Vegetation succession processes and fluvial dynamics of a mobile temperate riparian ecosystem: the lower Allier River (France)

[EN] Many riparian ecosystems in European temperate regions have lost their inherent, highly dynamic character due to human-induced impacts such as river channelization and flow regulation. The lower course of the Allier River (France) is one of the last remaining free meandering river segments, and thus, constitutes an opportunity to investigate riparian succession processes of a dynamic, temperate river system. We analyzed (i) the dynamics of the succession phases based on eight sets of aerial images of the riparian corridor over the last five decades (1967-2014), (ii) the dominant succession trajectories and (iii) their relation with the Allier River flow regime. Results revealed that the study site was characterized by a shifting habitat mosaic between 1967 and 2005, whilst floods did not change the overall habitat composition of the riparian corridor but their distribution in space. After the year 2005, progression and retrogression processes have been drastically reduced, with an increase of stability (i.e. no more channel migration and neither progression nor retrogression of patches), and a concomitant reduction of high and moderate magnitude floods. This study depicts a clear threshold of trajectory change in succession processes since the beginning of the 21st century and facilitates a better understanding of future trajectories under current global climate change.
We thank P.A. Dejaifve (conservationist of the Reserve Naturelle Nationale du Val d'Allier) for the information provided about the study area. We are grateful to A. Blaschka, E. Lautsch and K. Dolos for their help in a previous version of this manuscript. V. Garofano-Gomez received a post-doctoral grant from the University Blaise Pascal (now: Universite Clermont Auvergne, France). B. Hortobagyi was funded for her PhD by the French Ministry of National Education, Higher Education and Research. M. Diaz-Redondo was supported by a grant from the Fundacao para a Ciencia e Tecnologia as part of the FLUVIO Doctoral Programme - University of Lisbon (Portugal). The authors would like to thank the two anonymous reviewers for their constructive comments and suggestions.