Ecological restoration of shrub–steppe communities in the western United States is often hampered by invasion of exotic annual grasses during the process. An important question is how to create restored communities that can better resist reinvasion by these weeds. One hypothesis is that communities comprised of species that are functionally similar to the invader will best resist invasion, while an alternative hypothesis is that structurally more complex and diverse communities will result in more effective competitive exclusion. In this field experiment, we examined the effects of restored community structure on the invasion success of three annual grass weeds (downy brome, jointed goatgrass, and cereal rye). We created replicated community plots that varied in species composition, structural complexity and density, then seeded in annual grass weeds and measured their biomass and seed production the following year, and their cover after 1 and 3 yr. Annual grass weeds were not strongly suppressed by any of the restored communities, indicating that it was difficult for native species to completely capture available resources and exclude annual grass weeds in the first years after planting. Perennial grass monocultures, particularly of the early seral grass bottlebrush squirreltail, were the most highly invaded communities, while structurally complex and diverse mixtures of shrubs (big sagebrush, rubber rabbitbrush), perennial grasses (bluebunch wheatgrass and bottlebrush squirreltail) and forbs (Lewis flax, Utah sweetvetch, hairy golden aster, gooseberryleaf globemallow) were more resistant to invasion. These results suggest that restoration of sagebrush steppe communities resistant to annual grass invasion benefits from higher species diversity; significant reduction of weed propagule pressure prior to restoration may be required.

Nomenclature: Cereal rye, Secale cereale L.; downy brome, Bromus tectorum L.; jointed goatgrass, Aegilops cylindrica Host; big sagebrush, Artemisia tridentata Nutt.; bluebunch wheatgrass, Pseudoroegneria spicata (Pursh) Á. Löve; bottlebrush squirreltail, Elymus elymoides (Raf.) Swezey; gooseberryleaf globemallow, Sphaeralcea grossulariifolia (Hook. and Arn.) Rydb.; hairy golden aster, Heterotheca villosa (Pursh) Shinners; Lewis flax, Linum lewisii Pursh; rubber rabbitbrush, Ericameria nauseosa (Pall. ex Pursh) G.L. Nesom & Baird; Utah sweetvetch, Hedysarum boreale Nutt.

Management Implications: Our study of annual grass weed invasion dynamics in a sagebrush steppe restoration experiment emphasizes the importance of combining the basic principles of ecological restoration and weed science to understand how the plant community at a particular site is likely to respond to restoration activities, and how the restoration species will interact with invasive exotic species in the area through time. Fundamental properties of a restoration site include its intrinsic productivity, as defined by climate and soils, its history of disturbance and use, and the pool of potential colonizing species, both native and exotic, that already occupy the area. Ecological theory indicates that sites with a history of disturbance are most invasible, as the absence of an intact plant community means resources are likely to be incompletely utilized, thus providing more resources for an invader. Sites subject to high propagule pressure from invasive species in the area are also at higher risk. The least invasible sites are generally those with low levels of disturbance and an absence of potential invaders. Restoration strategies will be different for sites at different points along this continuum of invasibility. Our study site was historically highly disturbed, with a history of fertilizer additions. Under this scenario the best strategy was to establish a native commu

Four rates of aminopyralid (30, 60, 90, and 120 g ae ha⁻¹ [0.4, 0.9, 1.3, and 1.8 oz ae acre⁻¹]) were compared for their ability to reduce abundance of nonnative dicot species and favor native species in an invaded Cascade Mountain meadow near Trout Lake, WA. Treatments were applied in two replicated studies (June 2009 and 2010), and foliar cover and species richness were monitored for two years. First-year control of nonnative dicots from application of 30 g ae ha⁻¹ of aminopyralid (69%) was greater than that of native dicots (29%); whereas, significant control of both species groups occurred at the higher rates. By the second year after treatment, absolute differences in cover between treated and non-treated plots averaged −17% and −21% for native and nonnative dicots, respectively, and 1% and 27% for native and nonnative monocots, respectively. First-year control of Canada thistle and oxeye daisy was greater after treatment in 2009 (88% and 90%, respectively) than after treatment in 2010 (56% and 55%, respectively), probably because lower spring temperatures in 2010 limited vegetation development and plant susceptibility to aminopyralid. Cover of Kentucky bluegrass and sheep fescue averaged 20% and 6% greater, respectively, in treated plots than in non-treated plots. Application of 30 g ae ha⁻¹ of aminopyralid had no detectable effect on second-year richness of native and nonnative species relative to non-treated plots; however, higher rates caused 24% to 43% reductions in richness of each species group. Research results suggest that application of aminopyralid at 30 g ae ha⁻¹ has the potential to reduce abundance of nonnative dicot species in similar meadow communities of the Pacific Northwest with little or no negative impacts to abundance and richness of native species. As a potential strategy to limit the subsequent spread of Kentucky bluegrass, a grass herbicide, such as fluazifop or sethoxydim, could be added to the treatment.

