Adaptive management studies of invasive plants on non-agricultural lands typically employ an empirical approach based on designed field experiments that permit rigorous statistical analysis of results to quantify outcomes and assess the efficacy of management practices. When habitat restoration is the primary goal of a project, traditional plot-based study designs (e.g., the randomized complete-block design) are sometimes infeasible (this is often true in aquatic habitats) or inappropriate (e.g., when the goal is to assess effects of management practices on survival or resprouting of individual plants, such as trees or shrubs). Moreover, the assumptions of distribution-specific parametric statistical methods such as ANOVA often cannot be convincingly verified or are clearly untenable when properly assessed. For these reasons, it is worthwhile to be aware of alternative study designs that do not employ plots as experimental units and nonparametric statistical methods that require only weak distributional assumptions. The purpose of this paper is to review several of these alternative study designs and nonparametric statistical methods that we have found useful in our own studies of invasive aquatic and terrestrial plants. We motivate each statistical method by a research question it is well suited to answer, provide corresponding references to the statistical literature, and identify at least one R function that implements the method. In the Supplementary Material, we present additional technical information about the statistical methods, numerical examples with data, and a set of complete R programs to illustrate application of the statistical methods.

Fast and efficient identification is critical for reducing the likelihood of weed establishment and for appropriately managing established weeds. Traditional identification tools require either knowledge of technical morphological terminology or time-consuming image matching by the user. In recent years, deep learning computer vision models have become mature enough to enable automatic identification. The major remaining bottlenecks are the availability of a sufficient number of high-quality, reliably identified training images and the user-friendly, mobile operationalization of the technology. Here, we present the first weed identification and reporting app and website for all of Australia. It includes an image classification model covering more than 400 species of weeds and some Australian native relatives, with a focus on emerging biosecurity threats and spreading weeds that can still be eradicated or contained. It links the user to additional information provided by state and territory governments, flags species that are locally reportable or notifiable, and allows the creation of observation records in a central database. State and local weed officers can create notification profiles to be alerted of relevant weed observations in their area. We discuss the background of the WeedScan project, the approach taken in design and software development, the photo library used for training the WeedScan image classifier, the model itself and its accuracy, and technical challenges and how these were overcome.

Giant smutgrass [Sporobolus indicus (L.) R. Br. var. pyramidalis (P. Beauv.) Veldkamp] is an invasive species in grasslands, and herbicide application has been the most efficient management method to suppress this weed. Experiments were conducted in 2017 and 2018 to determine the effects of wiping glyphosate and hexazinone on S. indicus var. pyramidalis. A dose–response experiment using a handheld weed wiper was established with 20 treatments comprising two herbicides (glyphosate and hexazinone), uni- and bidirectional wiping methods, and 5 herbicide concentrations (6.25% v/v, 12.5% v/v, 25.0% v/v, 50.0% v/v, and 100% v/v basis). Data were collected 30 and 60 d after treatment (DAT). An ATV-mounted roto-type weed-wiper experiment was established in a strip-plot arrangement, with mowing as the horizontal strip, the wiping method (unidirectional vs. bidirectional) randomized as the vertical strip with three dosages of each herbicide for a total of 12 wiping treatments. Data were collected at 35 and 90 DAT. The percent plant mortality was calculated using differences in pre- and posttreatment plant counts. ANOVA and log-logistic linear regression were used to analyze the data. The dose–response experiment showed that S. indicus var. pyramidalis mortality increased with herbicide concentration, and mortality was greater with the bidirectional wiping method compared with the unidirectional method. Treatments wiped bidirectionally with glyphosate at 70% v/v, hexazinone at 30% v/v, and hexazinone at 60% v/v resulted in S. indicus var. pyramidalis mortality ranging from 75% to 98% by 90 DAT across all locations. The ATV-mounted weed-wiper experiment showed that mowing before herbicide application with weed wipers decreased the efficacy of both herbicides. Overall, both experiments indicate that S. indicus var. pyramidalis should be wiped bidirectionally using either glyphosate (70% v/v) or hexazinone (at least 30% v/v) to obtain satisfactory control. Further work should be conducted to determine whether seasonality impacts the response of S. indicus var. pyramidalis to mowing and the application of these herbicides.

