Plant invasion science in protected areas: progress and priorities

The preemptive control strategy for invasive plant seed banks triggering ecological threats through synchronized germination

Invasive alien plants threaten global ecosystems by disrupting biodiversity and degrading ecological functions. Soil seed banks-the reservoirs of viable seeds in the soil-play a crucial role in the persistence and spread of plant populations. However, current control measures for invasive plants predominantly target above-ground vegetation, neglecting these underground seed reserves, thereby allowing invasive plants to re-establish their populations. Inducing synchronous germination to deplete seed banks offers a potential preemptive control strategy. This study hypothesizes that seeds of invasive plants secrete secondary metabolites to promote the synchronous germination of conspecific seeds. Focusing on Ambrosia trifida L., a globally harmful annual invasive plant, where the soil seed bank plays a crucial role in its continued impact. We used metabolomics to identify such metabolites and found that Angelicin significantly enhances germination rates by up to 116.9 % (P < 0.01). Field experiments conducted in the native habitat demonstrated that applying Angelicin at concentrations of 0.015 μg ml-1 or higher depleted over 85 % of the seed bank (P < 0.01) without harming indigenous plant communities. These findings confirm the feasibility of depleting underground seed banks through induced germination. Integrating this strategy with traditional above-ground control methods can develop a comprehensive management system, offering a promising new approach for the widespread control of invasive plants.

Modulated use of high-concentration invasive biochar in waste-to-energy strategies: Impact analysis on microbial communities

As a potential amendment, biochar has attracted considerable attention for its impact on soil microbial communities. However, there is little consensus regarding the impacts of biochar derived from invasive plants on microbial communities in coastal saline wetland soils. In this study, we used Juglans regia biochar (JBC) and two other invasive plant biochar, Spartina alterniflora biochar (SBC) and Flaveria bidentis biochar (FBC) to saline soils at rates of 1%, 3%, and 5% (w/w). The results demonstrated that the application of biochar led to a reduction in microbial community diversity, particularly evident in the 5% SBC and FBC treatments. Furthermore, the 5% FBC treatment resulted in a notable decline in community richness. With regard to species composition, the addition of SBC and FBC resulted in a notable impact on the relative abundance of Acidobacteria in comparison to JBC. Additionally, 5% SBC led to a reduction in the relative abundance of Bacteroidetes by 21.49%-23.90%, and 5% FBC reduced the relative abundance of Nitrospirae by 14.71%-17.86%. The addition of biochar enhanced the overall complexity of the community. Specifically, adding 5% SBC boosted the complexity of the microbial network and encouraged cooperative relationships among microorganisms. However, this community became more vulnerable to environmental changes and exhibited weaker anti-interference capabilities. Moreover, 5% JBC and 5% SBC altered the community assembly process from deterministic to stochastic. We emphasize the importance of carefully selecting biochar types during soil remediation, with particular attention to the application of high concentrations of biochar. This paper lays the groundwork for long-term practice in soil remediation through the approach of "treating waste with waste".

Invasive Buttonweed Cotula coronopifolia (Asteraceae) Is Halotolerant and Has High Potential for Dispersal by Endozoochory

Buttonweed (Cotula coronopifolia) is native to South Africa but invasive in wetlands in Europe, North America, and Australasia, where it excludes native plants. Despite being dry-fruited, field studies suggest migratory waterbirds can disperse its seeds via gut passage (endozoochory), aiding its expansion. To explore the potential for endozoochory in different regions and habitats, we collected seeds from six populations in Spain, Sweden, and the UK. Germination was tested under different salinity levels (0, 5, 10, 15 g/L) and simulated gut passage treatments: scarification, acidification, or both. No germination occurred at 15 g/L. Higher salinity reduced and delayed germination, but full gut passage treatment (i.e., both scarification and acidification) increased germinability and accelerated germination. Scarification or acid treatment alone resulted in intermediate germination patterns. There were significant salinity × population and gut passage × population interactions on germinability. The acceleration effect of gut passage on germination was stronger at 5-10 g/L than at 0 g/L. This study highlights how migratory birds can facilitate the spread of alien plants introduced by humans. Endozoochory by waterbirds is an understudied mechanism for the long-distance dispersal of dry-fruited alien plants. Further research on C. coronopifolia, including population genetics, is necessary to understand dispersal mechanisms and facilitate management strategies.

Biological invasions negatively impact global protected areas

Protected areas underpin global biodiversity conservation and sustainability agendas. Biological invasions increasingly threaten the ecological functioning and long-term conservation value of protected areas, while a lack of information on impact impedes management decisions. We collated data from effects of biological invasions in protected areas to provide the first quantitative analysis of their global impacts. Based on 300 reported effects from 44 invasive species, we show that there are overall negative impacts from invasive species on both biotic and abiotic characteristics of protected areas globally. Impacts were pervasive across population, community, and ecosystem scales, and for the vast majority of invasive taxa with sufficient data. Negative impacts have been incurred around the world, with National Parks and World Heritage Sites in the Neartic and Neotropical regions the most studied. Notwithstanding context-dependencies and uneven research efforts, the recurrent negative impacts of invasive species indicate that current efforts are insufficient to curb current stressors and meet conservation and sustainability targets on land and in water. To address the risk of biological invasions in protected areas, it is imperative to prioritise fundamental research on ecological interactions, establish robust monitoring and prevention programs, and raise awareness through global initiatives.

Vulnerability of protected areas to future climate change, land use modification, and biological invasions in China

Anthropogenic climate change, land use modifications, and alien species invasions are major threats to global biodiversity. Protected areas (PAs) are regarded as the cornerstone of biodiversity conservation, however, few studies have quantified the vulnerability of PAs to these global change factors together. Here, we overlay the risks of climate change, land use change, and alien vertebrate establishment within boundaries of a total of 1020 PAs with different administrative levels in China to quantify their vulnerabilities. Our results show that 56.6% of PAs will face at least one stress factor, and 21 PAs are threatened under the highest risk with three stressors simultaneously. PAs designed for forest conservation in Southwest and South China are most sensitive to the three global change factors. In addition, wildlife and wetland PAs are predicted to mainly experience climate change and high land use anthropogenetic modifications, and many wildlife PAs can also provide suitable habitats for alien vertebrate establishment. Our study highlights the urgent need for proactive conservation and management planning of Chinese PAs by considering different global change factors together.

