Urban rivers as dispersal corridors for primarily wind-dispersed invasive tree species

Urbanization may have a large affect on biodiversity patterns by enhancing biological invasions. Urban habitats harbour high numbers of introduced plant species and may function as starting points for invasions along urban-rural gradients. As information on underlying mechanisms is critical for managing biological invasions, we test the role of rivers as dispersal corridors for primarily wind-dispersed ornamentals. We released tagged fruits of three invasive tree species in the Spree River (Berlin, Germany) and directly observed the fate of the floating samaras. The number of floating samaras declined exponentially with distance from the release point. A quarter floated 1200 m within 3 h. Despite marked differences in fruit morphology, there were no interspecific differences in floating capacity. We showed hydrochory to be an effective dispersal agent in wind-dispersed tree species, extending wind-related transport distances by several times. In this way, rivers are expected to link urban propagule sources with natural habitats downstream. Our results suggest that planting native tree species along river corridors would help prevent invasion risks and contribute to implementing principles of ecological design in urban greenways and generally consider the importance of eradicating wind-dispersed invasive tree species in floodplains in early invasion stages to prevent further water-mediated dispersal. (C) 2009 Elsevier B.V. All rights reserved.