Although research on human-mediated exchanges of species has substantially intensified during the last centuries, we know surprisingly little about temporal dynamics of alien species accumulations across regions and taxa. Using a novel database of 45,813 first records of 16,926 established alien species, we show that the annual rate of first records worldwide has increased during the last 200 years, with 37% of all first records reported most recently (1970–2014). Inter-continental and inter-taxonomic variation can be largely attributed to the diaspora of European settlers in the nineteenth century and to the acceleration in trade in the twentieth century. For all taxonomic groups, the increase in numbers of alien species does not show any sign of saturation and most taxa even show increases in the rate of first records over time. This highlights that past efforts to mitigate invasions have not been effective enough to keep up with increasing globalization.

Significance: Our ability to predict the identity of future invasive alien species is largely based upon knowledge of prior invasion history. Emerging alien species—those never before encountered as aliens—therefore pose a significant challenge to biosecurity interventions worldwide. Using a global database of the first regional records of alien species covering the years 1500–2005 we detected a surprisingly high proportion of species in recent records that have never been recorded as alien before. The high proportion of these emerging alien species mainly resulted from the increased accessibility of new source species pools in the native range. Risk assessment approaches that rely less on invasion history will need to be prioritized.

Expansive species classification with remote sensing techniques offers great support for botanical field works aimed at detection of their distribution within areas of conservation value and assessment of the threat caused to natural habitats. Large number of spectral bands and high spatial resolution allows for identification of particular species. LiDAR (Light Detection and Ranging) data provide information about areas such as vegetation structure. Because the species differ in terms of features during the growing season, it is important to know when their spectral responses are unique in the background of the surrounding vegetation. The aim of the study was to identify two expansive grass species: Molinia caerulea and Calamagrostis epigejos in the Natura 2000 area in Poland depending on the period and dataset used. Field work was carried out during late spring, summer and early autumn, in parallel with remote sensing data acquisition. Airborne 1-m resolution HySpex images and LiDAR data were used. HySpex images were corrected geometrically and atmospherically before Minimum Noise Fraction (MNF) transformation and vegetation indices calculation. Based on a LiDAR point cloud generated Canopy Height Model, vegetation structure from discrete and full-waveform data and topographic indexes were generated. Classifications were performed using a Random Forest algorithm. The results show post-classification maps and their accuracies: Kappa value and F1 score being the harmonic mean of producer (PA) and user (UA) accuracy, calculated iteratively. Based on these accuracies and botanical knowledge, it was possible to assess the best identification date and dataset used for analysing both species. For M. caerulea the highest median Kappa was 0.85 (F1 = 0.89) in August and for C. epigejos 0.65 (F1 = 0.73) in September. For both species, adding discrete or full-waveform LiDAR data improved the results. We conclude that hyperspectral (HS) and LiDAR airborne data could be useful to identify grassland species encroaching into Natura 2000 habitats and for supporting their monitoring.

This work synthesizes all aspects of Asclepias syriaca L. (Apocynaceae) including the taxonomy, distribution, history of introduction and spread, ecology, biology, uses and benefits, impacts on biodiversity and agriculture, legislation, and management. Asclepias syriaca is a perennial broad-leaved species native to North America. Introduced for ornamental and various other purposes, such as a source of fibre and rubber, it has become established in many regions of Europe and it had increasingly spread in the last decades (>1980s). Its reproductive behavior is characterized by a high production of wind-dispersed seeds and by the propagation of creeping lateral rhizomes, which allows the species to proliferate rapidly. The species persists in a wide range of edaphic and climatic environments. It occurs particularly in anthropogenic and (semi-)natural habitats, such as roadsides, agricultural land, abandoned sites and grasslands, open shrubland, and forests, respectively. Studies have demonstrated negative impacts on the biodiversity and ecosystem processes in invaded regions, namely in open sand grasslands in Hungary. Asclepias syriaca occurs as a competitive weed in crop fields. Since 2017, the species is regulated by the European Union (EU) under the Regulation No. 1143/2014, which states that A. syriaca is subjected to restrictions such as a ban on importing, selling, breeding and that EU member states are required to place effective management measures. Awareness raising activities are important to inform the public, farmers and stakeholders about the risks of this invasive alien plant. Effective direct control options include mechanical control as well as herbicide application.