Northern boreal alluvial meadows are ecologically significant semi-natural ecosystems within the riparian zone. The effects of disturbance like flooding, grazing, and mowing have historically maintained high nutrient turnover and succession disruption that led to high biodiversity, leading to their inclusion in the Natura 2000 network. Today, alluvial meadows are threatened by human abandonment and river flow regulations, both of which provided necessary disturbances. This leads to encroachment by woody plants and a significant reduction in biodiversity. The purpose of this project was to investigate the hydrological conditions required for the long-term maintenance of floodplains of the regulated lower Dal River and how varying water levels affect the species distribution and various vegetation characteristics. This was done by examining plant data from 3 sites in an alluvial meadow in Bredforsen and datalogger water level data to calculate the duration of flooding of plots in a transect study. The effects of altitude, flooding durations, and frequencies on species richness, proportion of woody plants, and vegetation cover were examined. Flooding times showed the most significant effects on vegetation characteristics, while altitude and flooding frequencies differed greatly between sites, with variability explained being low for all explanatory variables. On one hand, this shows that that a lack of seasonal flooding has a negative effect on the alluvial meadow ecosystem and an increase in water flow would be beneficial. On the other hand, the low degree of explained variability implies that flooding solely is not the determining factor and other management methods are necessary to maintain the alluvial meadows.

Three seasons of initial succession were followed in the frame of this thesis after a restoration project in a section of the Stropnice River and its floodplain. The succession tends towards formation of community of alluvial meadows, which is prevailing biotope in the neighborhood of the restored part. Strong factor influencing the course of succession is wetness of the substrate, which is partially given by distance of a site from the water-course and by the difference in the altitude of a site and of the river water table. Synantrophic species were most abundant in the first year (2014), followed by meadow and wetland species (2015, 2016).