The United States is charging toward the largest expansion of agriculture in 10,000 years with vast acreages of primarily exotic perennial grasses planted for bioenergy that possess many traits that may confer invasiveness. Cautious integration of these crops into the bioeconomy must be accompanied by development of best management practices and regulation to mitigate the risk of invasion posed by this emerging industry. Here I review the current status of United States policy drivers for bioenergy, the status of federal and state regulation related to invasion mitigation, and survey the scant quantitative literature attempting to quantify the invasive potential of bioenergy crops. A wealth of weed risk assessments are available on exotic bioenergy crops, and generally show a high risk of invasion, but should only be a first-step in quantifying the risk of invasion. The most information exists for sterile giant miscanthus, with preliminary empirical studies and demographic models suggesting a relatively low risk of invasion. However, most important bioenergy crops are poorly studied in the context of invasion risk, which is not simply confined to the production field; but also occurs in crop selection, harvest and transport, and feedstock storage. Thus, I propose a nested-feedback risk assessment (NFRA) that considers the entire bioenergy supply chain and includes the broad components of weed risk assessment, species distribution models, and quantitative empirical studies. New information from the NFRA is continuously fed back into other components to further refine the risk assessment; for example, empirical dispersal kernels are utilized in landscape-level species distribution models, which inform habitat invasibility studies. Importantly, the NFRA results in a relative invasion risk to known species (e.g., is giant reed a higher or lower invasion risk than johnsongrass). This information is used to design robust mitigation plans that include record keeping, regular scouting and reporting, prudent harvest and transport practices that consider species biology, and eradication protocols as an ultimate precaution. Finally, a socio-political balance must be struck (i.e., a cost-benefit analysis) among our energy choices that consider the broader implications, which includes the risk of future invasions.

Nomenclature: Giant miscanthus, Miscanthus × giganteus J. M. Greef and Deuter ex Hodk. and Renvoize, giant reed, Arundo donax L., Johnsongrass, Sorghum halepense (L.) Pers.

The spread of medusahead across the western United States has severe implications for a wide range of ecosystem services. Medusahead invasion reduces biodiversity, wildlife habitat and forage production, and often leads to increased fire frequency and restoration costs. Medusahead is problematic in the Intermountain West and California Annual Grasslands. The last review of medusahead ecology and management was completed 20 years ago. Since the last review, there have been scientific advances in medusahead management suggesting a significant need to develop an up-to-date synthesis. Medusahead continues to pose a serious threat to rangeland ecosystems. In this synthesis, we present new information regarding the ecology of medusahead, suggest a framework for managing medusahead based on invasion level, and identify research needs to further improve management of this invasive annual grass. Success of different management practices varies between the Intermountain West and California Annual Grasslands, signifying that the best management practices are those specifically tailored with consideration of climate, soil, plant community characteristics, and management objectives. Prevention and control treatments that are useful in the Intermountain West may not be practical or effective in the California Annual Grasslands and vice-versa.

Nomenclature: Medusahead, Taeniatherum caput-medusae (L.) Nevski; ELYCM.

Hyparrhenia cymbaria (boat thatching grass, ipopo grass) and Hyparrhenia variabilis (no common name), robust African savanna grasses with complex taxonomies, have not yet been reported for the Americas. Large populations were found in central Jalisco, northeastern Michoacán, and Morelos, Mexico. The species grow in maize and sorghum fields as well as on roadsides and in old fields, but always in association with present or past sorghum cultivation; this suggests introduction through contaminated seed material from Africa. Because of the size and density of the populations, and their native ecology, they are both agricultural pests as well as a potentially dangerous invaders for the American (sub)tropical grasslands and native scrublands, including the southern United States. The invasion underlines the importance of effective phytosanitary controls of the seed supply.

Nomenclature: Boat thatching grass, Hyparrhenia cymbaria (L.) Stapf, Hyparrhenia variabilis Stapf.

Biofuel crops such as napiergrass possess traits characteristic of invasive plant species, raising concern that biofuels might escape cultivation and invade surrounding agricultural and natural areas. Napiergrass biofuel types are being developed to have reduced invasion risk, but these might be cultivated in areas where naturalized populations of this species are already present. The successful management of napiergrass biofuel plantations will therefore require techniques to monitor for escaped biofuels as distinguished from existing naturalized populations. Here we used 20 microsatellite DNA markers developed for pearl millet to genotype 16 entries of napiergrass, including naturalized populations and accessions selected for biofuel traits. Use of the markers showed a clear genetic separation between the biofuel types and naturalized entries and revealed naturalized populations undergoing genetic isolation by distance. These findings demonstrated the utility of microsatellite marker transfer in the development of an important tool for managing the invasion risk of a potential biofuel crop.

Nomenclature: Napiergrass, Pennisetum purpureum Schumach., pearl millet, Pennisetum glaucum (L.) R. Br.

