Citizen science is becoming very useful in surveying and monitoring biodiversity. Within the European Union LIFE medCLIFFS project, a network of volunteers has been established for the detection and long-term monitoring of invasive plant species that threaten the endemic flora of Mediterranean cliffs in northeastern Spain. Through iNaturalist, volunteers record various data along a series of 1-km transects. Based on the ca. 700 observations collected by volunteers in 2023 (the first year of the project), a simple and visually attractive methodology for assessing the recorded populations has been developed. This method classifies populations into one of three population dynamics categories: (1) propagative behavior (i.e., populations with seedlings or young plants but lacking senescent or dead individuals); (2) senescent behavior (i.e., showing senescent/dead plants but lacking seedlings/juveniles); and (3) a mixed behavior (i.e., containing both). This methodology, whose outputs are easily interpretable as heat maps, allows the collection of large datasets on invasive plants by citizen scientists, with two main purposes: (1) knowing which species are most concerning based on simple, straightforward observations of their population dynamics; and (2) identifying which regions of the study area are more problematic and where management efforts should therefore be directed.

Reduced hack and squirt (RHS) is a herbicide-injection technique that controls woody species with a limited number of hacks. When used with aminopyralid or aminocyclopyrachlor, the technique controls multistemmed shrubs such as Brazilian peppertree (Schinus terebinthifolia Raddi) and Surinam cherry (Eugenia uniflora L.). However, additional data are needed to compare its effectiveness on other woody invasive species against standard individual-plant treatment techniques. We compared RHS with aminocyclopyrachlor or aminopyralid administered with 0.5 ml of undiluted concentrate (240 g L^–1) against traditional basal bark and cut stump techniques using triclopyr at 96 and 120 g L^–1, respectively, on six invasive trees in Florida, USA. For all species tested, the RHS technique with aminocyclopyrachlor was not different or was more effective than basal bark or cut stump treatment with triclopyr. The RHS technique with aminopyralid was effective on certain species but did not control as many species as RHS with aminocyclopyrachlor or cut stump treatment with triclopyr. The RHS technique required significantly less time than cut stump treatment but was not different from basal bark treatment. Across all species, when compared with basal bark and cut stump treatment with triclopyr, the RHS approach resulted in reductions of average total herbicide mix applied by 98% and 89%, respectively. For herbicide active ingredient, when compared with basal bark and cut stump treatment with triclopyr, RHS resulted in reductions of 95% and 86%, respectively. These results indicate that when compared to conventional individual plant treatment (IPT) approaches with triclopyr, the RHS approach yielded a high level of target efficacy on a broad spectrum of species, comparable or shorter application times, and substantial reductions in herbicide mix and active ingredient applied. Future research should seek continued refinement of this technique for woody plant control on other troublesome invaders.

Tree-afflicting pests, such as insects and pathogens, could change forests in ways promoting invasions by non-native plants. After tree death associated with the fungal pathogen oak wilt (Bretziella fagacearum) and its attempted containment (severing root connectivity and sanitation removal of infected trees), we examined change in cover of the non-native liana Oriental bittersweet (Celastrus orbiculatus Thunb.; hereafter Celastrus) at 28 sites in temperate black oak (Quercus velutina Lam.) forests, Ohio, USA. During our 5-yr study spanning 2020 to 2024, Celastrus cover increased significantly (P < 0.05) through time at oak wilt sites but not in untreated reference forest sites without evidence of oak wilt. Celastrus cover increased by an order of magnitude, up to an average of 32 times among oak wilt treatments up to 10 yr old. By 2024, Celastrus cover ranged from 6% to 22% on average in 5- to 10-yr-old oak wilt treatments, compared with 1% cover in reference forest. Results indicate that non-native plant invasion accelerated following disturbance associated with a fungal pathogen and its attempted containment and, more generally, suggest that tree-afflicting pests can promote invasive plants in forests. Co-management of tree-afflicting pests and non-native plants may become increasingly important to ensure forests recovering from tree mortality are dominated by native plants.

