New data on Alpine glacier fluctuations during the climatic transition 4 at ~4,000 cal. year BP from a buried log in the Forni Glacier forefield (Italy)

Glacier history can be reconstructed thanks to geomorphological documentation of previous advances, dating of glacial deposits, and investigation of buried soils and included organic material, which may be linked to vegetation dynamics. A buried log was retrieved at 2,385 m a.s.l. on the northeast-facing slope of the upper Forni Valley (Italian Alps), where the homonymous valley glacier is located. The glacier forefield is currently facing an early successional forest expansion after the ongoing tongue retreat, mainly dominated by young Picea abies Karst. and Larix decidua Mill. specimens. From dendrochronological and radiocarbon analyses on the retrieved log, coupled with sedimentological and geopedological data, the past environmental and glacier conditions were reconstructed. The log belongs to the Stone pine species (Pinus cembra L.), it has 283 tree rings and became buried in the deposit in the Subboreal, after 4,201-4,032 cal. year BP, age of the outermost tree ring. The retrieved log reveals that during the Subboreal in the Forni Valley, likely much older specimens of Stone pine were present on the slopes, in strong contrast to present-day conditions. The log's tree-ring growth rates were similar to those presented during the Little Ice Age peak by Stone pine trees of comparable age growing nowadays at the treeline.