Invasion of natural and agricultural cranberry bogs by introduced and native plants

Plant species invasions, i.e., the entry of additional plant species into a habitat with negative effects on species already there, are a major ecological problem in natural habitats and a major economic problem in agricultural habitats. Nutrient availability, disturbance, and proximity to other habitats are likely factors that may interact to control invasion in both types of habitat. We hypothesized (1) that elevated nutrient availability can promote the abundance of introduced species even when high cover of the existing plant community is maintained, and (2) that higher levels of invasion on the edges than in the interiors of habitats are due to differences in resource availability between edges and interiors. To test these hypotheses, we measured soil characteristics and the abundances of plant species in natural and agricultural cranberry (Vaccinium macrocarpon Ait.) bogs in southeastern Massachusetts. Contrary to the first hypothesis, agricultural bogs did not have higher cover or richness of introduced species than natural bogs, despite having higher levels of soil nutrients. Contrary to the second hypothesis, the edges of both agricultural and natural bogs had a higher cover and richness of introduced species than the interiors, even though only natural bogs showed differences in resource availabilities between edges and interiors. Results suggest that having a high cover of existing species can counter positive effects of elevated nutrients on the spread of introduced and non-crop species. However, maintaining similar resource availabilities on the edges and interiors of habitats may not prevent greater invasion of edges. Avoiding disturbances to natural communities, maintaining high crop cover, and focusing active control of introduced or non-crop species on the edges of habitats could help limit plant invasions into natural and agricultural habitats alike.     

Inverted invasions: Native plants can frequently colonise urban and highly disturbed habitats

There is an enormous body of literature on plant invasions, including many investigations of the types of introduced species that are most likely to invade natural ecosystems. In this study we turn invasion biology upside down, and ask what sort of native species colonise novel anthropogenic habitats such as roadside lawns, infrequently tended road shoulders, railway embankments and fire trails. We quantified species richness and cover in roadside lawns and infrequently tended road shoulders in five regions of New South Wales, Australia. The native vegetation in these regions included sclerophyll forest, fertile and infertile Eucalypt‐dominated woodlands, rainforest, and semi‐arid woodland. We performed a complementary survey of sites spanning five disturbance levels within the region containing sclerophyll forest vegetation. Although many non‐native species were present in disturbed, novel habitats, a total of 136 native species were also found. Most of these native species were in sites with low levels of disturbance (fire trails and railway embankments), but 35 native species were found to colonise roadside lawns, our most highly‐disturbed vegetation type. There was a significant negative relationship between the disturbance level in novel habitats and the number and cover of native species. Native species that colonised novel habitats were disproportionately likely be generalist species whose natural habitat includes both high and low light and high and low disturbance conditions. The native species colonising novel habitats also tended to have traits associated with a fast life‐history, including short stature and small seeds. A surprisingly high number of native plant species are colonising novel, anthropogenic habitats. Our findings highlight the potential importance of urban ecosystems for conservation and restoration biology.     

Non-Native Plant Invasion along Elevation and Canopy Closure Gradients in a Middle Rocky Mountain Ecosystem

Mountain environments are currently among the ecosystems least invaded by non-native species; however, mountains are increasingly under threat of non-native plant invasion. The slow pace of exotic plant invasions in mountain ecosystems is likely due to a combination of low anthropogenic disturbances, low propagule supply, and extreme/steep environmental gradients. The importance of any one of these factors is debated and likely ecosystem dependent. We evaluated the importance of various correlates of plant invasions in the Wallowa Mountain Range of northeastern Oregon and explored whether non-native species distributions differed from native species along an elevation gradient. Vascular plant communities were sampled in summer 2012 along three mountain roads. Transects (n = 20) were evenly stratified by elevation (~70 m intervals) along each road. Vascular plant species abundances and environmental parameters were measured. We used indicator species analysis to identify habitat affinities for non-native species. Plots were ordinated in species space, joint plots and non-parametric multiplicative regression were used to relate species and community variation to environmental variables. Non-native species richness decreased continuously with increasing elevation. In contrast, native species richness displayed a unimodal distribution with maximum richness occurring at mid–elevations. Species composition was strongly related to elevation and canopy openness. Overlays of trait and environmental factors onto non-metric multidimensional ordinations identified the montane-subalpine community transition and over-story canopy closure exceeding 60% as potential barriers to non-native species establishment. Unlike native species, non-native species showed little evidence for high-elevation or closed-canopy specialization. These data suggest that non-native plants currently found in the Wallowa Mountains are dependent on open canopies and disturbance for establishment in low and mid elevations. Current management objectives including restoration to more open canopies in dry Rocky Mountain forests, may increase immigration pressure of non-native plants from lower elevations into the montane and subalpine zones.     

