Land-cover change and the distribution pattern of natural and semi-natural alluvial vegetation remnants along the Upper Danube River

Abstract

Due to high spatio-temporal heterogeneity, floodplains are of high importance for ecological functions (e.g., as a buffer of flood events, erosion control, wood producers and pollutant filters but also as a provider of important habitats). During the past centuries, large areas of European floodplains have gone lost and many riparian habitats (e.g., riparian forests, floodplain grassland) have been threatened by human activities. The land-cover change along the Upper Danube from 1963 to 2010 as well as the distribution pattern of floodplain vegetation at different scales were analysed to quantify the human influences on the floodplain landscapes and vegetation.Landscapes in the Upper Danube Floodplain experienced an increasing fragmentation from 1963 to 2010, which resulted from agricultural intensification and infrastructure development (Chapter 2). Despite the decline of agricultural land in the floodplain in recent decades, it still accounted for a large proportion in the active floodplain due to agricultural intensification. The loss of riparian forests was a consequence of infrastructure development and forest clearance for flood protection. The land-cover transformation was mainly determined according to the hydrological, topographical and soil characteristics.The distribution and composition of plant communities in floodplains is a consequence of both natural (e.g., hydrological and geomorphological) and human factors (Chapter 3). The analysis indicated that in the Danube Floodplain under strong human influences, hydrological parameters were still the primary driving forces causing the distribution pattern of floodplain vegetation. Landscape structure as well as fragmentation played an essential role in the distribution pattern of floodplain vegetation. The rare occurrence of softwood remnants along the Danube in the fragmented landscape resulted from the dense infrastructure and intensified agriculture. Backwater and gravel ponds proved to be secondary habitats for the short-lived species (e.g., Glyceria maxima, Persicaria amphibia), which originally occurred at river banks. Besides the hydrological factors and landscape patterns, site characteristics such as site land use, soil texture and soil types were of minor but measurable importance to the species composition.Land-cover change led to the habitat loss of riparian forests and resulted in the shift of spatial distribution of some species groups. Due to the lack of historical vegetation data, the temporal comparison of species composition could not be conducted. However, based on previous researches it can be assumed that the increasing fragmentation might alter the species composition of floodplain vegetation, and the further fragmentation might become a problem in the future.Overall, the results suggest that in the floodplain under strong human interventions, analysing the landscape pattern is a useful tool for explaining the plant species composition and the distribution of floodplain vegetation. A quantitative analysis of the temporal and spatial pattern of land cover, the distribution of floodplain communities such as forests and meadows from the landscape scale to the local scale provides a framework for analyzing landscape patterns in floodplains from a comprehensive view, and demonstrates the negative impacts of infrastructure development on the riparian habitats and floodplain vegetation.