Macrophyte assemblages in the aquatic-terrestrial transitional zone of oxbow lakes in the Danube floodplain (Austria)

摘要

The Lobau wetland and oxbow ensemble is part of the large Danube River floodplain area between Vienna (Austria) and Bratislava (Slovakia). The Danube River regulation scheme implemented in the late 19th century considerably affected the Lobau area, which is part of the Danube National Park today. Terrestrialization processes in the floodplain started with the river regulation and pose an increasing threat to the aquatic and wetland vegetation of this ecosystem. Former vegetation studies were either directed toward phytosociological description of associations or to a general vegetation inventory and mapping, where transitions between vegetation types are not accounted for. Our purpose is to provide a detailed insight into the vegetation zonation pattern along the aquatic-terrestrial inundation gradient in the Lobau floodplain area. We sampled a total of 49 belt transects. Samples in each transect were classified into groups using two-way indicator species analysis (TWINSPAN). Resulting groups of all transects were subjected to fuzzy c-mean clustering (FCM), defining 'community types' by means of indicator species analysis (ISA). We found 36 significant indicator species typifying 14 community types. Nine types belong to the shoreline vegetation and five types characterize the aquatic habitats. In addition to these community types, two transitional zones were found, one defined as open water/wetland transition and one as wetland/upland transition. Along the aquaticterrestrial environmental gradient, different floristic and quantitative relations of community types and transition zones were identified. Finally, the importance of such a fine-scale description of zonation patterns along the inundation gradient is discussed in relation to longterm monitoring programmes as the basis for rehabilitation or wetland conservation measures.