Interaction of Species Traits and Environmental Disturbance Predicts Invasion Success of Aquatic Microorganisms

Factors such as increased mobility of humans, global trade and climate change are affecting the range of many species, and cause large-scale translocations of species beyond their native range. Many introduced species have a strong negative influence on the new local environment and lead to high economic costs. There is a strong interest to understand why some species are successful in invading new environments and others not. Most of our understanding and generalizations thereof, however, are based on studies of plants and animals, and little is known on invasion processes of microorganisms. We conducted a microcosm experiment to understand factors promoting the success of biological invasions of aquatic microorganisms. In a controlled lab experiment, protist and rotifer species originally isolated in North America invaded into a natural, field-collected community of microorganisms of European origin. To identify the importance of environmental disturbances on invasion success, we either repeatedly disturbed the local patches, or kept them as undisturbed controls. We measured both short-term establishment and long-term invasion success, and correlated it with species-specific life-history traits. We found that environmental disturbances significantly affected invasion success. Depending on the invading species’ identity, disturbances were either promoting or decreasing invasion success. The interaction between habitat disturbance and species identity was especially pronounced for long-term invasion success. Growth rate was the most important trait promoting invasion success, especially when the species invaded into a disturbed local community. We conclude that neither species traits nor environmental factors alone conclusively predict invasion success, but an integration of both of them is necessary.     

Pocket Gophers and the Invasion and Restoration of Native Bunchgrass Communities

More than 7 million hectares of California native plant communities are now dominated by exotic annual species, a biological invasion that has made native bunchgrass ecosystems in this region one of the most endangered ecosystems in North America. Many land use and environmental factors have contributed to the conversion of bunchgrass areas to annual grassland, but the role of gopher disturbance remains understudied. Here I report observational evidence that suggests gopher foraging is nonrandomly concentrated in the open spaces between clumps of bunchgrass and as a result may inhibit the recruitment of bunchgrass into these areas. Understanding patterns of direct gopher impact and coincident soil disturbance in bunchgrass versus annual grassland is important for successful restoration of bunchgrass habitats. While the prospect of excluding gophers is daunting, even short-term reductions in gopher populations would help to promote a restored community structure with a mature native bunchgrass and annual forb association.     

Non-native species in urban environments: patterns,processes, impacts and challenges

Although urban ecosystems are hotspots for biological invasions, the field of invasion science has given scant attention to invasion dynamics and the challenges facing managers in towns and cities. This paper provides an introduction to the growing challenges of understanding and managing invasive species in urban systems, and the context for a special issue of Biological Invasions, comprising 17 papers, that arose from a workshop on “Non-native species in urban environments: patterns, processes, impacts and challenges” held in Stellenbosch, South Africa, in November 2016. Contributions explore the following key questions: Are patterns and processes of urban invasions different from invasions in other contexts? Why is it important to manage non-native species in urban ecosystems? What are the special management needs in an urban context? How can we bridge the gaps between science, management, and policy with regards to biological invasions in urban ecosystems? The papers in this special issue show that patterns and processes of urban invasions differ in many ways from invasions in other contexts, and that managing invasive species in cities poses unique and increasingly complex challenges. Progress in urban invasion science requires further work to: (1) address key limitations that hinder our understanding of invasion dynamics in cities; (2) clarify whether fundamental concepts in the field of invasion science are appropriate for urban ecosystems; (3) integrate insights from invasion science with those from the burgeoning literature on the “Anthropocene biosphere”, novel ecosystems, social–ecological systems, human–wildlife conflicts, urban green infrastructure, urban planning and design, and ecosystem services/disservices.     

