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.

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.

We assessed the ability of climatic, environmental, and anthropogenic variables to predict areas of high-risk for plant invasion and consider the relative importance and contribution of these predictor variables by considering two spatial scales in a region of rapidly changing climate. We created predictive distribution models, using Maxent, for three highly invasive plant species (Canada thistle, white sweetclover, and reed canarygrass) in Alaska at both a regional scale and a local scale. Regional scale models encompassed southern coastal Alaska and were developed from topographic and climatic data at a 2 km (1.2 mi) spatial resolution. Models were applied to future climate (2030). Local scale models were spatially nested within the regional area; these models incorporated physiographic and anthropogenic variables at a 30 m (98.4 ft) resolution. Regional and local models performed well (AUC values > 0.7), with the exception of one species at each spatial scale. Regional models predict an increase in area of suitable habitat for all species by 2030 with a general shift to higher elevation areas; however, the distribution of each species was driven by different climate and topographical variables. In contrast local models indicate that distance to right-of-ways and elevation are associated with habitat suitability for all three species at this spatial level. Combining results from regional models, capturing long-term distribution, and local models, capturing near-term establishment and distribution, offers a new and effective tool for highlighting at-risk areas and provides insight on how variables acting at different scales contribute to suitability predictions. The combinations also provides easy comparison, highlighting agreement between the two scales, where long-term distribution factors predict suitability while near-term do not and vice versa.

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.

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.

Meadow knapweed is a fertile European hybrid between black and brown knapweed that has expanded its North American distribution to 27 of the United States and four provinces in Canada. Two experiments were conducted on meadow knapweed in northwestern Washington to determine (1) whether meadow knapweed is similarly sensitive to several herbicides commonly used to control related knapweeds, (2) if herbicide application timing plays a role in control of meadow knapweed, and (3) whether mowing before, after, or instead of herbicide treatment can aid in meadow knapweed control. In the first experiment, herbicides were applied to meadow knapweed at rosette or bolting stages of growth, and again with the same herbicides in the autumn. In the summer following treatment, clopyralid alone or with 2,4-D, dicamba + 2,4-D, and triclopyr ester + 2,4-D ester provided 81 to 100% meadow knapweed control; the only other treatment providing similar control was glyphosate + ammonium sulfate applied at bolting and in autumn in the 2004 to 2005 trial. In the second experiment, combinations of mowing and dicamba + 2,4-D were applied at rosette or early flowering stages of growth. In the 2002 to 2003 trial, control when dicamba + 2,4-D was used exceeded 90%, except when meadow knapweed was mowed at rosette and sprayed at early flowering (78% control). Mowing twice the previous year had only a slight effect on meadow knapweed (10% control). Grass biomass exceeded meadow knapweed biomass in all herbicide-treated plots. In the 2004 to 2005 trial, meadow knapweed control and grass biomass was maximized when plots were mowed at rosette and treated with dicamba + 2,4-D at early flowering or when treated twice with these herbicides; these were the only treatments where grass biomass exceeded meadow knapweed biomass.

Japanese hedgeparsley is a biennial plant that invades roadsides, rights-of way, and forested areas in the midwestern United States. Interest in managing populations by mechanical or hand-clipping techniques exists, but no information is available on the appropriate timing to maximize mortality and prevent the production of viable seed. To assess that, we applied clipping treatments at five periods throughout the summer to three Japanese hedgeparsley populations in southern Wisconsin and measured the number and viability of seeds produced by each plant during the year of treatment and the survival of plants clipped. Japanese hedgeparsley plants began producing seed by mid-July, but production was not maximized until early August. Viable seeds were not produced until early or mid-August, coinciding with the presence of ripened brown fruit. Clipping at any timing resulted in > 95% mortality by the fall of the treatment year. All plants that resprouted were in the vegetative stage when clipped, and no plants survived the following year. Results indicate that clipping Japanese hedgeparsley plants when they are in a reproductive phase before fruit turns brown is an effective management strategy for this invasive plant.

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.

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.

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.

Miscanthus × giganteus, a widely planted biofeedstock, is generally regarded as a relatively low invasion concern. As a seed-infertile species, it lacks a consistent mechanism of long-distance dispersal, a key contributor to invasion rate, and constitutes a low risk for cultivation escape. However, agricultural production shelters plants from stochasticity and increases propagule pressure, enhancing the potential for low-risk species to take advantage of rare dispersal opportunities. Weed risk assessments of M. × giganteus assume the rarity of events such as scouring and flooding that would facilitate secondary dispersal of vegetative rhizome fragments and the long-term sexual inviability of escapes. Combining data from small-scale rhizome fragmentation and movement experiments, and estimates from the literature, we parameterized an individual-based model to examine M. × giganteus spread given three dispersal scenarios. We further evaluated our estimates in response to different field edge buffer widths and monitoring intensities, two key strategies advised for containing biofuel crops. We found that clonal expansion from the field edge alone was sufficient to allow the crop to outgrow buffers of 3 m or less within 11 to 15 yr with low monitoring intensities. Further, models that included the possibility of rhizome dispersal from fields and scouring at field edges demonstrate the potential for long-distance dispersal and establishment with inadequate management. Our study highlights the importance of considering minimum enforced management guidelines for growers to maintain the ecological integrity of the agricultural landscape.

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.

