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Editorial

Laurent Astrade
p. 185-186
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Éditorial

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1This special issue of Géomorphologie : relief, processus, environnement, devoted to biogeomorphology, presents research work that on the one hand concerns the interactions between the ligneous vegetation established on alluvial banks and the hydromorphological dynamics in fluvial corridors, and on the other concerns the utilisation of trees as natural archives for spatio-temporal reconstruction of the dynamics of mountain slopes.

2The first two articles address the role of plant formations and hydrology in the successional trajectories and the evolution of river beds. V. Garófano-Gómez et al. trace the natural processes of succession on a segment of the lower course of the river Allier, considered to be one of the last fluviatile sectors that is still laterally mobile. This study analyses the dynamics of plant succession over a period of fifty years based on aerial photos, dominant trajectories and their relation to accounts of historic flow rates. It reveals a critical threshold of transition in the plant succession since the beginning of the 20th century and facilitates understanding of future trajectories of evolution of the river ecosystem in the present context of global climate change. C. Jourdain et al., also using a set of aerial photographs and hydrological data, show the relation, over more than twenty years, of the disappearance of surfaces with vegetation cover and the creation of bare soils (renewal of macroforms with vegetation cover) with hydrological episodes (frequent floods and four decennial floods) in a pebble bed subjected to high human impact, the dyked Isère river at Combe de Savoie. These two studies present a strong operational significance in the present context of European river ecosystems in temperate regions, which have lost their dynamic character because of channelling and the regulation of flow. They improve knowledge of the hydro-sedimentary factors/vegetation relationship and of the potentialities for auto-maintenance of river beds affected by plant growth and for the management of a biodiversity that closely depends on a regular renewal of fluvial forms. The releasing of artificial waters that simulate natural floodwaters is also an option that is more and more often considered in the context of river management.

3The following two articles address, this time on the scale of the plant, general questions concerning the features of alluvial species, the behaviours and survival of the seedlings of pioneer ligneous plants in different environments and under different degrees of mechanical constraints during flood episodes (stress, shearing off, uprooting, burying). An understanding and a quantification of the variation in morphological and biomechanical responses within populations according to their degree of exposure to the mechanical constraint are fundamental to better comprehend why and how plants influence geomorphology. B. Hortobágyi et al. analyse the physiological features of young Salicaceae plants in the different environments of a river bed. Their empirical study on the river Allier provides quantifications based on statistical analyses of the relation between the morphological and biomechanical features of the responses of the aerial and underground parts of black poplars (Polulus nigra L.) and their exposure to different degrees of mechanical constraint. C.‑L. Wintenberger et al. study at a fine spatio-temporal resolution the survival conditions of the seedlings of black poplars (Populus nigra L.) and white willows (Salix alba L.) to floods, both in the field and in controlled conditions in a nursery. The approach in situ was carried out on a sedimentary bank in the centre of a channel located in the middle Loire. The approach ex situ was based on fine measurements of root growth and stem growth as well as on measurements of resistance to uprooting. The comparison of the measurements carried out ex situ with the constraints exercised in situ enable refinement of the understanding of the distribution of the survival of the seedlings.

4Finally, the last two articles address the dynamics of slope and of risks, in this case mudflows and landslides, which in the Alps are the cause of the destruction of much road infrastructure and buildings, and in certain cases even loss of human lives. J. Blanpied et al., on the mudflows of a torrent in the massif of the Chartreuse (torrent of the ravine of the Diable, Mont Granier) and J. Lopez‑Saez et al., on the landslide of Schimbrig (Swiss Alps), reconstruct and map, by an applied integrative study (geomorphological cartography of the forms associated with the activity of the process, dendrogeomorphological dating, diachronic analysis of aerial photographs and historical archives), the frequency and spatial extension of past activity. This work reveals the complementarity (faced with the incomplete accounts taken from historical archives), the reliability and the operational importance of the dendro-geomorphological approach for understanding hazards, at high spatio-temporal resolution, and for the management of future risks.

5The drafting committee thanks the authors for their articles and all the readers for their contribution to this issue.

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Laurent Astrade, « Editorial », Géomorphologie : relief, processus, environnement, vol. 23 - n° 3 | 2017, 185-186.

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Laurent Astrade, « Editorial », Géomorphologie : relief, processus, environnement [En ligne], vol. 23 - n° 3 | 2017, mis en ligne le 04 octobre 2017, consulté le 22 novembre 2017. URL : http://geomorphologie.revues.org/11824

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Auteur

Laurent Astrade

Laboratoire EDYTEM/CNRS, UFR Sciences et Montagne, Université Savoie Mont Blanc – Pôle Montagne, Campus scientifique, 73 376 Le Bourget-du-Lac cedex, France (laurent.astrade@univ-smb.fr). Tél : +33 4 79 75 94 08.

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