Invasion of exotic earthworms into ecosystems inhabited by native earthworms

The most conspicuous biological invasions in terrestrial ecosystems have been by exotic plants, insects and vertebrates. Invasions by exotic earthworms, although not as well studied, may be increasing with global commerce in agriculture, waste management and bioremediation. A number of cases has documented where invasive earthworms have caused significant changes in soil profiles, nutrient and organic matter dynamics, other soil organisms or plant communities. Most of these cases are in areas that have been disturbed (e.g., agricultural systems) or were previously devoid of earthworms (e.g., north of Pleistocene glacial margins). It is not clear that such effects are common in ecosystems inhabited by native earthworms, especially where soils are undisturbed. We explore the idea that indigenous earthworm fauna and/or characteristics of their native habitats may resist invasion by exotic earthworms and thereby reduce the impact of exotic species on soil processes. We review data and case studies from temperate and tropical regions to test this idea. Specifically, we address the following questions: Is disturbance a prerequisite to invasion by exotic earthworms? What are the mechanisms by which exotic earthworms may succeed or fail to invade habitats occupied by native earthworms? Potential mechanisms could include (1) intensity of propagule pressure (how frequently and at what densities have exotic species been introduced and has there been adequate time for proliferation?); (2) degree of habitat matching (once introduced, are exotic species faced with unsuitable habitat conditions, unavailable resources, or unsuited feeding strategies?); and (3) degree of biotic resistance (after introduction into an otherwise suitable habitat, are exotic species exposed to biological barriers such as predation or parasitism, “unfamiliar” microflora, or competition by resident native species?). Once established, do exotic species co-exist with native species, or are the natives eventually excluded? Do exotic species impact soil processes differently in the presence or absence of native species? We conclude that (1) exotic earthworms do invade ecosystems inhabited by indigenous earthworms, even in the absence of obvious disturbance; (2) competitive exclusion of native earthworms by exotic earthworms is not easily demonstrated and, in fact, co-existence of native and exotic species appears to be common, even if transient; and (3) resistance to exotic earthworm invasions, if it occurs, may be more a function of physical and chemical characteristics of a habitat than of biological interactions between native and exotic earthworms.     

Historical ecology of a biological invasion: the interplay of eutrophication and pollution determines time lags in establishment and detection

Human disturbance modifies selection regimes, depressing native species fitness and enabling the establishment of non-indigenous species with suitable traits. A major impediment to test the effect of disturbance on invasion success is the lack of long-term data on the history of invasions. Here, we overcome this problem and reconstruct the effect of disturbance on the invasion of the bivalve Anadara transversa from sediment cores in the Adriatic Sea. We show that (1) the onset of major eutrophication in the 1970s shifted communities towards species tolerating hypoxia, and (2) A. transversa was introduced in the 1970s but failed to reach reproductive size until the late 1990s because of metal contamination, resulting in an establishment and detection lag of ~25 years. Subfossil assemblages enabled us to (1) disentangle the distinct stages of invasion, (2) quantify time-lags and (3) finely reconstruct the interaction between environmental factors and the invasion process, showing that while disturbance does promote invasions, a synergism of multiple disturbances can shift selection regimes beyond tolerance limits and induce significant time lags in establishment. The quantification of these time lags enabled us to reject the hypothesis that aquaculture was an initial vector of introduction, making shipping the most probable source.     

Historical land use and present-day canopy thinning differentially affect the distribution and abundance of invasive and native ant species

Disturbance may play a key role in affecting animal invasions; less appreciated is that past and present disturbances might interact to affect invasion. For example, although large portions of forest ecosystems worldwide are jointly affected by a history of past agricultural land use as well as contemporary timber harvest, it is unclear whether these disturbances facilitate biological invasions. We conducted a large-scale experiment that coupled adjacent non-agricultural and post-agricultural sites and a factorial canopy-thinning manipulation to understand how past agricultural land use might interact with contemporary canopy thinning to affect the distribution (i.e., presence/absence of mounds) and abundance of a highly invasive ant species, Solenopsis invicta, and common native ant species, Dorymyrmex bureni. Mounds of S. invicta were more likely to be present in unthinned post-agricultural habitats than unthinned non-agricultural habitats, but this legacy effect disappeared with canopy thinning. In unthinned habitats, the presence of D. bureni mounds did not differ based on past land use. However, presence of D. bureni mounds was greater in thinned non-agricultural habitats than thinned post-agricultural habitats. Once present in an area, mound abundance was largely related to temperature near the ground for both species, and negatively related to soil compaction for D. bureni. Our results provide large-scale evidence that an understanding of anthropogenic events that occur decades before present may be essential for interpreting contemporary invasion dynamics and the distribution of some species, and that local contemporary habitat characteristics play a key role in determining ant abundance once an area is colonized.     

