First multi-proxy Holocene growing season thermal conditions reconstruction from Central Europe

This study presents a multi-proxy reconstruction of Holocene growing season thermal conditions (GDD 5 ) in Central Europe based on Betula nana subfossil leaf micro-phenology and pollen data from a 12-m-long sediment sequence at Linje peatland. A site-specific inference model was developed using modern B. nana leaves to estimate growing season heat accumulation. The model shows lower sensitivity compared to subarctic calibrations but captures variability in GDD 5 within the local climatic range. Overlapping undulation index (UI) values observed in modern and subfossil material across differing thermal conditions highlight the importance of regional calibration. Reconstructed GDD 5 trends indicate variability in growing season conditions during the Early Holocene and from ∼5450 cal. yr BP to the present and show the strongest agreement with pollen-based estimates during the first half of the Late Holocene. As GDD 5 is an important factor controlling agricultural productivity, such reconstructions are important for understanding past changes in seasonality and their potential implications for prehistoric land use and settlement dynamics. The results demonstrate the applicability of combined micro-phenological and palynological approaches for reconstructing past growing season thermal conditions.