Search

Aim: Tree invasions are a threat to biodiversity conservation, and although it is hard to predict the future spread of invasive tree species, there are tools available which could allow some estimations. The magnitude of spatial spread (a proxy of invasiveness) can be predicted from species climatic requirement (climatic niche) and can be represented by species distribution models (SDMs). We aimed to assess whether Acacia dealbata conserves its niche in the new environment of south‐central Chile, and also, to estimate the invasive stage of the species. Location: South‐central area of Chile, between the O'Higgins (34°0″0′S) and Aysen Regions (47°0″0′S). Methods: We used a combination of global, native, and regional data to improve the estimation of the potential distribution of A. dealbata, which has been considered one of the most invasive species of the genus, being registered in at least 34 countries in all the Continents. Results: Our results show that A. dealbata does not conserve its niche in the study area, invading areas with climatic conditions different from those of the native range. It is also not at equilibrium with the environment. According to the global versus regional SDM comparisons, populations present in south‐central Chile present different invasion stages. There are some stable populations, but there are other populations colonizing new areas, occupying unsuitable habitats and some of them are adapting to new climatic conditions. Climatic factors, such as precipitation seasonality, could be acting behind the expansion to new environments, and biotic factors or dispersal limitations could be preventing the species to colonize suitable areas. Main conclusions: The invasion process of A. dealbata is far from stabilizing, and management options should focus on prevention, avoiding, for example, the introduction of the species to Patagonia where the species has not spread yet. More research is needed to complement our results and enhance the development of effective management strategies. [ABSTRACT FROM AUTHOR]

The aim was to assess patterns of plant diversity in response to elevation and disturbance in a tropical mountain. The study area was located in north-central portion of the Eastern Cordillera of the Ecuadorian Andes, on a road from 1,150 m a.s.l. (Osayacu) to 4,000 (Papallacta). Along a mountain road spanning a wide altitudinal gradient, at 20 elevations we sampled three plots: one at the roadside and two perpendicular to the roadside. The relationship between elevation and species richness was assessed using linear and quadratic regressions, the effect of disturbance on species richness was determined by ANCOVA and a t test with parameters obtained from quadratic equations. Similarity of species composition among the roadside and sites distant was evaluated with the Chao-Jaccard and classic Jaccard similarity indices, the distribution of non-native species according to their origin were analyzed with linear and quadratic regression. The native species showed a linearly monotonic decrease with elevation, whereas non-natives showed a quadratic distribution. Disturbed areas had the greatest number of non-native species and lower native species richness, showing also a high floristic similarity; less disturbed areas showed the opposite. The non-native species of temperate origin were more numerous and showed unimodal elevational distribution, while species of tropical origin were few and decreased linearly with elevation. We conclude that in a tropical highland mountain range, native and non-native plant species respond differently to elevation: native species exhibit a monotonically linear decrease, and non-native species show a unimodal trend. Disturbance positively affects non-native species showing higher richness and fewer species turnover. In addition, the non-native species are located along of the elevational gradient in relation to their biogeographic origin. [ABSTRACT FROM AUTHOR]

Questions Many studies report a decrease of native species richness in communities after plant invasion by exotic taxa, but the implications of species losses on community functional structure and ecosystem processes have been less explored. The questions addressed are: (1) what are the impacts of invasive plant taxa on the functional structure of the recipient community; and (2) are there links between such functional structure and ecosystem properties representing key ecosystem processes? Location Costal habitats of Mallorca and Menorca, Balearic Islands, Spain. Methods In paired invaded and non-invaded plots, species frequencies and ecosystem properties related to biogeochemical cycles (soil C and N content, soil moisture and decomposition rate) were assessed. For every native species we obtained values of several functional traits (plant height, woodiness, N fixation and evergreenness). Then we calculated indices of community functional structure (community-weighted means for each trait; functional diversity: richness, evenness, divergence and dispersion; and functional redundancy) and compared them between paired invaded and non-invaded plots. The relationship with ecosystem properties was assessed using GLM. Results The spectra of trait distribution changed in the invaded assemblages towards a higher frequency of woodiness and evergreenness. Invaded communities showed decreased species richness, and lower functional richness, divergence, dispersion and redundancy. In contrast, ecosystem properties were scarcely sensitive to invasion. Functional redundancy was negatively related to soil N of invaded plots and soil moisture in the dry season, which suggests higher depletion of soil resources when several species share the same combination of trait values. Conclusions Carpobrotus invasion led to a functional homogenization within communities, which probably reduces their resilience. The functional structure of the community was more responsive to invasion than the ecosystem properties. The weak relationship between functional indices and ecosystem properties suggests that they may respond to invasion at different rates. [ABSTRACT FROM AUTHOR]

Understanding biological invasions patterns and mechanisms is highly needed for forecasting and managing these processes and their negative impacts. At small scales, ecological processes driving plant invasions are expected to produce a spatially explicit pattern driven by propagule pressure and local ground heterogeneity. Our aim was to determine the interplay between the intensity of seed rain, using distance to a mature plantation as a proxy, and microsite heterogeneity in the spreading of Pinus contorta in the treeless Patagonian steppe. Three one-hectare plots were located under different degrees of P. contorta invasion (Coyhaique Alto, 45° 30′S and 71° 42′W). We fitted three types of inhomogeneous Poisson models to each pine plot in an attempt for describing the observed pattern as accurately as possible: the 'dispersal' models, 'local ground heterogeneity' models, and 'combined' models, using both types of covariates. To include the temporal axis in the invasion process, we analyzed both the pattern of young and old recruits and also of all recruits together. As hypothesized, the spatial patterns of recruited pines showed coarse scale heterogeneity. Early pine invasion spatial patterns in our Patagonian steppe site is not different from expectations of inhomogeneous Poisson processes taking into consideration a linear and negative dependency of pine recruit intensity on the distance to afforestations. Models including ground-cover predictors were able to describe the point pattern process only in a couple of cases but never better than dispersal models. This finding concurs with the idea that early invasions depend more on seed pressure than on the biotic and abiotic relationships seed and seedlings establish at the microsite scale. Our results show that without a timely and active management, P. contorta will invade the Patagonian steppe independently of the local ground-cover conditions. [ABSTRACT FROM AUTHOR]

