Carya as marker for tree refuges in southern Italy (Boiano basin) at the Middle Pleistocene
Résumé
The Carya genus, a tree of the Juglandaceae family, has a restricted geographical distribution today, mainly confined to North America and Southeast Asia and with a precise range of ecological requirements. During the Neogene, Carya had a wide distribution across the northern hemisphere; however, its habitat was reduced progressively in response to Pliocene and Quaternary climate changes. In the Early and Middle Pleistocene paleobotanical records, Carya is considered a relic which testifies to the final climatic deterioration of the Pliocene and to the global effect of the Quaternary climate cycles. The lacustrine and fluvio-palustrine sequence of Boiano (Molise, Italy) records the paleoenvironmental and climate changes since the Middle Pleistocene. The chronological framework is based on several tephra layers, related to known eruptions or directly dated, and indicates that the basal deposits are older than 440 ka. Palynological study of the sedimentary filling highlights vegetation changes from Oxygen Isotopic Stage (OIS) 13 to 2. The Boiano biotope, characterized by a continuous edaphic and climatic humidity, favored the persistence of hygrophilous tree taxa. Thus, Carya is present until the OIS 9, which represents its latest occurrence in Western Europe. The Boiano basin could have been an ecological refuge for the Middle Pleistocene arboreal flora. In fact, the physiography of the basin certainly softened the impacts of climatic deterioration during glacial episodes. Therefore, the late Carya occurrence within the Boiano palynological record in a time period when it is commonly supposed to be extinct from Europe, leads to a consideration of its ecological requirements as a tool for Quaternary paleoenvironmental reconstructions and for identification of refuge areas.