Strategies for the Management of Aggressive Invasive Plant Species

Current control methods for invasive alien plants (IAPs) have acceptable short-term outcomes but have proven to be unfeasible or unaffordable in the long-term or for large invaded areas. For these reasons, there is an urgent need to develop sustainable approaches to control or restrict the spread of aggressive IAPs. The use of waste derived from IAP control actions could contribute to motivating the long-term management and preservation of local biodiversity while promoting some economic returns for stakeholders. However, this strategy may raise some concerns that should be carefully addressed before its implementation. In this article, we summarize the most common methods to control IAPs, explaining their viability and limitations. We also compile the potential applications of IAP residues and discuss the risks and opportunities associated with this strategy.

Common juniper, an overlooked conifer with high invasion potential in protected areas of Patagonia

The benefits of early detection of biological invasions are widely recognized, especially for protected areas (PAs). However, research on incipient invasive plant species is scarce compared to species with a recognized history of invasion. Here, we characterized the invasion status of the non-native conifer Juniperus communis in PAs and interface areas of Andean Patagonia, Argentina. We mapped its distribution and described both the invasion and the environments this species inhabits through field studies, a literature review, and a citizen science initiative. We also modeled the species' potential distribution by comparing the climatic characteristics of its native range with those of the introduced ranges studied. The results show that J. communis is now widely distributed in the region, occurring naturally in diverse habitats, and frequently within and close to PAs. This species can be considered an incipient invader with a high potential for expansion in its regional distribution range, largely due to its high reproductive potential and the high habitat suitability of this environment. Early detection of a plant invasion affords a valuable opportunity to inform citizens of the potential risks to high conservation value ecosystems before the invader is perceived as a natural component of the landscape.

From UAV to PlanetScope: Upscaling fractional cover of an invasive species Rosa rugosa

Invasive plant species pose a direct threat to biodiversity and ecosystem services. Among these, Rosa rugosa has had a severe impact on Baltic coastal ecosystems in recent decades. Accurate mapping and monitoring tools are essential to quantify the location and spatial extent of invasive plant species to support eradication programs. In this paper we combined RGB images obtained using an Unoccupied Aerial Vehicle, with multispectral PlanetScope images to map the extent of R. rugosa at seven locations along the Estonian coastline. We used RGB-based vegetation indices and 3D canopy metrics in combination with a random forest algorithm to map R. rugosa thickets, obtaining high mapping accuracies (Sensitivity = 0.92, specificity = 0.96). We then used the R. rugosa presence/absence maps as a training dataset to predict the fractional cover based on multispectral vegetation indices derived from the PlanetScope constellation and an Extreme Gradient Boosting algorithm (XGBoost). The XGBoost algorithm yielded high fractional cover prediction accuracies (RMSE = 0.11, R² = 0.70). An in-depth accuracy assessment based on site-specific validations revealed notable differences in accuracy between study sites (highest R² = 0.74, lowest R² = 0.03). We attribute these differences to the various stages of R. rugosa invasion and the density of thickets. In conclusion, the combination of RGB UAV images and multispectral PlanetScope images is a cost-effective method to map R. rugosa in highly heterogeneous coastal ecosystems. We propose this approach as a valuable tool to extend the highly local geographical scope of UAV assessments into wider areas and regional evaluations.

Plant invasion risk inside and outside protected areas: Propagule pressure, abiotic and biotic factors definitively matter

Invasive alien species are among the main global drivers of biodiversity loss posing major challenges to nature conservation and to managers of protected areas. The present study applied a methodological framework that combined invasive Species Distribution Models, based on propagule pressure, abiotic and biotic factors for 14 invasive alien plants of Union concern in Italy, with the local interpretable model-agnostic explanation analysis aiming to map, evaluate and analyse the risk of plant invasions across the country, inside and outside the network of protected areas. Using a hierarchical invasive Species Distribution Model, we explored the combined effect of propagule pressure, abiotic and biotic factors on shaping invasive alien plant occurrence across three biogeographic regions (Alpine, Continental, and Mediterranean) and realms (terrestrial and aquatic) in Italy. We disentangled the role of propagule pressure, abiotic and biotic factors on invasive alien plant distribution and projected invasion risk maps. We compared the risk posed by invasive alien plants inside and outside protected areas. Invasive alien plant distribution varied across biogeographic regions and realms and unevenly threatens protected areas. As an alien's occurrence and risk on a national scale are linked with abiotic factors followed by propagule pressure, their local distribution in protected areas is shaped by propagule pressure and biotic filters. The proposed modelling framework for the assessment of the risk posed by invasive alien plants across spatial scales and under different protection regimes represents an attempt to fill the gap between theory and practice in conservation planning helping to identify scale, site, and species-specific priorities of management, monitoring and control actions. Based on solid theory and on free geographic information, it has great potential for application to wider networks of protected areas in the world and to any invasive alien plant, aiding improved management strategies claimed by the environmental legislation and national and global strategies.

The cost of not acting: Delaying invasive grass management increases costs and threatens assets in a national park, northern Australia

Globally, invasive grasses are a major threat to protected areas (PAs) due to their ability to alter community structure and function, reduce biodiversity, and alter fire regimes. However, there is often a mismatch between the threat posed by invasive grasses and the management response. We document a case study of the spread and management of the ecosystem-transforming invasive grass, Andropogon gayanus Kunth. (gamba grass), in Litchfield National Park; an iconic PA in northern Australia that contains significant natural, cultural and social values. We undertook helicopter-based surveys of A. gayanus across 143,931 ha of Litchfield National Park in 2014 and 2021-2022. We used these data to parametrise a spatially-explicit spread model, interfaced with a management simulation model to predict 10-year patterns of spread, and associated management costs, under three scenarios. Our survey showed that between 2014 and 2021-22 A. gayanus spread by 9463 ha, and 47%. The gross A. gayanus infestation covered 29,713 ha of the total survey area, making it the largest national park infestation in Australia. A. gayanus had not been locally eradicated within the Park's small existing 'gamba grass eradication zone', and instead increased by 206 ha over the 7-year timeframe. Our modelled scenarios predict that without active management A. gayanus will continue spreading, covering 42,388 ha of Litchfield within a decade. Alternative scenarios predict that: (i) eradicating A. gayanus in the small existing eradication zone would likely protect 18% of visitor sites, and cost ∼AU$825,000 over 5 years - more than double the original predicted cost in 2014; or (ii) eradicating A. gayanus in a much larger eradication zone would likely protect 86% of visitor sites and several species of conservation significance, and cost ∼AU$6.6 million over 5 years. Totally eradicating A. gayanus from the Park is no longer viable due to substantial spread since 2014. Our study demonstrates the value of systematic landscape-scale surveys and costed management scenarios to enable assessment and prioritisation of weed management. It also demonstrates the increased environmental and financial costs of delaying invasive grass management, and the serious threat A. gayanus poses to PAs across northern Australia.

