From the Roman Empire to the present: Two millennia of pollen-based environmental changes and climate-human interactions in the Po Delta area (NE Italy)

Abstract

Holocene prodelta lobes are key sedimentary archives of environmental change that can be used effectively for high-resolution palynological investigations, as they: (i) consist almost entirely of mud, (ii) represent stratigraphically expanded successions, and (iii) are strictly related to river dynamics, thus reflecting vegetation changes in river catchments. In this study, we focussed on the ~20 m-thick prodelta succession of the modern Po Delta (NE Italy), fed by two river branches (Volano and Goro) that were mostly active during the past two millennia, a period of rapid acceleration of natural resources’ exploitation and climate variability. Forty-eight samples with mean temporal resolution of 50 years were analysed. Eleven ecological groups and four pollen zones were identified, with distinct peaks of the secondary-primary pollen ratio marking major floods during the Volano-Goro lobe switching and the Little Ice Age. Five vegetation phases were detected since the 1st century AD. In the framework of a patchy natural-cultural landscape, patterns of wetland expansion/contraction reflect the combined effect of cool-wet oscillations (LALIA – Late Antique Little Ice Age), land management (reclamations) and river avulsion. Forest dynamics document warm conditions during the so-called ‘Roman Climate Optimum’ and ‘Medieval Warm Period’, although minor cool-wet episodes occurred in tune with solar minima, and bipartite climate conditions (cool-moist followed by cool-dry) characterized the LALIA. Since the 14th century, despite human-induced forest shrinking, peaks of montane vegetation followed a centennial-scale cyclicity likely influenced by solar minima and major plagues.