Aim: Analysis of the shifts in the climatic space for invasive species between native and introduced areas is a powerful tool for understanding their distribution patterns and the factors influencing their spread into new areas. In this study, we explored the shift in climatic distribution between ranges for invasive woody legumes and how the functional traits of these species are associated with their climatic distribution. Location: Global. Time period: Present. Major taxa studied: Invasive woody legumes. Methods: We evaluated the global patterns of occupation of the climatic space for 107 invasive woody legumes in their native and introduced distribution ranges, in addition to the differences in six key functional traits. We used the trait probability density (TPD) function to estimate species probabilistic niches. We then classified species into four groups according to the climatic differences between the distribution ranges. The comparisons between the climate shift groups and the distribution ranges were evaluated with mixed linear models. Additionally, we compared the functional traits between species groups using ANOVA. Results: Overall, we found that invasive species exhibited low to moderate climatic overlap between their native and introduced distribution ranges. However, climatic conditions in the introduced range were different from those in the native range. Invasive legumes were clustered in four groups (conserved, expansion, dissociation and unfilling), with dissociation between climate niches being the most common one. In terms of functional traits, the most relevant finding was that the species in the expansion group had larger leaves than species in the dissociation group. Main conclusions: Our results showed no consistent climatic range shift across all invasive woody legume species from their native to their introduced distribution. However, some species tended to invade climatic conditions that were different from those in their native range, supporting the hypothesis that some invasive species are able to adapt to novel environmental conditions. Finally, functional traits might be a good predictor of how these species modify their climatic spaces. [ABSTRACT FROM AUTHOR]

Aim Taxonomic comparisons of alien floras across climatically similar regions have been proposed as a powerful approach for increasing our understanding of plant invasions across scales. However, detailed comparisons between the alien biotas of climatically similar regions are scarce. This study aims to compare the taxonomic patterns of alien species richness in mediterranean-type climate areas of central Chile and California, in order to better understand how climatically similar regions converge or diverge in terms of their alien flora. Location Central Chile and California, United States. Methods We compared the alien floras of the state of California in the United States and central Chile, considering within-region variation and taxonomic composition up to the species level. To test for within-region variation, administrative units and counties were grouped within seven latitudinal bands for each region. We tested for differences in the relative contributions of the various origins of the naturalized species to each region. We used a family naturalization index to establish which families had relatively higher numbers of naturalized species in each region. We evaluated the similarity, using cluster analyses with Jaccard’s similarity index, of alien taxa between regions and latitudinal bands using presence–absence matrices at the species, genus and family levels. We used principal components analysis to determine the presence of a compositional gradient including all latitudinal bands. Results We recorded 1212 alien plant species in California and 593 in central Chile, of which 491 are shared between the two regions. These figures include 25 species that are native to California and 37 that are native to Chile. A comparison between the alien floras of central Chile and California reveals three major trends: (1) higher naturalized species diversity for California than for Chile, at all taxonomic levels; (2) differences in the proportion of species according to origin, with America, Africa, Asia and Australia providing a larger number of species in California than in Chile; (3) segregation between regions in terms of taxonomic composition of their alien flora, and a rather weak differentiation within regions; and (4) a trend towards higher similarity between the alien floras of latitudinal bands associated with higher levels of human disturbances. Main conclusions The alien floras of central Chile and California are significantly different, but this difference diminishes in highly disturbed areas. Thus, the current high levels of species movement caused by globalization, together with increasing levels of anthropogenic disturbances, should reduce the differentiation of the alien floras in these regions, increasing overall biotic homogenization. [ABSTRACT FROM AUTHOR]

Comparisons between regions with similar climates have traditionally helped to tackle big questions in evolutionary ecology and historical biogeography. We claim that plant invasion ecology can benefit greatly from further and better comparisons at regional and global scales. In this note we discuss the potentials and limitations of comparing climatically analogous regions to provide novel insights into the mechanisms of alien plant invasions. Comparisons among areas with similar climates have the advantage that some features of the abiotic environment are within a narrower range of variation, enabling the researcher to focus on the effects of propagule pressure, microenvironmental differences and, more importantly, the biotic environment in the invasion process. However, there are two major issues that limit the strengths of such comparisons: (1) non-standardized databases of alien species, especially in less developed countries; and (2) deficient sampling designs. We argue that we should take advantage of comparative studies of alien plant invasions across regions with similar climates not only to obtain useful insights about invasions, but to search for generalities beyond invasion ecology that contribute to our knowledge of natural systems. [ABSTRACT FROM AUTHOR]