Regional occupancy increases for widespread species but decreases for narrowly distributed species in metacommunity time series

While human activities are known to elicit rapid turnover in species composition through time, the properties of the species that increase or decrease their spatial occupancy underlying this turnover are less clear. Here, we used an extensive dataset of 238 metacommunity time series of multiple taxa spread across the globe to evaluate whether species that are more widespread (large-ranged species) differed in how they changed their site occupancy over the 10-90 years the metacommunities were monitored relative to species that are more narrowly distributed (small-ranged species). We found that on average, large-ranged species tended to increase in occupancy through time, whereas small-ranged species tended to decrease. These relationships were stronger in marine than in terrestrial and freshwater realms. However, in terrestrial regions, the directional changes in occupancy were less extreme in protected areas. Our findings provide evidence for systematic decreases in occupancy of small-ranged species, and that habitat protection could mitigate these losses in the face of environmental change.

Interacciones efectivas entre academia y gestión: participación de voluntarios para el control de una hiedra invasora en Puerto Blest, Parque Nacional Nahuel Huapi (Argentina)

Introducción y objetivos: Las prácticas de manejo de especies no-nativas e invasoras es tema prioritario en áreas protegidas, en especial en estadios tempranos de invasión, porque facilita la recuperación de sistemas nativos. Aquí presentamos una metodología para el control de una planta trepadora invasora, Hedera helix (Araliaceae).  M&M: Se realizó remoción manual y la disposición de los residuos se compostó en bolsas en el lugar. Luego se monitoreó la regeneración natural del bosque nativo. La propuesta incluye la convocatoria de voluntarios, enmarcados en un proyecto de investigación y extensión de la Universidad Nacional Comahue Bariloche con la colaboración de la Administración de Parques Nacionales.  Resultados: Desde 2019 participaron 47 voluntarios, se extrajeron 870 kg (peso húmedo) de material de cinco de los seis sitios identificados. Dos de los cinco sitios intervenidos se encuentran en la etapa de monitoreo de especies nativas.  Conclusión: La participación de voluntarios resultó efectiva en términos de las acciones de control manual, al estar los sitios controlados. De esta manera, se está logrando con éxito un mínimo impacto negativo sobre el entorno, al menos en las especies de plantas, evidenciado por una rápida recolonización pasiva de especies nativas y la eliminación la especie invasora en los sitios intervenidos. En particular, este modo de trabajo permite crear conciencia del problema de las invasiones biológicas en la comunidad y en futuros profesionales. También fortalece las relaciones entre instituciones vinculando la academia con la gestión en conservación, un aspecto a veces difícil de lograr. 

Vegetation of a hill grassland of the Paititi Natural Reserve (Pampa biome) and early detection of non-native species acting as invasive

Background and aims: Invasive species are the greatest threat to conservation. The objectives of this study were to identify the flora that thrive in a hill grassland of the Paititi Natural Reserve, to perform an early detection of non-native plant species that might be acting as invasive, and to establish the current situation of the native species considered threatened. M&M: Following the altitudinal gradient, 14 sites were selected; the environmental characteristics and cover-abundance of the vascular plant species were recorded in each site. With the collected data, a Principal Coordinate Analysis (PCooA) was performed to group the sites into vegetation units that were later described considering environmental characteristics, identified species and plant community type. Additionally, the threatened species were specified, as well as the most abundant exotic ones, therefore considered invasive.  Results: Total richness reached 370 species, 26.5% corresponding to non-native ones. Thirty threatened species were identified. The PCooA grouped the sites into eight vegetation units. The non-native species considered invasive were Dactylis glomerata, Senecio madagascariensis, Holcus lanatus and Racosperma melanoxylon, these last two reached the highest coverage-abundance values. Conclusions: To conserve biodiversity and minimize the invasion process, management efforts should be focused on monitoring the threatened species and controlling the advance of the non-native species acting as invasive. Early detection of those species in similar environments would be fundamental to facilitate rapid responses towards reducing invasions.

Phylogenetic Relationships and Disturbance Explain the Resistance of Different Habitats to Plant Invasions

Invasive alien plants have invaded various habitats, posing a threat to biodiversity. Several hypotheses have been proposed to explain the mechanisms of invasion, but few studies have considered the characteristics of the invaded communities and the effects of human interference in the invasion. In this study, we compared the invasibility of three different habitats: abandoned land, eucalyptus plantations, and natural secondary forests. We explored the effects of species diversity, phylogenetic diversity, and disturbance factors on the invasibility of different habitats. The results showed that the invasibility of abandoned land was the highest and the invasibility of the natural secondary forest was the lowest. Phylogenetic indicators affected the invasibility of abandoned land and eucalyptus plantations, and disturbance factors affected the invasibility of all three habitats, while the characteristics of the invaded communities had a weak impact. Our research provided supporting evidence for Darwin’s naturalization hypothesis and his disturbance hypothesis but found no relationship between biotic resistance and invasibility. This study indicated that the differences among habitats should be considered when we prove Darwin’s naturalization hypothesis in nature reserves.

Impact of European Beaver (Castor fiber L.) on Vegetation Diversity in Protected Area River Valleys

The aim of the study was to evaluate the impact of European beaver (Castor fiber L.) on vegetation diversity and the expansion of non-native plant species in areas surrounding watercourses in Polesie National Park, Poland. The investigation was carried out within six watercourses inhabited by beavers and four comparison watercourses where beaver were absent. European beaver living in the park had a small excursion range, reaching a maximum distance of 25 m from the watercourse so that effects on vegetation diversity were limited to the immediate vicinity of the watercourse. Beaver significantly influenced diversity of the tall tree and forest floor vegetation, while it did not significantly modify the diversity of the low tree and shrub layer. Five alien plant species were documented. The alien species most strongly associated with beaver activity was devil’s beggartick (Bidens frondosa L.), which occurred in the immediate vicinity of beaver dams. Other alien species most benefiting from the presence of beaver were giant goldenrod (Solidago gigantea Aiton) and black cherry (Prunus serotina Ehrh.). Our study confirmed hypotheses found in literature according to which beaver activities that reduce the proportion of native species can promote the expansion of plant alien species.

