Although glyphosate is typically used as a nonselective herbicide, low rates have the potential to provide selective control of seedling annuals in the understory of established perennial plants. In a repeated experiment on two adjacent sites at a single location near Alturas, CA (2009 and 2010), we evaluated the efficacy of glyphosate at several different rates on medusahead and nontarget species in northern California sagebrush scrub. We applied glyphosate at 10 rates ranging from 0 to 709 g ae ha⁻¹ (0 to 18 oz product acre⁻¹) at three separate timings in each trial: mid-March (medusahead in early seedling stage), late April to early May (tillering), and late May to early June (boot to early head). Plots measured 3 m by 9 m (10 ft by 30 ft) and were arranged in randomized complete blocks with four replications for each rate and timing. We visually estimated vegetative cover for all dominant species in July before medusahead seed drop using three 1-m² quadrats per plot. Medusahead cover declined with increasing rates of glyphosate, and the middle application timing (at tillering) was the most effective. In rate series regression models, we achieved 95% control of medusahead with 160 g ae ha⁻¹ glyphosate in midseason 2009, compared with 463 g ae ha⁻¹ in early season and 203 g ae ha⁻¹ in late season. In 2010, we achieved 95% control with 348 g ae ha⁻¹ in midseason, compared with > 709 g ae ha⁻¹ in early season. Medusahead seed production reflected changes in cover, though individual plants tended to produce more seed at low densities. We attribute reduced control early in the season and poorer overall control in 2010 to greater tolerance of medusahead to glyphosate at lower temperatures. Treatment effects on big sagebrush, as indicated by shoot tip vigor, were minor, although the midseason timing caused a slight reduction in vigor. These results show that low rates of glyphosate (158 to 315 g ae ha⁻¹) at a treatment timing corresponding to medusahead tillering can give economical and effective control of medusahead without long-term damage to big sagebrush.

Nomenclature: Glyphosate; medusahead, Taeniatherum caput-medusae (L.) Nevski; big sagebrush, Artemisia tridentata Nutt.

Management Implications: In a Great Basin sagebrush community, low rates of glyphosate applied at the medusahead tillering stage in late April to early May provided the best control of medusahead. At this timing, we achieved at least 95% control of medusahead cover and a corresponding reduction in seed production with 160 g ae ha⁻¹ (4.1 oz product acre⁻¹) in 2009 and 348 g ae ha⁻¹ (8.8 oz product acre⁻¹) in 2010. Generic glyphosate products have a lower concentration of glyphosate (3 lb ae gal⁻¹) compared to Roundup ProMax used in this study (4.5 lb ae gal⁻¹) and, thus, would require 6 to 13 oz product acre⁻¹ to provide effective control of medusahead at the optimum timing. These rates are far lower than those required to control perennial species and provide a more cost effective option to ranchers and land managers compared to other herbicide treatments. Earlier applications required significantly higher rates to achieve equivalent control. Later applications (close to heading) also gave excellent control at slightly higher rates than applications at tillering. However, late application timing not only provided less competitive release and increased injury of desirable understory species, but also left a cover of standing dead medusahead, increasing the risk of wildfire. A potential negative aspect to the middle application timing is the overlapping timing with big sagebrush bud break. This level of injury did not cause plant death, but did suppress

Japanese stiltgrass, an annual grass species native to eastern Asia, has become a serious invasive-plant problem in the eastern United States. We compared the efficacy of herbicides and nonchemical options found effective for controlling stiltgrass in earlier studies, with organic herbicides and herbicides used at reduced rates in a wooded floodplain along the lower Connecticut River. We compared the effect of 2 yr of conventional and alternative treatments on cover of other nonnative and native species. Four blocks of 18 plots (3 by 4 m [9.8 by 13.1 ft]) were established in May 2008. Treatments included directed heating with a propane torch (June, July), hand-pulling (July), mowing with a string trimmer (July, August), foliar applications of household vinegar [5% acetic acid] (June, July) and the herbicides imazapic (June), pelargonic acid (June, July), and pelargonic acid plus pendimethalin (June). The following herbicides were applied at labeled doses and at one-fourth labeled doses: fenoxaprop-p-ethyl (July), glufosinate (August), and glyphosate (August). Stiltgrass cover and height were evaluated periodically, and plant samples were collected in autumn of 2008 and 2009 to determine the number of viable seeds produced. Final evaluations were conducted in June 2010 after 2 yr of treatment. Stiltgrass cover averaged 88% on untreated plots in fall. All treatments reduced stiltgrass cover and seed production. The least-effective treatments were hand-pulling, pelargonic acid, and vinegar in July. Direct heating, mowing, and vinegar in June reduced seed production by more than 90%. All treatments containing imazapic, pelargonic acid plus pendimethalin, fenoxaprop-p-ethyl, glufosinate, and glyphosate completely prevented stiltgrass seed production in the second year of treatment. Effective control of stiltgrass can be achieved during a 2-yr period with a variety of herbicides, including herbicides at one-fourth of the labeled dose, and through nonchemical treatments.

