Abstract
This study compares the vegetation and seed deposits of free-flowing parts of a river with those regulated by straightening, as well as identifying the correlation between the breadth of the river-bed, existent vegetation and distribution of plant species along the river corridor. The 31 sampling plots in the Ukrainian Carpathians, at an equal distance of four km from each other, were positioned across different vegetation zones. Vegetation and seed bank data were collected. The study showed that effective distribution of plants has a place in native (non-regulated) river-corridors with a river-bed breadth of 15-30 m. The reduction and straightening of the river-bed decrease the number of species that can be dispersed along river. The percentage of seeds of alien species greatly increases, from 0.1% in the free-flowing to 10% in the regulated parts of rivers. River regulation causes transformation of native vegetation communities in these plots into associations of invasive herbaceous perennial species; such as associations of Helianthus tuberosus and Solidago gigantea. The analyses do not show a clear link between the breadth of the river-bed and number of invasive species in the vegetation community. The research suggests that river regulation has a clear negative effect on vegetation by decreasing the resistance of plant communities to alien species