Conservation Implications of Invasion by Plant Hybridization

The increasing number of invasive exotic plant species in many regions and the continuing alteration of natural ecosystems by humans promote hybridization between previously allopatric species; among both native as well as between native and introduced species. We review the ecological factors and mechanisms that promote such hybridization events and their negative consequences on biological diversity. Plant invasions through hybridization may occur in four different ways: hybridization between native species, hybridization between an exotic species and a native congener, hybridization between two exotics and by the introduction and subsequent spread of hybrids. The main harmful genetic effect of such hybrids on native species is the loss of both genetic diversity and of locally adapted populations, such as rare and threatened species. The spread of aggressive hybrid taxa can reduce the growth of, or replace, native species. The main factor promoting the formation of hybrids is species dispersal promoted by humans. However, the success and spread of hybrids is increased by disturbance and fragmentation of habitats, thus overcoming natural crossing barriers, and range expansions due to human activity. There are differences in flowering, pollination and seed dispersal patterns between parental species and hybrids. Hybrid resistance to pathogens and herbivores may also enhance the success of hybrids. To predict the mechanisms and consequences of invasions mediated by hybridization, extensive data on hybrid ecology and biology are needed, as well as carefully designed field experiments focused on the comparative ecology of parental populations and hybrids.     

Plant invasions in the rivers of the Iberian Peninsula,south-western Europe: A review

Aquatic and riparian ecosystems are known to be highly vulnerable to invasive alien species (IAS), especially when subjected to human-induced disturbances. In the last three decades, we have witnessed a growing increase in plant invasions in Portugal and Spain (Iberian Peninsula, south-western Europe), with very detrimental economic, social and ecological effects. Some of these species, such as the giant reed (Arundo donax L.) and the water hyacinth (Eichhornia crassipes (Mart.) Solms-Laub.), number among the world's worst weeds. We present an appraisal of this invasive alien river flora and the most problematic aquatic weeds. We review various aspects of invasion ecology, including spatial and temporal patterns of invasion, species invasiveness, species traits of invasive weeds, and relationships between human disturbance in rivers and surrounding areas and invasibility, and contextualize them in overall state-of-the-art terms. We also acknowledge the use of IAS as bioindicators of the ecological quality of rivers, wetlands and riparian zones. Remote-sensing tools and Geographic Information Systems for detecting and monitoring IAS in Iberian rivers are presented.     

Dominance As An Overlooked Measure of Invader Success

Recent multi-habitat studies across a range of spatial scales have shown that species-rich habitats are often highly invasible by exotic species. The primary measures of invasion in these and other studies are invader richness and the absolute cover or biomass of invaders. We argue that the relative biomass or cover of invaders (dominance) is an important but overlooked measure of plant invasion. We re-analyzed data presented in five previous studies to evaluate whether exotic relative abundance is positively correlated with native richness. There were either no relationships or negative relationships between native richness and relative exotic cover calculated from three spatial scales (1, 1000 and 4000 m²). Thus while the original studies reported high exotic richness or absolute cover in habitats rich in native species, native richness did not predict the degree to which exotics had become dominant or abundant relative to natives. Absolute measures of exotic cover reported in the original studies underestimated relative exotic cover in habitats with low native species richness. High exotic dominance in areas of low native richness may indicate that exotic richness and dominance are controlled by different factors. We conclude that it is useful for researchers to measure both invader richness and invader dominance when trying to understand the environmental factors that are associated with plant invasions.     

A functional trait perspective on plant invasion

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 future 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.     