Management Implications: Cellulosic biofuels offer opportunities for sustainable energy production, but many traits of biofuel crop species increase the potential for escape and invasion into surrounding natural areas. Biofuel crop accessions might be selected for high biomass and reduced invasion risk, but management of biofuel plantings will nevertheless require a means to monitor for the escape of cultivated varieties, especially in areas where naturalized populations of the same species are also present. DNA microsatellite markers offer technical and practical advantages for this purpose, including marker transferability. Markers that have already been developed for a crop or model species can be transferred to a related species, sparing the time and cost of marker development. Napiergrass (Pennisetum purpureum) is a crop that has tremendous potential for biofuel production in areas where naturalized populations are already present and creating weed problems. Exploiting napiergrass as a biofuel will require risk management strategies that include a means to genetically track both the cultivated and naturalized types. We found that microsatellite markers developed for pearl millet (Pennisetum glaucum) readily distinguished the naturalized populations of napiergrass collected across the state of Florida from the napiergrass selected for biomass traits. These findings demonstrate that naturalized, weedy populations of napiergrass have a different genetic origin from the biomass types and validate the transferred DNA markers as an effective management tool for distinguishing between the two.

Climate change, comprising an increase in carbon dioxide levels coupled with elevated temperature, may favor invasive plants, as they possess traits that will facilitate adaptation to a new climate. In particular, alien plants of subtropical origin introduced to a colder region are expected to increase the number and size of their populations and spread farther with climate change. Seedlings of three such woody alien species in New Zealand (Archontophoenix cunninghamiana, Psidium guajava, and Schefflera actinophylla) were grown in environmental chambers under the combination of two temperature (23.7 and 26 C [74.7 and 78.8 F]) and two CO₂ (450 and 900 ppmv) regimes, simulating current conditions and conditions projected for the end of the century. Total biomass of S. actinophylla was 45% higher and total leaf area 35% larger under doubled CO₂ compared to current CO₂. Root ∶ shoot ratio was higher under doubled CO₂ across all species, and the number of branches was increased for P. guajava. The only significant interactive effect of elevated temperature and doubled CO₂ was for relative growth rate of the height of S. actinophylla seedlings. This study provides strong evidence of more vigorous growth of S. actinophylla under future conditions, particularly increased CO₂, whereas the other two species appear likely to maintain current growth rates. Better knowledge of the types of future conditions that may benefit such species, together with results of species distribution models and competition and eco-physiology studies will ensure robust weed risk assessments.

Nomenclature: Bangalow palm, Archontophoenix cunninghamiana (H. Wendl.) H. Wendl. & Drude, common guava, Psidium guajava L., Queensland umbrella tree, Schefflera actinophylla (Endl.) Harms.

Management Implications: Archontophoenix cunninghamiana, Psidium guajava, and Schefflera actinophylla are popular ornamental alien woody plants in New Zealand and elsewhere. Such plants from subtropical and tropical origin may benefit from climate change, naturalize, and become invasive in more temperate regions once climatic constraints in colder climates are removed. Responses to climate change, such as rising temperatures and CO₂ levels appear to vary, even within a single vegetation type such as woody plants. Of the three subtropical species in this study, S. actinophylla grew more vigorously under doubled CO₂ levels, resulting in increased biomass and leaf area. It also grew taller under the combination of doubled CO₂ and elevated temperature. Growth rates of the other two species did not differ under elevated temperature and doubled CO₂ compared to current levels. Consequently, climate change is likely to have a neutral or positive effect on growth of these three alien species. Although S. actinophylla is at a very early stage of invasion in New Zealand, early control of this species should be considered, due to its possible increase in performance under rising CO₂ levels. If co-occurring native species show negative growth responses to climate change, A. cunninghamiana and P. guajava may also have a competitive advantage, but this will have to be further assessed within a community context in another study. Woody alien species have been shown to be important invaders, and there are numerous subtropical plants introduced to temperate regions globally. This study highlights that such woody, bird-dispersed, subtropical species, which may benefit from climate change, should be screened as potential sleeper weeds.

Restoration of exotic annual grass-invaded rangelands is needed to improve ecosystem function and services. Increasing plant species richness is generally believed to increase resistance to invasion and increase desired vegetation. However, the effects of species richness and individual plant life forms in seed mixes used to restore rangelands invaded by exotic annual grasses have not been investigated. We evaluated the effects of seeding different life forms and increasing species richness in seed mixes seeded after exotic annual grass control to restore desirable vegetation (perennial herbaceous vegetation) and limit exotic annual grasses at two sites in southeastern Oregon. We also investigated the effects of seeding two commonly used perennial grasses individually and together on plant community characteristics. Large perennial grasses, the dominant herbaceous plant life form, were the most important group to seed for increasing perennial herbaceous vegetation cover and density. We did not find evidence that greater seed mix species richness increased perennial herbaceous vegetation or decreased exotic annual grass dominance more than seeding only the dominant species. None of the seed mixes had a significant effect on exotic annual grass cover or density, but the lack of a measured effect may have been caused by low annual grass propagule pressure in the first couple of years after annual grass control and an unusually wet-cool spring in the third year post-seeding. Although our results suggest that seeding only the dominant plant life form will likely maximize plant community productivity and resistance to invasion in exotic annual grass-invaded northern Great Basin arid rangelands, seeding a species rich seed mix may have benefits to higher tropic levels and community stability. Clearly the dominant species are the most prudent to include in seed mixes to restore exotic annual grass-invaded plant communities, especially with finite resources and an increasingly large area in need of restoration.

Nomenclature: Imazapic, medusahead, Taeniatherum caput-medusae (L.) Nevski.