Nomenclature: Fenoxaprop-p-ethyl; glufosinate; glyphosate; imazapic; pelargonic acid; pendimethalin; Japanese stiltgrass, Microstegium vimineum (Trin.) A. Camus var. imberbe (Nees) Honda.

Management Implications: Japanese stiltgrass, an increasingly common, invasive grass species along riparian and transportation corridors, including hiking trails, can depress native, herbaceous plant populations and alter soil processes. Although earlier studies have shown that several herbicides provide effective control of stiltgrass infestations, many infestations occur in forests where regulations, deeds, or active public opposition can limit herbicide application as a management option. During a 2-yr period, we compared the relative effectiveness of several synthetic herbicides with an “organic” herbicide, acetic acid (household vinegar), and the nonchemical options of hand-pulling, cutting, and directed heating with a propane torch. We also examined the effectiveness of the herbicides fenoxaprop-p-ethyl, glufosinate, and glyphosate at labeled and one-fourth labeled doses. Hand-pulling, pelargonic acid, and vinegar in July were not sufficiently effective to be recommended. Vinegar in June and mowing provided better, but not complete, control. Directed heating and the other herbicides, even at one-fourth doses, provided nearly complete control of stiltgrass. Use of herbicides at low doses might minimize public opposition, provide effective control, and reduce environmental effects. Control of stiltgrass can be achieved without herbicides, but nonchemical methods will require additional time and labor costs.

Paragrass is a nonnative category I invasive species in central and south Florida. This perennial grass species outcompetes native vegetation and is capable of rapid spread by vegetative reproduction. Although glyphosate and imazapyr are effective herbicides for paragrass control, the use of herbicides in certain areas may be restricted because of application timing or environmental concerns. Therefore, our objectives were to examine the effect of water depth (saturated vs. flooded) after burning or cutting, and the effect of water depth and duration after simulated roller-chopping, on paragrass regrowth under controlled conditions. In the first study, paragrass plants were cut or burned with a propane burner to 1 cm (0.39 in) above the soil surface. Plants were either watered daily (control), or were subjected to one of two water treatments: water level at the soil surface (saturated) or flooded to a depth of 44 cm. Burned-saturated or burned-flooded plants had 92% less biomass 5 wk after treatment (WAT) than cut-saturated plants. Flooding resulted in plant death regardless of the plant treatment. In the second study, simulated roller-chopping was performed by cutting paragrass stolons into one-, two-, or three-node segments; planting them into flats; and subjecting them to water treatments for 3, 7, 14, 28, and 42 d. Burning, cutting, and roller-chopping could be useful to control paragrass if subsequent flooding is applied. Future research should focus on evaluating the response of these control techniques in natural areas where water depth can be managed.

Nomenclature: Paragrass, Urochloa mutica (Forsk.) T. Q. Nguyen.

Management Implications: Paragrass is a highly invasive perennial grass species that invades wetland ecosystems of central and south Florida as well as other tropical areas of the world. Invasion of paragrass into such ecosystems typically reduces native species diversity and abundance, and ultimately results in monotypic swards, an unsuitable wildlife habitat. The effect of water depth (saturated vs. flooded) after burning or cutting, and the effect of water depth and duration after simulated roller-chopping on paragrass regrowth were examined under controlled conditions. Burning, cutting, and simulated roller-chopping did not reduce paragrass regrowth without either soil saturation or inundation. In saturated conditions, burning significantly reduced all variables of plant growth compared to cutting. However, both burning and cutting killed paragrass equally when flooded for a period of 5 wk. At least 17 d of flooding or 29 d of saturated conditions were required to reduce paragrass biomass by 90% under our conditions. These results suggest that soil saturation or flooding is required after cultural techniques have been employed. Cutting or burning of paragrass followed by flooding may be an option for natural area managers in areas where herbicides may not be applied due to timing or environmental reasons. Roller-chopping followed by flooding could be an effective option to paragrass control where burning would not possible because of location and timing.

