Factors determining the distribution pattern of floodplain vegetation remnants along the Danube River between Straubing and Vilshofen

Floodplains are of high importance for biodiversity and ecological functions due to their spatio-temporal heterogeneity. To understand the human influences on the floodplain vegetation, we analyzed 108 vegetation releves in the Danube Floodplain in Germany. Ten vegetation types (e.g. floodplain meadows, river bank vegetation, softwood forests, hardwood forests) were identified among the woody and open land vegetation. They reflected the hydrological gradient in the floodplain. We explored the relationship between the species composition and environmental variables from the landscape level to the local level using Non -Metric Multidimensional Scaling (NMDS), Boosted Regression Trees (BRT), and Classification and Regression Trees (CART). Even in a floodplain that is heavily influenced and altered by humans, such as the study area, the hydrological regime was still the most important factor determining species composition. Furthermore, the landscape fragmentation and the land use (e.g. agriculture) also played an essential role. Although the composition of vegetation types along the Danube Floodplain is similar to floodplain vegetation under natural conditions, some groups lost their original habitats (e.g. softwood remnants) due to the landscape fragmentation caused by infrastructure or they occurred in atypical habitats. For instance, the short-lived species that typically occur at the river banks were confined to the banks of backwaters and gravel lakes due to the regulation of the main river channel. Therefore, factors at all levels need to be taken into consideration before starting a planning process in floodplains.