Mountain bike riding and hiking can contribute to the dispersal of weed seeds

Mountain biking and hiking are popular, but both recreational activities can contribute to the unintentional dispersal of seeds including non-native plants that cause environmental harm (e.g. environmental weeds). Addressing the requirement for more information about the ecological impacts of recreational activities, seed dispersal from mountain biking and hiking were compared under different climatic and environmental conditions. Seeds from a range of graminids and forbs were found to attach to the mountain bike, rider and hiker, including environmental weed seeds, on trails and in-field in montane Australia. While the composition of seeds differed between the two activities, no significant differences were found between traits, such as natives or environmental weed, graminids or forbs, perennial or annual, large or small, attachment or no attachment structures, although sample sizes were small. Few seeds attached to the mountain bike, rider or hiker on dry trails, some seeds attached when trails were wet, but more seeds attached when riding/hiking off trail in a field. Cleaning clothing and bikes and avoiding areas with environmental weed seeding could reduce the risk of this type of unintentional human mediated dispersal, but compliance with such measures may be challenging. Given the increasing popularity of mountain biking and the current controversy about the relative impacts of mountain biking in areas of high conservation concern, additional research assessing severity, duration and range of impacts of mountain biking on soil, wildlife, waterways and vegetation is critical.

The management success of the invasive late goldenrod (Solidago gigantea Aiton.) in a nature conservation area is strongly related to site, control measures and environmental factors

The late goldenrod (Soldiago gigantea Aiton; Asteraceae) is one of the most abundant invasive species in various types of habitats. Its long-creeping plagiotropic rhizomes enable the plant to build up dense, monospecific stands within a short time. Particularly in nature conservation areas, the invasion of goldenrod can cause severe disruptions in the naturally occuring mutualims between plants, insects and higher trophic levels, subsequently impeding the achievement of nature conservation goals. As management options of goldenrod in nature conservation areas are limited, this three-year study aimed to test the effectiveness of three management treatments (two-time mowing, triticale cultivation, and reverse rotary cutting) on four different sites in the Austrian Donau-Auen National Park. The number and height of goldenrod shoots were recorded three times a year on twelve permanent trial plots on each site to test for the effectiveness of the treatments. In addition, vegetation surveys were performed to observe the recovery potential of native plant species. Even though the three-years mowing and the triticale cultivation reduced goldenrod by 95.6% and 97.2% resp., we could find no relation between the effectiveness of the treatment and the intensity of disturbance created by the control option. On the contrary, with a reduction of only 5.4% in goldenrod density the most intensive treatment, the rotary cutting, showed the lowest efficiency. The highest positive effect on the re-establishment of native plant species was recorded with two mowing events per year. Even though the study revealed that certain management options have the potential to effectively reduce goldenrod and to simultaneously increase the establishment success of native species, results can only be seen as so-called snapshots. For example, as shown on site EJW one unforeseeable wild boar digging event transformed a 84.5% reduction into a 4.7% increase in goldenrod density. Therefore, a proper and regular monitoring is essential to be able to react to the effects of unpredictable events that can have severe impact on vegetation dynamics.

Active revegetation after mining: what is the contribution of peer-reviewed studies?

Knowing the state of the art on research related to post-mining active revegetation can help to improve revegetation success and identify research gaps. We performed a systematic review about active revegetation after mining and identified 203 relevant studies. Most studies were performed in the USA (34%), in regions with a temperate climate (59%) and in abandoned coal mines (45%). The studies were focused on the plantation of woody species (59%) or sowing of herbaceous species (39%). The most widely evaluated treatments were the addition of amendments (24%) and fertilizers (21%), mainly with positive and neutral effects; in general, organic amendments presented more positive effects than inorganic amendments and fertilizers. We also identified studies on the effects of plowing, inoculation of microorganisms, nurse plants, herbivore exclusion and watering. The results of these treatments should be taken with caution, because they can vary according to the functional strategies of the introduced species and the local context, such as the degree of nutrient limitation in the mining area and abiotic conditions. Further research is needed in non-temperate climates, involving long-term monitoring and with detailed descriptions of the interventions to better interpret results and general implications of active revegetation of mining areas.

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Most of the studies on post-mining active revegetation were performed in temperate climates.

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The most widely evaluated treatments were the addition of amendments and fertilizers.

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The effectiveness of the treatments varied plant species and the local context.

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Organic amendments were the most effective treatment based on indicators of plant performance.

Risk assessment and management framework for rapidly spreading species in a Kashmir Himalayan Ramsar site

In view of huge ecological impacts and exorbitantly high economic costs of biological invasions, the risk assessment for timely prediction of potential invaders and their effective management assumes central importance, yet having been little addressed. Hence, we did the risk analysis of 39 plant species, including both alien and fast-spreading native species, in Hokera wetland, an important Ramsar site in Kashmir Himalaya, using the post-border Australian Weed Risk Management (AWRM) framework. Based on the AWRM scores, we listed these species into different categories, such as alert, destroy infestation, contain spread, manage weed, manage sites and monitor, with management implications. Out of the eight decisions created for Hokera wetland, alien Alternanthera philoxeroides was identified as 'alert species', while Typha angustifolia, Typha latifolia, Phragmites australis, Sparganium ramosum and Myriophyllum aquaticum were placed under the 'manage weed' category of the management priorities. To check the predictability and reliability of the AWRM scheme, we developed the receiver operating characteristic (ROC) curve that yielded a positive diagonal value of above 0.5, with 88.6% and 83.1% area under the curve for comparative weed risk (CWR) score and the feasibility of coordinated control (FOC) score, respectively. The outcomes of the ROC analysis were compared with the results of the WRM evaluation of other regions across the globe. Our results indicate that the risk assessment using the AWRM model is quite efficient at discriminating and flagging the most troublesome plant species and offsetting their impacts on native biodiversity and ecosystem functioning in wetland ecosystems. Given the growing threat of biological invasions in the protected areas, we recommend an integrated and strategic approach, well informed by the data on the species biology and ecology, in the form of the AWRM management system to effectively deal with the alarmingly spreading species.

