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Globally, numerous ecosystems have been co-invaded by multiple exotic plant species that can have competitive or facilitative interactions with each other and with native plants. Invaded ecosystems often exhibit spatial heterogeneity in soil moisture and nutrient levels, with some habitats having more nutrient-rich and moist soils than others. The stress-gradient hypothesis predicts that plants are likely to engage in facilitative interactions when growing in stressful environments, such as nutrient-deficient or water-deficient soils. In contrast, when resources are abundant, competitive interactions between plants should prevail. The invasional meltdown hypothesis proposes that facilitative interactions between invasive species can enhance their establishment and amplify their ecological impact. Considering both hypotheses can offer insights into the complex interactions among invasive and native plants across environmental gradients. However, experimental tests of the effects of soil moisture and nutrient co-limitation on interactions between invasive and native plants at both interspecific and intraspecific levels in light of these hypotheses are lacking. We performed a greenhouse pot experiment in which we cultivated individual focal plants from five congeneric pairs of invasive and native species. Each focal plant was subjected to one of three levels of plant-plant interactions: (1) intraspecific, in which the focal plant was grown with another individual of the same species; (2) interspecific, involving a native and an invasive plant; and (3) interspecific, involving two native or invasive individuals. These plant-plant interaction treatments were fully crossed with two levels of water availability (drought vs. well-watered) and two levels of nutrient supply (low vs. high). Consistent with the stress-gradient and invasional meltdown hypotheses, our findings show that under low-nutrient conditions, the biomass production of invasive focal plants was facilitated by invasive interspecific neighbors. However, under high-nutrient conditions, the biomass production of invasive focal plants was suppressed by invasive interspecific neighbors. When competing with native interspecific neighbors, high-nutrient conditions similarly enhanced the biomass production of both invasive and native focal plants. Invasive and native focal plants were neither competitively suppressed nor facilitated by conspecific neighbors. Taken together, these results suggest that co-occurring invasive exotic plant species may facilitate each other in low-nutrient habitats but compete in high-nutrient habitats., (© 2024 The Ecological Society of America.)

The decomposition rates and stoichiometric characteristics of many aquatic plants remain unclear, and our understanding of material flow and nutrient cycles within freshwater ecosystems is limited. In this study, an in-situ experiment involving 23 aquatic plants (16 native and 7 exotic species) was carried out via the litter bag method for 63 days, during which time the mass loss and nutrient content (carbon (C), nitrogen (N), and phosphorus (P)) of plants were measured. Floating-leaved plants exhibited the highest decomposition rate (0.038 ± 0.002 day -1 ), followed by submerged plants and free-floating plants (0.029 ± 0.002 day -1 ), and emergent plants had the lowest decomposition rate (0.019 ± 0.001 day -1 ). Mass loss by aquatic plants correlated with stoichiometric characteristics; the decomposition rate increased with an increasing P content and with a decreasing C content, C:N ratio, and C:P ratio. Notably, the decomposition rate of submerged exotic plants (0.044 ± 0.002 day -1 ) significantly exceeded that of native plants (0.026 ± 0.004 day -1 ), while the decomposition rate of emergent exotic plants was 55 ± 4 % higher than that of native plants. The decomposition rates of floating-leaved and free-floating plants did not significantly differ between the native and exotic species. During decomposition, emergent plants displayed an increase in C content and a decrease in N content, contrary to patterns observed in other life forms. The P content decreased for submerged (128 ± 7 %), emergent (90 ± 5 %), floating-leaved (104 ± 6 %), and free-floating plants (32 ± 6 %). Exotic plants released more C and P but accumulated more N than did native plants. In conclusion, the decomposition of aquatic plants is closely linked to litter quality and influences nutrient cycling in freshwater ecosystems. Given these findings, the invasion of the littoral zone by submerged and emergent exotic plants deserves further attention., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

India has numerous invasive alien plant species (IAPSs), which seriously impact biodiversity, ecosystem services, and economic development. The availability of reliable occurrence records of IAPSs is of great importance for their successful management, prediction of distribution across time and space, and other research and development efforts. Global databases of occurrence data, like the Global Biodiversity Information Facility (GBIF), are often not exhaustive, especially for India, and poorly represent the actual distribution of IAPSs in the country. Our objective in creating this data set was threefold: (1) to compile occurrence data for the invasive and naturalized alien plant species of India, (2) to collect spatial and temporal information associated with occurrence records, and (3) to share the data in an accessible format so every record is traceable to its sources and allow users to submit data to increase the resolution of the data set. To achieve these objectives, we extracted data from 3137 literature records and 357 herbarium sheets. For each occurrence record, we curated information for 20 variables, which were arranged in a table with the Darwin Core (DwC) terms as column names. All data were subjected to technical validation before being included in the database. A total of 12,347 occurrence records were obtained for 362 species (195 invasive aliens and 167 naturalized aliens). The number of collected occurrence records was much higher for the invasive aliens (73.7%) than for the naturalized alien species (26.3%). Our data set will supplement the GBIF data by 60.39%, and occurrence records will be added for 64 invasive and naturalized alien plant species. The data set, as a part of the larger database of the Indian Alien Flora Information (ILORA) database, is made available without any restrictions on use as long as this data paper is properly cited. We have also made provisions for users to submit occurrence-related data following a data standard. The users are encouraged to cite the original reference when using a specific data record. The data set is expected to assist a wide range of stakeholders involved in India's scientific research, policy formulation, and decision-making related to IAPSs., (© 2022 The Authors. Ecology © 2022 The Ecological Society of America.)

