- Seed bank, seed dispersal and vegetation cover: Colonization along a newly-created river channel - 665 Journal of Vegetation Science 17: 665-674, 2006 © IAVS; Opulus Press Uppsala. Abstract Question: What is the relative importance of the initial seed bank and subsequent seed dispersal for floristic composition of bank vegetation two years after creation of a newly-cut reach of a river channel? Location: River Cole, West Midlands, United Kingdom. Methods: We took bank and bed sediment samples from a 0.5-km reach of a new river channel cut into intact flood-plain. After river diversion, seed samples deposited on artificial turf mats placed on the river banks and flood-plain edge were taken in summer and winter 2002 and 2003. Seed rain samples from funnel traps were taken during summer 2002 and 2003. We undertook greenhouse germination trials to assess viable seed species within these samples. In summer 2004, we sur- veyed river bank vegetation. Agglomerative cluster analysis was used to investigate floristic similarity between seed bank, seed rain, seed deposi- tion samples and final bank vegetation cover. DCA was used to explore contrasts between the samples and to assess whether these reflected interpretable environmental gradients. Results: Seed rain samples contained a small subset of species in the summer depositional samples. 38 species were found within the final vegetation, the seed bank, and at least one of the four sets of depositional samples; a further 30 species not present in the seed-bank samples were present in at least one of the four sets of depositional samples and the final vegetation. Floristic composition of the vegetation was most similar to the depositional samples from winter 2002 and 2003 and summer 2003. DCA axis 1 reflected a time sequence from seed-bank samples through depositional samples to the final vegetation. Conclusions: Newly cut river banks were colonized rapidly. Seed remobilization and hydrochorous transport from the upstream catchment are important for colonization. Species richness was highest in samples deposited during winter when high river flows can remobilize and transport viable seeds from upstream. This process would also have enhanced the species richness of seed production along the banks during the second summer (2003). Keywords: Artificial turf mat; Riparian vegetation; River bank colonization; Restoration. Nomenclature: Stace (1999). Seed bank, seed dispersal and vegetation cover: Colonization along a newly-created river channel Gurnell, A.M. 1* ; Boitsidis, A.J. 1,4 ; Thompson, K. 2 & Clifford, N.J. 3 1 Department of Geography, King’s College London, Strand, London, WC2R 2LS, UK; 2 Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK; 3 School of Geography, University of Nottingham, Nottingham, NG7 2RD, UK; 4 Jacobs Babtie, School Green, Shinfield, Reading, Berkshire, RG2 9HL, UK; * Corresponding author; E-mail angela.gurnell@kcl.ac.uk Introduction Within river margins, bare areas of river bank can become quickly colonized by vegetation, but the rela- tive importance of different propagule sources for this colonisation is difficult to identify. Although soil seed banks potentially influence vegetation composi- tion after disturbance (Décamps et al. 1995), species richness and abundance of germinable seeds vary widely in riparian seed banks (e.g. Abernethy & Willby 1999; Beismann et al. 1996; Skoglund 1990). Above- ground vegetation often does not correspond closely to the riparian seed bank (e.g. Beismann et al. 1996). Dissimilarity between species present in seed banks and in the overlying vegetation can be partly attrib- uted to reproductive strategies. Some species (e.g. Salix spp.) produce many short-lived seeds; some (e.g. Phalaris spp.) are predominantly vegetative and produce very few seeds, and some, such as many annual species and Juncus spp., often are more fre- quent in the seed bank than in the above-ground vegetation (Berge & Hestmark 1997; Thompson & Grime 1979). Riparian seed-bank composition can be influenced by physical processes, including the hydrological re- gime (inundation and soil moisture fluctuations) and erosion and deposition of mineral and organic sediment (Abernethy & Willby 1999; Bornette et al. 1998; Goodson et al. 2002). In addition, seeds are dispersed along river corridors by a variety of mechanisms including direct deposition from the parent plant and also transport by wind, water and animals (Goodson et al. 2001). Hydrochory has been shown to play an important role in riparian seed bank dynamics by transporting and depositing freshly- produced seeds (Boedeltje et al. 2003; Goodson et al. 2003; Merritt & Wohl 2002), remobilizing seeds (Goodson et al. 2003; Pettit & Froend 2001), and thus structuring riparian plant communities (Andersson et al. 2000; Johansson et al. 1996; Nilsson et al. 1991).