Carya as marker for tree refuges in southern Italy (Boiano basin) at the Middle Pleistocene

Abstract

The Carya genus, a tree of the Juglandaceae family, has a restricted geographical distribution today, mainly confined to North America and Southeastern 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 the Pliocene and Quaternary climate changes. In the Early and Middle Pleistocene palaeobotanical 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 palaeoenvironmental and climate changes since the Middle Pleistocene. The chronological framework is based on several tephra layers, identified as known eruptions or directly dated, and indicates that the basal deposits are older than 440 ka. Palynological study of the sedimentary filling highlights the specificities of the Boiano basin through the vegetation changes from Oxygen Isotopic Stage (OIS) 13 to 9. 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 revision of its palaeoecological and palaeoenvironmental significance. Due to its strict range of ecological requirements, Carya could therefore represent one of the more valuable palaeoenvironmental markers for the European Quaternary refuges