Management Implications: The minimal to no effect of seeding species, other than large perennial grasses, on total perennial herbaceous vegetation suggests that including them in restoration seed mixes will have limited impact on plant community resistance to exotic annual grass invasion in Wyoming big sagebrush rangelands. Our results suggest that seeding the dominant species is more critical to restoration success than seeding a mixture of species. In the Wyoming big sagebrush ecosystem, the most important herbaceous species to seed after disturbance is the large perennial grass group. These results probably do not apply to ecosystems with larger windows of time when conditions are adequate for plant growth. In these ecosystems, a more species rich seed mix containing species with varying temporal resource acquisition patterns is probably needed to effectively use available resources to limit invasibility. We recognize that seeding a mixture of species may have implications to productivity and invasibility over time because of species complementarity and that establishing a diverse community potentially has benefits to higher tropic levels and community stability. A mixture of species may also be more important in ecosystems with multiple invasive species. Species richness is important, but its importance may have been overly stated in some ecosystems. We suggest restoration practitioners can use the information in this study to help weight the cost-benefits of including additional plant species in restoration efforts.

The degree to which invasive species drive or respond to environmental change has important implications for conservation and invasion management. Often characterized as a driver of change in North American woodlands, the invasive herb garlic mustard may instead respond to declines in native plant cover and diversity. We tested effects of native herb cover, richness, and light availability on garlic mustard invasion in a Minnesota oak woodland. We planted 50 garlic mustard seeds into plots previously planted with 0 to 10 native herb species. We measured garlic mustard seedling establishment, survival to rosette and adult stages, and average (per plant) and total (per plot) biomass and silique production. With the use of structural equation models, we analyzed direct, indirect, and net effects of native cover, richness, and light on successive garlic mustard life stages. Native plant cover had a significant negative effect on all life stages. Species richness had a significant positive effect on native cover, resulting in indirect negative effects on all garlic mustard stages, and net negative effects on adult numbers, total biomass, and silique production. Light had a strong negative effect on garlic mustard seedling establishment and a positive effect on native herb cover, resulting in significant negative net effects on garlic mustard rosette and adult numbers. However, light's net effect on total garlic mustard biomass and silique production was positive; reproductive output was high even in low-light/high-cover conditions. Combined effects of cover, richness, and light suggest that native herbs provide biotic resistance to invasion by responding to increased light availability and suppressing garlic mustard responses, although this resistance may be overwhelmed by high propagule pressure. Garlic mustard invasion may occur, in part, in response to native plant decline. Restoring native herbs and controlling garlic mustard seed production may effectively reduce garlic mustard spread and restore woodland diversity.

Nomenclature: Garlic mustard [Alliaria petiolata (M. Bieb.) Cavara & Grande].

Management Implications: Observations of native herb decline and garlic mustard spread are often presented as evidence of garlic mustard's impacts on woodland plant communities. Alternative explanations include native plants affect garlic mustard invasion, both garlic mustard and native plants influence each other, or neither interact directly but are instead responding in opposite directions to other environmental pressures. Understanding the relationship between garlic mustard and native plants can inform invasion control and woodland management. To test the hypothesis that garlic mustard invades in response to declining herb richness and cover, we planted garlic mustard seeds into experimental native herb communities across a range of light levels and analyzed garlic mustard seedling establishment, survival to rosette and adult stages, and biomass and seed capsule (silique) production. We found that native cover strongly suppressed garlic mustard at every life stage. Higher herb species richness produced greater percent cover and thus contributed indirectly to invasion resistance. Garlic mustard demonstrated a flexible response to light: fewer garlic mustard seedlings established in high light plots, but these individuals were highly productive in the second year, whereas in low-light plots, garlic mustard plants were more numerous but less productive. Managing woodland light levels alone is therefore unlikely to prevent garlic mustard invasion. Woodlands with high resource availability and minimal native herb cover may be most vulnerable to invasion. Restoration of woodland herbaceous communities may play an important role in reducing invasibility, especially following management activities that reduce canopy cover and increase light availabilit

Yellow archangel is a twining perennial species that produces a dense evergreen canopy and may negatively affect forest floor vegetation. Because it is spreading rapidly in the Pacific Northwest (PNW), greenhouse and field trials were conducted on yellow archangel to determine its relative sensitivity to several herbicides. Products that slowed or prevented yellow archangel regrowth at 9 mo after treatment (MAT) in one or both iterations of the greenhouse trial were aminopyralid, diclobenil, glufosinate, imazapyr, isoxaben, metsulfuron, sulfometuron, triclopyr amine, and triclopyr ester 2,4-D ester. In the field trial at 10 MAT, triclopyr and imazapyr were controlling 81 and 78% of treated yellow archangel, respectively, similar to aminopyralid, glyphosate, and metsulfuron (61 to 65%). Two applications of 20% acetic acid or 20% clove oil were controlling 53% at the same timing. At 13 MAT, only imazapyr and glyphosate were still providing good control of yellow archangel (81 and 80%, respectively), while all other products were controlling the weed at 53% or less. By 7 or 8 MAT after a second application, only imazapyr and glyphosate provided effective control of yellow archangel (86 to 94%).

Nomenclature: 2,4-D, acetic acid, aminopyralid, clove oil, diclobenil, glufosinate, glyphosate, imazapyr, isoxaben, metsulfuron, sulfometuron, triclopyr, yellow archangel, Lamiastrum galeobdolon (L.) Ehrend. & Polatschek.

