[EN] A major aim in invasion ecology is to understand the role of exotic species in plant communities. Whereas most studies have explored the traits of exotic species in the context of the introduced community, functional comparisons of entire assemblages of species in their native and introduced communities have rarely been analysed. Taking advantage of the unidirectional invasion of plant species of European origin (i.e. colonizers) into California, this study aims to investigate the relative importance of plant traits, environmental factors and invasion status in biological invasions.
We compared the functional structure (i.e. trait composition and diversity) along resource availability gradients in recipient and native Mediterranean grassland communities in California and Spain, respectively. Traits were related to resource use in above-ground and below-ground organs and reproductive strategy. We also investigated how niche differences vary along environmental gradients between coexisting colonizer and native species assemblages within communities.
There were clear differences in the functional structure of Mediterranean grassland communities between regions, which were associated with the resource availability gradient. Paradoxically, the most acquisitive communities occurred in resource-poor sites, highlighting that rapid acquisition and use of resources permit species to cope with environmental stress through stress avoidance. In Spain, colonizer species had greater specific leaf area than non-colonizers. Yet, differences between colonizer and non-colonizer species in Spain for other traits were mostly absent and did not change along the gradient. This might be a result of the greater native species richness as a consequence of the agricultural practices that have taken place in Europe for millennia and reflect that the entire species pool of grasslands is adapted to agricultural landscapes. In comparison, in California, colonizer species were more acquisitive in their use of resources than natives under favourable conditions, but functionally converged in resource-limited sites.
Synthesis. These results underscore that the importance of niche differences between native and colonizer species as a community assembly mechanism is strongly subjected to the influence of habitat filtering. Trait comparisons are context dependent, and a correct interpretation of filtering processes in community assembly requires a regional perspective., SI

© 2024 Montserrat Vilà, Alejandro Trillo, Pilar Castro-Díez, Belinda Gallardo, Sven Bacher. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited., The impacts of invasive species can vary widely across invaded sites and depend on the ecological variable of study. In this paper, we describe the first harmonised database that compiles scientific evidence of the ecological impacts of invasive plant species at continental scale. We summarise results from 266 publications reporting 4259 field studies on 104 invasive species in 29 European countries. For each study, we recorded whether the effects were statistically significant and noted their direction (i.e. decrease or increase in the response variable when compared to uninvaded sites). We classified studies, based on the impacts on the levels of ecological organisation (species, communities and ecosystems), taxa and trophic level. More than half of the studies were conducted in temperate and boreal forests and woodlands and temperate grasslands. Notably, one third of the studies focused on just five invasive species. Most studies were on native species followed by studies on communities. Impacts on plants were more frequently studied than impacts on other taxa and trophic groups. Overall, 43% of the studies reported significant impacts, with more significant decreases (26%) than increases (17%) in the response variables. Significant impacts were more frequent on species and communities than on ecosystems; and on plants than on animals or microbes. This database is of interest for academic, management and policy-related purposes., This research was supported by the 2017–2018 Belmont Forum–BiodivERsA International joint call project InvasiBES under the BiodivScen ERA-Net COFUND programme and with the following funding organisations: the Spanish Ministry of Science and Innovation (PCI2018-092939, PCI2018-092986, MCI/AEI/FEDER, RED2022-134338-T) and the Swiss National Science Foundation (31BD30-184114 and 31003A_179491); also by EXARBIN (RTI2018-093504-B-100), RADIOPOPO (PDI2021-122690OB-100); the European Union FPS COST Actions FP1403 NNEXT; and through the European Regional Development Fund (SUMHAL, LIFEWATCH-2019-09-CSIC-4, POPE 2014-2020)., Peer reviewed

