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Patrons de sédimentation et caractéristiques de la ripisylve dans les casiers Girardon du Rhône : approche comparative pour une analyse des facteurs de contrôle et une évaluation des potentialités écologiques

Abstract : The multiple uses made of large rivers, such as the Rhône in south-eastern France, have provoked profound modifications of their fluvial dynamics. As a consequence, the hydro-sedimentary and ecological functioning of their channels and floodplains are highly altered. Integrated restoration programmes struggle in defining potentials and risks related to such ‘novel ecosystems’ and to understand the various interacting drivers which influence their formation. This study comparatively focused on 293 dike fields—rectangular units delimited by longitudinal and lateral submersible dikes constructed in the channel in the late 19th century to promote the navigability of the Rhône. They are distributed over four reaches by-passed in the 20th century for hydro-electric energy production. We investigated the spatio-temporal patterns of sediment deposition and the structure and composition of the forest stands using remote sensing and field data. We also propose a conceptual model of potential drivers and processes behind the observed patterns. Eighty percent of the dike fields have evolved from the aquatic to a terrestrial and forested stage, following variable historical trajectories both between and within reaches. The forest stands presented structural characteristics which differed from more natural reference stands and compositional characteristics closer to mature than to pioneer systems. They featured a high presence of non-native species, such as the invasive Box elder (Acer negundo). Our comparative approach constituted a first step to disentangle the cumulative effects of the drivers and define their individual roles: we discovered a prominent role of local factors, especially the connectivity to the main by-passed channel. The evolution of the environmental factors themselves added to the complexity of the patterns. This work provides a basis for future studies of novel ecosystems on rivers, and a new perspective to river managers on the Rhône due to its innovative spatial-scale.
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https://tel.archives-ouvertes.fr/tel-01998355
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Submitted on : Tuesday, January 29, 2019 - 3:33:27 PM
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  • HAL Id : tel-01998355, version 1

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Bianca Räpple. Patrons de sédimentation et caractéristiques de la ripisylve dans les casiers Girardon du Rhône : approche comparative pour une analyse des facteurs de contrôle et une évaluation des potentialités écologiques. Géographie. Université de Lyon, 2018. Français. ⟨NNT : 2018LYSEN006⟩. ⟨tel-01998355⟩

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