Management Implications: Yellow archangel is a fast-growing and dense-canopied perennial species that is quickly becoming problematic along both coasts of the United States and Canada, and is particularly troublesome in forest, park, and ornamental settings in western Oregon, Washington, and British Columbia. Because the susceptibility of yellow archangel to herbicides is not known, greenhouse and field trials were conducted to determine which products could be useful for land managers to aid in its control. Herbicides identified in greenhouse trials that rapidly defoliated yellow archangel included diclobenil, glufosinate, isoxaben, metribuzin, triclopyr amine, and triclopyr ester 2,4-D ester. Those products, in addition to aminopyralid, imazapyr, isoxaben, metsulfuron, and sulfometuron, effectively reduced yellow archangel regrowth at 9 mo after treatment (MAT) in one or both iterations of that trial. In the field, triclopyr amine, 20% acetic acid, and 20% clove oil quickly defoliated yellow archangel. However, control with acetic acid or clove oil had declined to only 53% at 10 MAT even after two applications. Control at 10 MAT with triclopyr and imazapyr was 81 and 78%, respectively, statistically similar to aminopyralid, glyphosate, and metsulfuron (61 to 65%). By 13 MAT, only imazapyr and glyphosate were still providing good control of yellow archangel (81 and 80%, respectively) and by 8 mo after a second application, control with these herbicides was 93 and 86%, respectively. Because yellow archangel seedlings were found in several of the treated plots, it is important to consider the seedbank when control programs for well-established patches are planned and conducted, and when maintaining the site following initial treatment.

Models have been developed to simulate the long-term effects of weed treatments across a landscape to determine effective management strategies, but those models might not be suitable for evaluating short-term action plans of weed treatments that are specific in time and place. In this study, we developed a simulation model to build and evaluate 5-yr weed treatment plan options in terms of their cost and effectiveness in minimizing total infestation areas over the short-term planning horizon. In an iterative, interactive process, 5-yr treatment plan options are developed based on user-defined weed treatment preferences, and evaluated in terms of total projected infestation areas at the end of the planning horizon. The simulation model was applied to a study area of 24,867 ha (61,447 ac) located in the Salmon River watershed in Idaho. Eight treatment plan options were developed using two treatment priority strategies and four increasing budget levels, and compared for their effectiveness. The application results showed that regardless of budget levels, site priority strategies were more cost-effective than the species priority strategies in reducing total infestation areas over time. This simulation model can provide weed managers with a useful tool to evaluate short-term treatment options, and thus support informed decision-making for effective weed management. Although the availability and quality of input data may be a practical limitation of using the simulation model, more data would become available and improved as more invasive species monitoring programs are implemented.

Management Implications: Managing multiple weed species over time and space is a challenging task. To help with this task, we developed a simulation model to build and compare 5-yr weed treatment plans. The model includes three modular components for treatment development, spread simulation and treatment plan evaluation. The model is capable of developing spatially-explicit, directly implementable, short-term treatment plan options based on user-preferred treatment strategies, as well as simulating the effects of treatments in terms of weeds spread to evaluate the given plan options. The simulation model can help weed managers analyze trade-offs among multiple treatment options and identify the most cost-effective treatment plan. This simulation model allows weed managers to direct resources towards areas where greater treatment effects can be realized across multiple weeds, and thus helps them achieve their weed management objectives efficiently. In addition, comparisons of the estimated effects of treatment plans developed under different budget levels can be used to measure budget efficiency in weed management and justify the current and future budget requests. Finally, the use of this simulation model may reveal critical data and knowledge gaps for efficient weed management. Although these limitations, the ongoing and future weed databases and monitoring programs may serve as source of input data for the simulation model.

Re-seeding efforts to restore or rehabilitate Great Basin rangelands invaded by exotic annual grasses are expensive and have generally achieved limited success. There is a need to identify new strategies to improve restoration outcomes. We tested the performance of a native early seral seed mix (annual forbs, early seral grasses and shrubs) with that of a native late seral mix representative of species commonly used in restoration when growing with medusahead in soils of contrasting texture (sandy loam and clay loam) through the first growing season after seeding. Natives were also seeded without medusahead. We found that the grasses and forbs in the early seral mix established significantly better than those in the late seral mix, and the early seral mix significantly reduced aboveground biomass and seed production of medusahead by 16 and 17% respectively, likely because of competition with the early seral native forb, bristly fiddleneck. Medusahead performance was reduced in both soil types, suggesting utility of bristly fiddleneck in restoration is not limited to only one soil type. In contrast, the late seral mix did not suppress medusahead establishment, aboveground biomass or seed production. Although the native perennial grasses, particularly early seral species, were able to establish with medusahead, these grasses did not appear to have a suppressive effect on medusahead during the first growing season. Medusahead was able to establish and produce seeds on both soil types, demonstrating an ability to expand its current range in the Intermountain West, though aboveground biomass and seed production was higher in the clay loam. Our results suggest that certain species may play a key role in restoration, and that targeting early seral species in particular to find additional native species with the ability to suppress exotic annual grasses is an important next step in improving restoration outcomes in desert ecosystems.

Nomenclature: Medusahead (Taeniatherum caput-medusae (L.) Nevski), bristly fiddleneck (Amsinckia tessellata A. Gray).