Alien plant species are a growing concern in protected areas, yet little information is available on the role of roads as corridors for alien species and the effects of elevation, land use, and landscape context in these invasions. These concerns are of particular interest in temperate zones of South America, where protected areas have high concentrations of endemic species. We studied roadside alien plant communities and forest-road edges in Villarrica and Huerquehue national parks in the Andean portion of south-central Chile. We sampled alien species and their abundance along 21 km of roads inside parks and 22 km outside parks, using 500-m roadside transects. We also sampled plant species and recorded their abundance in 15 transects located perpendicular to forest-road edges in four forest types. Of the 66 alien species encountered along roadsides, 61 were present outside parks and 39 inside parks. Elevation and alien species richness along roadsides were significantly and negatively correlated (R 2=− 0.56, p < 0.001). Elevation, land use, and their interaction explained 74% of the variation in alien species richness along roadsides (p < 0.001). Transects located in pasture or disturbed secondary forests had significantly more alien species. We found no significant edge effect on native and alien species richness in any forest type. Few alien species have percolated into forest interiors. Native and alien diversity in edge plots were not related. Almost half the alien species belonged to three families and 85% were native to Eurasia. Our results suggest that alien species are moving into parks along road corridors and that elevation and land use of the matrix influence these invasion processes. Our findings corroborate the importance of early detection and control of invasive species in protected areas and highlight the importance of considering surrounding matrix land use in developing conservation strategies for reserves. [ABSTRACT FROM AUTHOR]

Naturally treeless ecosystems are being replaced by native and non‐native trees worldwide, often through deliberate afforestation using forestry tree species. By introducing species having novel traits, such as relatively rapid growth, many afforestation efforts also produce numerous changes in ecosystems, at the landscape scale. Trees are considered critical for climate change mitigation; indeed, many current carbon sequestration strategies rely on trees. Planting trees or allowing trees to naturally colonize through range expansions can be seen as an ideal way to increase atmospheric carbon capture. For example, a snapshot approach may show that introducing trees into treeless ecosystems enhances aboveground accumulation of carbon, helping increase ecosystem carbon storage. However, considering other impacts such as reductions in soil carbon or albedo and increased fire severity (through increases in fuel loads and connectivity) reduces the effectiveness of afforestation strategies for climate change amelioration. Additional negative impacts of afforestation are also likely, such as the reduction of native biodiversity and productivity, substantial water yield losses, and changes in nutrient cycles, which can exacerbate other global change drivers. Further, tree invasions originating from afforestation can exacerbate these negative impacts. Synthesis. This review highlights that the positive and negative impacts of planting trees in naturally treeless ecosystems as a strategy to mitigate climate change are idiosyncratic, depending on the location where trees are introduced, the time period trees are allowed to grow, and risks of spread and impacts associated with specific tree species. Although planting trees can potentially be a tool to fight climate change, a greater consideration of their impacts is required to minimize the unexpected negative consequences of afforestation efforts. [ABSTRACT FROM AUTHOR]

Aim: To compare genetic diversity and structure between Acacia dealbata populations sampled across the species' native range in Australia and from its non‐native ranges in Chile, Madagascar, New Zealand, Portugal, La Réunion island, South Africa and the United States, and to investigate the most likely introduction scenarios to non‐native ranges. Location: Global. Taxon: Acacia dealbata, Fabaceae. Methods: Our dataset comprised 1615 samples representing 92 populations sampled in the species' native and non‐native ranges. We employed a combination of genetic fingerprinting (microsatellite markers) and genetic modelling approaches. We calculated genetic diversity for each population and tested for genetic isolation by distance within each range. A combination of Bayesian assignment tests and multivariate ordination was applied to identify genetic structure among populations. Approximate Bayesian Computation (ABC) analyses were conducted to test different competing introduction scenarios for each non‐native range. Results: The majority of the species' non‐native ranges was characterized by high genetic diversity and low levels of genetic structure. With regard to introduction histories, however, our results supported different introduction scenarios for different non‐native ranges. We did not find strong support for any of tested introduction scenarios for populations in Chile and Madagascar, but these likely originated from multiple introductions followed by admixture. Populations in New Zealand and La Réunion most likely originated directly from Tasmania, possibly through multiple introductions. Similar to previous findings for South African populations, no clear introduction history could be identified for populations in Portugal and the United States. Main conclusions: Our study shows that global introductions of A. dealbata were complex and one scenario does not fit the invasion history of the species in different regions. We discuss how this complexity needs to be considered when formulating strategies for the effective management of the species. Future research needs to help bridge persisting knowledge gaps are discussed. [ABSTRACT FROM AUTHOR]

Aim: Climate change is expected to impact mountain biodiversity by shifting species ranges and the biomes they shape. The extent and regional variation in these impacts are still poorly understood, particularly in the highly biodiverse Andes. Regional syntheses of climate change impacts on vegetation are pivotal to identify and guide research priorities. Here we review current data, knowledge and uncertainties in past, present and future climate change impacts on vegetation in the Andes. Location: Andes. Taxon: Plants. Methods: We (i) conducted a literature review on Andean vegetation responses to past and contemporary climatic change, (ii) analysed future climate projections for different elevations and slope orientations at 19 Andean locations using an ensemble of model outputs from the Coupled Model Intercomparison Project 5, and (iii) calculated changes in the suitable climate envelope area of Andean biomes and compared these results to studies that used species distribution models. Results: Future climatic changes (2040–2070) are projected to be stronger at high‐elevation areas in the tropical Andes (up to 4°C under RCP 8.5), while in the temperate Andes temperature increases are projected to be up to 2°C. Under this worst‐case scenario, temperate deciduous forests and the grasslands/steppes from the Central and Southern Andes are predicted to show the greatest losses of suitable climatic space (30% and 17%–23%, respectively). The high vulnerability of these biomes contrasts with the low attention from researchers modelling Andean species distributions. Critical knowledge gaps include a lack of an Andean wide plant checklist, insufficient density of weather stations at high‐elevation areas, a lack of high‐resolution climatologies that accommodates the Andes' complex topography and climatic processes, insufficient data to model demographic and ecological processes, and low use of palaeo data for distribution modelling. Main conclusions: Climate change is likely to profoundly affect the extent and composition of Andean biomes. Temperate Andean biomes in particular are susceptible to substantial area contractions. There are, however, considerable challenges and uncertainties in modelling species and biome responses and a pressing need for a region‐wide approach to address knowledge gaps and improve understanding and monitoring of climate change impacts in these globally important biomes. [ABSTRACT FROM AUTHOR]

