests. Forest restoration in urban/riparian habitats is a widespread management goal expected to create many ecological benefits, including improved habitat and water quality. Still, the stream–forest interface is inherently edge habitat, and invasive species thrive along forest edges. Increasing forest canopy may reduce invasive species communities, but the widespread presence of well-established riparian invaders and the mitigating effects of stream-bank edge habitat suggest that full eradication is unlikely. Moreover, we also found conflicting species-specific associations and habitat responses, suggesting that managing individual invasive species may require specific interventions.

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.

Nomenclature: Sethoxydim; reed canarygrass, Phalaris arundinacea L.

Management Implications: Adaptive management requires information exchange among researchers and managers to develop science-based decisions. Our example in Curtis Prairie shows there is no simple approach that will control reed canarygrass (Phalaris arundinacea) and restore native vegetation. Instead, we found variable outcomes over time for sequential field experiments. First, we removed the litter and standing dead biomass accumulated from the previous year with a site-preparation burn in early April 2005. Our subsequent test of the timing of a grass-specific herbicide showed that sethoxydim (as Vantage) temporarily halted flowering of Phalaris (thereby keeping the canopy short). We found the same response in two subsequent years (one herbicide application per year). At no time was there evidence that this herbicide could kill the invader. Sethoxydim was not effective despite being labeled a grass-specific herbicide.

In 2006, a new field experiment compared the sethoxydim treatment with and without a growing-season burn treatment in late May, expecting the burn to reduce the live canopy cover and potentially stimulate seed germination of native species. A late-May burn followed by sethoxydim in late June was effective in reducing cover in 2006; however, when we repeated the treatment in 2007 (our third experiment), there was little effect. The level of control achieved in this year deserves further research to find optimal conditions when the invader will respond to a burn followed by an herbicide.

Sowing seeds of 32 native perennial plants (excluding grasses) did not establish natives in 2005, but some species appeared by 2007. Carex stipata and Asclepias incarnata were found to be expanding in 2011 to 2012. Long-term follow-up is needed to document lag effects.

Adaptive restoration improved our understanding of limitations of both invader eradication and native plant restoration. Repeating the most promising treatment demonstrated the importance of conducting multiple tests before recommending