Las invasiones biológicas son un componente importante del cambio global, el cual está amenazando la biodiversidad y servicios ecosistémicos del planeta. Para gestionar y mitigar los impactos del cambio global, es importante disponer de herramientas de monitorización que permitan evaluar sistemática, periódica, rápida y eficazmente los impactos de las especies exóticas a diversas escalas. Los inventarios forestales nacionales (IFNs) constituyen una herramienta emergente para el seguimiento de la estructura y dinámica de los bosques a grandes escalas espaciales. Los IFNs han sido usados globalmente para evaluar la diversidad biológica, la distribución de especies y el aprovisionamiento de servicios ecosistémicos en bosques. Además, tienen potencial para estudiar diversos aspectos de las invasiones biológicas, tanto desde un punto de vista teórico como aplicado. En este estudio revisamos la bibliografía disponible para conocer qué trabajos sobre especies exóticas se han publicado utilizando IFNs. Encontramos 96 estudios que usaban IFNs para evaluar el estado o dinámica de las especies exóticas en Estados Unidos (74), Europa (20), Canadá (1) y Australia (1). Más de la mitad de los estudios fueron realizados sobre distribución, riesgo de expansión, demografía o impactos de plantas exóticas (64). Los estudios restantes utilizaron IFNs para investigar riesgo de expansión o daños causados por otro tipo de especies exóticas, como insectos (20), patógenos fúngicos o protistas (6), insectos y patógenos (4), ciervos (1) y por el caracol gigante africano (1). Finalmente, discutimos las oportunidades y las limitaciones de los IFNs, resaltando su potencial para ampliar estudios teóricos y aplicados sobre invasiones biológicas., Biological invasions are an important component of global change, which is threatening the planet's biodiversity and ecosystem services. To manage and mitigate the impacts of global change, it is important to have monitoring tools that allow assessing the impacts of exotic species at several scales in a systematic, periodic, rapid, and effective way. National forest inventories (NFIs) are an emerging tool for monitoring forest structure and dynamics at large spatial scales. NFIs have been used globally to assess biological diversity, species distributions, and ecosystem services provision in forests. Moreover, NFIs have the potential to study various theoretical and applied aspects of biological invasions. We conducted a literature review to evaluate what studies about exotic species have been published using information from NFIs. We found 96 studies that used NFIs to assess the status or dynamics of exotic species in the United States (74), Europe (20), Canada (1) and Australia (1). Over half of the studies were conducted on the distribution, expansion risk, demography, or impacts of exotic plants (64). The remaining studies used NFIs to investigate expansion risk or impacts caused by other types of exotic species, including insects (20), fungal or protist pathogens (6), insects and pathogens (4), deer (1) and the giant African land snail (1). Lastly, we discuss the opportunities and limitations of NFIs, highlighting their potential to expand theoretical and applied studies on biological invasions., Agencia Estatal de Investigación, Ministerio de Ciencia e Innovación, Fondo Europeo para el Desarrollo Regional-FEDER, Comunidad de Madrid

14 p., Upper reaches of temperate streams and oligotrophic lakes depend trophically on the organic matter coming from the surrounding watershed. These aquatic ecosystems accumulate particulate and dissolved organic matter, and chemical compounds liberated from decomposing leaves or from the leachates of leaf litter. These materials supply a wide range of chemical compounds, which may serve as food, but also cause ecotoxicological effects on aquatic organisms. However, this ecotoxicological risk has been amply ignored, especially for freshwater invertebrates. The aims of our study are: (1) to assess the direct toxicity of aqueous extracts of leaf litter from two native (Populus alba, Fraxinus angustifolia) and two tree species exotic to Europe (Robinia pseudoacacia, Ailanthus altissima) on a pelagic and a benthic species of model aquatic invertebrates: Daphnia magna (Cladocera) and Potamopyrgus antipodarum (Mollusca) and (2) to estimate the ecotoxicological risk of the leaf litter extracts to lacustrine ecosystems using different simulated scenarios of shallow lakes. For both invertebrate species, we assessed the effective concentration of leaf extract causing an effect on 50% of the population (EC50) by means of laboratory bioassays. Our results show that the extracts of leaf litter from all the tested trees have a potential ecotoxicological risk in some scenarios, whichisindependentfromthegeographicoriginofthe tree species., Universidad de Alcalá, Ministerio de Economía y Competitividad, Junta de Comunidades de Castilla La Mancha, Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT, Chile)

13 p., Questions
It is well documented that invasive alien plants can reduce species richness and diversity and modify the composition of invaded communities. However, our knowledge on the impacts of invasive alien plants on the community functional structure and ecosystem properties and the mechanisms underlying these changes is more limited. We evaluated how the community functional structure and ecosystem properties change along a gradient of Ligustrum lucidum abundance.