Competitive interactions between native plants and nonnative, invasive plant species have been extensively studied; however, within degraded landscapes, the effect of interspecific interactions among invasive plants is less explored. We investigated a competitive interaction between two sympatric, invasive mustard species that have similar life history strategies and growth forms: garlic mustard and damesrocket. Greenhouse experiments using a full range of reciprocal density ratios were conducted to investigate interspecific competition. Garlic mustard had a negative effect on the final biomass, number of leaves, and relative growth rate in height of damesrocket. Survival of damesrocket was not negatively affected by interspecific competition with garlic mustard; however, garlic mustard showed higher mortality because of intraspecific competition. These results indicated that although garlic mustard has been observed to be the dominant species in this landscape, it may not completely outcompete damesrocket in all situations. Studies of invasive species in competition are important in degraded landscapes because this is the common situation in many natural areas.

Nomenclature: Damesrocket, Hesperis matronalis L.; garlic mustard, Alliaria petiolata (Bieb.) Cavara & Grande.

Management Implications: In degraded habitats, nonnative, invasive plant species not only compete against the resident, native plant species but also compete against the other invasive species present. To take the first steps in understanding the dynamics of invasive plant competition, we conducted a greenhouse study in which we grew two species in competition that regularly occur together in northwest Indiana: garlic mustard [Alliaria petiolata (Bieb.) Cavara & Grande] and damesrocket (Hesperis matronalis L.). These two species are closely related (both are in the Brassicaceae [mustard] family) and share similar life histories (both are biennials). These species were grown both alone and together in a wide range of densities to determine which was the better competitor. Final aboveground biomass, final leaf number, height growth rate, and mortality were all monitored. At the end of the study, it was determined that when garlic mustard was grown in mixture with damesrocket, it had a negative effect on the aboveground biomass, final leaf number, and height growth rate of damesrocket. Garlic mustard, however, had greater mortality when grown in mixture with damesrocket because of intraspecific competition. Thus, based on this study, it is unclear which species would become dominant in areas where they coexist. Other factors, such as availability of light and moisture as well as differences in phenology, are most likely important in the final outcome and need to be researched further in field studies. The ability of damesrocket to survive in competition with garlic mustard indicates that despite the domination by garlic mustard in the northeastern U.S. landscape, damesrocket can compete with this species, at least in the context presented in the greenhouse study. Thus, it is possible that in certain scenarios, damesrocket may prove to be a threat similar to garlic mustard.

The eradication of an invasive plant species can provide substantial ecological and economic benefits by eliminating completely the negative effects of the weed and reducing the high cost of continuing control. A 5-yr program toward the eradication of hill raspberry (Rubus niveus Thunb.) in Santiago Island is evaluated using delimitation and extirpation criteria, as well as assessment of the ecological community response to management techniques. Currently, hill raspberry is located in the humid zone of Santiago island. It is distributed over three main infestations, small patches, and many scattered individuals within an area of approximately 1,000 ha. New infestations are constantly being found; every year, new detections add an area of approximately 175 ha. Adult and juvenile individuals are still found, both beyond and within known infestations. Both plant and seed bank density of hill raspberry decreased over time where infestations were controlled. Species composition in the seed bank and existing vegetation were significantly different between areas under intensive control and adjacent uninvaded forest. After 5 yr of intensive management, delimitation of hill raspberry has not been achieved; new populations are found every year, increasing the infested area that requires management. Off-target effects on native species resulting from control efforts seem to be substantial. Although a vast increase in economic investment would allow intensive searching that might enable all individuals to be found and controlled, the resultant disturbance and off-targets effects could outweigh the conservation benefits of eradication.

Nomenclature: Hill raspberry, Rubus niveus Thunb.