Surprisingly high economic costs of biological invasions in protected areas

Biological invasions are one of the main threats to biodiversity within protected areas (PAs) worldwide. Meanwhile, the resilience of PAs to invasions remains largely unknown. Consequently, providing a better understanding of how they are impacted by invasions is critical for informing policy responses and optimally allocating resources to prevention and control strategies. Here we use the InvaCost database to address this gap from three perspectives: (i) characterizing the total reported costs of invasive alien species (IAS) in PAs; (ii) comparing mean observed costs of IAS in PAs and non-PAs; and (iii) evaluating factors affecting mean observed costs of IAS in PAs. Our results first show that, overall, the reported economic costs of IAS in PAs amounted to US$ 22.24 billion between 1975 and 2020, of which US$ 930.61 million were observed costs (already incurred) and US$ 21.31 billion were potential costs (extrapolated or predicted). Expectedly, most of the observed costs were reported for management (73%) but damages were still much higher than expected for PAs (24%); in addition, the vast majority of management costs were reported for reactive, post-invasion actions (84% of management costs, focused on eradication and control). Second, differences between costs in PAs and non-PAs varied among continents and environments. We found significantly higher IAS costs in terrestrial PA environments compared to non-PAs, while regionally, Europe incurred higher costs in PAs and Africa and Temperate Asia incurred higher costs in non-PAs. Third, characterization of drivers of IAS costs within PAs showed an effect of environments (higher costs in terrestrial environments), continents (higher in Africa and South America), taxa (higher in invertebrates and vertebrates than plants) and Human Development Index (higher in more developed countries). Globally, our findings indicate that, counterintuitively, PAs are subject to very high costs from biological invasions. This highlights the need for more resources to be invested in the management of IAS to achieve the role of PAs in ensuring the long term conservation of nature. Accordingly, more spatially-balanced and integrative studies involving both scientists and stakeholders are required.

Response of Five Miscanthus sinensis Cultivars to Grasshopper Herbivory: Implications for Monitoring of Invasive Grasses in Protected Areas

Introduced grasses can aggressively expand their range and invade native habitats, including protected areas. Miscanthus sinensis is an introduced ornamental grass with 100+ cultivars of various invasive potential. Previous studies have demonstrated that the invasive potential of M. sinensis cultivars may be linked to seed viability, and some of the physiological traits, such as growth rate. Little is known, however, about whether these traits are associated with response of M. sinensis to insect herbivory, and whether plant tolerance and resistance to herbivory vary among its cultivars; which, in turn, can contribute to the invasive potential of some of M. sinensis cultivars. To address this issue, in our study we explored the response of five cultivars of M. sinensis to herbivory by Melanoplus grasshoppers. We demonstrated that plant responses varied among the cultivars during a season; all the cultivars, but “Zebrinus”, demonstrated a significant increase in plant tolerance by the end of the growing season regardless of the amount of sustained leaf damage. Different patterns in plant responses from “solid green” and “striped/spotted” varieties were recorded, with the lowest plant resistance detected for “Autumn Anthem” in the cage experiment. Our results have important applications for monitoring low-risk invaders in protected areas, as well as for biotic resistance of native communities to invasive grasses.

Effects of Ailanthus altissima Invasion and Removal on High-Biodiversity Mediterranean Grasslands

Ailanthus altissima is one of the worst invasive plants in Europe in several habitat types, including high-biodiversity grasslands. The aim of this work was to evaluate the impact of the invasive A. altissima on high-biodiversity grassland vegetation and the effects of its removal on the recovery of native plant communities. The study area was within the Alta Murgia National Park (SE Italy). Seventeen vegetation quadrats were sampled in invaded grasslands and nine quadrats were sampled in nearby uninvaded areas. A. altissima was removed from six quadrats, which were sampled for two years after plant removal. Cluster analysis and non-metric multidimensional scaling ordination were used to identify and visualize the general vegetation pattern. Generalised Linear Models with different error structures were used to analyse the effects of A. altissima on native grasslands and vegetation recovery after removal. Results showed that the invasion of A. altissima changed drastically the community composition, reduced plant richness and diversity. Invaded stands had a greater presence of ruderal and widely distributed taxa, as opposed to a lesser presence of endemic and Mediterranean ones. The differences in the community composition between invaded and uninvaded quadrats became clearly detectable when A. altissima plants exceeded a threshold of 1 m of height and 50% of coverage. After A. altissima removal, the recovery of the grassland community was not completely achieved after two years.

The invasive cactus Opuntia stricta creates fertility islands in African savannas and benefits from those created by native trees

The patchy distribution of trees typical of savannas often results in a discontinuous distribution of water, nutrient resources, and microbial communities in soil, commonly referred to as "islands of fertility". We assessed how this phenomenon may affect the establishment and impact of invasive plants, using the invasion of Opuntia stricta in South Africa's Kruger National Park as case study. We established uninvaded and O. stricta-invaded plots under the most common woody tree species in the study area (Vachellia nilotica subsp. kraussiana and Spirostachys africana) and in open patches with no tree cover. We then compared soil characteristics, diversity and composition of the soil bacterial communities, and germination performance of O. stricta and native trees between soils collected in each of the established plots. We found that the presence of native trees and invasive O. stricta increases soil water content and nutrients, and the abundance and diversity of bacterial communities, and alters soil bacterial composition. Moreover, the percentage and speed of germination of O. stricta were higher in soils conditioned by native trees compared to soils collected from open patches. Finally, while S. africana and V. nilotica trees appear to germinate equally well in invaded and uninvaded soils, O. stricta had lower and slower germination in invaded soils, suggesting the potential release of phytochemicals by O. stricta to avoid intraspecific competition. These results suggest that the presence of any tree or shrub in savanna ecosystems, regardless of origin (i.e. native or alien), can create favourable conditions for the establishment and growth of other plants.

An invasive species erodes the performance of coastal wetland protected areas

The world has increasingly relied on protected areas (PAs) to rescue highly valued ecosystems from human activities, but whether PAs will fare well with bioinvasions remains unknown. By analyzing three decades of seven of the largest coastal PAs in China, including World Natural Heritage and/or Wetlands of International Importance sites, we show that, although PAs are achieving success in rescuing iconic wetlands and critical shorebird habitats from once widespread reclamation, this success is counteracted by escalating plant invasions. Plant invasions were not only more extensive in PAs than non-PA controls but also undermined PA performance by, without human intervention, irreversibly replacing expansive native wetlands (primarily mudflats) and precluding successional formation of new native marshes. Exotic species are invading PAs globally. This study across large spatiotemporal scales highlights that the consequences of bioinvasions for humanity’s major conservation tool may be more profound, far reaching, and critical for management than currently recognized.