Plant invasion typically alters the microbial communities of soils, which affects ecosystem carbon (C) and nitrogen (N) cycles. The responses of the soil fungal communities to plant invasion along its chronosequence remain poorly understood. For this study, we investigated variations in soil fungal communities through Illumina MiSeq sequencing analyses of the fungal internal transcribed spacer (ITS) region, and quantitative polymerase chain reaction (qPCR), along a chronosequence (i.e., 9-, 13-, 20- and 23-year-old) of invasive Spartina alterniflora. We compared these variations with those of bare flat in a Chinese Yellow Sea coastal wetland. Our results highlighted that the abundance of soil fungi, the number of operational taxonomic units (OTUs), species richness, and Shannon diversity indices for soil fungal communities were highest in 9-year-old S. alterniflora soil, which gradually declined along the invasion chronosequence. The relative abundance of copiotrophic Basidiomycota revealed significant decreasing trend, while the relative abundance of oligotrophic Ascomycota gradually increased along the S. alterniflora invasion chronosequence. The relative abundance of soil saprotrophic fungi (e.g., undefined saprotrophs) was gradually reduced while symbiotic fungi (e.g., ectomycorrhizal fungi) and pathotrophic fungi (e.g., plant and animal pathogens) progressively increased along the S. alterniflora invasion chronosequence. Our results suggested that S. alterniflora invasion significantly altered soil fungal abundance and diversity, community composition, trophic modes, and functional groups along a chronosequence, via substantially reduced soil litter inputs, and gradually decreased soil pH, moisture, and soil nutrient substrates along the invasion chronosequence, from 9 to 23 years. These changes in soil fungal communities, particularly their trophic modes and functional groups along the S. alterniflora invasion chronosequence could well impact the decomposition and accumulation of soil C and N, while potentially altering ecosystem C and N sinks in a Chinese Yellow Sea coastal wetland., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background and Aims: Although urban gardens provide opportunities for pollinators in an otherwise inhospitable environment, most garden plants are not native to the recipient biogeographical region and their value to local pollinators is disputed. This study tested the hypothesis that bumblebees foraging in English urban gardens preferentially visited sympatric Palaearctic-range plants over species originating outside their native range., Methods: Twenty-seven surveys of flower availability and bumblebee visitation (Bombus spp.) were conducted over a 3-month summer period. Plants were categorized according to whether they were native British, Palaearctic or non-Palaearctic in origin. A phylogeny of the 119 plant species recorded was constructed and the relationship between floral abundance and the frequency of pollinator visits investigated by means of phylogenetically independent contrasts. Differentiation in utilization of plant species by the five bumblebee species encountered was investigated using niche overlap analyses., Key Results: There was conflicting evidence for preferential use of native-range Palaearctic plant species by bumblebees depending on which plants were included in the analysis. Evidence was also found for niche partitioning between species based on respective preferences for native and non-native biogeographical range plants. Two bumblebees (Bombus terrestris and B. pratorum) concentrated their foraging activity on non-Palaearctic plants, while two others (B. hortorum and B. pascourum) preferred Palaearctic species., Conclusions: The long-running debate about the value of native and non-native garden plants to pollinators probably stems from a failure to properly consider biogeographical overlap between plant and pollinator ranges. Gardeners can encourage pollinators without consideration of plant origin or bias towards 'local' biogeographical species. However, dietary specialist bumblebees seem to prefer plants sympatric with their own biogeographical range and, in addition to the cultivation of these species in gardens, provision of native non-horticultural ('weed') species may also be important for pollinator conservation.

In the cities, remnants of the vegetation that originally occupied these areas can be found. Exotic species have established in these relicts, and therefore these spaces require management aimed at recovering native vegetation. In this study, we evaluated the impact of the removing exotic species on the floristic composition of the remnants of an oak forest. We compared the abundance/cover and composition of exotic plants in a forest that has been managed through citizen participation with that of reference forests (both with remnants, but the former without protection and the latter with protection). We established 48 sampling sites to characterize the vegetation in three strata (upper, middle, and low) and monitored changes in composition in managed forest sites for a period of 3 years. The results indicate that the managed forest hosts different species than those found in the reference forests, with lower abundance and cover of exotic plants in the upper and lower strata. Regarding temporal changes, we observed shifts in floristic composition before and after management activities, and a reduction in the cover of exotic species before and after management, with consistently low cover three years later. This underscores the effectiveness of citizen-led management activities, offering a viable alternative for restoring native vegetation in urban environments. [ABSTRACT FROM AUTHOR]

Wildflower areas are increasingly used in both urban and rural settings to enhance landscape aesthetics and help the conservation of pollinators, whose dramatic decline threatens both ecosystem functioning and agricultural production. Consequently, today many 'pollinator-friendly' wildflower seed mixes can be found on the market. Criteria for the design of these mixes are focused on the ability of the plants to attract pollinators, whereas the identity of the plants themselves in terms of their alien or native status is often not adequately considered. Moreover, seed mixes often lack sufficient floral resources in the early spring and late-season months, which are important to sustain pollinators throughout their whole life cycle. In this study, we analyzed 36 'pollinator-friendly' wildflower seed mixes commercially available in Italy in terms of (1) the abundance of native and alien species, (2) the occurrence of locally alien species with reference to three Italian geographic areas (northern, peninsular, and insular Italy), and (3) the flowering period of native and alien species. Most (83%) of the analyzed seed mixes contain species alien to Italy, with three of them also including invasive alien species. Among native species, many (41%) are locally alien to at least one of the geographic areas. Overall, native species provide earlier blooms than alien species and around 35% of the seed mixes lack blooms in early-spring (March) or prolonged throughout autumn (September-November). These findings highlight the widespread use of alien plant species in 'pollinator-friendly' wildflower mixes, which poses serious risks for biodiversity and habitat conservation, especially when sown in agricultural areas. We suggest a more careful design and use of such wildflower mixes, promoting a wider adoption of native seeds of local origin and a greater attention to the blooming period. If properly designed, wildflower mixes can represent an effective strategy for biodiversity conservation in both urban and rural areas. [ABSTRACT FROM AUTHOR]

