A conservation paradox for river corridor plants

We investigated grassland composition and diversity aspects for the alluvial plain of the River Meuse, one of the larger Northwest European streams, with special emphasis on the river corridor plants of dry river grasslands. In order to define a conservation strategy for the river corridor plants we examined isolation and fragmentation aspects and the role of flooding. A mapping and sampling of vegetation and soil conditions over the alluvial plain was executed, together with a recruitment analysis for the rare species of dry river grasslands. The central question for the study was whether preservation of relicts is a sufficient means to preserve riparian diversity. In the DCA ordination the rare river corridor plants were clearly restricted to the pioneer dry river grasslands of gravel or sandy deposits further from the river. A significant isolation of the river corridor plant relicts was revealed. As for the cause of this isolation, our analysis indicated recruitment limitation to be the major threat for survival of most of the river corridor plants. The recovery of populations depends strongly on flood contact and recruitment potential in the creation of new habitat. The withdrawal of the hypothesis that conservation outside the river dynamic influence is a necessity, shows that the construction of conservation and rehabilitation strategies for species at risk needs a good knowledge of key processes that determine the population dynamics at the regional scale. For the investigated River Meuse reach, the flood dynamics proved an essential habitat creation process, strongly determining population dynamic strategies and restoration potentials at the reach scale.