Aim To determine whether one of the most invasive pine species introduced to the Southern Hemisphere, Pinus contorta, has changed plant species richness, composition, diversity, and litter depth where it has invaded into native open forest, shrub steppe and grassland communities and to assess whether changes were similar in its native and introduced ranges. Location Río Negro Province, Argentina; Aysén and Araucanía Regions, Chile; Greater Yellowstone Ecosystem, USA. Methods We measured changes in plant species richness, species composition and cover, diversity, and litter depth associated with increasing P. contorta tree cover along the invasion front at three sites in the introduced range (Argentina and Chile) and one in the native range (Montana, USA). Results Plant species richness and cover generally declined with increasing P. contorta canopy cover, at similar rates in both the introduced and native ranges. However, plant cover was not affected by P. contorta in a forested setting in the introduced range. P. contorta invasion explained more of the decline in species richness in the introduced than native range. Native species composition changed more strongly across the invasion gradient in the introduced than native range. Litter depth increased more rapidly with P. contorta cover in the native than introduced range. Main conclusions Our results highlight the potential of pines to alter plant communities whether encroaching from forests in the native range or from plantations in the introduced range. Species richness and plant cover declined in both settings; however, individual species abundance and species composition were more impacted in the introduced range than in the native range. We suggest that invading trees have a greater capacity to cause ecological impacts in their introduced than in their native range, particularly where they represent a novel life-form. [ABSTRACT FROM AUTHOR]

Aim To determine biotic and abiotic controls on pine invasion globally within six ecoregions that include both introduced and native ranges. Locations Río Negro province, Argentina; Aysén and Araucanía regions, Chile; South Island (two ecoregions), New Zealand; Greater Yellowstone ecosystem, USA. Methods We quantified tree abundance and size across invasion fronts of the widespread invasive tree species Pinus contorta at each of the nine sites, encompassing both the native and introduced range. We also determined the relative importance of propagule pressure, abiotic characteristics and biotic factors for invasion success. Finally, key plant population metrics such as individual tree growth rates and reproductive effort were compared between native and introduced ranges. Results Pinus contorta density decreased with increasing distance from source population in all cases, but the importance and shape of this relationship differed among sites due, primarily to biotic factors. For example, areas dominated by native southern beech forest (Fuscospora cliffortioides or Nothofagus spp.) were not invaded, and this biotic resistance was not overcome by high propagule pressure. In contrast, shrublands were more highly invaded than grasslands, contradicting previous generalizations about pine invasions. Pinus contorta growth was faster, age to maturity was earlier and reproductive effort was higher in the introduced ranges compared with the native range, suggesting a demographic shift towards more rapid population growth in introduced regions. Climatic differences between the ranges may explain, at least in part, the observed pattern. Main conclusions We demonstrate that although biological invasions are driven by propagule pressure across different ecoregions, these processes interact strongly with biotic factors. Intriguingly, our results suggest that propagule pressure may become less important than biotic interactions as invasions proceed. Multi-region studies including both the native and introduced ranges provide unparalleled opportunities for understanding how these interactions change among regions as invasions proceed. [ABSTRACT FROM AUTHOR]

Like all obligately ectomycorrhizal plants, pines require ectomycorrhizal fungal symbionts to complete their life cycle. Pines introduced into regions far from their native range are typically incompatible with local ectomycorrhizal fungi, and, when they invade, coinvade with fungi from their native range. While the identities and distributions of coinvasive fungal symbionts of pine invasions are poorly known, communities that have been studied are notably depauperate. However, it is not yet clear whether any number of fungal coinvaders is able to support a Pinaceae invasion, or whether very depauperate communities are unable to invade. Here, we ask whether there is evidence for a minimum species richness of fungal symbionts necessary to support a pine/ectomycorrhizal fungus coinvasion. We sampled a Pinus contorta invasion front near Coyhaique, Chile, using molecular barcoding to identify ectomycorrhizal fungi. We report that the site has a total richness of four species, and that many invasive trees appear to be supported by only a single ectomycorrhizal fungus, Suillus luteus. We conclude that a single ectomycorrhizal (ECM) fungus can suffice to enable a pine invasion. [ABSTRACT FROM AUTHOR]

Climate change and other global change drivers threaten plant diversity in mountains worldwide. A widely documented response to such environmental modifications is for plant species to change their elevational ranges. Range shifts are often idiosyncratic and difficult to generalize, partly due to variation in sampling methods. There is thus a need for a standardized monitoring strategy that can be applied across mountain regions to assess distribution changes and community turnover of native and non‐native plant species over space and time. Here, we present a conceptually intuitive and standardized protocol developed by the Mountain Invasion Research Network (MIREN) to systematically quantify global patterns of native and non‐native species distributions along elevation gradients and shifts arising from interactive effects of climate change and human disturbance. Usually repeated every five years, surveys consist of 20 sample sites located at equal elevation increments along three replicate roads per sampling region. At each site, three plots extend from the side of a mountain road into surrounding natural vegetation. The protocol has been successfully used in 18 regions worldwide from 2007 to present. Analyses of one point in time already generated some salient results, and revealed region‐specific elevational patterns of native plant species richness, but a globally consistent elevational decline in non‐native species richness. Non‐native plants were also more abundant directly adjacent to road edges, suggesting that disturbed roadsides serve as a vector for invasions into mountains. From the upcoming analyses of time series, even more exciting results can be expected, especially about range shifts. Implementing the protocol in more mountain regions globally would help to generate a more complete picture of how global change alters species distributions. This would inform conservation policy in mountain ecosystems, where some conservation policies remain poorly implemented. [ABSTRACT FROM AUTHOR]