Aims: Most naturalized plants are escapees from cultivation. Inventories of cultivated introduced species thus offer unique, still underutilized, opportunities to assess naturalization drivers of introduced plants. We used a comprehensive inventory of 13,718 introduced species cultivated in China's botanical gardens to test which species characteristics distinguish the 739 species that have naturalized. Locations: China. Methods: We used generalized linear models to test whether the naturalization of cultivated introduced plants in China is associated with functional traits, propagule pressure, environmental niche and introduction history. To test direct and indirect effects of those variables and their relative importance in driving naturalization, we used structural equation models. Results: We showed that species were more likely to naturalize when they originate from the Americas, are more widely cultivated, and have a longer residence time. Moreover, species were more likely to naturalize if they have a good environmental match, are short‐lived herbs, are predominantly propagated from seeds, and, in the case of herbs, are relatively tall compared to other herbs. Part of the latter effects are mediated by how these variables relate to propagule pressure proxies, and this varies among short‐lived herbs, long‐lived herbs and woody plants. Main Conclusions: Naturalization is partly driven by life‐form‐dependent cultivation biases. [ABSTRACT FROM AUTHOR]

The Revillagigedo Archipelago, located in the Eastern Pacific Ocean, stands out for its unique biological richness and endemism. These islands remained uninhabited until the second half of the twentieth century, allowing a better conservation status than on other oceanic islands. However, the continuous introduction of potentially invasive alien plant species, and the lack of adequate control or eradication actions, jeopardize the conservation and restoration of these islands' fragile ecosystems. We present the most complete vascular plant species inventory and an updated list of alien plant species of the Revillagigedo Archipelago, which was compiled through an extensive review of national and international plant collections and other sources. Our 272 species list includes 106 alien plant species (39.3%; 104 in Socorro, and 16 in Clarion): 67 (24.8%) are naturalized, 14 (5.2%) are casual aliens, and 25 (9.3%) subsist under cultivation. The documented alien species belong to 73 families. Annual and perennial herbs are the prevailing life forms in the alien flora, while naturalized species are primarily native to North America. The number of introduced species has increased significantly since the islands became inhabited. Many of the recently introduced species pose a major invasion risk like on other islands of the world. [ABSTRACT FROM AUTHOR]

Invasive exotic plants often impact native plant species through strong competition, yet their effects can vary across different native populations. Previous exposure to invasive species but also differentiation along abiotic gradients may determine to what extent native populations are competitively suppressed by plant invasive species. Here, we experimentally investigated whether competitive effects of the invasive exotic jewelweed Impatiens parviflora on its native congener Impatiens noli‐tangere are related to previous exposure to the invader or rather to topography of the source populations, i.e. to terrain features such as elevation, aspect or slope. We also asked whether, in return, topographic settings of invasive I. parviflora populations may explain competitive effects of the native jewelweed. In a common garden competition experiment we found that populations of native jewelweed from colder, higher altitude sites and from drier sites were on average seven and six times, respectively, more tolerant to interspecific competition than populations from warmer and wetter sites. In contrast, previous exposure of native jewelweed populations to the invader was not a significant predictor of invader's competitive effects. Further, topographic settings of populations of invasive jewelweed were not significantly related to the native's competitive effects. Our study suggests that the native jewelweed's population differentiation along topographic gradients is more important in determining competitive interactions with an invasive congener than invasion‐induced selection. As fine‐scale environmental variation can shape adaptation of native species to the effects of invasive species, such variation should be considered when predicting invasive species' impact on native plant communities. [ABSTRACT FROM AUTHOR]

Background and aims: The main goal of Protected Wild Areas (in spanish ASP) is to protect biodiversity. Limiting the entry of exotic species is an essential priority. The objective of this study was to register exotic plants species within Chile's ASP and to describe floristic patterns which determine species presence and distribution. M&M: Information was collected across 35 ASP, and total number of flora species and the proportion of exotic plants were reported. Richness was obtained and an invasibility index calculated on each ASP. Species composition analysis and floristic patterns determination were carried out through statistical analyses of ordering, similarity and regression. Results: A total of 355 exotic plant species were recorded across the studied ASP. The Reserva Nacional Rio Clarillo had the greatest species richness, while the highest proportion and invasibility occurred in the Monumento Natural Cerro Ñielol. The distance to the nearest city, precipitation and temperature were the environmental variables with the highest incidence on the different assemblages of exotic species that exhibit ASP. Discussion: Exotic plants richness within ASP was high, in relation to the total adventitious flora that Chile presents. The evidence shown suggests a low proportion of exotic plants shared among the ASP distributed in the different bioclimates considered. These types of studies constitute the basis for the preparation of risk lists and the design of management programs for exotic plant species. [ABSTRACT FROM AUTHOR]

Invasive plant species can modify ecosystem structure and function, potentially leading to the loss of native species, environmental and biotic homogenisation, changes in nutrient cycling, impairment of ecosystem services, and decrease in the rate of regeneration of plant recruits. We assessed the effects of the non-native and invasive vine Tradescantia zebrina on the germination and development of the native tree Hymenaea courbaril in north-eastern Brazil. We hypothesised that the invasive species would negatively impact the germination and development, and, via competition, the growth of the native species. We conducted a germination experiment for six months in seven forest patches. Seeds of H. courbaril were cultivated in four possible combinations of two treatments: under a cover with and without T. zebrina, and on soil that originated from places with and without T. zebrina present. Neither T. zebrina cover or soil affected the germination or biomass of H. courbaril during the experiment. H. courbaril seedlings were taller and had longer roots when cultivated in soil that originated from places with T. zebrina. T. zebrina presence alters soil properties in a way that triggers morphological responses in H. courbaril, which can be associated to a perceived competition context. [ABSTRACT FROM AUTHOR]

Invasive exotic species are problematic to biodiversity conservation. However, the knowledge of exotic invaders in tropical forests remains limited. Lessons from sites elsewhere suggest that the problem could be worse than is known. To increase our understanding of this problem, we surveyed exotic woody plants in Mabira Central Forest Reserve, Uganda. The site has a long history of anthropogenic disturbance. Seven woody exotic species were encountered, three of which had population structures indicative of invasiveness and distributions suggestive of the early stages of invasion. One of these species Senna spectabilis (DC.) H.S.Irwin & Barneby was localised to an 8.6 ha site north of the reserve. Terminalia superba Engl. & Diels occurred mainly in an 8.7 ha patch south of the reserve, while Artocarpus heterophyllus Lam. was more widely distributed. T. superba has been reported to be invasive in two other countries, but it is not yet clear whether or not the reported invasions are occurring in protected forests. A. heterophyllus is reported to be invasive in various countries, yet rarely quantitatively demonstrated outside the Brazilian Atlantic forests. S. spectabilis is a common invasive in forests throughout the tropics, and this is the first report of its invasiveness in this reserve. [ABSTRACT FROM AUTHOR]

