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The factors that promote invasive behavior in introduced plant species occur across many scales of biological and ecological organization. Factors that act at relatively small scales, for example the evolution of biological traits associated with invasiveness, scale up to shape species distributions amongst different climates and habitats, as well as other characteristics linked to invasion, such as attractiveness for cultivation (and by extension propagule pressure). To identify drivers of invasion it is therefore necessary to disentangle the contribution of multiple factors that are interdependent. To this end, we formulated a conceptual model describing the process of invasion of central European species into North America based on a sequence of 'drivers'. We then used confirmatory path analysis to test whether the conceptual model is supported by a statistical model inferred from a comprehensive database containing 466 species. The path analysis revealed that invasion of central-European plants in North America, in terms of the number of North American regions invaded, most strongly depends on minimum residence time in the invaded range and the number of habitats occupied by species in their native range. In addition to the confirmatory path analysis, we identified the effects of various biological traits on several important drivers of the conceptualized invasion process. The data supported a model, which included indirect effects of biological traits on invasion via their effect on the number of native range habitats occupied and cultivation in the native range. For example, persistent seed banks and longer flowering periods are positively correlated with number of native habitats, while a stress-tolerant life strategy is negatively correlated with native-range cultivation. However, the importance of the biological traits is nearly an order of magnitude less than that of the larger-scale drivers and highly dependent on the invasion stage (traits were associated only with native-range drivers). This suggests that future research should explicitly link biological traits to the different stages of invasion, and that a failure to consider minimum residence time or characteristics of the native range may seriously overestimate the role of biological traits, which in turn may result in spurious predictions of plant invasiveness.

A fundamental assumption in invasion biology is that most invasive species exhibit enhanced performance in their introduced range relative to their home ranges. This idea has given rise to numerous hypotheses explaining \"invasion success\" by virtue of altered ecological and evolutionary pressures. There are surprisingly few data, however, testing the underlying assumption that the performance of introduced populations, including organism size, reproductive output, and abundance, is enhanced in their introduced compared to their native range. Here, we combined data from published studies to test this hypothesis for 26 plant and 27 animal species that are considered to be invasive. On average, individuals of these 53 species were indeed larger, more fecund, and more abundant in their introduced ranges. The overall mean, however, belied significant variability among species, as roughly half of the investigated species ( N = 27) performed similarly when compared to conspecific populations in their native range. Thus, although some invasive species are performing better in their new ranges, the pattern is not universal, and just as many are performing largely the same across ranges.

Plant invasion potentially alters ecosystem carbon (C) and nitrogen (N) cycles. However, the overall direction and magnitude of such alterations are poorly quantified. Here, 94 experimental studies were synthesized, using a meta-analysis approach, to quantify the changes of 20 variables associated with C and N cycles, including their pools, fluxes, and other related parameters in response to plant invasion. Pool variables showed significant changes in invaded ecosystems relative to native ecosystems, ranging from a 5% increase in root carbon stock to a 133% increase in shoot C stock. Flux variables, such as above-ground net primary production and litter decomposition, increased by 50-120% in invaded ecosystems, compared with native ones. Plant N concentration, soil [graphic removed] and [graphic removed] concentrations were 40, 30 and 17% higher in invaded than in native ecosystems, respectively. Increases in plant production and soil N availability indicate that there was positive feedback between plant invasion and C and N cycles in invaded ecosystems. Invasions by woody and N-fixing plants tended to have greater impacts on C and N cycles than those by herbaceous and nonN-fixing plants, respectively. The responses to plant invasion are not different among forests, grasslands, and wetlands. All of these changes suggest that plant invasion profoundly influences ecosystem processes.

