Holocene climate-vegetation dynamics within the Mediterranean biodiversity hotspot - insights from an EU priority habitat: the Lago Lao case study (SW Alps)

Understanding long-term ecological responses to climate variability is critical for informing conservation strategies, particularly in regions of high biodiversity and climatic sensitivity such as the Mediterranean mountains. In this context, we present the Lago Lao case study - a sphagnum peat bog (7110* EU priority habitat) in the Ligurian Alps Regional Natural Park (NW Italy). The site is in a biodiversity-rich area, climatesensitive, and with a human history dating back to the Pleistocene (1). Pollen data are compared with other available records in the area, integrated with independent paleoclimatic curves at regional scale, simulated local climatic variables, and documented global events/periods, to obtain insights into the ecological dynamics in relation to climate and human influence over the last ~11,000 years. The results highlight the role of increasing warming, during the Younger Dryas-Early Holocene transition, in driving the succession from coldadapted steppe vegetation (Artemisia, Poaceae wild grass group, Aster type) to the colonization of heliophilous, cold-tolerant pioneer trees (Pinus, Betula). During the Holocene Climatic Optimum (HCO), mixed broadleaf forests (deciduous Quercus, Fraxinus excelsior type, Acer campestre type, Ulmus, Tilia) reached their maximum extent, while cold-tolerant taxa declined. A cooling event at 8.2 ka BP led to reduced local precipitation and temperature, possibly driving tree cover reduction. Subsequent warming in the Holocene Thermal Maximum (HTM) coincided with Abies expansion, treeline rise, and subalpine forests establishment. In the mid-to-late Holocene, increased climatic variability resulted in fluctuations in tree cover, including Abies decline and Fagus sylvatica expansion. These changes could be probably linked to regional-local climatic influence and land use during the Copper and Bronze Ages, as documented in the area (2) and the Mediterranean region (3). Over the past ~3,000 years, a progressive tree cover reduction trend culminated with its local decline during the Medieval Climate Anomaly (MCA), marked by higher temperatures, positive Mediterranean Sea Surface Temperature (SST) anomalies, and a positive North Atlantic Oscillation (NAO) phase. The Little Ice Age (LIA) is characterized by increased anthropogenic indicators and wet meadow expansion. Despite overall resilience, montane and subalpine mixed forests show emerging signs of vulnerability. The findings emphasize the importance of conserving high-altitude peatlands and reinforcing the altitudinal ecological connectivity to support long-term ecosystem stability. 1) Sparacello, V. S., Dori, I., Rossi, S., Varalli, A., Riel-Salvatore, J., Gravel-Miguel, C., ... & Moggi-Cecchi, J. (2021). New human remains from the Late Epigravettian necropolis of Arene Candide (Liguria, northwestern Italy): Direct radiocarbon evidence and inferences on the funerary use of the cave during the Younger Dryas. Quaternary Science Reviews, 268, 107131. 2) Finsinger, W., Vanel, Q., Ribolini, A., & Tinner, W. (2021). Early to late Holocene vegetation and fire dynamics at the treeline in the Maritime Alps. Vegetation History and Archaeobotany, 30, 507-524. 3) Mercuri, A. M., Mazzanti, M. B., Torri, P., Vigliotti, L., Bosi, G., Florenzano, A., ... & N’siala, I. M. (2012). A marine/terrestrial integration for mid-late Holocene vegetation history and the development of the cultural landscape in the Po valley as a result of human impact and climate change. Vegetation History and Archaeobotany, 21, 353-372.