Phenological studies for Cuban bulrush [Oxycaryum cubense (Poepp. & Kunth) Lye] have been limited to the monocephalous form in Lake Columbus (Mississippi). Accordingly, there is little available information on potential phenological differences among O. cubense forms (monocephalous vs. polycephalous) and populations in other geographic locations in the United States. Therefore, seasonal patterns of biomass and starch allocation in O. cubense were quantified from two populations in Lake Columbus on the Tennessee-Tombigbee Waterway in Mississippi (monocephalous), two populations from Lake Martin in Louisiana (polycephalous), and two populations from Orange Lake in Florida (polycephalous). Monthly samples of O. cubense inflorescence, emergent, and submersed tissue were harvested from two plots per state from October 2021 to September 2022. During monthly data collection, air temperature and photoperiod were recorded. Starch allocation patterns were similar among all sites, with starch storage being less than 1.5% dry weight for all plant tissues. Biomass was greatest in Lake Columbus (monocephalous; 600.7 g dry weight [DW] m−2) followed by Lake Martin (polycephalous; 392.3 g DW m−2) and Orange Lake (polycephalous; 233.85 g DW m−2). Peak inflorescence biomass occurred in the winter for the Lake Martin and Orange Lake populations and in the summer for the Lake Columbus population. Inflorescence biomass in Lake Columbus had a positive relationship (r2 = 0.53) with warmer air temperatures. Emergent and submersed biomass generally had negative relationships with both photoperiod and temperature (r2 = 0.02 to 0.77) in all sites. Peak biomass was also negatively related to temperature and photoperiod. Results from this study indicate that there are differences in biomass allocation between the two growth forms of O. cubense and that growth can occur at temperatures below freezing. Low temperature tolerance may allow this species to expand its range farther north than previously suspected.

Invasive plants may cause significant environmental risks by affecting biological diversity, ecosystem services, agriculture, and forestry. Safe utilization of invasive plant biomass by obtaining new outcome products useful for bioeconomics is a challenging but promising solution. Hydrothermal carbonization (HTC) presents a sustainable and cost-effective approach to transforming invasive plant biomass into new products while simultaneously supporting carbon capture aims. This study utilized invasive plants such as lupine [Lupinus polyphyllus Lindl.], Sosnowsky’s hogweed [Heracleum sosnowskyi Manden.], and Japanese knotweed [Polygonum cuspidatum Siebold & Zucc.] as biomass sources for HTC to produce artificial humic substances (AHS). The greatest impact on the yield of AHS (maximum gained yield of 62%) was the duration of the HTC process (up to 6 h) and temperature of the treatment (from 160 up to 250 C), as well as the catalyst used (an alkaline medium is preferable). During the HTC treatment, significant changes in the invasive plant biomass composition occur, as indicated by the removal of labile components of organic matter. The AHS obtained are essentially similar to natural humic matter and have biostimulatory properties; thus, they can be applied in agriculture and other areas of bioeconomics.

Regularly mown road verges are an important habitat for conservation of grassland vegetation. Disturbance and movement of seed-contaminated soil during road construction and maintenance makes road verges susceptible to the establishment of invasive alien plants such as garden lupine (Lupinus polyphyllus Lindl.). To combat the spread of L. polyphyllus via seeds, we tested methods for seed destruction using heat. This study aimed at developing heat eradication methods for dry and imbibed L. polyphyllus seeds applying dry heat (88, 93, 98, 103 C for 1, 3, 5, 10 min) in a laboratory, steam (85, 90, 95 C for 3, 5, 10 min) in a test box steaming device, and (97 C at 10 to 17 min; dry seeds only) in a stationary soil-steaming machine (S30). To speed up water absorption and posttreatment germination, the imbibed seeds were manually scarified before the heat treatment and the dry seeds afterward. Additionally, germination of two seed batches of different ages was tested applying dry heat (88, 98 C at 3, 5 min). Steam treatments inhibited seed germination more than dry heat in both dry and imbibed seeds. Germination dropped to <5% when steamed at ≥90 C or dry heated at >100 C. Seed germination decreased with higher temperatures and longer exposure times. Imbibed seeds exhibited lower germination compared with dry seeds for dry and steam heat. Approximately 0.5% of dry seeds germinated when steamed using the S30. The seeds collected in 2022 were less sensitive to dry heat than seeds from 2020. In conclusion, hot steam is more effective in reducing L. polyphyllus seed germination than dry heat. Thus, to successfully eradicate L. polyphyllus seeds in soil masses, we recommend steaming them at 97 C for at least 10 min.

