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Stemming from a recent freshwater invasives conference, Caffrey et al. (2014) identified 'the top 20 issues' that relate to invasive alien species (IAS) management in Europe. With a view to complement and balance the issues highlighted in their account, we offer six important additions that relate to the marine environment. These are: preventive measures, concerns of loss of taxonomic expertise and species identity, gaps in the knowledge of certain taxa and regions, inconsistencies of terminology, need for validation of data and the importance of concentrating on pathways, and their vectors, and levels of certainty associated with these routes.

We compared potential germination success (i.e., percentage of produced seeds that germinate under optimal conditions), the percentage of empty and insect-damaged seeds, germinability (Gmax), and time to germination (Tgerm) between the exoticsAilanthus altissima,Robinia pseudoacacia,andUlmus pumilaand two coexisting native trees (Fraxinus angustifoliaandUlmus minor) in the riparian forests of Central Spain. Additionally, we tested the effect of seed age, seed bank type (canopy or soil) and population onGmaxandTgermofA. altissimaandR. pseudoacacia, which are seed-banking species. Species ranked by their potential germination success wereA. altissima>U. pumila>R. pseudoacacia>U. minor>F. angustifolia. The combination of a highGmaxand negligible seed insect-damage providedA. altissimawith a potential germination advantage over the natives, which were the least successful due to an extremely high percentage of empty seeds or a very lowGmax.R. pseudoacaciashowed high vulnerability to insect seed predation which might be compensated with the maintenance of persistent seed banks with highGmax.GmaxandTgermwere strongly affected by seed age in the seed-banking invaders, but between-seed bank variation ofGmaxandTgermdid not show a consistent pattern across species and populations.

A widely accepted hypothesis in invasion ecology is that invasive species have higher survival through the early stages of establishment than do non-invasive species. In this study we explore the hypothesis that the sexual reproductive success of the invasive trees Ailanthus altissima (Mill.) Swingle and Robinia pseudoacacia L. is higher than that of the native Fraxinus angustifolia Vahl., all three species coexisting within the riparian forests of Central Spain. We compared different stages of the early life cycle, namely seed rain, seed infestation by insects, seed removal by local fauna, seed germination under optimal conditions and seedling abundance between the two invasive trees and the native, in order to assess their sexual reproductive success. The exotic species did not differ from the native reference (all three species displaying high seed rain and undergoing seed losses up to 50% due to seed removal by the local fauna). Even if the exotic R. pseudoacacia showed a high percentage of empty and insect-parasited seeds along with a low seedling emergence and the exotic A. altissima was the species with more viable seeds and of higher germinability, no differences were found regarding these variables when comparing them with the native F. angustifolia. Unsuitable conditions might have hampered either seedling emergence and survival, as seedling abundance in the field was lower than expected in all species -especially in R. pseudoacacia-. Our results rather suggest that the sexual reproductive success was not higher in the exotic trees than in the native reference, but studies focusing on long-term recruitment would help to shed light on this issue.