Management Implications: During the last two decades, the Galapagos National Park Directorate and the Charles Darwin Foundation have been carrying out control and eradication programs to restore natural areas that have been degraded by invasive plant species. Control has proved to be costly and perennial and at best has slowed the spread of invasives. Similarly, eradication has had limited success, with only four (targeting weeds with small distributions and transient seed banks) out of 30 programs reaching the goal. Hence, there is an obvious need to evaluate the current 5-yr eradication program targeting hill raspberry in Santiago Island. Eradication does not seem feasible with the current search methodology, primarily because of the failure to find all plants before they fruit. Therefore, one of the fundamental requirements for successful eradication is not being met. Increase in the frequency and extent of search and control operations would be needed to meet this requirement, with all known and potential sites being visited at 4- to 6-month intervals to prevent fruit production. Although larger infestations can be seen from a helicopter, the discovery of all individual plants would require cutting a very closely spaced network of paths through nearly impenetrable low spiny forest. This more effective search methodology would need to be implemented and maintained until the elimination of the seed bank has been achieved (a minimum of 4 yr and up to 10 yr). It is estimated that it would cost USD 10 million (USD 1 million yr⁻¹) over 10 yr to achieve eradication, a 6.7-fold increase in investment from the current level. Additionally, although herbicide control successfully kills individual plants, it has also affected natural vegetation, and opening a tight network of tracks would also cause concomitant disturbance. If the increased investment is not available or the off-target effects are considered greater than the benefits of eradication, or both, alternative objectives and methodologies (e.g., biocontrol) must be considered for the management of hill raspberry.

Because of its ability to transform ecosystems by increasing the prevalence of fire, the invasive annual red brome is a priority exotic species for management in arid lands of the southwestern United States. By sampling red brome presence and 97 environmental (climatic, topographic, and soil) and native vegetation (e.g., perennial species richness) variables on 126 sites, we assessed biophysical correlates with red brome distribution on a 755,000-ha (1.9 million ac) Mojave Desert landscape. Brome occupied 55 of 126 (44%) 0.09-ha plots. The simplest models (i.e., those containing the fewest or most easily obtained variables) in multivariate (classification trees and nonparametric multiplicative regression) and univariate (χ²) models often portrayed red brome distribution as well, or nearly as well, as more complicated models containing more variables harder to obtain. The models varied, however, in their abilities for describing brome presence compared with absence. For example, a simple classification tree using only elevation, soil great group, parent material, and vegetation type improved estimates of brome presence for 55% of sites, absences for 87%, and overall for 73% of sites compared with a naïve model containing the observed frequency of brome in the data. Conversely, a more complicated model, including soil boron and sulfur, performed better for presences (96%) than for absences (73%; 83% overall). Results also showed variable support for two general postulates in invasive species science. Red brome distribution was not correlated with soil N, which is inconsistent with the supposition that nutrient-rich soils are more prone to invasion. Brome was correlated with native perennial species richness to support the postulate that exotic species abundance is correlated with species-rich habitats, but the correlation was weak (r  =  0.38) and similar in strength to correlations with many other environmental variables. On this relatively low-elevation landscape, the areas currently most invaded by red brome include the higher elevations (> 777 m [2,549 ft]), limestone–sandstone soils, and burrobush and mixed perennial communities. Areas least inhabited by brome are the lowest elevations (< 491 m), gypsum soils, and creosotebush and saltbush communities.

Nomenclature: Burrobush, Ambrosia dumosa (A. Gray) Payne; creosotebush, Larrea tridentata (Sessé & Moc. ex DC.) Coville; red brome, Bromus rubens L.; saltbush, Atriplex spp.

Management Implications: Understanding distributions of exotic species is a key step in mapping, monitoring, and prioritizing management of invasions. On 126 sites within a Mojave Desert landscape, we evaluated the relationship of 97 environmental and native vegetation variables with the presence or absence of the invasive annual red brome (Bromus rubens). Simple models using readily obtainable elevation, soil, and vegetation type variables performed as well, or nearly as well, overall as more complicated models that included variables more expensive or difficult to measure. These simple models can help managers identify areas of the landscape that are currently most heavily invaded by B. rubens and support the development of predictive distributional maps. On this relatively low-elevation landscape (plot elevations ranged from 149 to 1,222 m [489–4,008 ft]), areas where B. rubens frequency was greatest included the higher elevations (> 777 m), limestone–sandstone soils, and burrobush (Ambrosia dumosa) and mixed perennial vegetation types. The lower elevations (< 491 m), creosotebush (Larrea tridentata) communities, and gypsum soils exhibited less B. rubens e