Invasive plants can gain a foothold in new environments by manipulating soil conditions through allelopathy or through the disruption of associations between native plants and their mycorrhizal associates. The resulting changes in soil conditions can affect the recovery of habitats long after the invasive plant has been removed. We conducted a series of greenhouse experiments to examine the effects of soil conditioned by pale swallow-wort [Vincetoxicum rossicum (Kleopow) Barbarich; Apocynaceae], on the growth of native plants. Additionally, we tested the effects of aqueous extracts of common milkweed (Asclepias syriaca L.; Apocynaceae), a related plant with known allelopathic effects, on the regrowth of V. rossicum from transplanted root crowns. Soil from a 15-yr-old V. rossicum infestation reduced seedling emergence in A. syriaca as well as in V. rossicum itself. Conversely, the same soil had no effect on the growth of mature A. syriaca plants. Soil conditioned by V. rossicum growth in the greenhouse had no effect on the biomass and percentage cover generated by two restoration seed mixes. Soil conditioned by A. syriaca, however, yielded lower biomass and percentage cover from both seed mixes. In contrast to the allelopathic effects of A. syriaca on seedlings, aqueous extracts of A. syriaca increased aboveground plant growth in V. rossicum. Our results suggest that the effects of V. rossicum–conditioned soil on native plants are concentrated at the seedling establishment phase. Additionally, the use of diverse native seed mixes shows great potential for restoring productivity to ecosystems affected by V. rossicum.

Stem galls and witch’s broom–like growths are locally abundant on the highly invasive Brazilian peppertree (Schinus terebinthifolia) at field sites in southern Florida where a thrips biological control agent (Pseudophilothrips ichini) is being released to reduce the invasive potential of the plant. Galls have also been observed on potted plants in nursery stock grown to feed laboratory colonies of the agent. Herein, our objective was to isolate and identify the causal agent of the galls and assess its ability to induce galls in naive plants. We obtained stem galls from both field- and nursery-grown plants, aseptically isolated a fungus in acidic potato dextrose agar, and purified fungal colonies. Stems of potted naive saplings were wound-inoculated with purified hyphal fragments from the purified colonies, which readily induced galls like those observed in the field and nursery. Simultaneous molecular analysis of the fungal DNA obtained from the galls of field and nursery plants, experimentally induced galls, and fungal colony isolates identified this gall-inducing fungus as Cophinforma sp.. We demonstrated that this Cophinforma sp. can infect S. terebinthifolia stems via mechanical wounds and induce visibly discernible stem galls in saplings within 3 mo. This will serve as a model for galled plant production for assessing the impacts of the gall-inducing fungus on S. terebinthifolia, with potential for further study to investigate interactions between the thrips and this naturalized fungus, which may synergistically and/or additively enhance S. terebinthifolia management efficacy.

Fireweed (Senecio madagascariensis Poir.) has invaded and colonized numerous habitats in the coastal areas of southeastern Australia and is a major weed in cultivated lands as well as in poorly grassed, neglected, and highly grazed pastures. To examine the seed germination ecology of two populations (Felton and Gatton) of S. madagascariensis, experiments were conducted in the laboratory and screen house. The germination of both populations increased as the alternating temperatures increased from the coolest temperatures (15/5 C) to warmer temperatures (25/15 C). However, the highest temperature regime (35/25 C) resulted in the lowest germination rates. The Gatton population exhibited greater tolerance to higher temperatures, resulting in significantly higher germination (2.4 times) than the Felton population at the highest alternating temperature of 35/25 C. Compared with the Felton population, the Gatton population demonstrated higher tolerance to salt and water stress. In comparison to alternating light and dark periods (12 h each) (97% to 98%), the germination of both populations of S. madagascariensis was significantly reduced under complete darkness (24 h) (33% to 39%). A screen house seed burial depth experiment revealed similar emergence of S. madagascariensis seedlings between the populations. The maximum emergence (60%) was observed for seeds placed at the soil surface, followed by a dramatic decline in seedling emergence with an increase in depth. No seedlings emerged from a burial depth of 4 cm. With the addition of wheat (Triticum aestivum L.) crop residue to the soil surface at rates comparable to 4,000 to 8,000 kg ha−1, seedling emergence of S. madagascariensis decreased significantly. Information acquired from this study could be utilized to manage and develop effective weed management strategies for controlling S. madagascariensis in different agroecological conditions.