The miconia (Miconia calvescens) invasion of the East Maui Watershed (EMW) started from a single introduction over 40 yr ago, establishing a nascent patch network spread across 20,000 ha. In 2012, an accelerated intervention strategy was implemented utilizing the Herbicide Ballistic Technology (HBT) platform in a Hughes 500D helicopter to reduce target densities of seven nascent patches in the EMW. In a 14-mo period, a total of 48 interventions eliminated 4,029 miconia targets, with an estimated 33% increase in operations and 168% increase in recorded targets relative to the adjusted means from 2005 to 2011 data (prior to HBT adoption). This sequence of interventions covered a total net area of 1,138 ha, creating a field mosaic of overlapping search coverage (saturation) for each patch (four to eight interventions per patch). Target density reduction for each patch fit exponential decay functions (R2 > 0.88, P < 0.05), with a majority of the target interventions spatially assigned to the highest saturation fields. The progressive decay in target density led to concomitant reductions in search efficiency (min ha−1) and herbicide use rate (grams ae ha−1) in subsequent interventions. Mean detection efficacy (± SE) between overlapping interventions (n = 41) was 0.62 ± 0.03, matching closely with the probability of detection for a random search operation and verifying imperfect (albeit precise) detection. The HBT platform increases the value of aerial surveillance operations with 98% efficacy in target elimination. Applying coverage saturation with an accelerated intervention schedule to known patch locations is an adaptive process for compensating imperfect detection and building intelligence with spatial and temporal relevance to the next operation.

Lepidium latifolium (perennial pepperweed) is a weedy alien crucifer that has invaded wetlands throughout the western United States. We monitored L. latifolium invasion of an Elytrigia elongata (tall wheatgrass) community at the Honey Lake Wildlife Refuge in northeastern California. In 1993, a 40-m2 plot was delineated, at which time only two single plants of L. latifolium were present. Beginning in 1994, L. latifolium stem density was measured yearly until 2011. From 1994 through 2000, the density of L. latifolium increased to greater than 120 stems m−2. At its height of stem density and stature between 1998 and 2000, it appeared that E. elongata had been extirpated. From 2001 through 2006, stem density and plant stature of L. latifolium declined, but there were still areas of the plot where stem density exceeded 60 stems m−2. From 2007 through 2009, stem density decreased considerably and averaged less than 30 stems m−2 and a healthy recovery of E. elongata occurred. In the years 2010 and especially 2011, stem density increased, but individual plants were small in stature. Soil bicarbonate-extractable phosphorus data suggest that phosphorus availability may be crucial to the invasiveness of L. latifolium. Long-term biogeochemical cycling by L. latifolium may reduce soil phosphorus availability in deeper soil horizons and enrich availability in the soil surface, which alters the competitive relationship between L. latifolium and E. elongata.

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.

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.

Restoration of abandoned agricultural lands to create resilient ecosystems in arid and semi-arid ecosystems typically requires seeding or transplanting native species, improving plant–soil–water relations, and controlling invasive species. We asked if improving water relations via irrigation or surface mulch would result in negative tradeoffs between native species establishment and invasive species competition. We examined the effects of sprinkler irrigation and straw mulch on native seed mixtures planted in two consecutive years in an abandoned agricultural field in a cold desert shrubland in southwestern Nevada, USA. Restoration effects differed among years because of contingency effects of growing season conditions. Precipitation was low during the first year and seeded plant density and biomass increased in response to irrigation. Precipitation was relatively high during the second year, seeded plant densities and biomass were generally high, and irrigation had inconsistent effects. Mulch increased native plant cover in the absence of irrigation during the dry year. Invasive plant biomass and cover also were influenced by year, but irrigation increased invasive plants regardless of precipitation. Positive effects of irrigation on seeded plant density, cover, and biomass outweighed negative tradeoffs of increases in invasive plants. In ecosystems with highly variable precipitation, the most effective restoration strategies will most likely be adaptive ones, requiring determination of timing and amount of irrigation based on precipitation, native plant establishment, and invasive species composition and abundance.

Himalaya blackberry is a nonnative shrub that has invaded sites throughout the Pacific Northwest. Its persistent canopy and large underground crowns create a competitive environment that prevents desirable species from germinating, establishing, or both. Cutleaf blackberry grows in association with Himalaya blackberry, and control efforts frequently target these two species. Control of Himalaya blackberry is complicated by vigorous vegetative regrowth after mechanical control, including mowing, and variable response to chemical methods. Recent interest in the use of goat browsing for invasive plant control has led land managers to use a variety of browsing regimes to control unwanted species through disturbance by herbivory. This study examined changes in functional group percent cover in a perennial grass pasture invaded by Himalaya blackberry and cutleaf blackberry in the southern Willamette Valley of Oregon. The appearance of species and their functional group membership after three treatment protocols are evaluated. Changes in the percentage of cover by Himalaya and cutleaf blackberries, annual grasses, perennial grasses, annual forbs, and perennial forbs were examined after two annual treatments with (1) high-intensity–short-duration goat browsing, (2) mowing, and (3) high-intensity–short-duration goat browsing followed by mowing. These data were then compiled by functional group to assess trends in the plants' revegetating the pasture after treatment. All treatments caused a significant decline in the percent cover of the invasive blackberries (P < 0.0001), but differences among treatments were not significant. The increase in the percent cover of perennial forbs for plots treated with goat browsing followed by mowing was significantly greater (P = 0.008) than it was in plots browsed only and those mowed only. Changes in percent cover of other functional groups were not significantly different with browsing or mowing treatments. Individual species within the perennial grass and perennial forb groups are discussed.

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.