In fragile ecosystems, the introduction of exotic species could alter some ecological processes. The Austral parakeet (Enicognathus ferrugineous) shows close ecological and evolutionary relationships with the Andean Araucaria (Araucaria araucana), so any alteration in these interactions may have negative consequences for both partners and for ecosystem functioning and structure. We conducted extensive roadside surveys to estimate the abundance of parakeets in the northern Patagonian Andes over 4 years and recorded the food plants consumed by foraging flocks. The use of native habitats and humanized areas like villages and farms was influenced by the Araucaria seed crop. In masting years, the large seed crop allowed a massive use of this resource during the non‐breeding season, and even during the breeding season. The exploitation of exotic plants was minor in the masting year, but became predominant in non‐masting years, especially during the non‐breeding season. This feeding switch towards exotic plants primarily arose because the low Araucaria seed crop in non‐masting years is entirely consumed just after production by domestic and wild exotic mammals living in Araucaria forests year‐round, thus forcing the displacement of parakeets towards anthropic habitats to exploit exotic plants. Given the degradation of the remaining Andean Araucaria forests due to the impact of exotic mammals on the ecological interaction between Araucaria and Austral parakeets, ambitious programs to exclude or reduce the density of these alien mammals, including livestock, are warranted. [ABSTRACT FROM AUTHOR]

[Display omitted] • Higher L. major biomass and cover in invaded range compared to the native range. • Reduced overall species richness, and abundance in the invaded range. • Higher L. major damage in the native range compared to the invaded range. • More herbivore association in native range compared to the invaded range. • These findings are consistent with the assumption of Enemy Release Hypothesis. The Enemy Release Hypothesis (ERH) suggests that the absence of natural enemies (herbivores, parasites, and diseases) in non-native environments allow exotic plants to allocate more resources towards growth and reproduction, resulting in increased invasiveness. This study uses the submerged macrophyte Lagarosiphon major (Ridl.) Moss ex Wager (Hydrocharitaceae), native to Southern Africa, as a case study of this hypothesis. This species is invasive in many parts of the world, including Ireland, the United Kingdom and New Zealand. Here, we investigate the applicability of the ERH in explaining the invasiveness of L. major in New Zealand. This was achieved by comparing L. major biomass and cover, and plant species richness between L. major 's native range in South Africa and its invaded range in New Zealand, where specialist natural enemies were presumed to be lacking. The findings revealed significantly higher L. major biomass (∼100 % increase), cover (∼28 % increase) and shoot production (∼91 % increase) in the invaded range compared to the native range. Additionally, overall species richness and abundance was negatively correlated with L. major abundance in the invaded range. Plants in the native range were associated with more natural enemies and experienced higher levels of damage relative to the invaded sites. Overall, these observations align with the ERH, but should be interpreted with caution as other influential factors such as competition were not measured. Nevertheless, this suggests that L. major could benefit from the integration of biological control measures with the existing methods of control. Two natural enemies, Polypedilum tuburcinatum Andersen (Diptera: Chironomidae) and Hydrellia lagarosiphon Deeming (Diptera: Ephydridae) have already been identified as promising candidates, for biological control of L. major in New Zealand and other regions invaded by this weed. [ABSTRACT FROM AUTHOR]

Numerous studies have highlighted the roles of nutrient availability and fluctuations therein for invasion success of alien plants. Many others also highlighted the role of herbivores in invasion success. However, how herbivory and the level and fluctuations in nutrient availability interact in driving alien plant invasion into native communities remains largely unexplored.We grew eight invasive alien species as target species in pot‐mesocosms with five different synthetic native communities in a three‐factorial design with two levels of nutrient availability (low vs. high), two levels of nutrient fluctuation (constant vs. pulsed) and two levels of above‐ground insect herbivory (with vs. without herbivores). As natural communities have both specialist and generalist herbivores, we simulated this using both a generalist and a specialist herbivorous grasshopper.The relative biomass production of the alien target plants to the total biomass production (i.e. alien biomass/total biomass) decreased in response to an increase in nutrient availability, but increased in response to the presence of herbivores. Furthermore, we found indications that the dominance of the alien target species may depend on interactions of herbivory with changes in nutrient availability and nutrient fluctuations, although these interactions were only marginally significant.Our multi‐trophic multi‐species experiment suggests that herbivory could mediate the interactive effect of nutrient enrichment and variability in nutrient supply on invasion of alien plants into native communities. Therefore, we recommend that studies testing the effects of resources on plant invasion should also consider interactive effects of other trophic levels. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

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The biotic resistance hypothesis asserts that native species may hinder the invasion of exotic species, which can occur either directly or indirectly by influencing interactions between exotic and local species. Aphid-tending ants may play a key role in the indirect biotic resistance to plant invasion. Ants may protect aphids, thus increasing their negative effect on exotic plants, but may also deter chewing herbivores, thus benefiting exotic plants. We studied native aphid-tending ants (Dorymyrmex tener, Camponotus distinguendus, and Dorymyrmex richteri) on exotic nodding thistles (Carduus thoermeri), which are attacked by thistle aphids (Brachycaudus cardui) and thistle-head weevils (Rhinocyllus conicus). We evaluated the impact of ants, aphids, and weevils on thistle seed set. We compared ant species aggressiveness towards aphid predators and weevils and performed ant-exclusion experiments to determine the effects of ants on aphid predators and weevils. We analysed whether ant species affected thistle seed set through their effects on aphids and/or weevils. The ant D. tener showed the most aggressive behaviour towards aphid predators and weevils. Further, D. tener successfully removed aphid predators from thistles but did not affect weevils. Excluding D. tener from thistles increased seed set. Analyses supported a negative indirect pathway between the aggressive D. tener and thistle seed set through aphid populations, while the other ant species showed no indirect effects on thistle reproduction. Therefore, aggressive aphid-tending ants may enhance biotic resistance by increasing aphid infestation on exotic invasive plants. This study highlights the importance of indirect biotic resistance in modulating the success of invasive species. [ABSTRACT FROM AUTHOR]