Medusahead [Taeniatherum caput-medusae (L.) Nevski] is an invasive winter annual grass of western North American grasslands and rangelands that negatively impacts forage production, wildlife habitat, and ecosystem processes. Growth regulator herbicides, such as aminopyralid, applied in spring reduced invasive annual grass seed viability in greenhouse and California annual grassland experiments. Beginning in fall 2017, we tested combinations of sequential fall (preemergence) and spring (postemergence) aminopyralid applications at low (103 g ae ha−1) and high (206 g ae ha−1) rates at two ecologically distinct sites in the Intermountain West. Preemergence and postemergence aminopyralid applications at low and high rates controlled T. caput-medusae by 76% to 100% the second summer after study initiation. At the Utah site (which is warmer, drier, and more degraded than the Idaho site), the high rate resulted in better control. The first summer, postemergence aminopyralid applications at low and high rates reduced seed viability 47% to 91% compared with nontreated seeds, with the greatest reductions seen in Utah, which was experiencing drought. Across study sites, reduced T. caput-medusae germination in one year was linked to improved control the following year. The Idaho site also had desirable perennial grasses, which we used to investigate non-target effects. In general, there was a correlation between high T. caput-medusae control and higher perennial grass cover, indicating that successful control can make desirable perennial grasses more vigorous in this system. The option of a spring aminopyralid application increases the management window for controlling invasive annual grasses by decreasing seed viability, thereby depleting short-lived seedbanks.

White-tailed deer (Odocoileus virginianus) (hereafter, ‘deer’) and invasive plants affect forest understories, but few studies have investigated their interaction. We investigated long-term (11-yr) effects of excluding deer and removing the invasive shrub, Amur honeysuckle [Lonicera maackii (Rupr.) Herder], on plants in southwest Ohio. Deer exclusion enhanced tree seedling richness and density, but reduced annual and bare ground cover. Vine density was reduced by Lonicera, especially where deer were excluded. Seedlings of several tree species, the invasive shrub, burning bush  [Euonymus alatus (Thunb.) Siebold], and the invasive vine, winter creeper [Euonymous fortunei (Turcz.) Hand.-Maz.], were indicator species of the deer exclosure by Lonicera removal treatment combination. The effect of deer on cover of native species depended on Lonicera treatment: where shrubs were removed, cover was higher where deer were excluded, but where shrubs were present, cover was higher where deer had access. We attribute these interactions to the reduced growth of, and shading by, Lonicera where deer had access and browsed this invasive shrub. Some of these effects were evident in the first 6 yr, but are now larger. Other effects were not evident in the earlier evaluation. These findings inform management of areas with high densities of deer and invasive shrubs palatable to deer. Control of only invasive shrubs will reduce native cover and not improve tree regeneration. Managing only deer will increase woody plants but reduce native cover. Management of both stressors is needed to promote tree regeneration and restoration of plant communities.

Invasive thistles reduce the productivity of pastures and rangelands because their structural defenses make them unpalatable to grazing livestock. However, plants potentially alter their growth patterns, including their allocation of resources to defense, in response to the presence of competing vegetation. Understanding the effects of competition on the structural defense of problematic pasture weeds can inform management plans that reduce the economic harm caused by these pests. We grew musk thistle (Carduus nutans L., also commonly called nodding thistle) in a fully crossed factorial field experiment in a single abandoned pasture in 2017 with two experimental factors: the level of thistle infestation (1 thistle or 5, resulting in densities of 4 or 20 plants m−2) and the presence or absence of grazing (simulated by weekly trimming of competing vegetation). We assessed the effects of treatments on defense by counting prickles >3-mm long on leaves. Our analysis included leaf age and leaf size as covariates. Competition reduced the number of prickles present on leaves. Regression analysis showed that an increase from, for example, 50 g to 200 g of competing vegetation within 50 by 50 cm study plots reduced the expected average number of prickles on intermediate-aged leaves with average length 25.5 cm by 76.9 prickles per leaf, or 41%. This pattern was similar for leaves of all ages, although the oldest leaves generally had fewer prickles than younger leaves. We did not observe differences in defense structures between plants neighbored by conspecifics and those neighbored by other competitors. Carduus nutans has been previously managed using high densities of grazers, and this practice may be more likely to damage less-defended individuals such as those we observed in our treatments with competition. This finding suggests that maintaining competition in pastures may increase C. nutans vulnerability to grazing.

