The human impact on flora and vegetation of floodplains is shown, using alpine rivers as an example. Typical for natural alpine floodplains are large gravel bars with pioneer vegetation. Their species are highly specialized and strongly adapted to the extreme living conditions (high hydro- and morphodynamics, alluvions poor of nutrients). Under the human impact (changes of landscapes in the catchment area, nutrient input in the river system, civil engineering measures, loss of biogeographical barriers) the specialized plants are replaced by more common species. Today plant- communities of the lowland floodplains and ruderal sites dominate. Agriophytes are mainly found in the parts with the strongest human impact in the lower reaches of the rivers. Among the different engineering measures the construction of barrage weirs has the greatest impact on vegetation. The reason is that the essential abiotic factors in floodplains i.e. the hydrodynamics and the morphodynamics are changed or disturbed by them.
