In the context of climate change, a long-term perspective is essential to understand future trajectories of mountain vegetation. We analysed the sediment record of Golzerensee (1411 m a.s.l.), a mountain lake in the transitional zone between the montane and subalpine vegetation belt in Uri, Central Switzerland. We reconstructed past vegetation responses to anthropogenic impact, fire activity and climatic changes dating back to c. 14 550 cal. a BP using pollen, stomata, macrofossil and microcharcoal analyses. The tree line, composed of Betula and Pinus sylvestris, reached Golzerensee during the Allerød c. 13 200 years ago, but tundra vegetation re-expanded during the Younger Dryas cooling (12 800–11 700 cal. a BP). With the rapid temperature increase at the onset of the Holocene, a closed forest established within a few decades around the study site. Concurrently, temperate taxa (Ulmus, Tilia, Acer, Corylus avellana) increased in the lowlands, likely reaching the elevation of the lake. Abies alba established locally during the Holocene Thermal Maximum (HTM) at 9600 cal. a BP and dominated closed, montane forests, delaying the westward expansion of Picea abies that established only from c. 7700 cal. a BP onwards. The concomitant occurrence of cultural indicator taxa, as well as an increase in charcoal influx and fungal dung spore concentrations suggest that human impact has facilitated the expansion of Picea abies by negatively affecting important competitors such as Abies alba through fire and browsing disturbance. With rising temperatures due to current climate change, Abies alba and other temperate species may regain their former relevance, leading to diverse mixed forests that were abundant during the HTM c. 10 000–5000 cal. a BP. However, future forest composition and landscape diversity will also be influenced by browsing disturbance and land use management.
