Pollen, macrofossils and sedaDNA reveal climate and land use impacts on Holocene mountain vegetation of the Lepontine Alps, Italy

Abstract

Both climate change and anthropogenic disturbance affect vegetation composition, but it is difficult to separate these drivers of vegetation change from one another. A better understanding of past vegetation dynamics is necessary to disentangle the influence of different forcing factors and assess future vegetation change. Here we present the first multi-proxy palaeoecological study combining sedimentary ancient DNA (sedaDNA), pollen, spores, stomata, charcoal and plant macrofossils from the Alps. We reconstructed the Holocene vegetation dynamics and fire history at Lago Inferiore del Sangiatto (1980 m asl), a small lake in the subalpine belt of the Ossola region, Italian Lepontine Alps. Afforestation in response to climate warming started at 10,700 cal yr BP with Larix decidua and tree Betula, which formed open forests together with Pinus cembra from 10,500 cal yr BP onwards. Human impact on the regional vegetation started at 5100 cal yr BP, resulting in expansions of Picea abies and Alnus viridis and the collapse of Abies alba. Species response models and ordination analysis show that livestock grazing and fire were major drivers of vegetation change at Lago Inferiore del Sangiatto during the late Holocene. Finally, increasing human impact during the Bronze (ca. 4200e2900 cal yr BP) and Iron Age (ca. 2900 e2000 cal yr BP) led to the formation of species-rich larch meadows and alpine pastures that are still dominant today. The palaeoecological data suggest that under projected climate change and land abandonment, the treeline ecotone will likely shift to higher altitudes, leading to important changes in species composition and increasing the risk of biodiversity loss.