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.

1. Natural succession trajectories of Central European forest ecosystems are poorly understood due to the absence of long-term observations and the pervasive effects of past human impacts on today's vegetation communities. This knowledge gap is significant given that currently forest ecosystems are expanding in Europe as a consequence of global change.2. Annually laminated sediments were extracted from two small lowland lakes (Moossee 521 m a.s.l.; Burgäschisee 465 m a.s.l.) on the Swiss Plateau. We combine high-resolution palaeoecological and quantitative analyses to assess changes in vegetation during the Neolithic. We test for regionally synchronous land-use phases and plant successional patterns that may originate from complex interactions between human and climatic impacts. 3. Mixed Fagus sylvatica forests dominated the Swiss Plateau vegetation over millennia. During the period 6,500-4,200 cal year bp, pronounced forest disruptions accompanied by increased fire and agricultural activities occurred at c. 6,400-6,000 cal year bp, 5,750-5,550 cal year bp, around 5,400 cal year bp and at 5,100-4,600 cal year bp. Biodiversity increased during these land-use phases, likely in response to the creation of new open habitats. After decades to centuries of land-use, arboreal vegetation re-expanded. In a first succession stage, heliophilous Corylus avellana shrubs were replaced by pioneer Betula trees. These open arboreal communities were out-competed within 150-200 years by late-successional F. sylvatica and Abies alba forests. Most strikingly, cross-correlations show that these successions occurred synchronously (±11 years) and repeatedly over large areas (>1,000 km 2 ) and millennia. 4. Synthesis. First notable human impact shaped the primeval mixed Fagus sylvatica forests in Central Europe from c. 6,800-6,500 cal year bp on. Agrarian societies were susceptible to climate changes and we hypothesize that climate-induced, simultaneous agricultural expansion and contraction phases resulted in synchronous regional forest successions. Currently, forests are expanding in Central Europe as a result of land abandonment in marginal areas. Our results imply that mixed Fagus sylvatica forests with Abies alba and Quercus may re-expand rapidly in | 1393 Journal of Ecology REY Et al.

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The European Alps are highly rich in species, but their future may be threatened by ongoing changes in human land use and climate. Here, we reconstructed vegetation, temperature, human impact and livestock over the past ~12,000 years from Lake Sulsseewli, based on sedimentary ancient plant and mammal DNA, pollen, spores, chironomids, and microcharcoal. We assembled a highly-complete local DNA reference library (PhyloAlps, 3923 plant taxa), and used this to obtain an exceptionally rich sedaDNA record of 366 plant taxa. Vegetation mainly responded to climate during the early Holocene, while human activity had an additional influence on vegetation from 6 ka onwards. Land-use shifted from episodic grazing during the Neolithic and Bronze Age to agropastoralism in the Middle Ages. Associated human deforestation allowed the coexistence of plant species typically found at different elevational belts, leading to levels of plant richness that characterise the current high diversity of this region. Our findings indicate a positive association between low intensity agropastoral activities and precipitation with the maintenance of the unique subalpine and alpine plant diversity of the European Alps.

High-resolution sediment chronologies with the best possible time control are essential for comparing palaeoecological studies with independent high-precision climatic, archaeological or historic data in order to disentangle causes and effects of past environmental, ecological and societal change. We present two varved lake sediment sequences from Moossee and Burgäschisee (Swiss Plateau) that have chronologies developed with Bayesian models and radiocarbon (14C) dating of terrestrial plant macrofossils extracted from sediment samples with constant age ranges. We illustrate the potential of high-resolution 14C dating for the construction of robust, high-precision sediment chronologies. The mean 2σ age uncertainties were reduced to±19 cal yr for Moossee and to±54 cal yr for Burgäschisee over the entire period of 3000 cal yr, while 2σ uncertainties of only±13 cal yr and±18 cal yr respectively, were achieved for shorter time intervals. These precisions are better than or comparable to those of previous varve studies. Our results imply that a sophisticated subsampling strategy and a careful selection of short-lived and well-defined terrestrial plant remains are crucial to avoid outlying 14C ages. A direct linkage between palaeoeological studies with dendrochronologically dated, local archaeological sites as well as a precise comparison with high-resolution climate proxy data have become feasible.

Abstract. Since the Last Glacial Maximum (LGM; end ca. 19 000 cal BP) central European plant communities have been shaped by changing climatic and anthropogenic disturbances. Understanding long-term ecosystem reorganizations in response to past environmental changes is crucial to draw conclusions about the impact of future climate change. So far, it has been difficult to address the post-deglaciation timing and ecosystem dynamics due to a lack of well-dated and continuous sediment sequences covering the entire period after the LGM. Here, we present a new paleoecological study with exceptional chronological time control using pollen, spores and microscopic charcoal from Moossee (Swiss Plateau, 521 m a.s.l.) to reconstruct the vegetation and fire history over the last ca. 19 000 years. After lake formation in response to deglaciation, five major pollen-inferred ecosystem rearrangements occurred at ca. 18 800 cal BP (establishment of steppe tundra), 16 000 cal BP (spread of shrub tundra), 14 600 cal BP (expansion of boreal forests), 11 600 cal BP (establishment of the first temperate deciduous tree stands composed of, e.g., Quercus, Ulmus, Alnus) and 8200 cal BP (first occurrence of mesophilous Fagus sylvatica trees). These vegetation shifts were caused by climate changes at ca. 19 000, 16 000, 14 700, 11 700 and 8200 cal BP. Vegetation responses occurred with no apparent time lag to climate change when the mutual chronological uncertainties are considered. This finding is in agreement with further evidence from southern and central Europe and might be explained by the proximity to the refugia of boreal and temperate trees (<400 km) and rapid species spreads. Our palynological record sets the beginning of millennial-scale land use with periodically increased fire and agricultural activities of the Neolithic period at ca. 7000 cal BP. Subsequently, humans rather than climate triggered changes in vegetation composition and structure. We conclude that Fagus sylvatica forests were resilient to long-term anthropogenic and climatic impacts of the Mid and the Late Holocene. However, future climate warming and in particular declining moisture availability may cause unprecedented reorganizations of central European beech-dominated forest ecosystems.