Aim: Climate warming and increasing human disturbance are expected to promote non‐native plant invasions in mountain ecosystems. Although biological invasions are also expected to be modulated by biotic interactions, it is still not clear how invertebrate herbivores can affect plant invasion dynamics. Using a large manipulative experiment, we aimed at testing: (1) the effect of soil disturbance and elevation on native and non‐native plant communities, and (2) the effect of plant‐herbivore interactions, nitrogen deposition, and elevation in driving plant establishment after soil disturbance. Location: European Alps, NE Italy. Taxon: Vascular plants. Methods: We selected remote, uninvaded dry semi‐natural grasslands along the core elevational range of non‐native plants in the European Alps (c. 100–1300 m) and manipulated soil disturbance, nitrogen deposition, and invertebrate herbivory. Then, we followed the natural establishment under real field conditions of both native and non‐native plants over one growing season. We used generalized mixed‐effects models to test the effects of the experimental treatments. Results: Native and non‐native species showed contrasting responses to soil disturbance and elevation. Low elevations and disturbance promoted non‐native success, while affecting native species diversity negatively. Two‐thirds of the experimental sites acquired novel non‐natives after disturbance. Most of the observed non‐natives were not present in the surrounding vegetation as mature plants, indicating that propagules were able to reach even remote natural areas. While current N deposition levels did not affect plant establishment, we found that after disturbance invertebrate herbivory might play an important role in facilitating non‐native invasions by reducing native cover. Main conclusions: Our findings show that highly resistant ecosystems such as continuous grasslands can be easily invaded once the resident vegetation has been removed, and that natural herbivory pressure from invertebrates might amplify the negative effects of disturbance on resident native species irrespective of elevation. Together, these results indicate increasing risks of future plant invasions on mountains under global change. [ABSTRACT FROM AUTHOR]

Introduction: Numbers of alien plant species are rising around the globe, but not all of them become invasive. Whereas introductions have been documented for several decades in some regions of the world, knowledge on alien species in Western Mexico is limited. Here, we study roadside vegetation along an elevational gradient, which includes a protected area. Objective: We analysed the floristic composition of herbaceous alien species, their distribution patterns, and their relationship with various environmental factors. A relative importance value index (IVI) identified the most important and, therefore, probably invasive taxa. Methods: During 2017 and 2018, roadside vegetation was documented with 4-6 transects every 300 altitudinal meters, from 0 to 2 100 m, for a total of 37 transects. Each transect consisted of five 1 m² plots. All herbaceous species were registered and alien taxa identified. A cluster analysis distinguished grouping of species based on elevation. The potentially invasive species were identified by their IVI, based on the sum of relative frequency and density values. The influence of environmental variables was analysed with a canonical correspondence analysis. Results: Most alien species were grasses; other families were represented by one or two species. The species were grouped into three main clusters. The first group included rare species, the second consisted of species restricted to higher altitudes, and the third group were tropical taxa with a distribution from sea level to medium altitudes. The most important potentially invasive species were: Urochloa maxima, Melinis repens, Eragrostis ciliaris and Cynodon dactylon, all African grasses introduced for grazing. The IVI of the species was related to tree cover, leaf litter depth and surface stone cover for some species and, for others, to soil compaction, distance to major roads and elevation. Conclusions: The alien ruderal species clustered according to the general climate (temperate vs. tropical). Grasses of African origin are of highest concern as invasive species. Although most introductions are related to human disturbance, each species becomes dominant under certain environmental conditions. Thus, management programs must be specifically adjusted to each individual invasive alien. [ABSTRACT FROM AUTHOR]

Questions: How does small‐scale soil disturbance influence establishment dynamics of native and exotic species along roadsides? Does soil disturbance provide potential opportunities to exotic invasions along elevational gradients? Does the established plant community after disturbance reflect the surrounding vegetation? Location: Prealps, Italy. Methods: To disentangle the role of elevation and soil disturbance in promoting exotic invasions, we performed a manipulative experiment along 12 roads spanning an elevational gradient of ca. 1,200 m. Additionally, we sampled species richness of native and exotic plants in the surroundings of the experimental plots. Results: Soil disturbance reduced species richness of native plants, total plant biomass and vegetation cover compared to the undisturbed plots. The decrease in species richness of natives and plant biomass was stronger at higher than lower elevations, suggesting higher colonization opportunities for exotics. However, exotic species richness did not increase with disturbance, probably due to a low propagule and colonization pressure. We observed strong species replacement between control and disturbed plots, indicating that plant communities established after disturbance were not a subset of species communities already occurring in the surrounding vegetation. Conclusions: With increasing elevation, disturbance had a stronger negative effect on native than on exotic species. Higher elevations, hitherto considered to have low invasibility, may provide new potential colonization opportunities for exotics but only if disturbance is coupled with an increased propagule pressure. Disturbance along roadsides promoted the establishment of species that did not occur in the surrounding vegetation. [ABSTRACT FROM AUTHOR]

