EFFECTS OF RIVER REGULATION ON PLANT DISPERSAL AND VEGETATION.

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 4 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. [ABSTRACT FROM AUTHOR]