Summary: The success of invasive plants is influenced by many interacting factors, but evaluating multiple possible mechanisms of invasion success and elucidating the relative importance of abiotic and biotic drivers is challenging, and therefore rarely achieved.We used live, sterile or inoculated soil from different soil origins (native range and introduced range plantation; and invaded plots spanning three different countries) in a fully factorial design to simultaneously examine the influence of soil origin and soil abiotic and biotic factors on the growth of invasive Pinus contorta.Our results displayed significant context dependency in that certain soil abiotic conditions in the introduced ranges (soil nitrogen, phosphorus or carbon content) influenced responses to inoculation treatments.Our findings do not support the enemy release hypothesis or the enhanced mutualism hypothesis, as biota from native and plantation ranges promoted growth similarly. Instead, our results support the missed mutualism hypothesis, as biota from invasive ranges were the least beneficial for seedling growth. Our study provides a novel perspective on how variation in soil abiotic factors can influence plant–soil feedbacks for an invasive tree across broad biogeographical contexts. [ABSTRACT FROM AUTHOR]

The significant portion of global terrestrial biodiversity harboured in the mountains is under increasing threat from various anthropogenic impacts. Protecting fragile mountain ecosystems requires understanding how these human disturbances affect biodiversity. As roads and railways are extended further into mountain ecosystems, understanding the long‐term impacts of this infrastructure on community composition and diversity gains urgency.We used railway corridors constructed across the mountainous landscapes of the Kashmir Himalaya from 1994 to 2013 to study the effects of anthropogenic disturbance on species distributions and community dynamics. In 2014 and 2017, we collected vegetation data along 31 T‐shaped transects laid perpendicular to the railway line, adopting the MIREN (Mountain Invasion Research Network) road survey methodology.Plant communities shifted significantly from 2014 to 2017, potentially because of an ongoing species redistribution after railway construction, driven mainly by declines in both native and non‐native species richness, and an increasing abundance of a few non‐native species, especially in areas away from the railway track.These patterns indicate an advancing succession, where initially—rare—pioneer species are replaced by increasingly dominant and often non‐native competitors, and potentially suggest a trend towards delayed local extinctions after the disturbance event. Native and non‐native species richness was negatively correlated with elevation, but that relationship diminished over time, with the abundance of non‐natives significantly increasing at higher elevations.Synthesis and applications. Transport corridors seem to facilitate the spread of non‐native species to higher elevations, which has serious implications considering the warming mountain tops. Our results indicate that the plant communities next to railways do not reach equilibrium quickly after a disturbance. More than 10 years after railway establishment within Kashmir Himalaya, succession continued, and signs pointed towards a landscape increasingly dominated by non‐native species. Our study indicates that the single disturbance event associated with constructing railway in this Himalayan region had large and long‐lasting effects on plant communities at and around this transport corridor and suggests the need for a long‐term region‐wide coordinated monitoring and management program. [ABSTRACT FROM AUTHOR]

Article impact statement: In an era of profound biodiversity crisis, invasion costs, invader impacts, and human agency should not be dismissed. [ABSTRACT FROM AUTHOR]

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

Understanding the likely future impacts of biological invasions is crucial yet highly challenging given the multiple relevant environmental, socio‐economic and societal contexts and drivers. In the absence of quantitative models, methods based on expert knowledge are the best option for assessing future invasion trajectories. Here, we present an expert assessment of the drivers of potential alien species impacts under contrasting scenarios and socioecological contexts through the mid‐21st century. Based on responses from 36 experts in biological invasions, moderate (20%–30%) increases in invasions, compared to the current conditions, are expected to cause major impacts on biodiversity in most socioecological contexts. Three main drivers of biological invasions—transport, climate change and socio‐economic change—were predicted to significantly affect future impacts of alien species on biodiversity even under a best‐case scenario. Other drivers (e.g. human demography and migration in tropical and subtropical regions) were also of high importance in specific global contexts (e.g. for individual taxonomic groups or biomes). We show that some best‐case scenarios can substantially reduce potential future impacts of biological invasions. However, rapid and comprehensive actions are necessary to use this potential and achieve the goals of the Post‐2020 Framework of the Convention on Biological Diversity. [ABSTRACT FROM AUTHOR]

Aim: Although species distribution models (SDMs) traditionally link species occurrences to free‐air temperature data at coarse spatio‐temporal resolution, the distribution of organisms might instead be driven by temperatures more proximal to their habitats. Several solutions are currently available, such as downscaled or interpolated coarse‐grained free‐air temperatures, satellite‐measured land surface temperatures (LST) or in‐situ‐measured soil temperatures. A comprehensive comparison of temperature data sources and their performance in SDMs is, however, currently lacking. Location: Northern Scandinavia. Time period: 1970–2017. Major taxa studied: Higher plants. Methods: We evaluated different sources of temperature data (WorldClim, CHELSA, MODIS, E‐OBS, topoclimate and soil temperature from miniature data loggers), differing in spatial resolution (from 1″ to 0.1°), measurement focus (free‐air, ground‐surface or soil temperature) and temporal extent (year‐long versus long‐term averages), and used them to fit SDMs for 50 plant species with different growth forms in a high‐latitudinal mountain region. Results: Differences between these temperature data sources originating from measurement focus and temporal extent overshadow the effects of temporal climatic differences and spatio‐temporal resolution, with elevational lapse rates ranging from −0.6°C per 100 m for long‐term free‐air temperature data to −0.2°C per 100 m for in‐situ soil temperatures. Most importantly, we found that the performance of the temperature data in SDMs depended on the growth forms of species. The use of in‐situ soil temperatures improved the explanatory power of our SDMs (R2 on average +16%), especially for forbs and graminoids (R2 +24 and +21% on average, respectively) compared with the other data sources. Main conclusions: We suggest that future studies using SDMs should use the temperature dataset that best reflects the ecology of the species, rather than automatically using coarse‐grained data from WorldClim or CHELSA. [ABSTRACT FROM AUTHOR]