Nomenclature: Aminopyralid; Canada thistle, Cirsium arvense (L.) Scop.; Kentucky bluegrass, Poa pratensis L.; oxeye daisy, Leucanthemum vulgare Lam.; sheep fescue, Festuca ovina L.

Management Implications: Herbicides can be used selectively to shift species composition of plant communities to favor native species over nonnative species. Such selectivity can be achieved through species' differences in herbicide tolerance, stature, and timing of development. Aminopyralid is an herbicide that provides selective control of dicot species with little or no injury to many monocot species. To test the feasibility of using aminopyralid to reduce abundance of nonnative dicots in an invaded meadow community in the Washington Cascade Mountains, we compared species abundance and richness one and two years after application of four rates of aminopyralid (30, 60, 90, and 120 g ae ha⁻¹) in separate replicated studies treated in June 2009 and 2010. At the lowest aminopyralid rate (30 g ae ha⁻¹), control of nonnative dicots was considerably greater than control of native dicots, and there was no detectable negative effect on richness of either native or nonnative species. Reductions in dicot abundance from the aminopyralid treatments stimulated a 27% increase in cover of nonnative monocots, primarily Kentucky bluegrass and sheep fescue. First-year control of Canada thistle and oxeye daisy was lower after treatment in 2010 than in 2009 because initial vegetation development had been limited by the cooler spring temperatures of 2010. These research results suggest that a low rate of aminopyralid can be used in similar meadow communities to control nonnative dicots with minimal injury to native dicots. A grass herbicide, such as fluazifop or sethoxydim, could be added to the treatment to control Kentucky bluegrass. Timing of treatme

Preventing the establishment of saltcedar in new areas requires early detection and rapid response. However, it is unclear when saltcedar develops perennating tissue and which treatments are most efficacious for young plants. The effectiveness of mowing, herbicide, and fire treatments, alone and in combination, was evaluated on saltcedar plants grown from seed to 4, 8, and 12 wk age in 2011 and 6 and 12 wk age in 2012. Plants were clipped to 2 cm height or remained intact. Plants were then exposed to no treatment (control), herbicide application (0.12 mg ae imazapyr), or treated with fire for 30 or 60 s. Six weeks after treatment, plant survival and tallest living shoot height were recorded and roots were dried and weighed for biomass comparison. Saltcedar survival increased with greater plant age. No 4-wk-old plants survived herbicide or fire treatments, whereas 6-wk-old plants were eliminated by fire. Clipping alone did not control plants of any age but clipping before fire was the most effective control for older plants. Herbicide alone did not kill 8- and 12-wk-old plants during the study period, but reduced plant vigor suggests that these applications may be effective in the long-term. Fire alone for 60 s was the most effective single treatment for 12-wk-old plants. Root biomass was reduced for all treatments relative to untreated plants with the lowest biomass typically associated with fire treatments. Resprouts were shortest for combined clipping and herbicide and clipping and fire treatments. Results indicate that saltcedar grown from seed can develop viable belowground reproductive tissues between 6 and 8 wk after germination. Multiple intensive control practices may be required to kill saltcedar plants ≥8 wk of age, whereas younger plants can be controlled by single, less-intensive treatments such as fire.

Nomenclature: Arsenal; imazapyr; saltcedar, Tamarix ramosissima Ledeb. TARA; T. chinensis Lour. TACH; Tamarix hybrids.

Interpretive Summary: Early detection and rapid response is the primary campaign for managing weeds in the United States, yet little is known about the best method for controlling new saltcedar infestations. Older saltcedar individuals are often difficult to control because of the presence of belowground reproductive tissues but when these structures become viable is poorly understood. This research found that young saltcedar response to control treatments is dependent on plant age and treatment. All plants treated with clipping between 4 and 12 wk of age were able to recover and produce robust plants. Destructive treatments such as fire eliminated 4- and 6-wk-old plants but 8- and 12-wk plants often regrew vigorous shoots from belowground buds following complete top-kill by fire. These results suggest that belowground reproductive tissues can become viable between 6 and 8 wk of age. Fire and herbicide alone resulted in younger plant mortality and reduced growth for older saltcedar but the use of these practices will depend on land management options. Clipping prior to herbicide or fire treatment was the most effective control and could be used to treat small populations or individual plants. Fire may be preferred over herbicide application in areas where vegetation is adapted to this disturbance and burn programs are already established. On the other hand, herbicide may be desired where saltcedar density is high, there is minimal herbicide-susceptible native vegetation, and/or the landscape is unsuitable for burning or other mechanical removal methods. Spot fire treatment to individual plants, rather than a large-scale field burn, may be another control option although this technique has not been field-tested.