Management Implications: Medusahead is an exotic annual grass that that has invaded into the Intermountain West of the U.S., reducing native species biodiversity and increasing fire frequency. In a study of native and medusahead performance, we found that the early seral native annual forb, bristly fiddleneck, was an effective competitor with medusahead in two soil types, significantly reducing biomass and seed production by 16 to 17%. Given that this effect was relatively small, further research to examine whether the use of increased seeding density of bristly fiddleneck and/or whether greater diversity of species in the seeding mix would enhance exotic suppression is warranted. Native perennial grasses, particularly early seral grasses, established in higher numbers than native forbs and shrubs, demonstrating their importance in restoration seedings. Although they did not appear to have a suppressive effect on medusahead during their first growing season, perennial grasses have been found to be effective competitors with exotic annual grasses once mature. Our findings suggest that efforts to find additional novel candidate species for seed mixtures may be best focused on early successional species, similar to bristly fiddleneck, to improve restoration/rehabilitation outcomes in disturbed rangeland ecosystems.

Greenhouse experiments were conducted to evaluate mile-a-minute response to selected herbicides. In the first experiment, mile-a-minute response was evaluated following the application of aminocyclopyrachlor, aminopyralid, fluroxypyr, glufosinate, glyphosate, imazamox, imazapic, metsulfuron, penoxsulam, and triclopyr. Applications of aminocyclopyrachlor, aminopyralid, fluroxypyr, glufosinate, glyphosate, and triclopyr all resulted in mile-a-minute control 70% or greater 8 wk after treatment (WAT). Mile-a-minute sensitivity to these six herbicides was further evaluated in a dose-response study. Although 90% growth reduction (GR₉₀) values were determined for aminopyralid and glyphosate, statistically significant results were not obtained for aminocyclopyrachlor, fluroxypyr, glufosinate, and triclopyr. The results of these experiments suggest that glyphosate, as well as the synthetic auxin herbicides aminocyclopyrachlor, aminopyralid, fluroxypyr, and triclopyr, should be further evaluated for mile-a-minute control in south Florida.

Nomenclature: Aminocyclopyrachlor, aminopyralid, fluroxypyr, glufosinate, glyphosate, imazamox, imazapic, metsulfuron, penoxsulam, triclopyr, mile-a-minute, Mikania micrantha Kunth.

Management Implications: Mile-a-minute is an aggressive vine that is very difficult to control in natural areas, lawns, forests, plantation crops, pastures, and other ecosystems throughout Australia, India, and southeast Asia. It was discovered in southern Florida in 2009. Limited information exists regarding the efficacy of recently developed postemergence herbicides on mile-a-minute. Mile-a-minute growth was measured following the application of the herbicides aminocyclopyrachlor, aminopyralid, fluroxypyr, glufosinate, glyphosate, imazamox, imazapic, metsulfuron, penoxsulam, and triclopyr to plants grown in a greenhouse. Imazamox, imazapic, metsulfuron, and penoxsulam did not effectively control mile-a-minute. The herbicides aminocyclopyrachlor, fluroxypyr, and triclopyr provided the greatest control of mile-a-minute. Glufosinate and glyphosate also provided acceptable control. These results indicate that mile-a-minute can potentially be controlled by herbicide applications; however, additional research is necessary to evaluate long-term management strategies for mile-a-minute in south Florida.

Tamarisk (a.k.a. saltcedar, Tamarix spp.) is an invasive plant species that occurs throughout western riparian and wetland ecosystems. It is implicated in alterations of ecosystem structure and function and is the subject of many local control projects, including removal using heavy equipment. We evaluated short-term vegetation responses to mechanical Tamarix spp. removal at sites ranging from 2 to 5 yr post-treatment along the Virgin River in Nevada, USA. Treatments resulted in lower density and cover (but not eradication) of Tamarix spp., increased cover of the native shrub Pluchea sericia (arrow weed), decreased density and cover of all woody species combined, increased density of both native annual forbs and the nonnative annual Salsola tragus (prickly Russian-thistle), and lower density of nonnative annual grasses. The treated plots had lower mean woody species richness, but greater herbaceous species richness and diversity. Among herbaceous species, native taxa increased in richness whereas nonnative species increased in both species richness and diversity. Thus, efforts to remove Tamarix spp. at the Virgin River reduced vegetative cover contributing to fuel loads and probability of fire, and resulted in positive effects for native plant diversity, with mixed effects on other nonnative species. However, absolute abundances of native species and species diversity were very low, suggesting that targets of restoring vegetation to pre-invasion conditions were not met. Longer evaluation periods are needed to adequately evaluate how short-term post-treatment patterns translate to long-term patterns of plant community dynamics.

Nomenclature: Tamarix (tamarisk).

Management Implications: Short-term reductions in density and cover of Tamarix spp. can be achieved with mechanical control techniques, as applied on the Virgin River, Nevada, USA. These treatments can also reduce total woody plant cover and may provide some reduction in flammable nonnative annual grass density, but have no net effect on total herbaceous density. Thus, treatments can reduce fuelbeds, and the potential for wildfire where fuel reduction is the principal goal of vegetation management. Nonnative annual forbs, Salsola tragus (Russian-thistle) in particular, can increase indicating that control treatments for Tamarix spp. can facilitate secondary invasion by other nonnative species. Treatments can also increase cover of rhizomatous native woody plants such as Pluchea sericea (arrowweed), and native forbs as a group, as well as increase diversity for various plant guilds. Treatments provided no significant benefit to arboreal native plants such as Prosopis spp. (mesquites) nor mesic taxa including Salix spp. (willows) and Populus fremontii (Fremont cottonwood) that may be of greater value to wildlife. The results of this short-term response study are the foundation for understanding longer-term (i.e. 5 yr) Tamarix spp. control efficacy or plant community trajectories, and provide a basis to assess how long the initial treatment effects may persist. In addition, it is unknown how the results of mechanical treatments evaluated in this study compare with those of other approaches (e.g. herbicide, fire, biological control, or combinations thereof). Both short and long term effects, and the relative pros and cons of various control techniques, should be considered when developing any Tamarix spp. management plan.