Invasive plant impacts vary widely across introduced ranges. We tested the hypothesis that differences in the eco‐evolutionary experience of native communities with the invader correspond with the impacts of invasive species on native vegetation, with impacts increasing with ecological novelty. We compared plant species richness and composition beneath Pinus contorta to that in adjacent vegetation and other P. contorta stands across a network of sites in its native (Canada and USA) and non‐native (Argentina, Chile, Finland, New Zealand, Scotland, Sweden) ranges. At sites in North America and Europe, within the natural distribution of the genus Pinus, P. contorta was not associated with decreases in diversity. In the Southern Hemisphere, where there are no native Pinaceae, plant communities beneath P. contorta were less diverse than in other regions and compared to uninvaded native vegetation. Effects on native vegetation were particularly pronounced where P. contorta was a more novel life form and exhibited higher growth rates. Our results support the hypothesis that the eco‐evolutionary experience of the native vegetation, and thus the novelty of the invader, determines the magnitude of invader impacts on native communities. Understanding the eco‐evolutionary context of invasions will help to better understand and predict where invasion impacts will be greatest and to prioritize invasive species management. [ABSTRACT FROM AUTHOR]

Alpine environments are currently relatively free from non‐native plant species, although their presence and abundance have recently been on the rise. It is however still unclear whether the observed low invasion levels in these areas are due to an inherent resistance of the alpine zone to invasions or whether an exponential increase in invasion is just a matter of time. Using a seed‐addition experiment on north‐ and south‐facing slopes (cf. microclimatic gradient) on two mountains in subarctic Sweden, we tested the establishment of six non‐native species at an elevation above their current distribution limits and under experimentally enhanced anthropogenic pressures (disturbance, added nutrients and increased propagule pressure). We found a large microclimatic variability in cumulative growing degree days (GDD) (range = 500.77°C, SD = 120.70°C) due to both physiographic (e.g. aspect) and biophysical (e.g. vegetation cover) features, the latter being altered by the experimental disturbance. Non‐native species establishment and biomass production were positively correlated with GDD along the studied microclimatic gradient. However, even though establishment on the north‐facing slopes caught up with that on the south‐facing slopes throughout the growing season, biomass production was limited on the north‐facing slopes due to a shorter growing season. On top of this microclimatic effect, all experimentally imposed anthropogenic factors enhanced non‐native species success. The observed microclimatic effect indicates a potential for non‐native species to use warm microsites as stepping stones for their establishment towards the cold end of the gradient. Combined with anthropogenic pressures this result suggests an increasing risk for plant invasion in cold ecosystems, as such stepping stones in alpine ecosystems are likely to be more common in a future that will combine a warming climate with persistent anthropogenic pressures. [ABSTRACT FROM AUTHOR]

Aim: We investigated patterns of species richness and community dissimilarity along elevation gradients using globally replicated, standardized surveys of vascular plants. We asked how these patterns of diversity are influenced by anthropogenic pressures (road construction and non-native species). Location: Global. Time period: 2008-2015. Major taxa studied: Vascular plants. Methods: Native and non-native vascular plant species were recorded in 943 plots along 25 elevation gradients, in nine mountain regions, on four continents. Sampling took place in plots along and away from roads. We analysed the effects of elevation and distance from road on species richness patterns and community dissimilarity (beta-diversity), and assessed how non-native species modified such elevational diversity patterns. Results: Globally, native and total species richness showed a unimodal relationship with elevation that peaked at lower-mid elevations, but these patterns were altered along roads and due to non-native species. Differences in elevational species richness patterns between regions disappeared along roadsides, and non-native species changed the patterns' character in all study regions. Community dissimilarity was reduced along roadsides and through non-native species. We also found a significant elevational decay of beta-diversity, which however was not affected by roads or non-native species. Main conclusions: Idiosyncratic native species richness patterns in plots away from roads implicate region-specific mechanisms underlying these patterns. However, along roadsides a clearer elevational signal emerged and species richness mostly peaked at mid-elevations. We conclude that both roads and non-native species lead to a homogenization of species richness patterns and plant communities in mountains. [ABSTRACT FROM AUTHOR]

Abstract: Rapid climatic changes and increasing human influence at high elevations around the world will have profound impacts on mountain biodiversity. However, forecasts from statistical models (e.g. species distribution models) rarely consider that plant community changes could substantially lag behind climatic changes, hindering our ability to make temporally realistic projections for the coming century. Indeed, the magnitudes of lags, and the relative importance of the different factors giving rise to them, remain poorly understood. We review evidence for three types of lag: “dispersal lags” affecting plant species’ spread along elevational gradients, “establishment lags” following their arrival in recipient communities, and “extinction lags” of resident species. Variation in lags is explained by variation among species in physiological and demographic responses, by effects of altered biotic interactions, and by aspects of the physical environment. Of these, altered biotic interactions could contribute substantially to establishment and extinction lags, yet impacts of biotic interactions on range dynamics are poorly understood. We develop a mechanistic community model to illustrate how species turnover in future communities might lag behind simple expectations based on species’ range shifts with unlimited dispersal. The model shows a combined contribution of altered biotic interactions and dispersal lags to plant community turnover along an elevational gradient following climate warming. Our review and simulation support the view that accounting for disequilibrium range dynamics will be essential for realistic forecasts of patterns of biodiversity under climate change, with implications for the conservation of mountain species and the ecosystem functions they provide. [ABSTRACT FROM AUTHOR]