Location
Subtropical mountain forest in NW Argentina.

Methods
We conducted tree vegetation sampling in 164 plots distributed along a gradient of L. lucidum abundance. For L. lucidum and for the most abundant tree species in these plots we estimated six functional traits (specific leaf area, leaf tensile strength, leaf nitrogen concentration, leaf water potential, wood density and maximum plant height), as well as their relative growth rates. Then, we calculated indices of community functional structure (community-weighted means for each trait; richness, evenness, divergence and dispersion). We explored the extent to which the invasive success of L. lucidum and its impact may be attributed to niche differentiation or to fitness superiority. Finally, we explored how L. lucidum abundance alters ecosystem properties.

Results
Some indicators of community functional structure changed linearly while others tended to saturate along the invasion gradient. L. lucidum has a higher growth rate than resident species and it lays close to the periphery, but within the limits of the functional space defined by resident trees. L. lucidum tends to displace more functionally similar resident species. Soil moisture and N content declined, while soil C:N increased with L. lucidum abundance.

Conclusions
Our findings suggest that both niche differentiation and fitness superiority contribute to explain the invasion success of L. lucidum and the changes in functional structure of the community along the gradient of L. lucidum abundance with evident impacts on ecosystem properties., Universidad de Alcalá, Ministerio de Ciencia e Innovación, Fondo Europeo de Desarrollo Regional (FEDER), Comunidad de Madrid

8 p., Species distribution models are frequently used to anticipate the expansion of invasive species under the assumption that climate affects habitat conditions. Here, we investigated the influence of two additional factors that determine the spread, establishment, and impact of aquatic organisms: propagule pressure and water chemistry. Our case study species is the New Zealand Mud Snail (Potamopyrgus antipodarum, Tateidae, Mollusca), one of the 100 worst invasive species in Europe. We calibrated species distribution models combining three types of indicators (climate, water chemistry, and propagule pressure), and two scales (Iberian Peninsula vs. Ebro River catchment) using the Maxent algorithm. Propagule pressure improved the accuracy of models and enlarged the area susceptible to invasion by 16% at the Iberian Peninsula scale, and by 36% at the catchment scale. Among propagule pressure indicators, accessibility was the single most important indicator of the species distribution (33?35% contribution), illustrating the role of human-mediated dispersal for aquatic invaders. The catchment model integrating climate, propagule pressure and water chemistry indicators was the best option to prioritize river segments most vulnerable to colonization, characterized by high temperature, human influence and water pollution (nitrate concentration). High risk areas according to our models include the Mediterranean and North Atlantic coasts, central Spain, and the lowlands of the Ebro River catchment. Based on this study, we recommend including indicators of propagule pressure such as accessibility to reflect the opportunity to invade, and using water chemistry to further prioritize the river stretches most suitable to invasion. We conclude that distribution models integrating indicators at multiple scales are feasible, consistent in their predictions across scales, and show great potential to optimize management resources towards the prevention and early eradication of aquatic invasive species., Universidad de Alcalá, Ministerio de Ciencia, Innovación y Universidades, Fondo Europeo de Desarrollo Regional (FEDER), Comunidad de Madrid