Several Elaeagnus species (autumn olive [Elaeagnus umbellata Thunb.], Russian olive [Elaeagnus angustifolia L.], and thorny olive [Elaeagnus pungens Thunb.]) are invasive in North America. Elaeagnus pungens is prevalent throughout much of the southeastern United States, commonly overtaking wooded and natural areas, bottomlands, and roadsides. While many management methods, including several herbicide treatments, have been evaluated, the efficacy of these methods can vary based on the size and density of the target plants. Further, personal communication with land managers revealed a lack of information that incorporated application effort, duration, and associated cost into treatment efficacy and usefulness. We evaluated three herbicide application methods using the free acid formulation of triclopyr in an E. pungens–infested forest in South Carolina, USA, to determine the effectiveness of each application method. We estimated pretreatment E. pungens biomass and destructively harvested all live material posttreatment to obtain actual biomass values. Foliar herbicide application was ineffective, but both cut stump and basal bark application nearly eliminated E. pungens in the treatment plots. The basal bark application took slightly more time to complete than cut stump treatments but was described as less physically demanding by applicators. Based on treatment efficacy and time required, the basal bark application method seems most prudent for controlling E. pungens in these areas. These results will help land managers more effectively use their resources for invasive woody plant control.

Invasive plants' ability to extend their range depends upon their local environments and both positive and negative interactions with native species. Interactions between invasive and native plants may be indirectly linked to the soil fungal community, which may enhance or suppress invasion through mutualism or parasitism. Many invasive plants preferentially select fungal communities or change soil chemistry to gain a competitive advantage, and such changes can remain even after the invader is removed, known as legacy effects. Yellow toadflax (Linaria vulgaris Mill.) is an invasive forb that is aggressive in the western United States but is nonaggressive in the midwestern United States. We evaluated the relationship between soil abiotic properties, nitrogen (N) enrichment, arbuscular mycorrhizal fungal (AMF) community composition, and L. vulgaris invasion in aggressive (CO) and nonaggressive (IL) populations. We collected soil from uninvaded and invaded sites in Gothic, CO, and near Chicago, IL, and sequenced AMF community composition in each site. Using the same soil, we grew L. vulgaris and native species in pots for 120 d, with half of the pots receiving N fertilization, and harvested biomass. We also injected a ¹⁵N-labeled tracer in pots and analyzed plant tissue for ¹⁵N enrichment and net uptake rates (NUR). In CO soil, L. vulgaris rhizomes sprouted more in invaded soil, whereas in IL soil, L. vulgaris only sprouted in uninvaded soil. N fertilization had no impact on biomass, and NUR did not differ significantly between any treatments. AMF communities differed between the two sites but were not significantly influenced by invasion history. Our results suggest that L. vulgaris leaves legacy effects but that these effects are different between aggressive and nonaggressive populations. Legacy effects may facilitate reinvasion in CO, but we did not find conclusive evidence of legacy effects in IL, and differences between the sites could be shaped by endemic AMF communities.

Amur honeysuckle [Lonicera maackii (Rupr.) Herder] is an aggressive invader of forests throughout the eastern United States. While self-pollination has been identified as an important trait of invasive plant species, this trait is understudied, and L. maackii is anecdotally described as lacking this characteristic. To examine the ability of L. maackii to self-pollinate, we selected 171 individual shrubs distributed across nine sites. Each site was grouped into one of three invasion types: heavy, light, and sprouting (sites on which a basal cutting treatment previously occurred, but L. maackii was allowed to reestablish). We compared the number of berries, seeds per berry, and seed germination rates of self- and open-pollinated flowers by pairing branches covered with pollination bags before flower emergence with uncovered branches on the same individual shrub. Out of 171 individuals, 48 produced berries from self-pollination within pollination bags (28%), with 48% of bagged branches exhibiting some degree of necrosis or chlorosis, presumably due to increased temperature and humidity. Berries from self-pollination produced 1.5 ± 1.4 (mean ± 1 SD) seeds per berry, whereas berries resulting from open pollination produced 3.3 ± 1.5 seeds per berry. In a germination trial, 47.3% of self-pollinated seeds germinated compared with 41.7% of open-pollinated seeds. This study has shown that L. maackii can self-pollinate and set viable seed, providing the species with an important mechanism to increase population abundance during the early stages of invasion.