Rodent seed predation as a biotic filter influencing exotic plant abundance and distribution

Biotic resistance is commonly invoked to explain why many exotic plants fail to thrive in introduced ranges, but the role of seed predation as an invasion filter is understudied. Abiotic conditions may also influence plant populations and can interact with consumers to determine plant distributions, but how these factors jointly influence invasions is poorly understood. In central Argentina’s Caldenal savannas, we experimentally examined how seed predation and water availability influenced recruitment/establishment of nine exotic plant invaders over 2 years. We then explored how seed predation patterns related to invasion patterns. Excluding rodent seed predators dramatically increased seedling recruitment for eight of nine exotic species (by 100–300 % in most cases) and increased young/adult plant abundance for four species in one or both years. Adding water to ameliorate drought tended to increase seedling numbers for most species, but these trends were not significant. Vegetation surveys revealed that exotic plant richness was 50 % lower in matrix habitat compared with disturbed roadsides and that cover of the two most aggressive invaders, which were both strongly suppressed by seed predation, was 75–80 % lower in matrix than roadside habitats. Seed offerings indicated seed removal by rodents was 11 times greater in intact matrix habitat compared with roadsides. Rodent seed predation represents a significant source of biotic resistance to plant invasions. Ubiquitous disturbances such as road construction can disrupt this filter. The widely recognized role that disturbance plays in facilitating invasions, which is largely attributed solely to reduced plant competition, may also arise from disruption of top–down controls.     

Revegetation following Soil Disturbance and Invasion in a Californian Meadow: a 10-year History of Recovery

Disturbance is necessary for the regeneration of many native plant species, but can also facilitate biological invasions. As a result, disturbance can play complex roles in vulnerable habitats such as remnant Californian perennial grasslands. To investigate these conflicts, plots in a northern Californian coastal grassland were experimentally disturbed in the winter of 1990–1991; these plots differed in the area and intensity (depth) of the soil disturbance applied. When these plots were revisited after 10 growing seasons, patterns of revegetation differed significantly from those observed early in recolonization (0–3 years). At the earlier samplings, exotic annual grasses rapidly increased in most disturbance types. After 10 years, these exotic annuals had retreated from the depth experiment, which had recovered to a vegetation dominated by native perennials in all but the most severely disturbed plots. In contrast, although differences between control and disturbed plots also disappeared in the area experiment, the average abundance of aliens did not decline substantially relative to 1993 levels, especially in larger disturbances. Nonetheless, populations of aliens remained small compared to the peak populations in the depth experiment, probably reflecting wetter soils at the site used for the area experiment. These results differ from those of other recent studies of soil disturbance in coastal Californian ecosystems, which indicate disturbance may result in the permanent replacement of native perennial vegetation by dense populations of exotic annual grasses. This difference may reflect the high resilience of northern coastal grasslands as well as the scale of disturbances considered by different studies.     

植物外来种入侵及其对生态系统的影响

对植物外来种的入侵及生态系统的影响进行综述与分析,植物入侵多种因子的影响,可分为外因和内因两类,植物外来种对生态系统的影响主要体现在生产力,土壤营养,水分,干扰体制,群落的结构和动态等方面,在管理外来种时,需对外来种的特性和影响因子进行系统的观察研究,采用机械法,化学方法和生物控制法等综合办法控制植物的入侵,引进植物引来种时,要对引进种的行为特性进行了调查研究,注意其安全性。     

Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

Riparian zones are formed by interactions between fluvio-geomorphological processes, such as sediment deposition, and biota, such as vegetation. Establishment of invasive alien plant (IAP) species along rivers may influence vegetation dynamics, evidenced as higher seasonal or inter-annual fluctuations in native plant diversity when IAP cover is high. This could impact the overall functioning of riparian ecosystems. Conversely, fine sediment deposited in riparian zones after floods may replenish propagule banks, thus supporting recruitment of native species. The interactive effects of invasion and fine sediment deposition have hitherto, however, been ignored. Vegetation surveys across rivers varying in flow regime were carried out over 2 years to assess changes in community composition and diversity. Artificial turf mats were used to quantify over-winter sediment deposition. The viable propagule bank in soil and freshly deposited sediment was then quantified by germination trials. Structural Equation Models were used to assess causal pathways between environmental variables, IAPs and native vegetation. Greater variation in flow increased the cover of IAPs along riverbanks. An increased in high flow events and sediment deposition were positively associated with the diversity of propagules deposited. However, greater diversity of propagules did not result in a more diverse plant community at invaded sites, as greater cover of IAPs in summer reduced native plant diversity. Seasonal turnover in the above-ground vegetation was also accentuated at previously invaded sites, suggesting that a legacy of increased competition in previous years, not recent sediment deposition, drives above-ground vegetation structure at invaded sites. The interaction between fluvial disturbance via sediment deposition and invasion pressure is of growing importance in the management of riparian habitats. Our results suggest that invasion can uncouple the processes that contribute to resilience in dynamic habitats making already invaded habitats vulnerable to further invasions.     