Tourism, one of the world largest economic sectors, moves a substantial body of individuals and materials about the world and is implicated in the spread of invasive plants and is itself impacted by biological invasions that can degrade touristic landscapes and affect destination communities. Tourists constitute not only an immediate biological threat, but through their landscape and biota preferences also constitute a substantial economic and ecological force that has implications for invasive plant management in destinations. Tourists and the tourism industry are therefore significant stakeholders in invasive plant introduction, spread, and management. This paper discusses an onsite survey (n = 231) of domestic and international visitors in New Zealand, a destination where invasive species are an important ecological and economic issue. Findings show that visitors have a low understanding of the presence and level of threat of invasive plants and express preferences for some plants that are highly invasive. However, there were substantial variations across the international sample, with visitors from Asian and European ethnicities expressing significantly different attitudes toward a range of invasive plants. Asian visitors were more likely to show preferences for some plants that were seriously invasive and to be more accepting in general of invasive plants within landscapes and less supportive of invasive species eradication. These findings suggest that attitudes toward invasive plants and their management may be culturally determined, which poses challenges for managers aiming to generate awareness and support from across diverse tourist cohorts for invasive species control. There are also challenges for gaining support from the tourism industry for invasive plant control programs where particular “charismatic” or attractive invasive plants may contribute to touristic landscapes and visitor itineraries.

Brazilian peppertree (Schinus terebinthifolia Raddi) is an aggressive shrub that infests more than 280,000 ha in Florida. Individual plant treatments (IPT), including basal bark and cut stump application with triclopyr butoxyethylester and triethylamine formulations, respectively, have been used for decades. While they are both effective, resprouting can occur, which requires retreatment for control. Recent research on other woody invasive plants has indicated additional non-crop herbicides used in natural areas can be effective with these IPT techniques and therefore warrant testing on S. terebinthifolia. In 2018 and 2019, basal bark and cut stump studies were conducted at Cape Canaveral Air Force Station in natural areas infested with S. terebinthifolia. In the basal bark application studies, we found aminocyclopyrachlor applied at 12 and 24 g L−1 and triclopyr acid applied at 34 and 69 g L−1 each provided 100% defoliation of multistemmed S. terebinthifolia individuals with a mean root collar diameter up to 20.2 cm at 360 d after treatment (DAT). These were not different from triclopyr ester applied at 96 g L−1. Imazamox applied at 30 g L−1 resulted in 86% defoliation at 360 DAT. However, we observed formulation incompatibility when imazamox was mixed with basal bark oil which may limit its utility. In cut stump studies, we found aminocyclopyrachlor and aminopyralid each individually applied at 6, 12, and 24 g L−1, resulted in stump mortality that was not different from the commercial standard triclopyr amine applied at 180 g L−1. Similar results were found for a triclopyr acid formulation applied at 86 and 172 g L−1 and imazamox applied at 60 g L−1. For both treatment techniques, we found that alternative treatments provided control at lower herbicide concentrations than triclopyr ester and amine commercial standards. These results advance our understanding of IPT and expand access to additional effective herbicide options for S. terebinthifolia management.