FP1403 - Non-native tree species for european forests - experiences, risks and opportunities (NNEXT), Tree taxa are often planted beyond their native range to increase the provision of some ecosystem services. Yet,
they can disrupt ecosystem processes in their new ranges, causing changes in the provision of other services.
Here we review the effects of five widespread tree taxa (Acacia, Ailanthus, Eucalyptus, Pinus and Robinia) on six
regulating ecosystem services in areas where they are non-native. We conducted a literature search for pairwise comparisons between sites dominated by any of the selected taxa and sites with native vegetation. An
array of variables were used as indicators for each ecosystem service. Data were analysed using multi-level
meta-analyses to compare effects of taxa on each ecosystem service, and effects of the same taxa across contexts.
We compiled 857 case studies from 107 source papers. Several taxa tended to increase climate regulation, mostly
Eucalyptus. Acacia decreased fire risk prevention. Robinia, Acacia and Ailanthus increased soil fertility, while
Eucalyptus and Pinus, tended to decrease it. Soil formation was enhanced by Robinia and Ailanthus. Acacia
promoted the increase of water in land pools, while Eucalyptus tended to decrease them. All effects show a
large heterogeneity across case studies. Part of this heterogeneity could be attributed to gross climatic differences
(i.e. biome), to species differences within each genus, to the structure of the recipient ecosystem, and/or to
human management. Managers and policy-makers should consider the context-dependency and the potential
effects of non-native trees on a wide range of services to ground their decisions. Our analyses also revealed
important gaps of knowledge (e.g. on fire risk prevention, erosion control or water cycle regulation) and some
potential publication bias. The methodology used here easily allows for future updates as new information will
become available., Agencia Estatal de Investigación, Comunidad de Madrid

26 p., Ligustrum lucidum is a highly invasive East Asian tree that successfully colonizes several subtropical and temperate areas around the world. Its invasion capacity results from a widespread human use mostly in urban and periurban settings, very abundant fruit and seed production, small bird-dispersed fruits, high germination rates, resprouting capacity, fast growth rates, low herbivory levels and tolerance to a wide range of light, temperature and soil. All these traits contribute to its ability to rapidly increase in abundance, alter biodiversity, landscape ecology and limit its management. This paper reviews the current knowledge on L. lucidum with particular focus on its uses, distribution, invasiveness, ecological and economic impacts and control measures. Most relevant aspect of the review highlight the negative ecological impacts of L. lucidum, its potential to continue expanding its range of distribution and the need of further studies on the eco-physiology of the species, economic impact and social perception of its invasion and early warning systems., Ministerio de Ciencia, Innovación y Universidades, Comunidad de Madrid, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina)

13 p., One of the suggested mechanisms behind the success of non-native plants inrecipient ecosystems is competition avoidance with natives by means of differ-ent resource-use strategies, such as deeper water uptake under dry conditions.2. We aimed at evaluating water source partitioning between native and non-nativetree species coexisting in central Spain floodplains; determining the dependencyon drought stress of such water sources use; and assessing if the reliance ondeeper water sources relates with physiological and growth performance.3. We assessed water uptake depth, leaf functional traits related to physiologicalperformance and growth of native (Populus alba) and non-native trees (Ailanthusaltissima, Robinia pseudoacacia) coexisting in riparian forests under different droughtconditions (drier, intermediate and wetter). We analysed ?2H and ?18O isotopes inxylem water and in soil water from top, mid and deep soil depths and determinedthe contribution of each water source to overall plant xylem water. Leaf traits re-lated with resource use and secondary growth were assessed for each species.4. We found stronger differences between sites than between species, with allspecies taking more deep water in the driest site (~45% of the xylem water) thanin the wettest (~15%). However, under drier conditions, species differences weresignificant for top-soil water use, with R. pseudocacia withdrawing more super-ficial water (~22%) than A. altissima (~8%). These results indicate stronger waterpartitioning under drier conditions. Non-native species showed a physiologicalstrategy characterized by greater leaf N, water content, and enriched ?13 C and?15N values independently of the deep- water uptake. However, a positive rela-tionship between deep soil water use and such strategy was found for P. alba.5. We highlight that those native and non-native species differences were moreevident regarding physiological performance at leaf level than for deep-wateruptake or growth. Furthermore, our results suggest that differences in watersources used by coexisting species may increase under drier conditions., Ministerio de Ciencia, Innovación y Universidades, Comunidad de Madrid, Comisión Europea, Fondo Europeo de Desarrollo Regional (FEDER), Ministerio de Ciencia e Innovación, Universidad de Alcalá