Propagule pressure and an invasion syndrome determine invasion success in a plant community model

The success of species invasions depends on multiple factors, including propagule pressure, disturbance, productivity, and the traits of native and non‐native species. While the importance of many of these determinants has already been investigated in relative isolation, they are rarely studied in combination. Here, we address this shortcoming by exploring the effect of the above‐listed factors on the success of invasions using an individual‐based mechanistic model. This approach enables us to explicitly control environmental factors (temperature as surrogate for productivity, disturbance, and propagule pressure) as well as to monitor whole‐community trait distributions of environmental adaptation, mass, and dispersal abilities. We simulated introductions of plant individuals to an oceanic island to assess which factors and species traits contribute to invasion success. We found that the most influential factors were higher propagule pressure and a particular set of traits. This invasion trait syndrome was characterized by a relative similarity in functional traits of invasive to native species, while invasive species had on average higher environmental adaptation, higher body mass, and increased dispersal distances, that is, had greater competitive and dispersive abilities. Our results highlight the importance in management practice of reducing the import of alien species, especially those that display this trait syndrome and come from similar habitats as those being managed.     

What drives invasibility? A multi‐model inference test and spatial modelling of alien plant species richness patterns in northern Portugal

Understanding and predicting biological invasions can focus either on traits that favour species invasiveness or on features of the receiving communities, habitats or landscapes that promote their invasibility. Here, we address invasibility at the regional scale, testing whether some habitats and landscapes are more invasible than others by fitting models that relate alien plant species richness to various environmental predictors. We use a multi‐model information‐theoretic approach to assess invasibility by modelling spatial and ecological patterns of alien invasion in landscape mosaics, and by testing competing hypotheses of environmental factors that may control invasibility. Because invasibility may be mediated by particular characteristics of invasiveness, we classified alien species according to their C‐S‐R plant strategies. We illustrate this approach with a set of 86 alien species in northern Portugal. We first focus on predictors influencing species richness and expressing invasibility, and then evaluate whether distinct plant strategies respond to the same or different groups of environmental predictors. We confirmed climate as a primary determinant of alien invasions, and as a primary environmental gradient determining landscape invasibility. The effects of secondary gradients were detected only when the area was sub‐sampled according to predictions based on the primary gradient. Then, multiple predictor types influenced patterns of alien species richness, with some types (landscape composition, topography and fire regime) prevailing over others. Alien species richness responded most strongly to extreme land management regimes, suggesting that intermediate disturbance induces biotic resistance by favouring native species richness. Land‐use intensification facilitated alien invasion, whereas conservation areas hosted few invaders, highlighting the importance of ecosystem stability in preventing invasions. Plants with different strategies exhibited different responses to environmental gradients, particularly when the variations of the primary gradient were narrowed by sub‐sampling. Such differential responses of plant strategies suggest using distinct control and eradication approaches for different areas and alien plant groups.     

Landscape context modulates alien plant invasion in Mediterranean forest edges

Natural habitats in human-altered landscapes are especially vulnerable to biological invasions, especially in their edges. We aim to understand the influence of landscape and local characteristics on biological invasions by exploring the level of plant invasion and alien species traits in forest edges in highly urbanized landscapes. We identified all plant species in 73 paired plots in the edge and 50 m towards the interior of the forest. We explored the association between alien species richness and similarity in species composition between edge and interior plots with landscape and local variables, using generalized linear models and variance partitioning techniques. Then, we performed Fourth-corner analyses to explore the association between alien plant traits and local and landscape variables. In contrast to native species richness, alien species richness was more affected by the surrounding landscape than by the local characteristics of the edge. Road proximity was positively associated with alien species richness and proportion and was its most important correlate, whereas disturbance was negatively associated with native species richness and was its most influential factor. Alien plant traits were also primarily associated with landscape characteristics. For instance, species of Mediterranean origin and introduced for agriculture were associated with higher agriculture use in the landscape. Our findings suggest that risk analyses of habitat vulnerability to invasion must consider the landscape context in order to successfully predict highly invaded areas and identify potentially successful invaders.