Prevention is an integral component of many management strategies for aquatic invasive species, yet this represents a formidable task when the landscapes to be managed include multiple invasive species, thousands of waterbodies, and limited resources to implement action. Species distributional modeling can facilitate prevention efforts by identifying locations that are most vulnerable to future invasion based on the likelihood of introduction and environmental suitability for establishment. We used a classification tree approach to predict the vulnerability of lakes in Washington State (United States) to three noxious invasive plants: Eurasian watermilfoil (Myriophyllum spicatum), Brazilian egeria (Egeria densa), and curlyleaf pondweed (Potamogeton crispus). Overall, the distribution models predicted that approximately one-fifth (54 out of 319 study lakes) of lakes were at risk of being invaded by at least one aquatic invasive plant, and many of these predicted vulnerable lakes currently support high native plant diversity and endemism. Highly vulnerable lakes are concentrated in western Washington in areas with the highest human population densities, and in eastern Washington along the Columbia Basin Irrigation Project and the Okanogan River Basin that boast hundreds of lakes subject to recreational use. Overall, invasion potential for the three species was highly predictable as a function of lake attributes describing human accessibility (e.g., public boat launch, urban land use) and physical–chemical conditions (e.g., lake area, elevation, productivity, total phosphorous). By identifying highly vulnerable lake ecosystems, our study offers a strategy for prioritizing on-the-ground management action and informing the most efficient allocation of resources to minimize future plant invasions in vast freshwater networks.

Nomenclature: Eurasian watermilfoil, Myriophyllum spicatum L. MYPSP; Brazilian egeria, Egeria densa Planch. ELDDE; curlyleaf pondweed, Potamogeton crispus L. PTMCR.

Management Implications: Preventing introductions of aquatic invasive plants to new ecosystems requires predictive models that can be used to help guide resource allocation and prioritize management activities. The present study identifies those lakes most vulnerable to future invasions of three widespread nonnative plants — Eurasian watermilfoil, Brazilian egeria, and curlyleaf pondweed — with the goal of preventing aquatic plant invasions in Washington State (United States) by focusing on surveillance, control, education, and future research. These are management themes that are relevant to other regions of the United States and elsewhere.

First, surveillance of the 54 lakes identified as having the greatest risk of future plant invasions is paramount to prevent new invasions (see  Supplemental Table 1 (),  http://dx.doi.org/10.1614/IPSM-D-13-00036.TS1). Based on habitat suitability, areas within and around human populated areas in western Washington, the Columbia Basin Irrigation Project, and the Okanogan River should be prioritized because they have the greatest number of vulnerable lakes and may be key invasion hubs. Second, there is a need for early detection and rapid response strategies to eradicate and control early infestations that are discovered by lake monitoring. These strategies can reduce the risk of heavy infestation and may even lead to successful eradication. One strategy is to adopt an online early detection network to link existing local, regional, and national databases on invasive species and provide a data portal where new data can be added and shared easily through an interacti

The common edible fig is a subcanopy tree that has invaded many of the remnant riparian forests of California's Central Valley. Fig is unusual in its ability to invade low-light, low-disturbance, native-plant–dominated environments. Dendrochronology combined with regression and spatial analyses allowed us to empirically quantify the expansion rate and spatial pattern of the fig invasion into the native plant community at Caswell Memorial State Park (Ripon, CA) over a 70-year invasion period. Fig uses a combination of short-distance dispersal, which results in constant, linear expansion at source population sites and long-distance dispersal, which eventually leads to high recruitment of satellite populations in ideal environments. Although fig initially experienced a long lag in its invasion rate, at the time of this study, it was expanding at an exponential rate at the landscape scale in Caswell. We identified a number of characteristics intrinsic to the fig population (shade suppression, pollinator presence, highly specialized reproduction, and propagule pressure) as well as extrinsic characteristics of the receiving environment (hydrologic alteration from the construction of a dam, safe sites for juvenile recruitment, and target effects from environmental heterogeneity) that may have influenced the rate and pattern of fig invasion. The Central Valley riparian forests have been reduced to less than 6% of their original area, and invasive fig is a significant threat to the remaining fragments of this important vegetation community. We include suggestions for fig eradication based on knowledge gained in this study.

Nomenclature: Fig, Ficus carica L.

Management Implications: Although fig (Ficus carica) initially exhibited a substantial lag in its invasion of Caswell Memorial State Park (Ripon, CA), our study found that it was expanding at an exponential rate 70-yr later. Figs' expansion rate and spatial distribution are influenced both by intrinsic factors (shade suppression, pollinator presence, and highly specialized reproduction), as well as by extrinsic factors (hydrology changes and environmental heterogeneity). Because figs are able to invade the remnant riparian forests of the Central Valley, CA, and form dense groves that exclude native vegetation, they constitute a significant threat to this unique and imperiled habitat. Given fig's ability to expand rapidly once critical, intrinsic and extrinsic conditions are met, it would be prudent for managers of riparian areas to eradicate even small populations of fig.

Based on patterns of invasion at Caswell, floodplain positions that are moist well into spring, such as seasonal sloughs or low-elevation alluvial floodplains, are at greater risk of high levels of fig recruitment. However, as demonstrated in Caswell, even higher-elevation riparian sites are not exempt from fig invasion.