An online survey was distributed to South Dakota stakeholders to understand how noxious weeds are currently being managed. The response rate was 26%; 129 stakeholders completed the survey of the 491 stakeholders who opened the survey. Eighty percent of respondents stated noxious weeds were a problem. Canada thistle [Cirsium arvense (L.) Scop.], leafy spurge (Euphorbia esula L.), and absinth wormwood (Artemisia absinthium L.) were the most common and troublesome, but all statewide noxious weeds were reported. The most common singular response to manage noxious weeds was herbicides alone (25%), but respondents utilized two (27%) to three (24%) other tactics as well. Most respondents (47%) were somewhat satisfied with management tactics, while others were completely satisfied (9%), neither satisfied nor dissatisfied (20%), somewhat unsatisfied (11%), or very unsatisfied (15%). A covariate analysis showed that the more management tactics individual stakeholders utilized, the less satisfied they were with control (P < 0.0001). The most common barrier of adopting new tactics was effectiveness (26%) followed by a combination of effectiveness + current production practices + cost + labor (13%). An additional covariate analysis showed that the increase in management tactics increased the barriers of adoption (P = 0.04) and increasing the number of barriers of adoption resulted in stakeholders being dissatisfied with control (P = 0.0003). Overall, the results of the survey suggest that statewide noxious weeds remain a problem, and multiple tactics are used to manage these weeds. However, Cooperative extension efforts need to address how to use current management and implement new management strategies to increase effectiveness.

We report a pair of simple polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) assays based on two independently segregating nuclear genes that can differentiate the North American native [Phragmites australis (Cav.) Trin. ex Steud. ssp. americanus Saltonst., P.M. Peterson & Soreng] from other lineages. Because nuclear markers are inherited biparentally, researchers can also use them to screen for F₁ hybrids between P. australis ssp. americanus and the other lineages. We show that a previously described assay based on an indel in the nuclear gene NRT2 consistently identifies a wide range of P. australis ssp. americanus haplotypes and distinguishes them from the Gulf Coast type [Phragmites australis (Cav.) Trin. ex Steud. ssp. berlandieri (E. Fourn.) Saltonst. & Hauber]. We also demonstrate a new PCR-RFLP assay for a previously described diagnostic single-nucleotide polymorphism adjacent to the PaGT4 microsatellite marker that also distinguishes P. australis ssp. americanus from the other lineages. In addition, we report the first case of Asian haplotype AS identified in North America and make recommendations for its detection. Our findings expand the tools available to those monitoring for invasion by introduced Phragmites in North America.

While invasive plants can modify community and ecosystem attributes, there is little information on their impact across different trophic levels. Here, we examined the effects of Chilean rhubarb [Gunnera tinctoria Molina (Mirb.), Gunneraceae] on the soil detrital food chain, the major pathway for energy flow in terrestrial ecosystems and the recycling of nutrients. Measurements of soil physiochemical properties and the natural abundances of carbon (C) and nitrogen (N) isotopes, along with assessments of microbial and earthworm populations were used to verify whether G. tinctoria drives the soil food web and how C is transferred from decomposing litter to worm populations. Based on the C isotope compositions of plant material and detritivorous worms (i.e., earthworms and enchytraeid worms), all worms contribute to G. tinctoria litter decomposition, irrespective of their feeding preference. The increased role of larger earthworm populations in litter decomposition was also associated with changes in the soil microbial community, with some bacterial genera being absent from invaded areas. Of particular interest was a 3-fold increase in Nitrospira spp. in invaded areas, likely due to an increase in earthworm-related ammonia production, with this being rapidly converted to nitrate. Given the poor representation of other ammonia- and nitrite-oxidizing soil bacteria, many of the Nitrospira spp. present in invaded soils may perform complete ammonia oxidation (i.e., COMAMMOX). Our results indicate a greater role for native earthworms in decomposition processes in areas invaded by G. tinctoria, resulting in modifications in the other soil biota and an increase in soil nitrate.