Short-term impact of river restoration and grazing on floodplain vegetation in Luxembourg

In 2003, the Syr River was redirected from a channel running along the valley edge into a slightly reshaped riverbed on the valley floor, after which, in 2004, a low intensity (1.0 livestock units ha−1), year-round grazing system with Galloway cattle was introduced on a 24 ha floodplain pasture. 200 permanent plots were randomly distributed on the floodplain pasture to study vegetation development between 2004 and 2006 under the influence of the combined rewetting and grazing regime. The effect of grazing was investigated separately in 16 grazing exclosures (comprising 64 grazed and 64 control plots) in different habitat types during 2005–2007. At each plot, vegetation composition was surveyed using a decimal scale to determine cover estimates, and vegetation structure and grazing impact indicators were determined. Non-metric multidimensional scaling revealed that the restoration measures triggered a marked short-term shift in vegetation composition. The intensity and direction of this shift varied clearly along a topographical gradient in the floodplain. Species richness increased significantly, and typical wetland species and Red Data Book species were favoured in the riparian area. Grazing hindered rapid species turnover since the turnover rate in grazed plots (from 2006 to 2007: 0.29) was significantly (p < 0.05) lower than in control plots (0.35). Species richness differed significantly (p < 0.001) between 15.8 species per plot in the grazed to 10.1 in the control treatment (in 2007). The short-term trial suggests that river restoration and moderate grazing in combination may represent a promising strategy for the restoration of floodplain wetlands.