Some research has indicated that when controlling invasive plants, satellite populations should be targeted first because reproduction at the edge of an invader's range substantially increases its rate of expansion. In cases where fig is invading shady riparian forests, however, it may be better to first control reproductive source populations, because figs appear to have an extended nonreproductive juvenile period in these habitats.

Figs' extended juvenile period also means that once all adult and juvenile individuals have been eradicated, follow-up control measures at 5-year intervals should be sufficient to catch figs germinating from the soil seedbank before they become reproductive. Thankfully, our monitoring of former fig-invaded sites at Caswell indicates that fig recruitment from the seedbank may be quite limited, an observation that has also been noted for other Ficus species.

Propagule pressure significantly contributes to and limits the potential success of a biological invasion, especially during transport, introduction, and establishment. Events such as multiple introductions of foreign parent material and gene flow among them can increase genetic diversity in founding populations, often leading to greater invasion success. We applied the tools and theory of population genetics to better understand the dynamics of successful biological invasion. The focal species, cogongrass, is a perennial invasive grass species significantly affecting the Gulf Coast and southeastern region of the United States. The literature indicates separate, allopatric introductions of material from East Asia (Philippines and Japan) into the U.S. states of Mississippi and Alabama. Molecular analysis of samples from those two states utilized amplified fragment length polymorphism (AFLP) markers on 388 individuals from 21 localities. We hypothesized that previously isolated lineages of cogongrass are present and crossing in the Southeast. We observed genetic variation within localities (0.013 ≤ heterozygosity (H_e) ≤ 0.051, mean  =  0.028 ± 0.001) with significant and substantial population structure (F_ST  =  0.534, P < 0.001). Population structure analyses detected two genetically defined and statistically supported populations, which appear to have experienced some admixture. The geographic distribution of those populations was consistent with the two-introduction scenario reported previously. These results are also consistent with contact in the invasive range of previously isolated lineages from the native range.

Nomenclature: Imperata cylindrica (L.) Beauv. IMCY.

Management Implications: Cogongrass is a major invasive weed of forestlands, rights-of-way, agricultural areas, and natural ecosystems of the southeastern United States. The present study investigated patterns of genetic diversity and divergence in cogongrass from areas near the reported sites of this species' initial introduction to the United States. Data from this study provide support for the reports that the species was introduced from two locations in the native range, as we detected two distinct genetic groups: one in central Mississippi and another in southern Mississippi and Alabama. A further insight from this work is the finding that cogongrass appears to rely much more heavily on sexual reproduction than was previously thought. At most of the localized patches examined in this study (19 of 21 localities) each sampled individual had a unique genotype, suggesting that sexual reproduction dominates. Furthermore, population structure suggests a greater reliance on sexual outcrossing throughout the range examined here, than previously believed. Knowledge of cogongrass' genotypic distribution could yield benefits for future management efforts, particularly if management tactics affect the two genetic groups differentially.

Aquarium release is a vector for introducing nonnative species that threatens the ecological integrity of aquatic systems. Following coastal invasions by released aquarium strains of Caulerpa taxifolia, aquarists began using the macroalgal genus Chaetomorpha. Use of Chaetomorpha now exceeds 50% of U.S. aquarium hobbyists we surveyed. Aquarium strains of this macroalgal genus possess broad environmental tolerances, demonstrate high nutrient uptake and growth rates, and reproduce by fragmentation. Although these characteristics make Chaetomorpha a desirable aquarium inhabitant, they may also promote invasive tendencies if the alga is introduced into a natural ecosystem. We sought to proactively mitigate this potential invasion risk by testing algal disposal techniques that serve as responsible alternatives to releasing viable individuals. We tested methods used by aquarium hobbyists—boiling, microwaving, freezing, desiccation, and exposure to freshwater. We determined the minimum durations that these techniques must be used in order to induce mortality in three aquarium purchases of Chaetomorpha. We found that boiling for at least 1 min, microwaving for at least 15 s, or freezing for at least 24 h were sufficient to induce 100% mortality in 1-cm-long fragments and clumps up to 1.5 g. Desiccation required more than 24 h when exposed to air and 6 d for samples kept in closed containers. Freshwater exposure was effective at 6 d. These results indicate that disposal of excess or unwanted Chaetomorpha via garbage (if destined for a landfill) or indoor plumbing (e.g., sinks and toilets) represent safe alternatives to release. Disposal of algal tissue, shipping water, or tank water containing small algal fragments down stormwater drains, however, could introduce this hardy species into favorable conditions that could result in detrimental biological invasions.