Pale swallowwort (PSW) and black swallowwort (BSW) are two viney milkweeds native to Europe that have increasingly become problematic and noxious weeds in eastern North America. An indigenous fungal isolate, Sclerotium rolfsii VrNY, was discovered causing significant mortality in a dense stand of PSW in a park in upstate New York. Although this fungus is a known pathogen with a broad host range, we evaluated the host potential of S. rolfsii VrNY on a limited range of related and nonrelated U.S. species as a critical first step to assess its suitability as a mycoherbicide for PSW and BSW. In addition, PSW and BSW produce the specific stereoisomer (−)-antofine, a compound with antimicrobial and phytotoxic activity that could inhibit the pathogen. Tests revealed this compound had no effect on S. rolfsii VrNY. This isolate caused significant mortality on all broadleaf plants tested (Asclepias syriaca, Asclepias curassavica, Apocynum cannabinum, Monarda fistulosa, Rudbeckia hirta, PSW, BSW) with the exception of Glycine max, and had no effect on the monocots Schizachyrium scoparium and Zea mays. Although these laboratory studies indicate that most broadleaf vegetation may be susceptible to the pathogen, S. rolfsii might have potential as a mycoherbicide in natural eco-niche environments where invasive PSW and BSW have already become the predominant vegetation. Further laboratory testing of S. rolfsii and limited field testing at the initial discovery site are needed in order to prevent premature rejection of this isolate as a potential management tool against these highly invasive weeds.

Nomenclature: Black (or Louise's) swallowwort, Vincetoxicum nigrum (L.) Moench, syn. Cynanchum louiseae Kartesz & Gandhi, bloodflower milkweed, Asclepias curassavica L., common milkweed, Asclepias syriaca L, hairy coneflower, Rudbeckia hirta L., hemp dogbane, Apocynum cannabinum L., little bluestem, Schizachyrium scoparium (Michx.) Nash, pale (or European) swallowwort, Vincetoxicum rossicum (Kleopow) Barb., syn. Cynanchum rossicum (Kleopow) Borhidi, wild bergamot, Monarda fistulosa L., corn, Zea mays L., soybean, Glycine max (L.) Merr.

Management Implications: Pale swallowwort (PSW) and black swallowwort (BSW) are two viney milkweeds native to Europe that have become invasive in eastern North America. Long term biological control efforts are the best hope for mitigating the spread of these weeds, but mycoherbicides might also offer a complementary approach for integrated pest management. An indigenous fungal isolate, Sclerotium rolfsii VrNY, was discovered casuing significant mortality in a dense stand of PSW in a park in upstate NY. This fungus is known to be a pathogen of a wide range of plants, but the possibility exists for a pathogen strain to occur that has a narrower host range. Even if not, the fungus might still have potential as a mycoherbicide in limited natural environments where PSW and BSW have become the predominant vegetation. In a laboratory study, we tested the ability of S. rolfsii VrNY to infect related and nonrelated (habitat associated) native U.S. species as well as soybean and corn, known hosts in the southern U.S. The isolate caused significant mortality on all broadleaf plants tested (common milkweed, bloodflower milkweed, hemp dogbane, wild bergamot, and hairy coneflower) except soybean, and had no effect on the monocots little bluestem and corn. Further laboratory testing of S. rolfsii and limited field testing at the initial discovery site are needed in order to prevent premature rejection of this isolate as a potential management tool against these highly invasive weeds.

Old World climbing fern (OWCF) spores had lower germination rates (P  =  0.0072) after being frozen for ≥ 3 h compared to < 3 h, and were highly susceptible to freezing periods ≥ 6 h with a 5.8- to 13.3-fold reduction in spore germination compared to controls. Freezing temperature did not affect germination of Japanese climbing fern (JCF) spores compared to controls (P  =  0.32). OWCF gametophytes had reduced survival at all exposures to freezing temperatures compared to controls (P < 0.0001), and had < 0.5% survival for exposure times ≥ 3 h. The gametophytes of JCF had reduced survival at exposures to freezing temperatures ≥ 1 h (P < 0.0001) compared to controls. JCF gametophyte survival was 52.5% at 3-h exposure time, but was reduced to ≤ 0.1% at exposure times ≥ 6 h. All OWCF sporophytes exhibited 100% necrosis for all exposure times 24 h postexposure, but new growth from resprouts was observed for exposure time ≤ 6 h at 6 mo postfreezing. OWCF sporophytes' dry weight biomass was greatly reduced for all exposure times compared to controls (P < 0.0001). Results with nonlinear regression (P < 0.0001, R²  =  0.92) indicated that a single freeze for 2.4 h at −2.2 C reduced OWCF dry weight biomass to 0.01 g, a 10-fold reduction, at 6 mo postfreezing. These results indicate that JCF spores and gametophytes are more tolerant of longer exposure periods to freezing temperatures than OWCF, but OWCF exhibited the potential to spread further into northern Florida.

