An investigation of the composition of the urban riparian soil propagule bank along the River Brent, Greater London, UK, in comparison with previous propagule bank studies in rural areas

Most propagule bank research has been conducted in rural areas and has emphasised agricultural soils, although research on rural riparian propagule banks has expanded rapidly over the last decade. This paper presents observations of the species abundance of plant propagules in urban riparian soils along the River Brent, Greater London, UK. The data are analysed to explore changes in species abundance of the propagule bank with depth (0?C5?cm compared with 5?C10?cm soil layer), with distance from the river (0?C1?m, 1?C2?m, 2?C3?m), and at different locations on the river network. No significant differences were found in propagule abundance with soil depth or distance from the river??s edge, but significantly more species were found in the propagule bank close to the river??s edge. The species composition of the Brent??s propagule bank is then compared with riparian propagule banks from the rural rivers Dove, Frome and Tern, UK. Species richness of the Brent propagule bank samples was generally lower than was found in the three rural rivers and, in total, 21%, 4%, 5% and 4% of observed species were aliens in the Brent, Dove, Frome and Tern soil samples, respectively. When the species present in the Brent??s propagule bank were compared with published data on urban garden soils in another UK city, the latter were found to support a higher number of alien species, suggesting that other propagule sources to urban river systems support lower numbers of alien species in riparian zones than domestic gardens.