Management Implications: Dumping of aquarium contents or used tank water into natural waterways can introduce live organisms that are not native to these environments. This activity has led to numerous aquatic invasions, the most notable of which have been those of Caulerpa taxifolia in several locations around the globe. At present, the most commonly used macroalga by U.S. aquarium hobbyists is the genus Chaetomorpha. With its popularity among hobbyists, the opportunity for its introduction is considerable. In order to mitigate this potential invasion risk, we present here disposal mechanisms for aquarium algae as safe alternatives to release. Minimum durations necessary to ensure algal mortality are listed for aquarium strains of Chaetomorpha through treatment by boiling, microwaving, freezing, desiccation, and exposure to freshwater. Boiling for 1 min or microwaving for 15 s, as well as freezing for 24 h, are sufficient for fragments and clumps of Chaetomorpha up to 1.5 g. Desiccation can take more than 24 h for larger quantities of algal tissue if exposed to circulating air and requires 6 d of desiccation if kept in a closed container. Freshwater exposure combined with light deprivation requires 6 d to ensure full mortality. Based on our results, disposal by garbage (destined for a landfill) or by indoor plumbing are safe methods for disposal of aquarium macroalgae. Disposal of algae or tank water down stormwater drains, however, might introduce live fragments to natural waterways. Experiments of this sort are needed to determine safe disposal methods of other aquarium species; providing this information to aquaculturists and aquarium hobbyists will empower them to prevent future invasions by selecting safe and convenient disposal methods as alternatives to aquarium release.

The objective of this article is to identify growth patterns of Japanese knotweed propagules distributed by high-water events. Along four river systems, we collected and measured Japanese knotweed propagules that had been distributed by flooding approximately 1 yr earlier. Results indicate that the size of the emergent shoot may be determined by the extent of underground growth late in the growing season, although initially it is linked to the size of the propagule. Our results show that 70% of new plants originated from rhizome fragments, and 30% from stems. This proportion is similar to regeneration rates shown in laboratory studies. We suggest that the best way to prevent the spread of Japanese knotweed along rivers is to focus control efforts on those stands most susceptible to erosion and propagule dispersal. We also suggest that an early detection and rapid response management approach can be effectively utilized to eradicate these propagules, and effectively suppress the spread of Japanese knotweed. Our data-collection method also provides evidence that control of newly distributed propagules can be effectively accomplished without the use of herbicides or heavy mechanical tools.

Nomenclature: Knotweed sensu lato; Japanese knotweed; Fallopia japonica (Houtt.) Ronse Decr.; Polygonum cuspidatum Siebold & Zucc.; Reynoutria japonica Houtt.

Management Implications:Once established, stands of the invasive species knotweed s.l. requires several seasons of intensive effort to eliminate, often requiring the use of hand tools, heavy machinery, or herbicides. This is due to its ability to regenerate from very small pieces of stem or rhizome. Currently, management techniques focus on eliminating established stands, rather than new plants. After the flooding caused by tropical storm Irene in Vermont in 2011, land managers anticipated that knotweed would become widely distributed across floodplains throughout the state. A coordinator was hired for the summer of 2012 to arrange the removal of as many new plants as possible, by only manual labor. Over the course of the summer, 5,000 to 6,000 plants were eliminated over approximately 30 acres (12.1 ha). It was quickly recognized during initial removal efforts that a better understanding of the relationship between the sprout above ground and lateral underground growth could be a quick and simple assessment tool that would generate more efficient and site-specific strategies for eliminating new knotweed plants. Though our study does not reveal a consistent relationship between the sprout above ground and lateral underground growth for knotweed s.l., there may be a window of time during which such a relationship does exist. We also found that stem and rhizome fragments retained their ability to regenerate and grow up to 13 mo after tropical storm Irene. We also found that 86% of new plants were growing from propagules buried under less than 4 in. (10 cm) of sediment. Given this relatively shallow burial depth, we suggest that whole plants can be easily removed by hand within a year of the dispersal event. When properly integrated into a long-term management strategy, these techniques may significantly reduce the need for more costly, and potentially environmentally disruptive, treatments in the future. We suggest that every new knotweed dispersal event is an opportunity to use early detection and rapid response (EDRR) procedures that take advantage of the window of opportunity when manual labor is an effective means of knotweed control.

The sterile hybrid, giant miscanthus, has emerged as a promising cellulosic bioenergy crop because of its rapid growth rate, high biomass yields, and tolerance to poor growing conditions; these are traits that are desirable for cultivation, but also have caused concern for their contribution to invasiveness. New seed-bearing lines of giant miscanthus would decrease establishment costs for growers, yet this previously unresearched propagule source increases fears of escape from cultivation. To evaluate the consequences of seed escape, we compared seedling establishment among seven habitats: no-till agricultural field, agricultural field edge, forest understory, forest edge, riparian, pasture and roadside; these were replicated in Virginia (Blacksburg and Virginia Beach) and Georgia (Tifton), USA. We use a novel head-to-head comparison of giant miscanthus against five invasive and three noninvasive species, thus generating relative comparisons. Overall seed germination was low, with no single species achieving germination rates >37%, in all habitats and geographies. However, habitats with available bare ground and low resident plant competition, such as the agricultural field and forest understory, were more invasible by all species. Giant miscanthus seeds emerged in the roadside and forest edge habitats at all sites. Early in the growing season, we observed significantly more seedlings of giant miscanthus than the invasive and noninvasive species in the agricultural field. Interestingly, overall seedling mortality of giant miscanthus was 99.9%, with only a single 4 cm (1.58 in) tall giant miscanthus seedling surviving at the conclusion of the 6-mo study. The ability to make relative comparisons, by using multiple control species, was necessary for our conclusions in which both giant miscanthus and the noninvasive control species survival (≤1%) contrasted with that of our well-documented invasive species (≤10%). Considering the low overall emergence, increased propagule pressure may be necessary to increase the possibility of giant miscanthus escape. Knowledge gained from our results may help prepare for widespread commercialization, while helping to identify susceptible habitats to seedling establishment and aiding in the development of management protocols.