Roads are known to act as corridors for dispersal of plant species. With their variable microclimate, role as corridors for species movement and reoccurring disturbance events, they show several characteristics that might influence range dynamics of both native and non-native species. Previous research on plant species ranges in mountains however seldom included the effects of roads. To study how ranges of native and non-native species differ between roads and adjacent vegetation, we used a global dataset of plant species composition along mountain roads. We compared average elevation and range width of species, and used generalized linear mixed models (GLMMs) to compile their range optimum and amplitude. We then explored differences between roadside and adjacent plots based on a species' origin (native vs non-native) and nitrogen and temperature affinity. Most non-native species had on average higher elevational ranges and broader amplitudes in roadsides. Higher optima for non-native species were associated with high nitrogen and temperature affinity. While lowland native species showed patterns comparable to those in non-native species, highland native species had significantly lower elevational ranges in roadsides compared to the adjacent vegetation. We conclude that roadsides indeed change the elevational ranges of a variety of species. These changes are not limited to the expansion of non-native species along mountain roads, but also include both upward and downward changes in ranges of native species. Roadsides may thus facilitate upward range shifts, for instance related to climate change, and they could serve as corridors to facilitate migration of alpine species between adjacent high-elevation areas. We recommend including the effects of mountain roads in species distribution models to fine-tune the predictions of range changes in a warming climate. [ABSTRACT FROM AUTHOR]

Invasive plant species that have the potential to alter fire regimes have significant impacts on native ecosystems. Concern that pine invasions in the Southern Hemisphere will increase fire activity and severity and subsequently promote further pine invasion prompted us to examine the potential for feedbacks between Pinus contorta invasions and fire in Patagonia and New Zealand. We determined how fuel loads and fire effects were altered by P. contorta invasion. We also examined post-fire plant communities across invasion gradients at a subset of sites to assess how invasion alters the post-fire vegetation trajectory. We found that fuel loads and soil heating during simulated fire increase with increasing P. contorta invasion age or density at all sites. However, P. contorta density did not always increase post-fire. In the largest fire, P. contorta density only increased significantly post-fire where the pre-fire P. contorta density was above an invasion threshold. Below this threshold, P. contorta did not dominate after fire and plant communities responded to fire in a similar manner as uninvaded communities. The positive feedback observed at high densities is caused by the accumulation of fuel that in turn results in greater soil heating during fires and high P. contorta density post-fire. Therefore, a positive feedback may form between P. contorta invasions and fire, but only above an invasion density threshold. These results suggest that management of pine invasions before they reach the invasion density threshold is important for reducing fire risk and preventing a transition to an alternate ecosystem state dominated by pines and novel understory plant communities. [ABSTRACT FROM AUTHOR]

Plant species sometimes perform extraordinarily well when introduced to new environments, through achieving higher growth rates, individual biomasses or higher densities in their receiving communities compared to their native range communities. One hypothesis proposed to explain enhanced performance in species' new environments is that their soil microbial communities may be different and provide greater benefit than microbial communities encountered in species' native environments. However, detailed descriptions of soil biota associated with species in both their native and introduced environments remain scarce., We established a global network of sites in regions where the tree species Pinus contorta has been introduced (Chile, New Zealand, Finland, Scotland and Sweden), as well as native range sites where the introduced populations originated (Canada and USA). We conducted pyrosequencing analysis to compare the root fungal endophyte communities associated with P. contorta in its native environments and in introduced environments with phylogenetically similar and dissimilar tree species (i.e. P. sylvestris in Europe and Nothofagus spp. in the Southern Hemisphere)., Fungal communities associated with P. contorta consistently differed between its introduced and native environments. In Europe, P. contorta associated with the same community as P. sylvestris, where one particular species ( Piloderma sphaerosporum) was particularly abundant relative to Canadian sites. In the Southern Hemisphere, P. contorta fungal communities were composed primarily of North American taxa and exhibited very little overlap with fungal communities associated with native Nothofagus spp., Synthesis. Our work shows that plants exhibit considerable plasticity in their interaction with fungi, by associating with different fungal communities across native and introduced environments. Our work also indicates that fungal communities associated with introduced plants can assemble through different mechanisms, that is by associating with existing fungal communities of phylogenetically close species, or through reassembly of co-introduced and co-invading fungi. The identification of different fungal communities in a plant species new environment provides an important step forward in understanding how soil biota may impact growth and invasion when a species is introduced to new environments. [ABSTRACT FROM AUTHOR]

Terrestrial invasive plants are a global problem and are becoming ubiquitous components of most ecosystems. They are implicated in altering disturbance regimes, reducing biodiversity, and changing ecosystem function, sometimes in profound and irreversible ways. However, the ecological impacts of most invasive plants have not been studied experimentally, and most research to date focuses on few types of impacts, which can vary greatly among studies. Thus, our knowledge of existing ecological impacts ascribed to invasive plants is surprisingly limited in both breadth and depth. Our aim was to propose a standard methodology for quantifying baseline ecological impact that, in theory, is scalable to any terrestrial plant invader (e.g., annual grasses to trees) and any invaded system (e.g., grassland to forest). The Global Invader Impact Network ( GIIN) is a coordinated distributed experiment composed of an observational and manipulative methodology. The protocol consists of a series of plots located in (1) an invaded area; (2) an adjacent removal treatment within the invaded area; and (3) a spatially separate uninvaded area thought to be similar to pre-invasion conditions of the invaded area. A standardized and inexpensive suite of community, soil, and ecosystem metrics are collected allowing broad comparisons among measurements, populations, and species. The method allows for one-time comparisons and for long-term monitoring enabling one to derive information about change due to invasion over time. Invader removal plots will also allow for quantification of legacy effects and their return rates, which will be monitored for several years. GIIN uses a nested hierarchical scale approach encompassing multiple sites, regions, and continents. Currently, GIIN has network members in six countries, with new members encouraged. To date, study species include representatives of annual and perennial grasses; annual and perennial forbs; shrubs; and trees. The goal of the GIIN framework is to create a standard yet flexible platform for understanding the ecological impacts of invasive plants, allowing both individual and synthetic analyses across a range of taxa and ecosystems. If broadly adopted, this standard approach will offer unique insight into the ecological impacts of invasive plants at local, regional, and global scales. [ABSTRACT FROM AUTHOR]

