The composition of nonnative floras is influenced by a region’s socioeconomic history, yet rarely are these factors studied alongside plant naturalization rates over time. Such information is especially critical for archipelagos, which often host large numbers of nonnative plants and would benefit from prevention of inter-island spread. We compiled the first record of occurrence and first record of naturalization for all naturalized plants in Hawai‘i alongside data on their origin, native climate types, taxonomy, and likely introduction pathway and compared rates of naturalization with socioeconomic trends. We found that the rate of total plant naturalizations has increased at a roughly constant rate during the past century without any sign of plateauing. However, this relatively steady increase is underlain by notable fluctuations in naturalization rates for different introduction pathways, with ornamentals increasing recently, while agriculture-related plants have decreased. Furthermore, this trend mirrors a shift from an agriculture-dominated economy to a tourism-based one associated with increases in both resident and tourist populations as well as general economic well-being. We further found that the average naturalized species spreads at a rate of 1.86 islands per decade, eventually occupying most major islands in the archipelago, and the rate of spread appears to be increasing since Hawai‘i’s economic shift. Our findings also emphasize the diversity of Hawai‘i’s nonnative flora, which originates from a variety of climates, continents, and taxonomic groups. We demonstrated that many nonnative species have native ranges that include temperate climates, which is important, because these climates typically co-occur with higher-elevation, remnant patches of native-dominated ecosystems in Hawai‘i. This study reveals trends that may help predict a species’ ability to naturalize and spread within and between islands, and we discuss management implications that may be extended to other regions.

Arbuscular mycorrhizal fungi (AMF, Glomeromycota) are globally distributed symbionts of plant roots. Relationships with arbuscular mycorrhizae can provide crucial support for the establishment of any plant in an unfavorable environment. We hypothesized that invasions of neophytes are associated with changes in the colonization of native plants and early invaders (archeophytes) by AMF. We examined changes in AMF colonization in yarrow (Achillea millefolium L.) and wild carrot (Daucus carota L.) (native plants) and tansy (Tanacetum vulgare L.) and false oatgrass [Arrhenatherum elatius (L.) P. Beauv. ex J. Presl & C. Presl] (archeophytes) in response to the invasion of four neophytes from the Asteraceae family, namely great globethistle (Echinops sphaerocephalus L.), New York aster [Symphyotrichum novi-belgii (L.) G. L. Nesom agg.], annual fleabane [Erigeron annuus (L.) Pers.], and Canada goldenrod (Solidago canadensis L.). We found that the AMF colonization of the Asteraceae neophytes was high in the studied monodominant invasions, and the AMF colonization of the neophytes was higher than or equal to that of the studied native plants and archeophytes. Changes in plant dominance did not serve as predictors of the extent of AMF colonization of the native plants and archeophytes despite the invaded plots being associated with strong changes in the availability of primary and secondary mineral nutrients. The absence of a response of AMF colonization of native and archeophyte plant species to the invasion of neophytes suggests that AMF are passengers, rather than drivers, in the course of Asteraceae invasions in central European environments.

Ventenata [Ventenata dubia (Leers) Coss.] is one of several annual grass invaders of the western United States. Ventenata dubia is documented reducing the forage availability for livestock and wildlife as well as lowering biodiversity in the Great Basin. This species has recently spread to the Great Plains, where it could bring these impacts with it. We attempt to answer questions on whether or not conservation practices, in this case removal of V. dubia with herbicide, result in recovery of forage resources and biodiversity. We answer these questions by measuring biomass, cover, and nutrient content 1-yr posttreatment at 9 sites in Sheridan County, WY, conducted in two years. Perennial grasses have higher crude protein and total digestible nutrients than V. dubia, and removal of V. dubia resulted in a positive perennial grass response both years. Further, the differences in pattern of growth between perennial and annual species, with annual grasses quickly senescing early in the year, make perennial grasses a more dependable forage base with higher available nutrients. Interestingly, total biomass and nutrient mass did not change after V. dubia removal due to equal replacement with perennial grasses. Species richness and diversity were unaffected by removal of V. dubia. Our results suggest that managing invasive annual grasses, particularly V. dubia, in the Northern Great Plains can improve forage resources for livestock and wildlife while maintaining species diversity. Therefore, proactive monitoring and management efforts to prevent spread should be prioritized in this region.

Eradication of alien invasive species in the soil with steam as an alternative to chemical fumigation may allow contaminated soil to be reused. We have investigated steam disinfestation of soil to combat invasive plant species in three experiments including different temperatures and exposure durations using a prototype stationary soil-steaming device. The experiments included effects on seed germination of bigleaf lupine (Lupinus polyphyllus Lindl.), ornamental jewelweed (Impatiens glandulifera Royle), and wild oat (Avena fatua L.; one population from Poland and one from Norway), as well as effects on sprouting rhizome fragments of Canada goldenrod (Solidago canadensis L.) and Bohemian knotweed (Reynoutria x bohemica Chrtek & Chrtková). In Experiment 1, we tested four different soil temperatures of 64, 75, 79, and 98 C with an exposure duration of 90 s. In Experiments 2 and 3, we tested exposure durations of 30, 90, and 180 s and 90, 180, and 540 s, respectively, at 98 C. Seed pretreatment of 14 d cooling for L. polyphyllus and I. glandulifera, no seed pretreatment and 12-h moistening for A. fatua populations, and 5- and 10-cm cutting size for R. x bohemica were applied. Our results showed germination/sprouting was inhibited at 75 C for I. glandulifera (for 90 s) and 98 C for the other species; however, longer exposure duration was needed for L. polyphyllus. While 30 s at 98 C was enough to kill A. fatua seeds and S. canadensis and R. x bohemica rhizome fragments, 180-s exposure duration was needed to kill L. polyphyllus seeds. The results showed promising control levels of invasive plant propagules in contaminated soil by steaming, supporting the steam treatment method as a potential way of disinfecting soil to prevent dispersal of invasive species.