Nomenclature: Giant miscanthus, Miscanthus × giganteus J. M. Greef and Deuter ex Hodk. and Renvoize.

Management Implications: There is tremendous concern about exotic bioenergy crops escaping cultivation and becoming invasive species. One such crop, the sterile hybrid Miscanthus × giganteus, possesses many desirable agronomic traits, but is expensive to plant. Newly developed fertile lines add a previously under-researched source of wind-dispersed propagules, increasing the chance for establishment outside cultivated fields. Contrary to previous studies of M. × giganteus drought tolerance using vegetative propagules, we found much lower survival of seedlings in dry environments. Of the seven habitats we examined, those with more bare ground and low competition from resident vegetation were more susceptible to invasion. Low competition environments and adequate seed to soil contact is important for seed germination. While M. × giganteus did not exhibit the same ability to establish (one of 16,000 introduced seeds survived 6 mo) as other well-known invasive species we examined, the ability of this species to produce as many as 2.5 billion spikelets ha⁻¹ yr⁻¹, increases the chance of successful establishment. Based on our findings, M. × giganteus is less likely to be problematic in conventional agricultural fields subject to tillage or herbicide applications. Scouting areas near production fields or along transport routes, especially those with low resident plant competition, may help detect young plants

Mile-a-minute weed or devil's tearthumb (Polygonum perfoliatum, syn.  =  Persicaria perfoliata) is an invasive annual vine in the Mid-Atlantic and Northeastern United States that reproduces solely through seeds. Our study aimed to identify how mile-a-minute seed viability is affected by time of year and the maturity of the fruit surrounding the achene. Full-sized immature (green) and mature (blue) fruits were collected from five field sites every 2 wk over a 3 mo period, and seed viability was assessed using a triphenyl tetrazolium chloride (TZ) assay. At the onset of seed production in mid-August, 35% of seeds from immature fruits were viable. This percentage increased steadily, peaking at 84% in late September before declining at some sites around the time of the first frost. In contrast nearly all seeds with mature fruits (96%) were viable at all collection dates. Thus land managers who apply physical or chemical control methods for mile-a-minute weed should do so before the onset of any seed production and not simply before fruit maturation. If it is necessary to apply control methods after fruit set, it should be done as early in the season as possible.

Nomenclature: Mile-a-minute weed; devil's tearthumb; Persicaria perfoliata (L.) H. Gross; Polygonum perfoliatum L., POPE10.

Management Implications: This study highlights two important implications for managing the invasive vine mile-a-minute weed (devil's tearthumb) using either chemical or physical control methods. First, mile-a-minute seeds surrounded by immature fruits were shown to be viable to some extent throughout the entire season of seed production. Therefore, physical and chemical controls should be applied before any full-sized immature (green) fruits are produced and not just before mature (blue) fruits are present. Second, the viability of seeds in green fruits increased throughout the season, peaking before the first frost. This indicates that if it is necessary to apply physical or chemical control methods during the fruiting period, these methods should be applied as early in the season as possible, when immature fruits are less likely to contain viable seeds.

Miscanthus sinensis is a perennial grass native to Asia, but since its introduction to the United States in the late 19th century, it has become both a major ornamental crop and invasive species. Previous studies of the ecology of M. sinensis in both its introduced and native ranges have suggested that it may be occupying a novel ecological niche in the introduced range. Miscanthus sinensis and its daughter species, Miscanthus × giganteus, are under evaluation as bioenergy crops; therefore, characterization of the ecology and environmental niche of M. sinensis is essential to mitigate the risk of fostering future invasion in the United States. In July 2011, we surveyed 18 naturalized M. sinensis populations spanning the U.S. distribution, covering a 6° latitudinal gradient from North Carolina to Massachusetts. Miscanthus sinensis populations ranged in size from 3 to 181,763 m² with densities between 0.0012 and 2.2 individuals m⁻², and strongly favored highly disturbed and unmanaged habitats such as roadsides and forest edges. Population size and individual plant morphology (i.e., tiller height, basal diameter, and tiller number) were not affected by soil characteristics and nutrient availability, though increased tree canopy cover was associated with reduced population size (P < 0.0001). Plant size and vigor were not significantly affected by low light availability, which supports previous suggestions of shade tolerance of M. sinensis. In summary, M. sinensis can tolerate a broad range of climatic conditions, light availability, and nutrient availability in the eastern United States, suggesting risk of further invasion beyond its current distribution in the United States.