Questions: The Pacific Northwest Bunchgrass ecosystem is one of the most endangered in the United States, yet community‐level patterns of non‐native plant distribution and abundance remain largely unexplored. To address this information gap, we asked the following questions: What are the distinct plant communities within Zumwalt Prairie Preserve? What are the most widespread and abundant non‐native species and how does non‐native species composition and dominance vary across plant communities? How do historic land use, biotic and environmental factors influence plant community composition, particularly in terms of non‐native species abundance and dominance? Location: Zumwalt Prairie Preserve, Wallowa County, Oregon, USA. Methods: We sampled 123 plots using point‐intercept methods within a stratified random sampling approach. We analyzed community variation using cluster analysis, indicator species analysis, and non‐metric multidimensional scaling, and related composition and non‐native plant abundance to historical land use, biotic and environmental variables using joint plots, linear regression, and non‐parametric multiplicative regression. Results: While native perennial grasses were the most abundant species, non‐native species accounted for 27% of species encountered and four of the ten most abundant species were non‐native annual grasses (e.g., Ventenata dubia) or non‐native perennial grasses (e.g., Poa pratensis). Abundance patterns of non‐native perennial grasses differed markedly from those of non‐native annual grasses; non‐native perennial grasses were concentrated in old fields, while non‐native annual grasses were abundant in moisture‐limited uncultivated sites. Conclusions: Despite its protected status, non‐native plant species pose a serious threat to the biotic integrity of the Preserve, with unknown consequences to ecosystem dynamics and function. Moreover, patterns of non‐native abundance vary considerably, with different species responding individually to land‐use, environmental, and biotic gradients. An improved understanding of the relationship between non‐native species distributions and historical, environmental, and biotic factors can help in the development of ecologically appropriate, cost‐effective strategies for the conservation and restoration of this unique landscape. [ABSTRACT FROM AUTHOR]

Highlights • Shadier conditions were observed in the invaded than native woodlands. • Emergence was similar but seedling survival tended to be lower in invaded woodlands. • Success of the exotic species was equal or lower than native species. • Lower light quantity was related with a reduction in the growth of seedlings. • C. ehrenbergiana seems to be the most suitable species to start restoration. Abstract Nowadays forests, which were formerly considered resistant to invasion due to its shady understories, are been transformed to invaded landscapes. Thus, the aim of this study was to evaluate the regeneration of native woody species in Ligustrum lucidum invaded woodlands. In addition, we aim to identify the main environmental differences between the native and invaded woodlands and evaluate the effect of those conditions in the regeneration phase of dominant native woody species. Finally, we analyze how is the emergence and survival of the exotic species in relation to that exhibited by native species in both environmental situations. For this, we performed a seed addition experiment placing three native woody species (Celtis ehrenbergiana, Lithraea molleoides, Vachellia caven) and the dominant exotic (L. lucidum) in native and invaded woodlands of the Chaco mountains, central Argentina. Also, we performed a laboratory experiment simulating the differences in light recorded at the field (main abiotic difference between both woodland types). Our field experiment indicated that, if seeds are actively added, the percentage of seedlings emergence of native species could be similar in invaded and native woodlands. However, we observed a trend of lower seedling survival after winter within the exotic monospecific stands, which was significant only for the native species C. ehrenbergiana. We suggest that this constraint could be partly related to the shadier conditions imposed by L. lucidum , since this is the major environmental change within the invaded woodlands in comparison with native ones. Consistently, the experimental simulation showed that the increased in shade reduced the overall growth of seedlings. As was mostly observed in temperate biome, our study in a subtropical seasonally dry region indicates that invaded areas may not affect the emergence stage but limit the survival of seedlings. Among the native species, C. ehrenbergiana seems to be the most suitable species to start restoration, showing the highest performance throughout the year. Combined actions of seed addition and canopy opening might counteract the abiotic constraint and contribute to restoration success of this invaded landscape. [ABSTRACT FROM AUTHOR]

Aims: Grasslands dominated by non-native (exotic) species have replaced purely native-dominated areas in many parts of the world forming 'novel' ecosystems. Altered precipitation patterns are predicted to exacerbate this trend. It is still poorly understood how soil microbial communities and their functions differ between high diversity native- and low diversity exotic-dominated sites and how altered precipitation will impact this difference.Methods: We sampled 64 experimental grassland plots in central Texas with plant species mixtures of either all native or all exotic species; half with summer irrigation. We tested how native vs. exotic plant species mixtures and summer irrigation affected bacterial and fungal community composition and structure, the influence of niche vs. neutral processes for microbial phylotype co-occurrence (C-score analysis), and rates of phosphorus and nitrogen mineralization across an 8-year experiment.Results: Native and exotic-dominated plots had significantly different fungal community composition and structure, but not diversity, throughout the length of the study, while changes in bacterial communities were limited to certain wet and cool years. Nitrogen and phosphorus mineralization rates were higher under native plant mixtures and correlated with the abundance of particular fungal species. Microbial communities were more structured in exotic than native grassland plots, especially for the fungal community.Conclusions: The results indicate that conversion of native to exotic C4 dominated grasslands will more strongly impact fungal than bacterial community structure. Furthermore, these impacts can alter ecosystem functioning belowground via changes in nitrogen and phosphorus cycling. [ABSTRACT FROM AUTHOR]

Exotic species introductions are a global phenomenon and protected areas are susceptible to them. Understanding the drivers of exotic species richness is vital for prioritizing natural resource management, particularly in developing countries with limited resources. We analyzed the influence of coarse resolution factors on exotic species richness (plants, mammals, and birds) in Argentina's National Parks System. We collected data on native species richness, year of park formation, park area, region, elevation range, number of rivers crossing area boundaries, roads entering area, mean annual rainfall, mean annual temperature, mean annual number of visitors, and Human Influence Index within and surrounding each park. We compiled 1,688 exotic records in 36 protected areas: 83% plants and 17% animals (9.5% mammals, 5.5% birds, 1.5% fishes, 0% amphibians, 0% reptiles). The five parks with the most exotic species (all taxa combined) were in north Patagonia. Exotic grasses were the most common exotic plants, and within animals, lagomorphs and feral ungulates were remarkably widespread. Exotic plant richness was mostly influenced by temperature and native plant richness, while exotic mammal and bird richness was driven mostly by anthropogenic variables, with models explaining 36-45% of data deviance. Most variables that positively influenced exotic taxa were indirectly related to an increase in spatial heterogeneity (natural or anthropogenic), suggesting greater niche space variability as facilitators of exotic richness increase. Additional data are needed to further investigate the patterns and mechanisms of exotic species richness in protected areas, which will help to prioritize the greatest needs of monitoring and management. [ABSTRACT FROM AUTHOR]