10 p., El seminario celebrado el 29 y 30 de noviembre de 2018 y la edición del presente libro han sido financiados por la Cátedra Parques Nacionales, Ministerio de Ciencia, Innovación y Universidades, Fondo Europeo de Desarrollo Regional (FEDER), Agencia Estatal de Investigación, Cátedra Parques Nacionales

15 p., El seminario celebrado el 29 y 30 de noviembre de 2018 y la edición del presente libro han sido financiados por la Cátedra Parques Nacionales, Cátedra Parques Nacionales, Agencia Estatal de Investigación, Ministerio de Ciencia, Innovación y Universidades, Fondo Europeo de Desarrollo Regional (FEDER)

Aridification due to climate change and water table lowering due to human management are intensifying the environmental filter of summer aridity for Mediterranean riparian forests. This may represent an opportunity for the entry of non-native (NNT) species which might be pre-adapted to these new conditions, thus favoring their invasive potential. Differences in water uptake depth by coexisting native (NT) and NNT tree species could be one of the reasons why some of the latter species might become successful invaders in riparian ecosystems. To test whether spatial ecohydrological niche segregation occurs during dry summers, we analyzed stable water isotopes from different sources in a riparian ecosystem of central Spain. Xylem water δ 18 O was analyzed in 6 NT and 6 NNT (2 of them invasive) coexisting tree species. We used Bayesian isotope mixing models to estimate the proportion of water from different depths used by trees. We also tested the relationship between the δ 18 xylem water and leaf δ 13 O from C to test if species with deeper access to water have lower intrinsic water use efficiency (iWUE). We found no segregation between NT and NNT species in water uptake depth, but a species-specific vertical partitioning of water resources, with both invasive species extracting more water from the deepest soil layers. NNT species had higher leaf δ 13 C. A negative relationship between xylem water δ 18 O and leaf δ C was found at interspecific level, indicating that species with greater access to deep water are also those bearing higher iWUE. Our results indicate a pronounced niche partitioning promoting species coexistence. The ability of invasive species to tap into deeper water layers combined with higher iWUE led to a competition-avoidance strategy together with a water stress-avoidance strategy. Deeper water uptake and greater iWUE could be important driving the success of tree species in Mediterranean floodplains under drier conditions., Agencia Estatal de Investigación, Comunidad de Madrid, Universidad de Alcalá

Aims Plant invasions generally lead to mixtures betweennative and non-native litter. We assess the interactionsbetween leaf litters from two invasive non-native trees(Robinia pseudoacia or Ailanthus altissima) and the nativePopulus alba on litter decomposition, nutrient releaseand soil properties along two gradients of invasion.Methods Microcosms with field-collected soil coveredby varying proportions of native and non-native littersimulated the two invasion gradients. We assessed theproportion of remaining litter mass and nutrient mass(N, P, C), and soil C, N-NO3−, total N, and pH, fivetimes throughout a period of 11 months. Observedvalues were compared to the expected values on theassumption of no interactions.Results Litter mass and C mass decayed slower inRobinia and faster in Ailanthus than in Populus. Thethree species immobilized N and P. Soil properties didnot differ across pure litters. Both litter mixture gradientsshowed additive or antagonistic interactions onlitter decomposition, whereas N and P mass were equalor higher than expected. The proportion of non-nativelitter in the mixture had non-linear effects on mostvariables, suggesting that the impact of these nonnativetrees on litter decay levels off or even declinesas they become more abundant.Conclusion The impacts of Ailanthus and Robinia litteron soil processes should not be derived from singlespecies experiments, both due to non-additive effectsand to non-linear responses to litter abundance., Ministerio de Ciencia, Innovación y Universidades, Comunidad de Madrid, Agencia Estatal de Investigación

