Late-glacial and Holocene vegetation dynamics in response to climate, land use and fire at Lago di Andromia (Ossola, Italian Alps)

Understanding of past vegetation dynamics provides valuable information to better assess future ecosystem impacts under global change. In this context, the European Alps offer the opportunity to study diverse environments. Here, we present a multi-proxy palaeoecological study from the Pennine Alps combining pollen, spores, stomata, charcoal and plant macrofossil analysis. We reconstructed the vegetation dynamics over the past ca. 14,000 years based on sediment cores from Lago di Andromia (1926 m a.s.l.), a small lake located in the subalpine belt of the Ossola valley (Italy). During the Allerød the site was just above the treeline, before Larix decidua trees reached it ca. 11,500 years ago, in response to Holocene warming. Pinus cembra established locally ca. 500 years later, whereas Abies alba reached the site at the latest ca. 10,500 years ago and became co-dominant after 10,000 cal yr BP . Our new evidence confirms that the Ossola valley was an important corridor for the spread of Abies alba across the Alps, highlighting the crucial role of mid-to high elevations for its Holocene range expansion. Vegetation structure and composition remained rather stable during the Holocene Thermal Maximum (ca. 10,000–5000 cal yr BP). Earliest evidence for local pastoralism dates to 5500 years ago and was linked to anthropogenic fires to clear forests. During the Early Bronze Age (ca. 4200 years ago), both pastoral and arable farming increased in the valley, leading to a marked opening in the vegetation. Although sparse, evidence of Juglans regia cultivation during the Late-Neolithic coincides with similar results in Northern Italy, suggesting a striking centrality of the Andromia area, likely tied to its position at the confluence of five Alpine valleys close to the present-day city of Domodossola.