ABSTRACT Aim To investigate how species richness and similarity of non-native plants varies along gradients of elevation and human disturbance. Location Eight mountain regions on four continents and two oceanic islands. Methods We compared the distribution of non-native plant species along roads in eight mountainous regions. Within each region, abundance of plant species was recorded at 41-84 sites along elevational gradients using 100-m2 plots located 0, 25 and 75 m from roadsides. We used mixed-effects models to examine how local variation in species richness and similarity were affected by processes at three scales: among regions (global), along elevational gradients (regional) and with distance from the road (local). We used model selection and information criteria to choose best-fit models of species richness along elevational gradients. We performed a hierarchical clustering of similarity to investigate human-related factors and environmental filtering as potential drivers at the global scale. Results Species richness and similarity of non-native plant species along elevational gradients were strongly influenced by factors operating at scales ranging from 100 m to 1000s of km. Non-native species richness was highest in the New World regions, reflecting the effects of colonization from Europe. Similarity among regions was low and due mainly to certain Eurasian species, mostly native to temperate Europe, occurring in all New World regions. Elevation and distance from the road explained little of the variation in similarity. The elevational distribution of non-native species richness varied, but was always greatest in the lower third of the range. In all regions, non-native species richness declined away from roadsides. In three regions, this decline was steeper at higher elevations, and there was an interaction between distance and elevation. Main conclusions Because non-native plant species are affected by processes operating at global, regional and local scales, a multi-scale perspective is needed to understand their patterns of distribution. The processes involved include global dispersal, filtering along elevational gradients and differential establishment with distance from roadsides. [ABSTRACT FROM AUTHOR]

Aim To examine the different uses and perceptions of introduced Australian acacias (wattles; Acacia subgenus Phyllodineae) by rural households and communities. Location Eighteen landscape-scale case studies around the world, in Vietnam, India, Réunion, Madagascar, South Africa, Congo, Niger, Ethiopia, Israel, France, Portugal, Brazil, Chile, Dominican Republic and Hawai'i. Methods Qualitative comparison of case studies, based on questionnaire sent to network of acacia researchers. Information based on individual knowledge of local experts, published and unpublished sources. Results We propose a conceptual model to explain current uses and perceptions of introduced acacias. It highlights historically and geographically contingent processes, including economic development, environmental discourses, political context, and local or regional needs. Four main groupings of case studies were united by similar patterns: (1) poor communities benefiting from targeted agroforestry projects; (2) places where residents, generally poor, take advantage of a valuable resource already present in their landscape via plantation and/or invasion; (3) regions of small and mid-scale tree farmers participating in the forestry industry; and (4) a number of high-income communities dealing with the legacies of former or niche use of introduced acacia in a context of increased concern over biodiversity and ecosystem services. Main conclusions Economic conditions play a key role shaping acacia use. Poorer communities rely strongly on acacias (often in, or escaped from, formal plantations) for household needs and, sometimes, for income. Middle-income regions more typically host private farm investments in acacia woodlots for commercialization. Efforts at control of invasive acacias must take care to not adversely impact poor dependent communities. [ABSTRACT FROM AUTHOR]

Aim The biophysical impacts of invasive Australian acacias and their effects on ecosystem services are explored and used to develop a framework for improved restoration practices. Location South Africa, Portugal and Chile. Methods A conceptual model of ecosystem responses to the increasing severity (density and duration) of invasions was developed from the literature and our knowledge of how these impacts affect options for restoration. Case studies are used to identify similarities and differences between three regions severely affected by invasions of Australian acacias: Acacia dealbata in Chile, Acacia longifolia in Portugal and Acacia saligna in South Africa. Results Australian acacias have a wide range of impacts on ecosystems that increase with time and disturbance, transform ecosystems and alter and reduce ecosystem service delivery. A shared trait is the accumulation of massive seed banks, which enables them to become dominant after disturbances. Ecosystem trajectories and recovery potential suggest that there are important thresholds in ecosystem state and resilience. When these are crossed, options for restoration are radically altered; in many cases, autogenic (self-driven and self-sustaining) recovery to a pre-invasion condition is inhibited, necessitating active intervention to restore composition and function. Main conclusions The conceptual model demonstrates the degree, nature and reversibility of ecosystem degradation and identifies key actions needed to restore ecosystems to desired states. Control and restoration operations, particularly active restoration, require substantial short- to medium-term investments, which can reduce losses of biodiversity and ecosystem services, and the costs to society in the long term. Increasing restoration effectiveness will require further research into linkages between impacts and restoration. This research should involve scientists, practitioners and managers engaged in invasive plant control and restoration programmes, together with society as both the investors in, and beneficiaries of, more effective restoration. [ABSTRACT FROM AUTHOR]

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. Australia, Canada, Chile, India, New Zealand, South Africa, Spain, Switzerland, USA. 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. 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. 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. [ABSTRACT FROM AUTHOR]