Trait differences between invasive plants and the plants in their recipient communities moderate the impact of invaders on community composition. Callery pear (Pyrus calleryana Decne.) is a fast-growing, stress-tolerant tree native to China that has been widely planted for its ornamental value. In recent decades, P. calleryana has naturalized throughout the eastern United States, where it spreads rapidly and achieves high abundance in early-successional environments. Here we compare the impacts of low-density, establishment-phase P. calleryana to those of functionally similar native trees on the understory community diversity and total cover of three early-successional meadows in Indiana’s Eastern Corn Belt Plains. In contrast to our prediction that P. calleryana would have greater negative effects on the total abundance and diversity of the understory plant community compared with native tuliptree (Liriodendron tulipifera L.), American sycamore (Platanus occidentalis L.), or non-tree control plots, we found that these low-density populations of P. calleryana had no significant impact on total cover, species richness, or diversity indices for the understory community compared with the native trees and non-tree control plots. Likewise, the studied populations of P. calleryana had no significant impact on the native, introduced, woody, or native tree subsets of the understory community. These results indicate that in young, low-density populations situated in early-successional meadows, the trait differences between P. calleryana and functionally similar native trees are not of a great enough magnitude to produce changes in community composition. Going forward, complementary research on the impacts of P. calleryana on community composition and ecosystem processes in areas with long-established, dense invasions or invasions in more sensitive ecosystems would allow us to more fully understand how this widespread invader disrupts its host ecosystems.

An important route of introduction of some nonnative species that subsequently become invasive in the United States is through horticulture. One such plant is Euonymus fortunei (Turcz.) Hand.-Maz., commonly known as wintercreeper, an evergreen groundcover with more than 52 different horticultural varieties, which is still sold at many plant nurseries and garden centers in the midwestern United States. Although several states have recognized E. fortunei as an invasive species, it is unknown how its escape from cultivation has occurred and even the identity of spreading populations, including whether hybrids or cultivars are involved. Using codominant microsatellite markers, we sampled multiple invasive populations in Ohio, Kentucky, Kansas, and Minnesota and compared their genotypes with commercially available cultivars to determine how spread has occurred. All samples collected from invasive populations were genetically identical to one another and matched perfectly with the ‘Coloratus’ cultivar, the only cultivar to exhibit polyploidy. The data also suggest that E. fortunei may potentially reproduce via apomixis and/or clonally through propagule fragments, which can quickly fix favorable genotypes within a population. To curb continued invasive spread, we suggest that Coloratus be removed from commercial sale and distribution. We also propose that land managers, horticultural and landscaping businesses, and governmental agencies carefully monitor other Euonymus cultivars for invasive potential and spread.

Invasive nonindigenous species pose a serious threat to native biodiversity and ecosystem functioning. Understanding how species’ performance varies under conditions in the current and invaded range can help to predict the dynamics of the invading species in its new environment. Plants with the ability to alter growth in response to variation in light conditions may be favored in landscapes that experience frequent disturbance, as these species may be able to exploit a wide range of niches. Seedbank persistence may also play a critical role in successful plant invasion, as extended seed viability may increase the chance of outlasting unfavorable conditions, maintain population genetic diversity, and allow reinvasions. This study investigated seed longevity and the effect of light intensity on germination of wavyleaf basketgrass [Oplismenus undulatifolius (Ard.) Roem. & Schult.], a newly established invasive species in U.S. mid-Atlantic forest understories. Oplismenus undulatifolius seeds were collected across 5 yr from the original site of introduction in Maryland, USA, and stored in standard lab conditions, then subjected to germination trials under four light conditions in a controlled growth chamber. Seeds remained viable for at least 9 yr, and light intensity did not significantly impact seed germination. Our study demonstrates the importance of evaluating environmental and temporal effects on germination traits, because the scope of surveillance in the field may need to be expanded based on new information about environmental tolerance. Long-term monitoring may also be necessary to effectively control invasive plant populations capable of forming a persistent seedbank.

