Résumé
Wetland conservation and management are generally only based on present-day studies, without integrating historical considerations. However, wetlands contain palaeoecological archives that can provide accurate records of their own history. Our study aims at reconciling this paradox in the central French Alps, by reconstructing the past wetland diversity/richness and the controls of Holocene hydroseral dynamics, and by discussing on this historical basis their conservation, management and restoration. Previously published data, complemented by the palaeoecological study of a sedge mire, reveal three main stages in the regional hydroseral succession: initial aquatic plant communities (Nymphaea alba, Nuphar cf. lutea, Menyanthes trifoliata), carrs (Alnus glutinosa/incana, Salix spp., Thelypteris palustris), then sedge meadows (Cyperaceae, Poaceae, Lythrum salicaria…). This dynamic comprises (1) a classical evolution from open water bodies to treed wet communities, controlled by the relationships between sedimentation processes and climate, and (2) an unexpected return to herbaceous wet habitats mainly triggered by Subatlantic human-induced managements. Such recent changes induced in the studied region the decline of Alnus cf. glutinosa, the disappearance of Thelypteris palustris, and the extinction of the carr communities they constituted. The historically-based assessment of community naturalness and resilience appears critical for defining conservation priorities, refining management actions, and identifying baseline conditions for restoration initiatives. The main implications of our results are to reinforce conservation measures on the less impacted habitats and to increase the diversity/richness of isolated lowland mires, notably by restoring alder communities in some of them.
► Palaeoecological data were used for identifying conservation priorities for wetlands. ► The past diversity and dynamics of hydrophytic communities were reconstructed. ► The role of human activities and climate in past wetland changes was discussed. ► Naturalness and resilience of wetland plant communities were assessed. ► Palaeoecological data appear useful to manage and restore wetlands.