Nomenclature: Old World climbing fern, Lygodium microphyllum (Cav.) R. Br., Japanese climbing fern, L. japonicum (Thunb.) Sw.

Management Implications: Old World climbing fern (Lygodium microphyllum; OWCF) is likely to invade regions of USDA Plant Hardiness Zone 9A in northern Florida. Based on this study, OWCF will remain a minor component of the flora in northern Florida due to a single or multiple freezes that will affect all life stages of the fern. Spores and gametophytes of OWCF were susceptible to a freeze of −2.2 C at 3 and 0.25 h, respectively. Japanese climbing fern spores and gametophytes were more tolerant of a freeze at −2.2 C, with spore and gametophyte tolerance levels of 12 and 3 h, respectively. Nonlinear regression indicted that a single freeze of 2.4 h reduced OWCF dry weight biomass by a 10-fold reduction at 6 mo postfreezing compared to controls. The susceptibility of OWCF to a single freeze or multiple freezes will limit it spore production, gametophyte survival, and sporophyte growth. The higher tolerance of JCF to a single freeze could explain why JCF occurs throughout the southeastern United States, whereas OWCF is currently restricted to Florida. Land managers in natural areas of northern Florida should become familiar with the identification and habitat preferences of OWCF and report any occurrence to Florida Fish and Wildlife Conservation Commission's Invasive Plant Management Section.

We investigated the relative importance of stand and landscape characteristics in the invasion of a nonnative shrub, Amur honeysuckle, in 40 woodlots in an agricultural matrix in southwest Ohio. We quantified stand characteristics that could influence invasibility, the intrinsic susceptibility of an area to invasion, including woodlot size, perimeter-to-area ratio, tree basal area, and stand age. At the landscape scale we included factors that potentially influence propagule rain (the contribution of seeds from individuals established outside the focal area), including the land cover and road density in a 1,500-m buffer around each woodlot, as well as the extent to which the perimeter was forested at two points in the past, and latitude (based on an apparent south-to-north invasion in this region). Based on stepwise regression, we determined that honeysuckle cover was determined primarily by landscape parameters, particularly the percent of the buffer comprised of cropland. Woodlots surrounded by more cropland had less honeysuckle cover, which we attribute to paucity of nearby seed sources and/or minimal movement of seed-dispersing animals. From these findings, we argue that impediments to propagule rain are more important in shaping the invasion of this exotic shrub than are characteristics of the woodlots themselves, i.e., community invasibility.

Nomenclature: Amur honeysuckle, Lonicera maackii (Rupr.) Herder.

Management Implications: Understanding the factors that make forests susceptible to invasion can inform management strategies, including identifying forest stands at greatest risk of invasion and formulating steps that can be taken to minimize invasion risk. We investigated what stand and landscape characteristics best explained the cover of the invasive shrub Lonicera maackii (Amur honeysuckle), in a landscape it recently invaded, consisting of woodlots in an agricultural matrix in southwest Ohio. We found that cover of this shrub was best explained by landscape characteristics, rather than by stand characteristics, such as age or basal area. Specifically, the percentage of the 1,500-m buffer around the woodlot that was comprised of cropland, as opposed to pasture, forest, and other land-cover types, was the best predictor of honeysuckle cover. Woodlots surrounded by more cropland had lower cover, which we think indicates more recent colonization. Thus cropland impedes honeysuckle invasion, either by providing a buffer free of seed sources (fruiting shrubs), or a land cover that is unlikely to be crossed by animals dispersing seeds from more distant sources. These findings suggest that woodlots surrounded by cropland, and perhaps by other shrub-free land covers, are at lower risk of invasion by animal-dispersed nonnative plants, and that active management of buffers around forest stands will reduce invasion risk.

Biological control is one of the most common approaches used to manage invasive weeds of wetlands and other natural areas. Before candidate agents can be released, research is conducted to support biological control, which can be protracted and expensive, leading to a scientific and potentially lengthy regulatory review. To increase biological control safety, efficacy, and transparency, we suggest that during the early phases of a weed project, the feasibility of the invasive plant as a target should be studied explicitly. Our purpose here is to summarize information of an important invasive weed that can serve to judge whether the project is appropriate. Chinese tallowtree, Triadica sebifera, is one of the worst invasive species invading coastal wetlands and other riparian areas of the southeastern United States. Current management practices have not controlled the spread of this weed into these sensitive habitats. Initial surveys in the plant's native Chinese range for potential biological control agents have recovered several herbivore species that could be developed. These potential agents include defoliators, root and foliage feeders, and gall formers, whose biology, apparent host specificity, and impacts on plant fitness suggest that biological control offers great promise against Chinese tallowtree. When conducted during the initial phase of a project, this type of feasibility study can address potential conflicts of interest and risks, ultimately producing projects that are more effective and safer for biological control.

Nomenclature: Chinese tallowtree, Sapium sebiferum (L.) Roxb., Triadica sebifera (L.) Small.