Nomenclature: Chinese silvergrass; Eulalia japonica Trin.; Miscanthus sinensis Andersson (Poaceae).

Management Implications: Miscanthus sinensis is an extremely popular ornamental grass, and is currently naturalized across much of the eastern United States. There are > 100 named cultivars commercially available with tremendous phenotypic variation that may facilitate tolerance to a broad range of geographies in the introduced range. In this study, we surveyed 18 naturalized M. sinensis populations from North Carolina to Massachusetts to characterize the environmental, climate, and edaphic factors in invaded habitats, as well as describe individual and population-level phenotypic variation. The vast majority of M. sinensis populations are found in heavily disturbed habitats such as roadsides, utility rights-of-way, and managed forest edges. Populations ranged in size from 3 m² to > 18 ha, and exhibited tolerance to edaphic conditions ranging in pH (4.2 to 7.3) and nutrient availability. The sampled latitudes represent a range of annual precipitation amounts and minimum temperatures—further support that M. sinensis has a broad environmental niche. Whether the populations originated from intentional plantings or from escaped ornamental plantings is equivocal. Thus, managers cultivating M. sinensis for commercial purposes (e.g., bioenergy, breeding, ornamental nursery stock) should employ best management practices to ensure that the wind-dispersed seeds do not enter sensitive habitat. It appears that M. sinensis is tolerant to disturbance common to rights-of-way (e.g., mowing), and prefers high light environments. Land managers should control M. sinensis prior to seed development to reduce propagule spread further, and integrate chemical and mechanical management to reduce population size. Because M. sinensis is such a popular ornamental grass it is unlikely that future introductions will be prevented; thus, future invasion mitigation would be facilitated by determining if specific cultivars are contrib

Although much is known about the physiological capabilities of reed canarygrass (RCG) and the consequences of invasion, less is known about the roles that wetland type and surrounding disturbances play in facilitating the spread of RCG in predominantly forested landscapes. Therefore, the goals of our study were to test if (1) certain wetland types in the Northern Great Lakes region were more susceptible to RCG invasion, (2) certain disturbances facilitated RCG, and (3) the level of road development and the presence or absence of a ditch bordering each observed road influences the frequency of adjacent RCG populations. We randomly selected 28 wetlands within the Keweenaw Bay Indian Community reservation in the Upper Peninsula of Michigan. At each wetland, we collected plant community and environmental data and catalogued disturbances. In all, 287 plant species were identified. Cluster analysis revealed 16 distinct vegetation communities, which were distributed among three broader wetland community types: (1) nonforested graminoid, (2) Sphagnum peatlands, and (3) forested wetlands. Occurrence of RCG was most common in the nonforested graminoid communities and was also positively correlated to disturbance. The most frequent disturbances were roads, off-road vehicle trails, and logging activity. Additionally, paved and graded roads, and roads with ditches, were more likely to have RCG alongside them than unpaved dirt roads. Our data suggest that RCG occurrence is controlled by interactions between wetland types and disturbance.

Nomenclature: Reed canarygrass, Phalaris arundinacea L.; Sphagnum spp.

Management Implications: Reed canarygrass (RCG; Phalaris arundinacea) is a widespread invasive species that colonizes wetlands and converts them to near monocultures. Currently, RCG is difficult to remove once established. Therefore, the best control may be to prevent its colonization in new areas. Our results indicate that RCG preferentially invaded certain wetland types more than others. RCG was most likely to invade nutrient-rich graminoid wetlands and shrubby wetlands. RCG did not invade low-nutrient Sphagnum peatlands, and shady forested wetlands were not typically invaded unless the canopy was opened. We also found that RCG density was correlated with disturbance, particularly roadsides and roadside ditches, road development, off-road vehicle trails, and logging activity. Additionally, paved and graded roads were more likely to have RCG alongside them than were unpaved, dirt roads. This indicates that transportation corridors are effective in facilitating the movement of RCG into wetland areas. Additionally, many rich conifer-forested wetlands are normally too shady to have large populations of RCG, but roads, logging activity, walking trails, power lines, pipelines, and other openings were found to open the canopy sufficiently to allow the invasion of RCG. This can have major implications as simple management activities such as thinning or putting in a hiking trail into rich conifer wetlands can facilitate the invasion of RCG into these systems.

Buffelgrass (Pennisetum ciliare) is a fire-prone, African bunchgrass spreading rapidly across the southern Arizona desert. This article introduces a model that simulates buffelgrass spread over a gridded landscape over time to evaluate strategies to control this invasive species. Weed-carrying capacity, treatment costs, and damages vary across grid cells. Damage from buffelgrass depends on its density and proximity to valued resources. Damages include negative effects on native species (through spatial competition) and increased fire risk to land and buildings. We evaluate recommended “rule of thumb” control strategies in terms of their ability to prevent weed establishment in newly infested areas and to reduce damage indices over time. Two such strategies—potential damage weighting and consecutive year treatment—used in combination, provided significant improvements in long-term control over no control and over a strategy of minimizing current damages in each year. Results suggest specific recommendations for deploying rapid-response teams to prevent establishment in new areas. The long-run population size and spatial distribution of buffelgrass is sensitive to the priority given to protecting different resources. Land managers with different priorities may pursue quite different control strategies, posing a challenge for coordinating control across jurisdictions.