Eurasian watermilfoil (Myriophyllum spicatum L.) is an aquatic vascular plant that forms extensive dense beds in lakes. This invader competes with native plants, interferes with aquatic activities, and decreases riparian property values. In Canada, the use of aquatic herbicides is highly restricted. Environmental managers must therefore rely on physical methods such as hand pulling or benthic matting for control. Although these methods are not new, there has been little scientific investigation regarding their effectiveness and cost over multiple years. Benthic matting and hand pulling were used in Lac des Abénaquis (area: 1.2 km2) to control 3.6 ha of M. spicatum beds. Initiated by citizens in 2016, control procedures were scientifically studied in 2020 and 2021. Benthic fiberglass mats were deployed on dense M. spicatum patches for 10 wk. Isolated plants and patches <100 m2 were hand pulled by divers, and the harvested material surfaced via a suction hose or in hand-filled bags. By August 2021, all the M. spicatum patches had been eliminated, and only 560 widely scattered plants remained. Over the last 2 yr of control, hand pulling required 243 person-hours and removed 2,245 kg of biomass. The biomass brought to the surface was 2.4 times higher per person-hour with the suction system than with bags. The use of 1,000 m2 of benthic mats required 47 to 51 person-hours per summer season, including installation, removal, and maintenance. Intensive management (years 1 to 5) using benthic mats and hand pulling cost an estimated Can$185,000 (US$140,000) ha−1 of M. spicatum bed. Hand pulling of scattered individuals (years 6+), estimated at Can$20,000 (US$15,000) per summer, is essential to avoid reinfestation. An invasion of M. spicatum can successfully be managed in small lakes without herbicides, but control remains a costly and long-term endeavor.

One way that climate change is projected to affect invasive plant management is by shifting the ranges of invasive plants. In some regions, hundreds of new, potentially invasive species could establish in coming decades. These species are prime candidates for early detection and rapid response. However, with limited resources, it is unlikely that invasive plant managers will be able to monitor and treat this large number of novel species. Determining which species are likely to have the greatest impacts could inform further risk assessment and mitigate the greatest amount of potential damage. Here, we used the Environmental Impact Classification for Alien Taxa (EICAT) protocol to evaluate the potential impacts of 104 invasive plant species that are projected to establish in Delaware, Kentucky, Maryland, New Jersey, Ohio, Pennsylvania, Virginia, and/or West Virginia by midcentury with climate change. These species were identified using the Invasive Range Expanders Listing Tool to predict which invasive species are likely to shift their ranges into the target states by midcentury. We used Web of Science to search for studies on each species involving impacts to ecological or socioeconomic sectors. We scored ecological impacts on a scale of 1 (“minimal concern”) to 4 (“major concern”) and socioeconomic impacts as present or not present. We evaluated 674 papers and categorized the species into these categories: 32 high-impact species, 20 moderate-impact species, and 13 minor- or minimal-impact species. Two of the 32 high-impact species (panic veldtgrass [Ehrharta erecta Lam.] and Athel tamarisk [Tamarix aphylla (L.) Karst.]) pose a risk to all eight mid-Atlantic states. There were also 46 species that pose a risk to socioeconomic sectors, including agriculture, the economy, and human health. Twenty-four species were listed as data deficient (no data could be found on them). This study provides a comprehensive review of reported impacts of range-shifting invasive plants in the mid-Atlantic.

Eastern redcedar (Juniperus virginiana L. var. virginiana; hereafter ERC) is a native species currently invading open areas and grasslands outside of its original range in the United States. We studied ERC’s invasion patterns in the Lakeside Daisy State Nature Preserve (LDSNP), a short grass prairie located on the Marblehead Peninsula in Ohio, examining the changes in the genetic diversity and structure of the encroaching population. We investigated the relative importance of long-distance dispersal versus diffusion in the invasion of this short grass prairie by ERC. We use eight microsatellite marker loci to infer gene flow from external sources versus within-population recruitment. We found that the older trees in this preserve were less than 50 yr old, indicating that the population was established between 1970 and 1980. When we grouped trees into five age categories of 10-yr increments, we found that the allelic diversity, as indicated by the average number of alleles per locus, increased as the age of the trees decreased. We also found that not all loci were in Hardy-Weinberg equilibrium, probably due to the arrival of new variants in the preserve. Moreover, heterozygosity remained high, with an excess of heterozygotes in all age groups (F = −0.163 ± 0.046). Principal coordinate analysis showed two distinct groups of trees in the LDSNP. Analysis of the cryptic population structure of the ERC trees using STRUCTURE revealed four ancestral clusters in the ERC population. All ancestral clusters are present in all age groups, suggesting that all trees sampled are derived from an admixed population. Furthermore, the high observed heterozygosity and lack of inbreeding in this dioecious species maintained all ancestral clusters over time. Overall, our findings indicate that ERC encroachment of the LDSNP results from multiple and reiterated gene flow events from the edge of the range through animal-mediated seed dispersal.