The management of exotic, invasive plants is among the most challenging undertakings of natural resource managers, particularly in large, remote landscapes. The availability of information on the distribution and abundance of invasive plants is vital for effective strategic planning yet is often unavailable because of high costs and long procurement times. This paper presents results of a large-scale invasive plant mapping effort in the Florida Everglades utilizing digital aerial sketch mapping (DASM) and evaluates its utility for guiding management decisions. The distribution and abundance (cover) of four priority invasive plant species—Australian pine, Brazilian pepper, melaleuca, and Old World climbing fern—were mapped over 728,000 ha in the Everglades during 2010 to 2012. Brazilian peppertree was the most widely distributed and abundant species, occupying 30,379 ha. Melaleuca was also widely distributed and occupied 17,802 ha. Old World climbing fern occupied only 7,033 ha but its distribution was generally concentrated in heavy infestations in the northern Everglades. Australian pine was the least abundant of the mapped species and tended to be limited to the southeastern Everglades region. DASM proved to be a cost-effective means of obtaining region-wide distribution and abundance information for these species at broad scales (> 500 m), but detection rates and positional accuracy declined at finer scales. Both canopy type (forested vs. unforested) and distance from flight transect appear to be important factors for detection accuracy.

Nomenclature: Australian-pine, Casuarina equisetifolia L. ex J.R. & G. Forst., Brazilian peppertree, Schinus terebinthifolius Raddi, melaleuca, Melaleuca quinquenervia (Cav.) Blake, Old World climbing fern, Lygodium microphyllum (Cav.) R. Br.

Management Implications: Spatially-explicit information on the distribution and abundance of invasive plant species is an important resource for land managers seeking to implement and assess invasive plant management programs. Obtaining such data for large landscapes is often cost-prohibitive, especially with continued decreases in operating budgets. This paper highlights the use of digital aerial sketch mapping (DASM) for collecting spatial information on invasive tree, shrub, and vine species across a vast and difficult to access wilderness—the Florida Everglades. Using specialized software on touchpad computers linked to global positioning system receivers, observers mapped infestations of four regionally significant invasive plant species—Australian-pine (Casuarina equisetifolia), Brazilian peppertree (Schinus terebinthifolius), melaleuca (Melaleuca quinquenervia), and Old World climbing fern (Lygodium microphyllum)—from low flying aircraft over a 728,000 ha region. DASM resulted in relatively rapid (roughly 10,000 ha/hr) and inexpensive ($0.11 ha^-1) collection of landscape level distribution and abundance data for these species. Data validation results indicate that trained observers were able to discern the four target species across a variety of ground conditions and accurately digitize the infestations “on-the-fly.” However, detection of small and widely scattered individuals was inconsistent, indicating limited usefulness of this technique for early detection of low-level infestations, especially in the sub-canopy of forested plant communities. Thus, DASM provided a practical and cost-efficient means for identifying the spatial extent and abundance of larger individuals and patches of the targeted species in the vast Everglades landscape. Access to this data enables land managers to more effectively plan invasive plant management strategies as well as to prioritize locations for supplemental monitoring aimed at early detection of incipient populations.

Alligatorweed, waterhyacinth, and hydrilla are three nonnative aquatic species of concern in the Ross Barnett Reservoir near Jackson, MS. Point-intercept surveys were conducted on the reservoir from 2005 to 2010 to monitor native and nonnative species' distributions and assess herbicide treatment efficacy across the reservoir. Foliar applications of 2,4-D, glyphosate, imazapyr, and diquat were made during summer months for emergent and free-floating vegetation, whereas submersed applications of liquid copper and granular fluridone were applied in spring and late summer for subsurface hydrilla populations. American lotus is the native species that has been observed the most throughout the survey years, with occurrence frequencies averaging between 17 and 27%. Alligatorweed populations significantly decreased from 21% in 2005 to 4% in 2006; however, they consistently increased in the next 4 yr to 12% occurrence in 2010. Waterhyacinth occurrence has remained relatively constant over the study period, averaging below 10% occurrence. Hydrilla was discovered in the reservoir in late 2005 and has remained below 2% in frequency of occurrence since 2006. Suppression of these nonnative species has been attributed to rigorous monitoring and herbicide applications conducted on the reservoir since 2005. A logistic regression model indicated that as native species richness increased, the likelihood of a nonnative species occurring also increased.

Nomenclature: Alligatorweed, Alternanthera philoxeroides (Mart.) Griseb., American lotus, Nelumbo lutea Willd., hydrilla, Hydrilla verticillata (L. f.) Royle, waterhyacinth, Eichhornia crassipes (Mart.) Solms.

Management Implications: This research was conducted over a 6-yr time span to assess long-term management techniques for tracking the distribution and monitoring the control of several invasive aquatic plant species. In addition, this research was designed to determine the impact on the composition of the native plant community within this reservoir. A point-intercept survey of the entire Ross Barnett Reservoir was conducted each year using point locations at 300-m intervals within a grid system established by geographic information system (GIS) across the reservoir. Each year (2005 to 2010), these locations were surveyed for all plant species present. Aquatic herbicides were the primary method used for nonnative plant management in the reservoir over the previous 6 yr. By comparing how often each plant species occurred over consecutive years, we determined how effective our management program was. A logistic model was also utilized to decipher the effects of native species richness on the likelihood of nonnative species invasion. This model showed that a greater native species richness favored nonnative species establishment. We concluded that our herbicide applications were effective in reducing nonnative plant coverage; however, source plant populations upstream of the reservoir were likely supplying propagules capable of producing future populations throughout the reservoir. Employing an Early Detection and Rapid Response program based on results gathered from the logistics model could significantly reduce nonnative plant establishment by defining locations that are more favorable or susceptible to invasion, based on native species richness at that particular location. Integrating a prevention program in addition to effective postestablishment practices such as herbicide applications is the most effective way to reduce invasive plant establishment and spread.