Perennial pepperweed is an invasive plant that is expanding rapidly in several plant communities in the western United States. In California, perennial pepperweed has aggressively invaded seasonal wetlands, resulting in degradation of habitat quality. We evaluated the rate and dynamics of population spread, assessed the effect of disturbance on spread, and determined the biotic and abiotic factors influencing the likelihood of invasion. The study was conducted at eight sites within two wetland regions of California. Results indicate that in undisturbed sites, spread was almost exclusively through vegetative expansion, and the average rate of spread was 0.85 m yr⁻¹ from the leading edge. Spread in sites that were disked was more than three times greater than in undisturbed sites. While smaller infestations increased at a faster rate compared with larger populations, larger infestations accumulated more newly infested areas than smaller infestations from year to year. Stem density was consistently higher in the center of the infestations, with about 2.4 times more stems per square meter compared with the leading edge at the perimeter of the population. The invasion by perennial pepperweed was positively correlated with increased water availability but was negatively correlated with the cover of perennial and annual species. Thus, high cover of resident vegetation can have a suppressive effect on the rate of invasion, even in wetland ecosystems. On the basis of these results, we recommend that resident plant cover not be disturbed, especially in wet areas adjacent to areas currently infested with perennial pepperweed. For infested areas, management efforts should be prioritized to focus on controlling satellite populations as well as the leading edge of larger infestations first. This strategy could reduce the need for costly active restoration efforts by maximizing the probability of successful re-establishment of resident vegetation from the adjacent seedbank.

Nomenclature: Perennial pepperweed, Lepidium latifolium L. LEPLA.

Management Implications: Perennial pepperweed is one of the most important invasive plants of wetland areas in the western United States. In several undisturbed plots at two locations, we showed that its spread was almost exclusively through vegetative expansion along the perimeter of the infestation at an average of 0.85 m yr⁻¹. By comparison, the spread rate was three times greater in a site that was disked, which can explain why disking is not recommended for perennial pepperweed control. Stem densities were nearly 2.5 times higher in the interior of the infestations compared with the leading edge. Because of the reduced stem density, the perimeter of the patch is considered to be easier to control compared with the denser patch centers. Small infestations expanded at a faster rate compared with larger patches, but larger patches added more newly infested areas. We determined that the expansion of perennial pepperweed was more closely correlated with increased water availability but was negatively correlated with resident plant cover. Thus, we conclude that the most appropriate strategy for managing perennial pepperweed is to minimize disturbance of plant cover and control both the rapidly expanding satellite infestations and the perimeter of larger infestations. Concentrating management efforts on the densely stemmed, more difficult to control, and highly thatched regions at the center of the infestation might not be cost effective. These areas also have less resident vegetation. Furthermore, the ability of desirable resident vegetation to re-establish from the adjacent seedbank at the perimeter of the infestation could also prevent the need for expensive active restoration programs when focusing on the center of large infestations.

Integrated weed management strategies (IWM) are being advocated and employed to control invasive plants species. In this study, we compared three management strategies (biological control alone [BC], BC with fire [BC F], and BC with mowing [BC M]) to determine if physical controls reduce seed production by Scotch broom and interfere with the action of the biological control agent—the Scotch broom seed weevil. We measured seed production and seed predation by the weevil at both pod and plant scale, and seed bank density over two field seasons. We found no difference in the number of seeds per pod among management strategies. However, combining management strategies (BC M and BC F) resulted in significant reductions in pods per plant, mature seeds per plant, and seed bank density relative to biological control alone. We did not find differences among management strategies in number of weevils per pod or proportion of seeds predated by the weevil at either pod or whole-plant scale. However, combining management strategies (BC M and BC F) resulted in a significant reduction in healthy mature seeds per plant relative to biological control alone. Although both integrated strategies outperformed biological control alone in reducing seed production and the seed bank, with no statistical difference between them, we propose that short-rotation prescribed fire could prove to be a more effective strategy for long-term management of Scotch broom due to its potential for slightly greater depletion of the seed bank.

Nomenclature: Scotch broom, Cytisus scoparius (L.) Link; Scotch broom seed weevil, Exapion fuscirostre Fabricius.