Explaining the Geographic Pattern of Plant Invasion in 67 Nature Reserves in China

Biological invasion is a serious threat to biodiversity and ecosystem function in nature reserves. However, the knowledge of the spatial patterns and underlying mechanisms of plant invasions in nature reserves is still limited. Based on a recent dataset on both invasive and native plants in 67 nature reserves of China, we used correlation, regression, and variation partitioning methods to statistically assess the relative roles of the “human activity,” “biotic acceptance,” and “environmental heterogeneity” hypotheses in explaining the geographic pattern of plant invasion. A total of 235 invasive plant species were compiled from 67 nature reserves. The high explanatory power of the human activity variables supported the human activity hypothesis. The biotic acceptance hypothesis was weakly supported since no significant correlations between climatic variables and invasion levels were found when the effects of the other factors were controlled. The environmental heterogeneity hypothesis was partially supported, since the number of native plants, representing environmental heterogeneity at fine-scale explained remarkable proportion of spatial variance of invasive plants but not that of the proportion of invasive plants. We predict that nature reserves with high plant diversity affected by rapid economic development and increasing temperature will face a serious threat of exotic plant invasion. In conclusion, our results provide crucial clues for understanding geographic variance of plant invasion in China’s nature reserves and spatial risk assessment.

Invasive tree cover covaries with environmental factors to explain the functional composition of riparian plant communities

Invasive species are a major cause of biodiversity loss worldwide, but their impact on communities and the mechanisms driving those impacts are varied and not well understood. This study employs functional diversity metrics and guilds-suites of species with similar traits-to assess the influence of an invasive tree (Tamarix spp.) on riparian plant communities in the southwestern United States. We asked: (1) What traits define riparian plant guilds in this system? (2) How do the abundances of guilds vary along gradients of Tamarix cover and abiotic conditions? (3) How does the functional diversity of the plant community respond to the gradients of Tamarix cover and abiotic conditions? We found nine distinct guilds primarily defined by reproductive strategy, as well as growth form, height, seed weight, specific leaf area, drought and anaerobic tolerance. Guild abundance varied along a covarying gradient of local and regional environmental factors and Tamarix cover. Guilds relying on sexual reproduction, in particular, those producing many light seeds over a long period of time were more strongly associated with drier sites and higher Tamarix cover. Tamarix itself appeared to facilitate more shade-tolerant species with higher specific leaf areas than would be expected in resource-poor environments. Additionally, we found a high degree of specialization (low functional diversity) in the wettest, most flood-prone, lowest Tamarix cover sites as well as in the driest, most stable, highest Tamarix cover sites. These guilds can be used to anticipate plant community response to restoration efforts and in selecting appropriate species for revegetation.

Tourist vehicle as a selective mechanism for plant dispersal: Evidence from a national park in the eastern Himalaya

It is increasingly recognised that human vehicle may act as a vector to spread species, but research remains sparse to examine vehicle-mediated spread to natural areas, in particular to protected areas by urbanized societies through increasing tourism/recreation traffic. This study assessed the role of tourist vehicle in driving biotic exchange to Laojun Mountain National Park in the eastern Himalaya. A stratified random sampling method was applied to compare plant seeds in muds collected from different vehicles (sedan, SUV and others) entering the park in different seasons (May, August and October) from different regions. Across the 663 mud samples, 3119 seedlings of 124 species germinated which were predominately roadside ruderals and non-native species. The number of vehicle-dispersed flora was found to be correlated with the amount of mud attached on vehicles, with more seed carried by vehicles travelling in autumn, sport utility vehicles and those from local areas. When seed traits were analysed using generalized linear models, vehicles were more likely disperse appendaged and compact seeds, and those released from low-stature plants such as forb or grass. The results highlight the risks of species introduction and homogenization of flora from seeds on tourist vehicles entering protected areas. Strategies like vehicle washing and managing roadside vegetation may help reduce risks from tourism traffic in the eastern Himalayan parks as well as other sensitive ecosystems around the world.

Ecological restoration of habitats invaded by Leucanthemum vulgare that alters key ecosystem functions

Precise assessment of the impacts of invasive alien species (IAS) on ecosystem structure and functions is paramount for implementing appropriate management and restoration strategies. Here we investigated the impacts of Leucanthemum vulgare (ox-eye daisy), an aggressive invader in Kashmir Himalaya, on species diversity and primary productivity. We also evaluated bunch of strategies for the ecological restoration of the habitats invaded by this species. We found that uninvaded plots harbored on an average of 6.11 (±2.92) more species per 1m2 of quadrat than invaded plots. At multivariate scale, the ordination (nMDS) and ANOSIM exhibited significant differences between invaded and uninvaded plots with R = 0.7889 and p < 0.001. The decrease in diversity indices in invaded as compared to uninvaded plots was associated with more productive plant communities due to Leucanthemum invasion. Higher altitude Gulmarg site was more affected by Leucanthemum invasion than lower altitude Drung site. We tested different approaches for restoration and management of invaded habitats that include herbicide treatment at seedling stage, herbicide treatment before and after flowering stage, mowing and herbicide treatment together, joint mowing, digging and herbicide treatment and Leucanthemum uprooting. Among these treatments, uprooting and combined digging, mowing and herbicide treatment proved to be most effective in controlling Leucanthemum invasion. The implications of these results for effective management of ecologically sensitive and socio-culturally important landscapes are discussed.

Harmonising the fields of invasion science and forest pathology

Invasive alien species are widely recognised as significant drivers of global environmental change, with far reaching ecological and socio-economic impacts. The trend of continuous increases in first records, with no apparent sign of saturation, is consistent across all taxonomic groups. However, taxonomic biases exist in the extent to which invasion processes have been studied. Invasive forest pathogens have caused, and they continue to result in dramatic damage to natural forests and woody ecosystems, yet their impacts are substantially underrepresented in the invasion science literature. Conversely, most studies of forest pathogens have been undertaken in the absence of a connection to the frameworks developed and used to study biological invasions. We believe this is, in part, a consequence of the mechanistic approach of the discipline of forest pathology; one that has been inherited from the broader discipline of plant pathology. Rather than investigating the origins of, and the processes driving the arrival of invasive microorganisms, the focus of pathologists is generally to investigate specific interactions between hosts and pathogens, with an emphasis on controlling the resulting disease problems. In contrast, central to the field of invasion science, which finds its roots in ecology, is the development and testing of general concepts and frameworks. The lack of knowledge of microbial biodiversity and ecology, speciation and geographic origin present challenges in understanding invasive forest pathogens under existing frameworks, and there is a need to address this shortfall. Advances in molecular technologies such as gene and genome sequencing and metagenomics studies have increased the “visibility” of microorganisms. We consider whether these technologies are being adequately applied to address the gaps between forest pathology and invasion science. We also interrogate the extent to which the two fields stand to gain by becoming more closely linked.