• Background and Aims Global environmental change will affect non-native plant invasions, with profound potential impacts on native plant populations, communities and ecosystems. In this context, we review plant functional traits, particularly those that drive invader abundance (invasiveness) and impacts, as well as the integration of these traits across multiple ecological scales, and as a basis for restoration and management. • Scope We review the concepts and terminology surrounding functional traits and how functional traits influence processes at the individual level. We explore how phenotypic plasticity may lead to rapid evolution of novel traits facilitating invasiveness in changing environments and then 'scale up' to evaluate the relative importance of demographic traits and their links to invasion rates. We then suggest a functional trait framework for assessing per capita effects and, ultimately, impacts of invasive plants on plant communities and ecosystems. Lastly, we focus on the role of functional trait-based approaches in invasive species management and restoration in the context of rapid, global environmental change. • Conclusions To understand how the abundance and impacts of invasive plants will respond to rapid environmental changes it is essential to link trait-based responses of invaders to changes in community and ecosystem properties. To do so requires a comprehensive effort that considers dynamic environmental controls and a targeted approach to understand key functional traits driving both invader abundance and impacts. If we are to predict ftiture invasions, manage those at hand and use restoration technology to mitigate invasive species impacts, future research must focus on functional traits that promote invasiveness and invader impacts under changing conditions, and integrate major factors driving invasions from individual to ecosystem levels.

1. Facilitation among species may promote non-native plant invasions through alteration of environmental conditions, enemies or mutualists. However, the role of non-trophic indirect facilitation in invasions has rarely been examined. 2. We used a long-term field experiment to test for indirect facilitation by invasions of Microstegium vimineum (stiltgrass) on a secondary invasion of Alliaria petiolata (garlic mustard) by introducing Alliaria seed into replicated plots previously invaded experimentally by Microstegium. 3. Alliaria more readily colonized control plots without Microstegium but produced almost seven times more biomass and nearly four times as many siliques per plant in Microstegium-invaded plots. Improved performance of Alliaria in Microstegium-invaded plots compared to control plots overwhelmed differences in total number of plants such that, on average, invaded plots contained 327% greater total Alliaria biomass and 234% more total siliques compared to control plots. 4. The facilitation of Alliaria in Microstegium-invaded plots was associated with an 85% reduction in the biomass of resident species at the peak of the growing season and significantly greater light availability in Microstegium-invaded than control plots early in the growing season. 5. Synthesis. Our results demonstrate that an initial plant invasion associated with suppression of resident species and increased resource availability can facilitate a secondary plant invasion. Such positive interactions among species with similar habitat requirements, but offset phenologies, may exacerbate invasions and their impacts on native ecosystems.

Exotic species are widely assumed to thrive because they lack natural enemies in their new ranges. However, a meta-analysis of 63 manipulative field studies including more than 100 exotic plant species revealed that native herbivores suppressed exotic plants, whereas exotic herbivores facilitated both the abundance and species richness of exotic plants. Both outcomes suggest that plants are especially susceptible to novel, generalist herbivores that they have not been selected to resist. Thus, native herbivores provide biotic resistance to plant invasions, but the widespread replacement of native with exotic herbivores eliminates this ecosystem service, facilitates plant invasions, and triggers an invasional \"meltdown.\"

Aim We use data from 13 mountain regions and surrounding lowland areas to identify (1) the origins, traits and cultural uses of alien plant species that establish in mountains, (2) the alien species that are most likely to be a threat and (3) how managers might use this information to prevent further invasions. Location Australia, Canada, Chile, India, New Zealand, South Africa, Spain, Switzerland, USA. Methods Lists of alien species were compiled for mountains and their surrounding or nearby lowlands. Principal co-ordinates analysis was performed on a matrix of similarities created using presence/absence data for alien species. The significance of differences between means for (1) similarity metrics of lowland and mountain groups and (2) species traits of lowland and mountain alien floras was determined using t-tests. In seven of the 13 mountain regions, lists of alien species undergoing management were compiled. The significance of differences between proportions of traits for species requiring and not requiring management input was determined with chi-square tests. Results We found that the proximal lowland alien flora is the main determinant of a mountain region's alien species composition. The highest similarities between mountain floras were in the Americas/Pacific Region. The majority of alien species commonly found in mountains have agricultural origins and are of little concern to land managers. Woody species and those used for ornamental purposes will often pose the greatest threat. Main conclusions Given the documented potential threat of alien species invading mountains, we advise natural resource managers to take preventive measures against the risk of alien plant invasion in mountains. A strategy for prevention should extend to the surrounding lowland areas and in particular regulate the introduction of species that are already of management concern in other mountains as well as climatically pre-adapted alien mountain plants. These may well become more problematic than the majority of alien plants currently in mountains.

