Dynamic minimum flows in the bypass reach of Juktån : A post-implementation evaluation of the effects on riparian vegetation

Abstract: The purpose of the paper was to evaluate the effects of the restoration efforts in Juktån on the plant species richness and composition, vegetation zonation and soil composition. The restoration involved implementation of a dynamic flow, in addition to hydro-geomorphological alterations. Three sites were inventoried in the bypass reach, representing one reach affected only by flow restoration and two reaches affected both by flow and morphological restoration, along with an upstream reference reach unaffected by regulation. Inventories were conducted along an elevational gradient perpendicular to the water and involved occurring species, plant cover, bare ground and soil composition. The results showed a change in species composition after restoration. Riparian associated species were more common after restoration and the proportions of herbs and graminoids increased. Higher flooding caused a change in zonation, increasing the graminoid, riparian forest and amphibious zones along the riparian habitat. Species richness, as well as soil composition remained largely the same. The effects of the hydro-geomorphological alterations were hard to interpret due to lack of data. The results indicate a positive effect of the new flow on the plant species community in the bypass reach, whilst also highlighting the hydro-geomorphologically altered locations as biodiversity hotspots. Time-delay in ecological response is acknowledged as driving factor for the indifference in species richness and soil composition. The hydrological restoration is concluded to be an effective way of simulating natural flow regimes, improving ecological integrity of riparian communities and structural vegetational patterns in the riparian zone of bypass reaches.