Into the great wide open: do alien plants spread from rivers to dry savanna in the Kruger National Park?

Protected areas play an important role as refuges from invasive species impacts on biodiversity. Within the MOSAIK (Monitoring Savanna Biodiversity in the Kruger National Park) project, plant species were recorded in a representative set of 60 plots, 50 × 50 m in size, across the entire KNP, distributed so as to cover a range of savanna habitats, i.e. perennial rivers, seasonal rivers and dry crests, and two main bedrock types (granite and basalt). The data were used to assess the role of rivers in the dispersal of alien plants and study whether the alien plant species spread from rivers to open dry savanna. The resulting dataset provided the first thorough information on the spatial distribution of naturalised alien plants in KNP. In total, we recorded 20 plant species that are alien to the park, four of them considered invasive: Parthenium hysterophorus, Opuntia stricta, Xanthium strumarium and Zinnia peruviana. The most widespread species in KNP was Tridax procumbens, recorded in 11 plots (i.e. 18% of all sampled), four other species were found in &gt; 10% of the plots. One species, Bidens bipinnata, was not previously reported from the park and represents a new record. The majority of aliens were concentrated along perennial rivers (60% of all occurrences), but some were repeatedly recorded at seasonal rivers as well and two of the most invasive species in KNP, Opuntia stricta and Parthenium hysterophorus, occurred also on dry crests away from water. The average number of alien species per plot was low (1.6), as was their mean percentage contribution to all species in a plot (2.2%), but some plots harboured as many as seven species and contributed up to 11.9%. Moreover, only 21 plots (35%) were alien-species free. In terms of the total species number per habitat, perennial rivers had significantly more aliens than crests and were marginally significantly richer than seasonal rivers. By recording all naturalised alien species occurring in the plots – many of them are not invasive but may become so in the future – and by using the GloNAF database of global distribution of naturalised species, we assessed the invasion potential of the recorded species.

The social-ecological system driving effective invasive plant management: two case studies of non-native Phragmites

Globally, the management of invasive plants is motivated by a desire to improve ecosystem services (e.g., recreation, flood mitigation, soil fertility for agriculture, aesthetics) and critical habitat for imperiled species. To reduce invader populations and impacts, it is important to document the social and ecological basis (i.e., the social-ecological system) for the management that has been employed and areas where a greater level of coordination among stakeholder groups (managers, scientists, legislators, resource users) could improve efforts. We present a conceptual model that builds on current thinking for how best to connect these four stakeholder groups-to foster stronger citizen lobbying for impacted resources, science-based governance, legislator-driven noxious weed laws and funding for management and science, knowledge co-production by scientists and managers, and co-management by managers and resource users. In light of our model, we present two case studies based in Nebraska and Utah, U.S.A. involving a common North American wetland invader, Phragmites australis (non-native common reed). In Nebraska, potential lawsuits stemming from water conveyance was strong motivation for funding management. In Utah, duck hunters and other resource users initially instigated management. Progress toward the successful management of Phragmites has been the result of manager-scientist partnerships addressing a knowing-doing gap among practitioners, the complexities of management mosaics, as well as overcoming economic and logistical constraints. Our model demonstrates how legislative initiatives can fund new research and bolster on-going management, while organically building strong partnerships among scientists, managers, and resource users that are key for successfully managing invasive species.

Scientists' warning on invasive alien species

Biological invasions are a global consequence of an increasingly connected world and the rise in human population size. The numbers of invasive alien species – the subset of alien species that spread widely in areas where they are not native, affecting the environment or human livelihoods – are increasing. Synergies with other global changes are exacerbating current invasions and facilitating new ones, thereby escalating the extent and impacts of invaders. Invasions have complex and often immense long‐term direct and indirect impacts. In many cases, such impacts become apparent or problematic only when invaders are well established and have large ranges. Invasive alien species break down biogeographic realms, affect native species richness and abundance, increase the risk of native species extinction, affect the genetic composition of native populations, change native animal behaviour, alter phylogenetic diversity across communities, and modify trophic networks. Many invasive alien species also change ecosystem functioning and the delivery of ecosystem services by altering nutrient and contaminant cycling, hydrology, habitat structure, and disturbance regimes. These biodiversity and ecosystem impacts are accelerating and will increase further in the future. Scientific evidence has identified policy strategies to reduce future invasions, but these strategies are often insufficiently implemented. For some nations, notably Australia and New Zealand, biosecurity has become a national priority. There have been long‐term successes, such as eradication of rats and cats on increasingly large islands and biological control of weeds across continental areas. However, in many countries, invasions receive little attention. Improved international cooperation is crucial to reduce the impacts of invasive alien species on biodiversity, ecosystem services, and human livelihoods. Countries can strengthen their biosecurity regulations to implement and enforce more effective management strategies that should also address other global changes that interact with invasions.

Invasive alien species add to the uncertain future of protected areas

Establishing and managing protected areas (national parks, nature reserves and other sites of conservation value) represent the most common approach to conserving species and ecosystems, but these areas are vulnerable to global environmental change. Recently, Golden Kroner et al. (2019) suggested protected area downgrading, downsizing, and degazettement (PADDD) as one of the main threats to biodiversity conservation. However, there are several other elements, of similar concern, that threaten conservation efforts in protected areas, such as climate change and pollution. Here, in a commentary to the Golden Kroner et al. (2019) paper, we address an additional important element affecting protected area dynamics and robustness that was overlooked by these authors – invasions by alien species. We argue that invasive alien species (IAS) contribute directly to the pressures of biodiversity loss by competing with native species and modifying the characteristics of the invaded ecosystems, and virtually no protected areas are free from these effects. Therefore, excluding IAS from legal instruments and policy frameworks underpinning current conservation approaches in protected areas presents a great risk for nature conservation. Consequently, this aligns poorly with the idea of protected areas being a cornerstone for conservation at local, regional and national levels. For that reason and to paint a more complete picture of the effectiveness of protected areas, we argue that when other factors threatening the existence and functioning of protected areas are discussed, we also need to account for biological invasions. This will ensure that adaptive conservation management strategies protect a wide range of species, ecosystems, and landscapes. Hence, this commentary aims to be of general interest for policymakers, managers and researchers.