Management Implications: High fecundity and large seed banks have limited the success of biological control of Scotch broom in the United States. However, there is awareness among land managers that effective control of weeds requires the integration of biological control with other control techniques. For example, land managers at Fort Lewis in Washington have used repeated prescribed fire and mechanical removal since the late 1980s to manage Scotch broom. In this study we examined if the integration of physical controls with biological control by the Scotch broom seed weevil could reduce seed production by Scotch broom and interfere with the action of the biological control agent.

We measured the impact of three management strategies, biological control alone (BC), and combination of BC with either fire (BC F) or mowing (BC M), on seed production and seed bank size, and seed predation by the weevil at both the pod and plant scale. Combining management strategies (BC M and BC F) resulted in significant reductions in the number of pods per plant, mature seeds per plant, and seed bank density relative to biological control alone. Weevil seed predation rates were enhanced in BC M and BC F plots, compared to BC-alone plots, but these differences were not consistently statistically significant. However, there was a reduction in number of healthy mature seeds per plant in both BC M and BC F plots, compared to BC-alone plots. We found no differences between BC M and BC F plots for any of these variables. There also was no difference among management strategies in the number of weevils per pod. These results show that management of Scotch broom necessitates the integration of biological control with repeated applications of physical control methods. Although both integrated strategies outperformed BC alone in reducing seed production and the seed bank, short-rotation prescribed fire might be more effective than mowing for long-term management of Scotch broom due to its potential for slightly greater depletion of the seed bank.

Where the nonnative annual grass downy brome proliferates, it has changed ecosystem processes, such as nutrient, energy, and water cycles; successional pathways; and fire regimes. The objective of this study was to develop a model that predicts the presence of downy brome in Central Oregon and to test whether high presence correlates with greater cover. Understory data from the U.S. Department of Agriculture (USDA) Forest Service's Current Vegetation Survey (CVS) database for the Deschutes National Forest, the Ochoco National Forest, and the Crooked River National Grassland were compiled, and the presence of downy brome was determined for 1,092 systematically located plots. Logistic regression techniques were used to develop models for predicting downy brome populations. For the landscape including the eastside of the Cascade Mountains to the northwestern edge of the Great Basin, the following were selected as the best predictors of downy brome: low average March precipitation, warm minimum May temperature, few total trees per acre, many western junipers per acre, and a short distance to nearest road. The concordance index  =  0.92. Using the equation from logistic regression, a probability for downy brome infestation was calculated for each CVS plot. The plots were assigned to a plant association group (PAG), and the average probability was calculated for the PAGs in which the CVS plots were located. This method could be duplicated in other areas where vegetation inventories take place.

Nomenclature: Downy brome, Bromus tectorum L.; western juniper, Juniperus occidentalis Hook. var. occidentalis.

Management Implications: Currently, there is interest in how downy brome might change fire return intervals throughout the West and whether prescribed fire will help or cause further problems by favoring downy brome infestations. Of special interest is the question of how to manage dry western rangelands and forests in the face of climate change with the recent push by the U.S. Federal Government to recognize climate change and manage forests for future climates. Land managers must consider how large-scale disturbances may reset plant association groups as climate changes. Areas with healthy native plant populations can keep downy brome populations minimized; however, if the native plants are wiped out by a large-scale disturbance and the climate is slightly warmer and drier than it had been historically, downy brome could easily spread and then alter fire regimes that maintain the downy brome population. Keeping downy brome out of an area is far easier than trying to eradicate it once it becomes established.

This article presents a statistical model that land managers can use to predict the presence of downy brome in Central Oregon. For example, land managers in Central Oregon who know the values of average March precipitation, minimum May temperature, total trees per acre, western junipers per acre, and distance to the nearest road can calculate the probability of downy brome presence. For land managers in the Deschutes National Forest, Ochoco National Forest, and Crooked River National Grassland, a map has been generated showing the probability of finding downy brome. Land managers in other areas can use the methods in this article to create a statistical model, using standard inventories, such as Current Vegetation Survey or Forest Inventory and Analysis. The probability of downy brome presence can be used to make informed decisions about fuels treatments and other management actions.