Using species distribution models (SDMs), we predicted the distribution of 170 plant species under different climatic scenarios (current and future climatic conditions) and used this information to create invasion risk maps to identify potential invasion hot spots in California. The risk of invasion by individual species was also assessed using species’ predicted area in combination with some biological traits associated with invasiveness (growth form, reproduction mechanisms, and age of maturity). A higher number of species would find suitable climatic conditions along the coast; the Central Western (CW) and South Western (SW) were ecoregions where a higher number of species were predicted. Overall, hot spots of species distribution were similar under current and future climatic conditions; however, individual species’ predicted area (increase or decrease) was variable depending on the climate change scenario and the greenhouse gas emission. Out of the 170 species assessed, 22% ranked as high-risk species, with herbs, grasses, and vines accounting for 78% within this risk class, and a high proportion (67%) of Asteraceae species ranked as high risk. This study suggests that current climatic conditions of the central and south coastal regions of California would be considered as hot spots of new invasions, and for some species this risk might increase with hotter and drier future climatic conditions.

Invasive species management in natural landscapes is generally executed at the scale of independent jurisdictions, yet the ecological processes and biodiversity to be protected from invasion occur over large spatial scales and across multiple jurisdictions. Jurisdictional land boundaries can influence the flows and dynamics of ecological systems, as well as the social systems that exist in these complex landscapes. Land management entities in large, protected area–centered ecosystems may use different approaches to address cross-boundary management challenges. To understand these differing strategies and their effects on cooperative invasive plant management, we interviewed employees with federal, county, and state agencies, research organizations, nonprofits, and local stakeholder groups in two national parks and their surrounding lands in California, USA. Although all participants stressed the importance of working together, they did so along a continuum of strategies ranging from simple communication to coordination of independent efforts to active collaboration. Barriers to collaboration can be categorized as originating within or externally to the management unit, including limited resources, differing agency priorities, paperwork requirements, and lack of support by higher-level managers. Strategies to reduce barriers depend on where they originate.

Mangroves are a critical component of many coastal ecosystems in Florida. Woody species, including Brazilian peppertree (Schinus terebinthifolia Raddi), have invaded thousands of hectares of mangrove habitat. The difficulty associated with ground-based management of invasive plants in mangrove communities has warranted a need to identify selective herbicides that can be applied aerially. Recent work suggests that Florida mangrove species are extremely sensitive to synthetic auxin herbicides; however, other herbicides have yet to be tested for selectivity. Greenhouse studies in 2018 and 2019 evaluated broadcast foliar applications of the acetolactate synthase inhibitor imazamox and protoporphyrinogen oxidase inhibitor carfentrazone-ethyl, both as individual treatments and in combinations, for control of S. terebinthifolia and injury to four non-target mangrove species. Across all posttreatment sample dates and species tested, there were no significant interactions between imazamox applied at 0.28 or 0.56 kg ai ha−1 in combination with carfentrazone-ethyl applied at 0 or 0.1 kg ha−1. Main effects of imazamox applied at 0.56 kg ai ha−1 and carfentrazone-ethyl applied at 0.1 kg ha−1 resulted in 99% and 97% defoliation, respectively, of Schinus terebinthifolia at 180 DAT. However, S. terebinthifolia percent survival was 56% and 44% for the same treatments. Both herbicides severely injured all four mangroves by 90 DAT and resulted in 58% to 100% defoliation across species. At 180 DAT, significant increases in percent cambium kill were also observed for all four species. Across species, mangrove survival varied, but red mangrove (Rhizophora mangle L.) survival was reduced to 6% when imazamox was applied at 0.56 kg ha−1. These results indicate both imazamox and carfentrazone-ethyl exhibit activity on S. terebinthifolia but also injure all four mangroves enough to preclude their use as selective treatments.

Waterhyacinth [Eichhornia crassipes (Mart.) Solm] is an aquatic invasive plant that is widespread in Puerto Rico, where it negatively effects estuaries, freshwater wetlands, potable water reservoirs, and wildlife refuges. Specifically, the tropical estuary San Juan Bay Estuary (SJBE) has been impacted with the presence of E. crassipes. Infestations have led to a reduction of water circulation in the system and have facilitated the establishment of invasive fauna. Therefore, a field study was conducted in a cove between Laguna San Jose and Peninsula Cantera to assess the use of glyphosate and hand removal as a management tool for E. crassipes control. Aquatic macroinvertebrates and water quality were also monitored as a measure of environmental impact due to management activities. Results indicated that at 2 wk after glyphosate application, E. crassipes biomass (dry weight) was significantly reduced to 0.27 kg DW m−2 at the treated plot compared with the nontreated plot, which yielded 0.62 kg DW m−2. Fresh weight of E. crassipes decreased more than 90% when hand removal was used compared with glyphosate treatment. Dissolved oxygen and water pH were not significantly different between sites; however, water salinity increased to 8 to 9 ppt at both plots as a result of tidal activity. The order Hemiptera followed by Sarcoptiformes were common in the aquatic macroinvertebrate community. Macroinvertebrate species found associated with E. crassipes and considered natural enemies were: Orthogalumna terebrantis Wallwork, Niphograpta albigutalis (Warren), and Neochetina eichhorniae Warner. The use of glyphosate to manage E. crassipes at the Laguna San Jose was useful as a short-term control method, and its efficacy may be enhanced over time with follow-up applications in combination with hand removal.