Invasive alien plant species: Their impact on environment, ecosystem services and human health

Ecological perturbations caused by biotic invasion have been identified as a growing threat to global sustainability. Invasive alien plants species (IAPS) are considered to be one of the major drivers of biodiversity loss and thereby altering the ecosystem services and socio-economic conditions through different mechanisms. Although the ecological impacts of IAPS are well documented, there is a dearth of studies regarding their economic quantification, livelihood considerations, biotechnological prospects (phytoremediation, bioenergy, phyto-synthesis of nanoparticles, biomedical, industrial applications etc.) and human health risk assessments of IAPS. In this context, the current panoramic review aimed to investigate the environmental, socio-ecological and health risks posed by IAPS as well as the compounded impact of IAPS with habitat fragmentation, climate and land use changes. To this end, the need of an integrated trans-disciplinary research is emphasized for the sustainable management of IAPS. The management prospects can be further strengthened through their linkage with geo-spatial technologies (remote sensing and GIS) by mapping and monitoring the IAPS spread. Further, the horizon of IAPS management is expanded to ecological indicator perspectives of IAPS, biosecurity, and risk assessment protocols with critical discussion. Moreover, positive as well as negative implications of the IAPS on environment, health, ecosystem services and socio-economy (livelihood) are listed so that a judicious policy framework could be developed for the IAPS management in order to mitigate the human health implications.

Effective governance for management of invasive alien plants: evidence from the perspective of forest and wildlife officers in Sri Lanka

Invasive alien plants (IAPs) are a significant cause of socio-ecological change in Sri Lanka. Many studies have focused on the ecological dimensions of this problem, but few have addressed sociological factors such as the knowledge and perceptions of individuals and groups tasked with addressing IAPs. This study investigates how IAP issues are understood and perceived by professional forest and wildlife officers in Sri Lanka. The data analyzed were gathered using a questionnaire that covered three themes: the respondents' ability to identify IAPs, the impacts of IAPs and the threats they pose, and knowledge regarding control and mitigation. The questionnaire was completed by 186 field officers, and the resulting descriptive statistics and a probit regression analysis were used to analyze the data. The results show that almost all of the participating forest and wildlife officers were aware of the problems associated with IAPs but more than 75% of them lacked an accurate understanding of scientific means for controlling them and control policies established by the government of Sri Lanka. Generally, wildlife officers had a better understanding than forest officers. In addition, the analysis shows that officers' knowledge and perceptions of IAPs were positively correlated with their level of education and position within the organization. The analysis points to several recommendations for Sri Lankan officials when designing and implementing comprehensive policies and professional programs, particularly for lower-level field officers.

Invasive alien plants in Polish national parks-threats to species diversity

Due to the relevance of protected areas to the conservation of native biota, the magnitude of invasions and threats posed by alien plants are currently important issues for the preservation of these areas. The paper summarises data on invasive alien plant species presence in the most valuable protected areas in Poland, i.e. national parks (NPs). We investigated the distribution of invasive alien plant species and management attempts concerning those species. We analysed data obtained from 23 national parks originating from published and unpublished sources. Invasive plants were present in all protected areas analysed, from two to 42 species in a particular national park, and 68 in total. The most widely distributed species were: Impatiens parviflora (present in 19 NPs), I. glandulifera (17), Solidago gigantea (17), Reynoutria japonica (17), and Robinia pseudoacacia (16). The conducted analyses showed that the number of invasive species decreased with the higher altitude (asl) of the national park. The most often managed species were Impatiens glandulifera (being removed in seven NPs), I. parviflora (six), Padus serotina (four) and Quercus rubra (four). In the majority of NPs, control activities are limited to small areas and singular species, thus having an incidental character. Only in five objects (Białowieża NP, Biebrza NP, Kampinos NP, Tuchola NP, Wigry NP), management has been focused on several species. We conclude that a lack of comprehensive management of invasive plant species in the majority of national parks currently limits the effectiveness of IAS (invasive alien species) eradication. Exchange of expertise among protected areas, documenting best practice examples, synthesising lessons learnt in IAS management, as well as the development of minimum standards for invasive plants surveillance and management are pivotal.

Alien Plants in the Eastern Cape Province in South Africa: Perceptions of Their Contributions to Livelihoods of Local Communities

Invasive alien plant species are plant species that establish themselves outside their native distributional range. The current study documented utilization of alien plant species in the Eastern Cape province in South Africa. Information about utilization of alien plant species was gathered through interviews conducted with 120 participants, which included 13 traditional healers, 27 herbalists, ten farmers and 70 laypeople. Ethnobotanical importance of documented species was assessed through evaluation of use value (UV), fidelity level (FL) and relative frequency citation (RFC). A third of the participants (33.3%) perceived alien plant species as undesirable, while 71.1% of the participants argued that alien plant species had beneficial effects. A total of 26 alien plant species were recorded, seven species being fruit trees, followed by ornamental plants (five species), fodder and herbal medicines (four species each), construction materials, erosion control and vegetables (two species each). The popular alien plant species with UV > 0.1, RFC > 0.4 and FL > 4.0% included Amaranthus spinosus, Cannabis sativa, Cereus jamaracu, Harrisia balansae, Opuntia engelmannii, Opuntia ficus-indica, Opuntia monocantha and Prunus persica. Information on perceptions of local communities in the Eastern Cape province on the contributions of alien plant species to livelihood needs is an important stage of initiating a management protocol that incorporates public perceptions and values associated with alien plant species.

Assessing the environmental impacts of invasive alien plants: a review of assessment approaches

Assessing the impacts of alien plant species is a major task in invasion science and vitally important for supporting invasion-related policies. Since 1993, a range of assessment approaches have been developed to support decisions on the introduction or management of alien species. Here we review the extent to which assessments (27 approaches) appraised the following: (i) different types of environmental impacts, (ii) context dependence of environmental impacts, (iii) prospects for successful management, and (iv) transparency of assessment methods and criteria, underlying values and terminology. While nearly all approaches covered environmental effects, changes in genetic diversity and the incorporation of relevant impact parameters were less likely to be included. Many approaches considered context dependence by incorporating information about the actual or potential range of alien species. However, only a few went further and identified which resources of conservation concern might be affected by specific alien plant species. Only some approaches acknowledged underlying values by distinguishing negative from positive impacts or by considering the conservation value of affected resources. Several approaches directly addressed the feasibility of management, whereas relevant factors such as availability of suitable management methods were rarely considered. Finally, underlying values were rarely disclosed, and definitions of value-laden or controversial terms were often lacking. We conclude that despite important progress in assessing the manifold facets of invasion impacts, opportunities remain for further developing impact assessment approaches. These changes can improve assessment results and their acceptance in invasion-related environmental policies.