Changes in land‐snail communities and steppe environments in the lower Rhône valley during the Lateglacial–Holocene transition

The French Mediterranean region, like others in southern Europe, is thought to have hosted glacial refugia for temperate plants and animals. At its heart, the Rhône valley appears to have been a pathway for various organisms towards the northern areas. Two well‐dated postglacial molluscan successions were investigated. They allow for the reconstruction of postglacial palaeoenvironments and recolonization stages by temperate snails. Particularly responsive to habitat structure, the mollusc fauna invites reassessment of the extent of Lateglacial and Early Holocene steppe‐like formations which often appear underestimated. Only a few species with forest affinities appear since c . 10 500 cal. a BP. They are not very demanding in terms of tree cover and their abundance remains insignificant. For taphonomic reasons, the only truly forest snails are found here late, as relicts of a maximum known elsewhere between c . 8000 and 7400 cal. a BP. After the Lateglacial, steppe and wooded steppe snail communities are exclusive throughout the Early Holocene. They correspond with the juniper shrub‐steppe of anthracologists between c . 11 400 and 8900 cal. a BP. The cold‐stage species Xerocrassa geyeri coexists until c . 10 400 cal. a BP with newly recruited xerothermic snails. The return of the endemic Candidula rugosiuscula , as early as 13 100 cal. a BP, suggests the existence of local refugia during the LGM and the preceding glacial stages. Backeljaia gigaxii , absent from the Pleistocene before the Late Glacial Interstadial (LGI), could be an immigrant. The existence of local glacial refugia for open‐ground Mediterranean snails remains a priority question. The role of local refugia for forest snails only becomes effective after the 9.3 ka event due to aridity. That of classical forest macrorefugia is not apparent. In the future, we will be able to refer to these stratigraphic sequences and their malacological content to correlate the scattered and incomplete successions that are most frequent in the Lateglacial and Early Holocene regional record.