Urbanization leads to the restructuring of plant-animal interactions due to environmental changes and introduction of non-native species that become part of local ecological processes. The conservation of pollinators in urban areas has received increasing attention. However, detailed quantification of available floral resources and their use by pollinators are rarely conducted. Here, we characterized the interaction network between hummingbirds and native and non-native plants, the behavior of resource use by pollinators and the temporal availability of nectar resources in an extensive urban green area from Brazil. We found that more than half of the interactions between hummingbirds and plants were illegitimate, which do not constitute potential pollination. The interaction network was generalized, indicating low level of niche partitioning, which is usual for urban environments. Inclusion of non-pollination interactions increased specialization. Although native and non-native plants provide a similar amount of nectar when considering each plant species for a given month, the latter contributed most to the total nectar availability owed to their higher abundance and longer flowering phenologies. Importantly, non-native plants provided resources when native flowers were scarce. Our results show how non-native plants may sometimes have relevant contributions for maintenance of pollinators in cities throughout the year, supporting them during periods of resource shortage. At the same time, urban pollinator-plant communities may be characterized by high prevalence of illegitimate interactions, which highlights the opportunistic use of resources by animals. In conclusion, our study suggests that biodiversity-friendly urban planning should consider the relevant role played by non-native species and that pollinator support may require different types of interactions with flowers. • We quantified temporal nectar availability and use by hummingbirds. • Non-native plants contributed substantially to nectar availability. • Native and non-native plants showed distinct phenologies. • Most visits were illegitimate, without touching the reproductive structures. • Pollinator conservation in urban areas should consider non-mutualistic interactions. [ABSTRACT FROM AUTHOR]

Knowledge from basic plant ecology suggests that impact of one plant species on another is driven by either competition for the same limiting resources, or by unique plant traits. These processes might be context specific, explaining a differential impact of exotic plant invaders in the native vs. introduced range. With the help of a conceptual framework, we aimed at identifying the relationship between invader biomass and impact in the invasive Centaurea stoebe by conducting pairwise competition experiments with 15 European (old) and 15 North American (new) neighboring species. Old neighbors grew larger and could use available soil moisture more efficiently for growth than new neighbors. Interestingly, biomass of C. stoebe explained a substantial amount of the variation in biomass of the coevolved neighbors, but not of the new "naïve" neighbors. Thus, impact in the home range appears to be driven by competition for the same limiting resources, but by other factors in the introduced range, possibly by exploitation of resources that are not used by the new neighbors or by interference competition. This distinction has important consequences for the management of invasive species, as in our study ecosystem recovery is less likely after simple biomass reduction. [ABSTRACT FROM AUTHOR]

The biotic resistance hypothesis is a dominant paradigm for why some introduced species fail to become invasive in novel environments. However, predictions of this hypothesis require further empirical field tests. Here, we focus on evaluating two biotic factors known to severely limit plants, interspecific competition and insect herbivory, as mechanisms of biotic resistance. We experimentally evaluated the independent and combined effects of three levels of competition by tallgrass prairie vegetation and two levels of herbivory by native insects on seedling regeneration, size, and subsequent flowering of the Eurasian Cirsium vulgare, a known invasive species elsewhere, and compared its responses to those of the ecologically similar and co-occurring native congener C. altissimum. Seedling emergence of C. vulgare was greater than that of C. altissimum, and that emergence was reduced by the highest level of interspecific competition. Insect leaf herbivory was also greater on C. vulgare than on C. altissimum at all levels of competition. Herbivory on seedlings dramatically decreased the proportion of C. vulgare producing flower heads at all competition levels, but especially at the high competition level. Competition and herbivory interacted to significantly decrease plant survival and biomass, especially for C. vulgare. Thus, both competition and herbivory limited regeneration of both thistles, but their effects on seedling emergence, survival, size and subsequent reproduction were greater for C. vulgare than for C. altissimum. These results help explain the unexpectedly low abundance recorded for C. vulgare in western tallgrass prairie, and also provide strong support for the biotic resistance hypothesis. [ABSTRACT FROM AUTHOR]

We examined temporal introduction patterns of 132 invasive alien plant species (IAPS) to Australia since European colonisation in 1770. Introductions of IAPS were high during 1810-1820 (10 species), 1840-1880 (51 species, 38 of these between 1840 and 1860) and 1930-1940 (9 species). Conspicuously few introductions occurred during 10-year periods directly preceding each introduction peak. Peaks during early European settlement (1810-1820) and human range expansion across the continent (1840-1860) both coincided with considerable growth in Australia's human population. We suggest that population growth during these times increased the likelihood of introduced plant species becoming invasive as a result of increased colonization and propagule pressure. Deliberate introductions of IAPS (104 species) far outnumbered accidental introductions (28 species) and were particularly prominent during early settlement. Cosmopolitan IAPS (25 species) and those native solely to South America (53 species), Africa (27 species) and Asia (19 species) have been introduced deliberately and accidentally to Australia across a broad period of time. A small number of IAPS, native solely to Europe (5 species) and North America (2 species), were all introduced to Australia prior to 1880. These contrasting findings for native range suggest some role for habitat matching, with similar environmental conditions in Australia potentially driving the proliferation of IAPS native to southern-hemisphere regions. Shrub, tree and vine species dominated IAPS introduced prior to 1840, with no grasses or forbs introduced during early colonisation. Since 1840, all five growth forms have been introduced deliberately and accidentally in relatively large numbers across a broad period of time. In particular, a large number of grass and forb IAPS were deliberately introduced between 1840 and 1860, most likely a direct result of the introduction of legislation promoting intensive agriculture across large areas of the continent. Since the 1980s, only three IAPS have been introduced (all deliberately introduced forbs). The decline in IAPS introductions is most likely a reflection of both increased surveillance and biosecurity efforts and the likelihood that many potential IAPS are still within a pre-expansion lag period. [ABSTRACT FROM AUTHOR]