Nomenclature: Buffelgrass, Pennisetum ciliare (L.) Link.

Management Implications: A key challenge facing land managers is how best to allocate limited resources to control invasive plant species across space and time. Optimization models are useful tools for exploring alternative strategies to optimally allocate scarce resources, such as treatment control teams and budgets, and to protect valued resources from invasion of nonnative species. In this article, we developed a mathematical model to provide guidance to land managers for addressing the following concerns: (1) the optimal size of treatment teams; (2) where, when, and what size of infestation those teams should target; and (3) the number of years for which follow-up treatments should continue. Because of the many variables interrelated across both space and time, solving such a completely forward-looking (i.e., takes full account of how all current decisions affect all future options and decisions) problem may prove intractable. Instead, we compare three “rules-of-thumb” strategies: (1) minimize current invasive species damage; (2) minimize current damage, given that any areas treated are treated in at least 3 consecutive yr; and (3) prioritize treatment based not only on current damages but also on the potential future damages of leaving an infested area untreated. The second and third strategies are also considered in combination. We evaluate those rules of thumb for their ability to prevent weed establishment in newly infested areas and to reduce damage indices over time. The rules have the advantage of telling land managers to “treat these lands now.”

Another advantage of this approach is its applicability because Microsoft Excel spreadsheets—used broadly by land and resource managers in the area—are customized to (1) manage data layers, (2) use cell formulae to maintain relationships across space and time, and (3) use the chart function to produce maps of costs, damages, weed population, and treatment recommendations. The ILOG CPLEX software package (IBM), a powerful tool for solving linear integer (binary) programs, interfaces with Excel programs so that model solutions can be readily converted to treatment priority (and other) maps. We found that the long-run population size and spatial distribution of buffelgrass are sensitive to priority weights for protecting resources. Results also indicate that resources must be increased because they are currently insufficient to control the spread of b

The United States created national parks to conserve indigenous species, ecological processes, and cultural resources unimpaired for future generations. Curtailing impacts of exotic species is important to meeting this mission. This synthesis identified 56 studies reported in 60 publications that evaluated effects of exotic plant treatments on National Park Service lands. Studies encompassed 35 parks in 20 states and one U.S. territory and included 157 exotic plant species. Eighty-seven percent of studies reported that at least one treatment reduced focal exotic species. Of 30 studies evaluating response of native vegetation, 53% reported that natives increased, 40% reported neutral responses, and 7% reported that natives decreased. For at least some of the neutral cases, neutrality was consistent with management objectives. In other cases, insufficient time may have elapsed to thoroughly characterize responses, or restoration might be needed. Nonfocal exotic species increased in 44% of the 16 studies evaluating them, but the other 56% of studies reported no increase. Results suggest that: (1) a range of exotic species spanning annual forbs to trees have been effectively treated; (2) developing effective treatments often required extensive experimentation and balancing nontarget impacts; (3) presence of multiple exotic species complicated treatment efforts, highlighting importance of preventing invasions; and (4) placing treatment objectives and outcomes in context, such as pretreatment condition of native vegetation, is important to evaluating effectiveness. Attaining the goal in national parks of conserving native species and ecological processes minimally influenced by exotic species will likely require comprehensive management strategies inclusive of treatment interactions with focal exotic species, other potential invaders, and native species.

Management Implications: National parks in the United States are areas where a management goal is to conserve native species and processes free from influences of exotic species (National Park Service 2006). Meeting this goal in light of the approximately 4,000 exotic plant species (in addition to other types of exotic organisms) already present in parks will be challenging and require effective treatment strategies applied at different scales in comprehensive ecological and social frameworks. A systematic search of published literature uncovered 56 projects conducted on National Park Service lands in which effects of exotic plant treatments were assessed.

On one hand, results were encouraging in that most projects (87%) found at least one treatment reduced focal exotic species. Moreover, treatments negatively affected native vegetation in only two projects. There also were five projects reporting eradication of 1 to 21 species within parks and some examples of effective broad-scale treatments aligned with large-area infestations. On the other hand, < 4% of exotic plant species already present in national parks have had effects of treatments upon them evaluated on National Park Service lands. There also is little to no documented information on overall trends of exotic plant abundance for most parks (Allen et al. 2009). Priorities for increasing effectiveness of management interventions include evaluating treatment effects in a comprehensive ecosystem benefits/tradeoffs approach (Steers and Allen 2010), enhancing knowledge on species trends and impacts to facilitate prioritization of limited treatment resources (Vilà et al. 2011), continued development of single- and multi-species treatments that minimize undesired effects and are cost-effective (