Development of vegetation in created wetlands in western Norway

Abstract

The Myrkdalen lake, western Norway was subjected to a permanent 1.4 m drawdown in June 1987. After the drawdown, channels and artificial islands were constructed within the exposed floodplain system. Two permanent transects were established within this man-made environment, and these have been analyzed annually until 1995. The quadrats lie all on the same type of substrate, are at different elevations in relation to the water-level. This paper describes vegetation development on these newly created islands. The investigation shows major vegetational changes during the eight year period. Two main processes have taken place, vegetation zonation and primary succession. The first year after the construction, most of the created sites had a similar floristic composition, regardless of elevation. Major dominants during the first three years (e.g., Subularia aquatica, Marchantia polymorpha, Blasia pusilla, and numerous acrocarpous mosses) disappeared or were greatly reduced, and they were gradually replaced by species which were climax species in the wetland communities before the drawdown (e.g., Carex rostrata, C. vesicaria, Phalaris arundinacea, Salix nigricans). The main vegetational change occurred between the third and the fourth year. After three years characteristic vegetation zones were differentiated, with aquatic plants and helophytes in the lowermost parts, and willow shrubs in the uppermost parts of the islands