ABSTRACT Aim Classic theory suggests that species-rich communities should be more resistant to the establishment of exotic species than species-poor communities. Although this theory predicts that exotic species should be less diverse in regions that contain more native species, macroecological analyses often find that the correlation between exotic and native species richness is positive rather than negative. To reconcile results with theory, we explore to what extent climatic conditions, landscape heterogeneity and anthropogenic disturbance may explain the positive relationship between native and exotic plant richness. Location Catalonia (western Mediterranean region). Methods We integrated floristic records and GIS-based environmental measures to make spatially explicit 10-km grid cells. We asked whether the observed positive relationship between native and exotic plant richness ( R2= 0.11) resulted from the addition of several negative correlations corresponding to different environmental conditions identified with cluster analysis. Moreover, we directly quantified the importance of common causal effects with a structural equation modelling framework. Results We found no evidence that the relationship between native and exotic plant richness was negative when the comparison was made within environmentally homogeneous groups. Although there were common factors explaining both native and exotic richness, mainly associated with landscape heterogeneity and human pressure, these factors only explained 17.2% of the total correlation. Nevertheless, when the comparison was restricted to native plants associated with human-disturbed (i.e. ruderal) ecosystems, the relationship was stronger ( R2= 0.52) and the fraction explained by common factors increased substantially (58.3%). Main conclusions While our results confirm that the positive correlation between exotic and native plant richness is in part explained by common extrinsic factors, they also highlight the great importance of anthropic factors that - by reducing biotic resistance - facilitate the establishment and spread of both exotic and native plants that tolerate disturbed environments. [ABSTRACT FROM AUTHOR]

The current rate of invasive species introductions is unprecedented, and the dramatic impacts of exotic invasive plants on community and ecosystem properties have been well documented. Despite the pressing management implications, the mechanisms that control exotic plant invasion remain poorly understood. Several factors, such as disturbance, propagule pressure, species diversity, and herbivory, are widely believed to play a critical role in exotic plant invasions. However, few studies have examined the relative importance of these factors, and little is known about how propagule pressure interacts with various mechanisms of ecological resistance to determine invasion success. We quantified the relative importance of canopy disturbance, propagule pressure, species diversity, and herbivory in determining exotic plant invasion in 10 eastern hemlock forests in Pennsylvania and New Jersey (USA). Use of a maximum-likelihood estimation framework and information theoretics allowed us to quantify the strength of evidence for alternative models of the influence of these factors on changes in exotic plant abundance. In addition, we developed models to determine the importance of interactions between ecosystem properties and propagule pressure. These analyses were conducted for three abundant, aggressive exotic species that represent a range of life histories: Alliaria petiolata, Berberis thunbergii, and Microstegium vimineum. Of the four hypothesized determinants of exotic plant invasion considered in this study, canopy disturbance and propagule pressure appear to be the most important predictors of A. petiolata, B. thunbergii, and M. vimineum invasion. Herbivory was also found to be important in contributing to the invasion of some species. In addition, we found compelling evidence of an important interaction between propagule pressure and canopy disturbance. This is the first study to demonstrate the dominant role of the interaction between canopy disturbance and propagule pressure in determining forest invasibility relative to other potential controlling factors. The importance of the disturbance-propagule supply interaction, and its nonlinear functional form, has profound implications for the management of exotic plant species populations. Improving our ability to predict exotic plant invasions will require enhanced understanding of the interaction between propagule pressure and ecological resistance mechanisms. [ABSTRACT FROM AUTHOR]

Successful plant invasions are often attributed to increased plant size, reproduction, or release from natural enemies, but the generality and persistence of these patterns remains widely debated, Meta-analysis was used to quantitatively assess invasive plant performance and release from enemy damage and how these change with residence time and geographic distribution. Invasive plants were compared either in their introduced and home ranges or with native congeners in the introduced range. Invasive plants in the introduced range were generally larger, allocated more to reproduction, and had lower levels of herbivore damage compared with conspecifics in the home range; pathogen attack, however, varied widely. In congener comparisons, invasive and native plants did not differ in size or herbivory, but invaders did allocate less to reproduction and had lower levels of pathogen damage. Time since introduction was a significant nonlinear predictor of enemy release for both herbivores and pathogens, with initial release in recently arrived species and little to no release after 50 to 200 years. Geographic distribution was also a significant nonlinear predictor of enemy release. The observed nonlinear relationships are consistent with dynamic invasions and may define targets for eradication efforts if these patterns hold up for individual species. [ABSTRACT FROM AUTHOR]

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The article presents a study on the effects of predator abundance and the variability of climate. It highlights the success of veeries (Catharus fuscescens) in creating nests in the Japanese barberry (Berberis thunbergii) in New York. An overview of the white-footed mouse, substrates and the effect of invasive species on communities is also presented.

The article presents a study which describes the dynamics of invasion in highly invaded biotic and abiotic nonserpentine oak woodlands and serpentine habitats. It uses a historical experiment in the introduction of several nonnative species for post-mining revegetation, supplemented by a pot experiment and a factorial field experiment. It implies that the spread of introduced exotic species is slower than in more fertile and more invaded oak woodlands with harsh serpentine soils.

• Heterospecific pollen from alien donors affects negatively native recipients. • Heterospecific pollen from native species reduces fruit set for alien species. • Phylogenetic distance between donor and recipient species does not matter. • Trait distance between donor and recipient species does not matter. • Heterospecific pollen interference could mediate biotic resistance. Heterospecific pollen interference has recently been proposed as a mechanism contributing to the success of alien invaders, as heterospecific pollen of alien plants can interfere with the reproduction of natives by reducing fruit and seed set. However, no study has looked at the opposite interaction. Moreover, few studies have considered the roles of phylogenetic and floral trait distances between pollen donors and recipients. We did a large multi-species experiment in which we used alien and native species both as pollen recipients and as pollen donors, and included phylogenetic as well as single floral trait distance as explanatory variables. We found that both alien and native recipients suffered from heterospecific pollen from donors of the opposite status in terms of seed and fruit set. Phylogenetic distance did not affect fruit and seed set. However, style-length distance decreased, while pollen-size distance increased heterospecific pollen interference. We conclude that heterospecific pollen interference affects both native and alien recipients, thus indirectly altering community composition. Importantly, we found that heterospecific pollen interference can be a mechanism that increases biotic resistance of natives against invaders. [ABSTRACT FROM AUTHOR]