Roads function as prime habitats and corridors for invasive plant species, and can contribute significantly to the spread and establishment of weeds inside protected areas. Smooth bedstraw (Galium mollugo) populations have recently expanded in the abandoned agricultural fields of Bic National Park (Quebec, Canada), and may represent a threat to the preservation of plant diversity and to the quality of visitor experience. The main objective of this study was to map the distribution of the species in the park and to delineate factors influencing the abundance of the plant in fallow fields. We hypothesized that road proximity was the main factor explaining the presence and abundance (frequency of recording) of smooth bedstraw in fields. Vegetation surveys were conducted in abandoned agricultural fields, and two logistic regression models were built to examine the relationship between the presence and abundance of smooth bedstraw and environmental and historical variables. Smooth bedstraw populations were also mapped along transportation corridors. The abundance of smooth bedstraw significantly increases within 125 m (410 ft) of a paved road. The recent proliferation of smooth bedstraw in Bic National Park is likely associated with the construction of road embankments during the paving of gravel roads. The paved road network has probably acted as a dispersal corridor for smooth bedstraw, while the abandoned agricultural fields located close to the paved roads provided suitable habitats facilitating population establishment over large areas. We recommended to the park's authorities to cease paving all remaining gravel roads in the park, not only to stop smooth bedstraw invasion, but also the spread of other invasive species of concern.

Nomenclature: Smooth bedstraw, Galium mollugo L.

Management Implications: Roads function as prime habitats and corridors for invasive plant species, and can contribute significantly to the spread and establishment of weeds inside protected areas. We observed this phenomenon in a small national park in eastern Canada, where smooth bedstraw recently invaded abandoned agricultural fields. Plant diversity of these fields is at risk. Abandoned agricultural fields transformed into monotonous white-colored landscapes could also detract from visitor experience. We show in this study that the recent paving of some road sections of the park has probably initiated the invasion. The abundance of smooth bedstraw in abandoned agricultural fields significantly increases within 125 m of a paved road. Controlling smooth bedstraw with herbicides is not an option is this natural park. We recommended ceasing paving all remaining gravel road sections in the park in order to stop not only smooth bedstraw invasion, but also the spread of other invasive species of concern. This presents a challenge, because park authorities face strong pressure from vacationers to pave roads. This study nevertheless provides strong arguments in favour of a nonpaving solution, for the benefit of a more diverse landscape.

Common reed (Phragmites australis) is an invasive perennial grass in aquatic and riparian environments across the United States, forming monotypic stands that displace native vegetation that provides food and cover for wildlife. Genetic variation in global populations of common reed has given rise to two invasive haplotypes, I and M, in the United States. Our objectives were to (1) determine if any differences in herbicide efficacy exist with respect to common reed haplotypes I and M and (2) screen for other labeled aquatic herbicides that may have activity on common reed haplotypes I and M, most notably imazamox and diquat. A replicated outdoor mesocosm study was conducted in 1,136-L (300-gal) tanks using haplotypes I and M of common reed. Restriction fragment length polymorphism methodologies were used to verify the identification of I and M haplotypes used in this study. Diquat at 2.2 (1.9) and 4.5 (4.0) kg ai ha⁻¹ (lb ai ac⁻¹), glyphosate at 2.1 (1.8) and 4.2 (3.7) kg ae ha⁻¹ (lb ae ac⁻¹), imazamox at 0.6 (0.5) and 1.1 (0.9) kg ai ha⁻¹ (lb ai ac⁻¹), imazapyr at 0.8 (0.7) and 1.7 (1.5) kg ai ha⁻¹ (lb ai ac⁻¹), and triclopyr at 3.4 (3.0) and 6.7 (5.9) kg ae ha⁻¹ (lb ae ac⁻¹) were applied to the foliage of common reed. After 12 wk, no difference (P  =  0.28) in herbicide tolerance was seen between the two haplotypes with respect to biomass. The 4.2-kg ae ha⁻¹ rate of glyphosate and the 0.8- and 1.7 kg ai ha⁻¹ rates of imazapyr reduced common reed by > 90% at 12 wk after treatment (WAT). Imazamox at 0.6 and 1.1 kg ai ha⁻¹, and triclopyr at 3.4 and 6.7 kg ae ha⁻¹ reduced common reed biomass (62–86%) at 12 WAT, though regrowth occurred. Diquat did not significantly reduce biomass by 12 wk. Glyphosate and imazapyr were the only herbicides that resulted in > 90% biomass reduction and corroborate control from previous studies.

Nomenclature: Diquat; glyphosate; imazamox; imazapyr; triclopyr; common reed, Phragmites australis (Cav.) Trin. ex Steud PHRCO.

