Summary1. The resilience, diversity and stability of mountain ecosystems are threatened by climatic as well as land-use changes, but the combined effects of these drivers are only poorly understood. 2. We combine two high-resolution sediment records from Iffigsee (2065 m a.s.l.) and Lauenensee (1382 m a.s.l.) at different elevations in the Northern Swiss Alps to provide a detailed history of vegetational changes during the period of first pastoralism (ca. 7000-5000 cal. BP, 5000-3000 BC) in order to understand ongoing and future changes in mountain ecosystems. 3. We use palaeoecological methods (fossil pollen, spore, microscopic charcoal and macrofossil analysis) as well as ecological ordination techniques and time-series analysis to quantify the impact of fire and grazing on natural mountain vegetation at Iffigsee. 4. Fire was used by Neolithic people to create pastures at timberline and clear forests for arable farming in the valley. This had a significant, long-term effect on the mountain vegetation and a negative impact on keystone forest species such as Abies alba, Larix decidua and Pinus cembra. 5. The mass expansion of Picea abies at ca. 5500 cal. BP (ca. 3500 BC) was facilitated by anthropogenic disturbance (fire, grazing and logging) causing an irreversible decline in Abies alba. Temperate Abies alba forests, which existed under warmer-than-today conditions, might be better adapted to projected climate change than today's drought-sensitive Picea abies forests, especially under low anthropogenic disturbance following land abandonment. 6. Synthesis. Human impact for millennia has shaped mountain vegetation in the Alps and still continues to have a large effect on today's species composition and distribution. Fire and traditional pastoralism have the potential to mitigate the effects of climate change, maintain species-rich highalpine meadows and prevent biodiversity losses.

Lake sediments from Lauenensee (1381 m a.s.l.), a small lake in the Bernese Alps, were analysed to reconstruct the vegetation and fire history. The chronology is based on 11 calibrated radiocarbon dates on terrestrial plant macrofossils suggesting a basal age of 14,200 cal. BP. Pollen and macrofossil data imply that treeline never reached the lake catchment during the Bølling-Allerød interstadial. Treeline north of the Alps was depressed by c. 300 altitudinal meters, if compared with southern locations. We attribute this difference to colder temperatures and to unbuffered cold air excursions from the ice masses in northern Europe. Afforestation started after the Younger Dryas at 11,600 cal. BP. Early-Holocene tree-Betula and Pinus sylvestris forests were replaced by Abies alba forests around 7500 cal. BP. Continuous high-resolution pollen and macrofossil series allow quantitative assessments of vegetation dynamics at 5900-5200 cal. BP (first expansion of Picea abies, decline of Abies alba) and 4100-2900 cal. BP (first collapse of Abies alba). The first signs of human activity became noticeable during the late Neolithic c. 5700-5200 cal. BP. Cross-correlation analysis shows that the expansion of Alnus viridis and the replacement of Abies alba by Picea abies after c. 5500 cal. BP was most likely a consequence of human disturbance. Abies alba responded very sensitively to a combination of fire and grazing disturbance. Our results imply that the current dominance of Picea abies in the upper montane and subalpine belts is a consequence of anthropogenic activities through the millennia.

Little is known about the timing and the vegetation dynamics shortly after the Last Glacial Maximum (LGM) on the Swiss Plateau 19,000−15,000 cal B.P. Subsequent Late Glacial and Holocene vegetation changes are better known; however, it is unclear if the few available palynological and macrofossil records are able to capture the entire vegetation variability of the region. A new palaeoecological multiproxy study using pollen, spores, charcoal and X-ray fluorescence (XRF) from Burgäschisee (Swiss Plateau, 465 m a.s.l.) is used to reconstruct vegetation, fire and land use for the past 19,000 cal. years. Steppe tundra vegetation established at c. 18,700 cal B.P. only c. 300 years after the end of the LGM and deglaciation. A shift from steppe tundra (Artemisia, Helianthemum) to shrub tundra (Betula nana, Salix, Juniperus) with sporadic tree Betula stands occurred around 16,000 cal B.P., most likely in response to climate warming after the end of Heinrich event 1. Abundant spores of coprophilous fungi (Sporormiella, Cercophora) may reflect the presence of Pleistocene large herbivores (e.g. Mammuthus primigenius, Bison bonasus, Rangifer tarandus). Afforestation started more than 2,000 years later with Juniperus and tree Betula around 14,500 cal B.P. Mixed Betula and Pinus sylvestris forests persisted until the onset of the Holocene at 10,800 cal B.P., when mixed elm forests expanded into the region in response to climate warming. Around 8,200 cal B.P., mesophilous Fagus sylvatica and Abies alba partly replaced more heliophilous species in the forests, when climate became less continental and more moist. Pollen of Cerealia, Plantago lanceolata and other crops and weeds suggest that agricultural activities became significant during the Neolithic around 6,500 cal B.P. (4,550 cal B.C.). Archaeological findings from Neolithic pile dwellings around 5,950 cal B.P. (4,000 cal B.C.) indicate local settlements around the lake. The lake sediments are laminated for most of the last c. 6,800 years. With two independent proxies (XRF and pollen), we can demonstrate that these laminations are annual, suggesting short-term mixing of the lake water due to a more open landscape in response to land use. Our study shows that the annually laminated (varved) sediments from Burgäschisee have a great potential for high resolution multi-proxy analyses covering the past c. 6,800 years. They can provide accurate ages of cultural phases that might be compared with dendro-chronologically dated evidence from lake dwellings.