AIM: To determine seed retention rates on vehicles as a function of distance driven, road surface, weather condition and seed location on the vehicle undercarriage. LOCATION: Montana, United States. METHODS: Metal plates were covered with a seed‐soil slurry, dried and attached to different locations underneath a vehicle. The vehicle was then driven on paved and unpaved roads under both wet and dry conditions. Plates were removed from the vehicle at seven distances between 4 and 256 km. The number of seeds remaining was determined. Four general models were assessed to explain observed seed retention. RESULTS: Under dry conditions, seed retention rates were high on both unpaved and paved roads, with 86–99% of the seeds remaining at 256 km. Under wet conditions, lower rates of seed retention were observed for both road surfaces: 0.3–80% of seeds were retained at 256 km on paved wet roads and 50–96% of seeds were retained at 256 km on unpaved wet roads. Plate location had a significant effect on seed retention under certain road surfaces and conditions, with loss generally being highest from the wheel wells. Of the statistical models compared, a double exponential model explained the most variation in seed retention. MAIN CONCLUSIONS: Vehicles act as vectors of long‐distance dispersal. Seed adhered to vehicles can be retained for hundreds of kilometres under dry conditions. When wet conditions occur, a greater proportion of seeds will be dispersed shorter distances. Consequently, vehicle seed dispersal has implications for plant invasions and species migration rates, and those concerned with prevention and control of non‐native plant invasions should consider vehicle seed transport when developing management strategies and plans.

Invasive microbes, plants and animals are a major threat to the composition and functioning of ecosystems; however, the mechanistic basis of why exotic species can be so abundant and disruptive is not well understood. Most studies have focused on invasive plants and animals, although few have considered the effects of invasive microbes, or interactions of invasive plant and animal species with microbial communities. Here, we review effects of invasive plants on soil microbial communities and discuss consequences for plant performance, plant community structure and ecosystem processes. In addition, we briefly discuss effects of invasive soil microbes on plant communities, which has been less well studied, and effects of invasive animals on soil decomposers and ecosystem functioning. We do this by considering each of three important functional groups of microbes, namely soil microbial parasites and pathogens, mutualistic symbionts and decomposers. We conclude that invasive plants, pathogenic and symbiotic soil microbes will have strongest effects on the abundance of individual species, community diversity and ecosystem functioning. Invasive decomposer microbes probably have little impact, because of limited specificity and great functional redundancy. However, invasive plants and animals can have major effects on microbial decomposition in soil. We propose that understanding, predicting and counteracting consequences of enhanced global homogenization of natural communities through introducing exotic plants, animals and microbes will require future studies on how pathogenic, symbiotic and decomposer soil microbes interact, how they are influenced by higher trophic level organisms and how their combined effects are influencing the composition and functioning of ecosystems.

As exotic plant species invade ecosystems, ecologists have been attempting to assess the effects of these invasions on native communities and to determine what factors influence invasion processes. Although much of this work has focused on aboveground flora and fauna, structurally and functionally diverse soil communities also can respond to and mediate exotic plant invasions. In numerous ecosystems, the invasion of exotic plant species has caused major shifts in the composition and function of soil communities. Soil organisms, such as pathogenic or mutualistic fungi, have direct effects on the establishment, growth, and biotic interactions of exotic plants. An integrated understanding of how aboveground and belowground biota interact with exotic plants is necessary to manage and restore communities invaded by exotic plant species.