Management Implications: Common reed (Phragmites australis) is an invasive perennial grass in aquatic and riparian environments across the United States. Common reed has high genetic variability, with two unique haplotypes, I and M, having the greatest distribution. Our common garden mesocosm study indicated that there was no difference in the susceptibility of the two most common haplotypes (I and M) to a selection of aquatic herbicides. Glyphosate and imazapyr at all rates evaluated provided excellent control of common reed and would be recommended for large-scale applications. Triclopyr provided good control only at the maximum application rate, and regrowth tended be quicker (as observed new shoot growth) than in plants treated with either glyphosate or imazapyr, but may be a more selective option depending upon associated species. Identifying effective herbicides and use patterns for controlling common reed will provide land managers with necessary information on effective selective and nonselective control of this invasive plant in aquatic systems.

The negative effect of invasive species on native species, communities, and ecosystems is widely recognized, and the economic effects in the United States are estimated to be billions of dollars annually. Studies often examine traits of nonnative species or examine what makes a particular habitat invasible. To better understand the factors governing invasions, we used the flora of Nebraska to characterize and compare native and nonnative plant occurrences throughout the state. In addition, we assessed four critical landscape predictors of nonnative plant richness: human population size and three land cover attributes that included percentage of grassland, percentage of agriculture, and percentage of public lands. Results indicated that individual plant species richness has increased by about 35% through invasions (primarily of annuals from the family Poaceae). In addition, human population density, percentage of agriculture, and percentage of public lands all show a positive association with nonnative plant richness. Successful plant invasions may change the composition of species communities, basic ecological functions, and the delivery of ecosystem services. Thus, identifying the factors that influence such variation in distribution patterns can be fundamental to recognizing the present and potential future extent of nonnative plant infestations and, in turn, developing appropriate management programs.

The widespread recognition that nonnative plants can have significant biological and economic effects on the habitats they invade has led to a variety of strategies to remove them. Removal alone, however, is often not sufficient to allow the restoration of altered communities or ecosystems. The invasive plant's effects may persist after its removal thus exerting a “legacy” that influences community composition or the ecosystem properties or both over some ensuing period. Here, we review evidence of such legacy effects on plant and soil communities, soil chemistry, and soil physical structure. We discuss this evidence in the context of efforts to restore community composition and ecosystem function in invaded habitats. Legacies are especially likely to develop in cases where invasive species cause local extirpations of resident species, alter resource pools, and interact with other aspects of global change including land-use changes, atmospheric N deposition, acid rain, and climate change. In cases where legacies of invasive plants develop, the removal of the nonnative species must also be accompanied by strategies to overcome the legacies if restoration goals are to be achieved.

Plant invasions can have large effects on ecosystem services. Some plant invaders were introduced specifically to restore key services to ecosystems, and other invaders are having unintended, detrimental effects on services, such as the quantity and quality of water delivered, flood control, erosion control, and food production. Many ecosystem services are difficult to measure directly, and although there are extensive studies on plant invaders and ecosystem processes, a number of challenges prevent us from confidently extrapolating those processes as proxies for services. To extrapolate local, short-term measures of processes to ecosystem services, we must: (1) determine which processes are the key contributors to a service, (2) assess how multiple processes interact to provide a given service, (3) determine how vegetation types and species affect those processes, and (4) explicitly assess how ecosystem services and their controls vary over space and time, including reliance of ecosystem services on “hot spots” and “hot moments” and a minimum size of a vegetation type in the landscape. A given invader can have positive effects on some services and negative effects on others. It is important to consider that, in some systems, shifting environmental conditions may no longer support native species and that invasive species may be critical contributors to the resilience of ecosystem services.

Management Implications: There is increasing interest in managing for multiple ecosystem services, but ecosystem science cannot yet provide the information needed by managers to select management approaches that can reliably provide a given service at a given site, or even to reliably measure the effects of management practices on some services. Few studies have quantified the effects of invasive species on ecosystem services (the benefits provided to humans), although many have documented effects on ecosystem processes, which are the fundamental drivers of services. In order to use ecosystem processes as proxies for estimating ecosystem services, we must:

This approach will improve our ability to measure and predict the effects of invasive plants, improving our criteria for prioritizing invasive species management. It is important to consider that invaders can have positive effects on some services and negative effects on others, relative to native species. Invasive species may degrade some systems, but in others, shifting environmental conditions may no longer support native species, making invasive species critical contributors to the resilience of ecosystem services.