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Biological invasions are a threat to ecosystems across all biogeographical realms. Riparian habitats are considered to be particularly prone to invasion by alien plant species and, because riparian vegetation plays a key role in both aquatic and terrestrial ecosystems, research in this field has increased. Most studies have focused on the biology and autecology of invasive species and biogeographical aspects of their spread. However, given that hydrogeomorphological processes greatly influence the structure of riparian plant communities, and that these communities in turn affect hydrology and fluvial geomorphology, scant attention has been paid to the interactions between invasions and these physical processes. Similarly, relatively little research has been undertaken on competitive interactions between alien and native riparian plant species. Further research in these fields is necessary at a variety of spatial and temporal scales before the dynamics of riparian invasions, and their impacts, can be properly understood.

This paper examines the ecological impacts arising from road networks and the potential ameliorating effects of roadside habitat in a highly modified landscape. A U.K. focus has been adopted to illustrate the effects of roads in a landscape with a long history of land use and intensive land management where the impacts and the potential for improvement are considerable. The impacts of roads in the ecological landscape include habitat loss, fragmentation, and degradation. These interrupt and modify natural processes altering community structures and in the longer term, population dynamics. The large number of fauna fatalities each year from road traffic accidents is also of concern. Road verges can however also provide habitat opportunities and restore connectivity in an otherwise fragmented landscape offering potential to offset some of the adverse impacts of the existing road network. This review demonstrates that roads can present both ecological costs and ecological benefits although currently there is insufficient evidence to confirm some of the key theories which relate to the impact of the barrier effects (at population level) or the value of road verges as ecological corridors. In the absence of complete information the full extent of the problems and opportunities cannot be gauged and every effort should be made therefore to enhance the habitat adjacent to existing roads and to constrain further fragmentation caused by the development of the existing road network. Where further construction is unavoidable conditions should be enforced to prevent roads from reducing further the remaining habitats of conservation value and the connectivity between such habitats.

After a brief description of the evolution of seed bank research, this review highlights the importance of the seed bank in understanding the character and dynamics of river margins. Through a discussion of published research on wetlands in general, the lack of research focused on riparian systems is highlighted. This is followed by an evaluation of current knowledge concerning the nature and dynamics of riparian seed banks and the factors that control the erosion, transport and deposition of riparian seeds. The paper concludes by (i) indicating the complexity of the interactions that control the riparian seed bank and that require understanding if the consequences of alterations in river flow regime and riparian management are to be fully understood and (ii) identifying some major research gaps relating to interactions between fluvial processes and riparian seed banks.