Scientific and grey literature on invasive alien species (IAS) is conditioned by social, economic and political priorities, editorial preferences and species and ecosystem characteristics. This leads to knowledge gaps and mismatches between scientific research interests and management needs. We reviewed the literature on IAS management in Spain found in Scopus, Web of Science, Google Scholar and Dialnet to identify key deficiencies and priority research areas. The collected literature was classified, employing features describing formal aspects and content. We used bibliometric and keyword co-occurrence network analyses to assess the relationship between features and reveal the existence of additional topics. Most of the compiled documents (n = 388) were focused on terrestrial ecosystems and inland waters, whereas marine and urban ecosystems were under-represented. The literature was largely generic and not species-specific, focusing on raising awareness and proposing changes on current regulation as prominent approaches to prevent further introductions. The compiled authors exhibited many clear publishing preferences (e.g. language or document type), but less regarding target taxa. In addition, there was a strong association between species and the different features considered, especially between the methodological approach (e.g. review, field experiment) and the primary emphasis of study (i.e. basic/theoretical, applied or interdisciplinary). This indicates that research on IAS has had a strong species-specific focus. References about terrestrial species focused mainly on vascular plants, whereas references about inland waters were mostly on fishes and the giant reed (Arundo donax), which has been managed with partial success. Animal culling and plant removal were the most frequent eradication and small-scale control treatments, whereas the documents addressing wider spatial scales were largely theoretical. Consequently, the success of described treatments was largely uncertain. Spanish invasion science research has been occasionally innovative, incorporating novel technologies (e.g. species distribution modelling) and engaging society with citizen-science approaches. However, the ratio between basic/theoretical and applied studies indicates that more applied research/management is needed, especially in inland waters and marine ecosystems. We call for increasing effort in the effective dissemination of experience in IAS management to enhance current practical knowledge, including that of schemes undertaken by public agencies., Generalitat de Cataluña, Ministerio de Ciencia e Innovación, Fondo Europeo de Desarrollo Regional-FEDER

Non-native trees enhance services that are fundamental for human well-being. Yet, the extensive use of non-native trees has the potential of causing environmental and socio-economic harm. Eucalyptus and Pinus are the most widely distributed and extensively planted tree genera worldwide, because their rapid growth allows profitable production of timber and pulp. Their naturalization is causing severe effects on the environment, but the relative importance of underlying factors determining their demographic performance is not well known. Thus, our aim was to evaluate the relative importance of biotic, abiotic, and anthropogenic factors driving demographic changes of Eucalyptus and Pinus at the regional scale. We compiled environmental variables and demographic data for Eucalyptus globulus, Eucalyptus camaldulensis, and Pinus radiata across 6388 permanent forestland plots surveyed in the Spanish Forest Inventory (SFI). We used the second (1986?1996), third (1997?2007), and fourth (2008?2017) SFI datasets to quantify annual changes in basal area per plot between consecutive inventories (?BA; m2 ha?1 year?1). We also quantified the components of ?BA: tree ingrowth (transitions from juvenile to adult trees), growth, and mortality. We evaluated juvenile recruitment with in-situ regeneration (No. juvenile trees ha?1) within plots already occupied by the focal species in the previous inventory, and with natural colonization of plots where the focal species was absent at the beginning of the time interval. We found that the structure of the biotic community was especially important to explain demographic performance of non-native trees growing in benign environments (E. globulus and P. radiata), whereas abiotic factors were particularly important regulating basal area increments of E. camaldulensis, which occurs in harsher environments. Basal area increments decreased with species and functional richness, heterospecific density, mean annual temperature, and increased with soil capacity to retain nutrients and water. Colonization of new plots increased with propagule availability in the surrounding landscape. Tree cutting was beneficial for P. radiata. Collectively, our results suggest that non-native trees perform better in forests with high propagule pressure, low biotic resistance, favourable abiotic conditions, and human management., Agencia Estatal de Investigación, Universidad de Alcalá, Ministerio de Ciencia e Innovación, Comunidad de Madrid

Full datasets for the research entitled 'Proportion of non-native plants in urban parks correlates with climate, socioeconomic factors and plant traits'.