A conservation paradox for riparian habitats and river corridor species

The floodplain meadows of the River Meuse, one of the larger Northwest European streams, harbour a specific group of river corridor plant species. These species are mostly restricted to small habitat patches of dikes and natural levees as these locations provide the necessary microclimate conditions for this species group with a more southern Central European range. This spatial restriction of habitat together with the intensified agricultural use of the floodplains means that these habitat fragments have become rare in the river valley. The central question for the study was whether preservation of these relics is a sufficient means to preserve this group of species and the overall riparian diversity. We investigated the composition and diversity of the floodplain meadows of the alluvial plain of a 40 km river reach. Emphasis was on the specific conditions of the dry river grasslands with river corridor plants. A mapping and sampling of vegetation and soil conditions over the alluvial plain was executed. This analysis was completed with a colonisation survey for the rare species of dry river grasslands in newly generated habitat after two consecutive flood peak periods of the mid-nineties and the beginning of this century. Comparative analysis of the recruitment over the different meadow types was done by defining a colonisation rate per type. In the DCA ordination the dry river grasslands appeared separated from the other floodplain meadow communities, and the rare river corridor plants showed a strong preference to the pioneer dry river grasslands. These communities are restricted to the gravel or sandy deposits on the more elevated parts of the floodplain. A significant isolation of the river corridor plant relics was revealed.