Summary0 Pollen and charcoal analysis at two lakes in southern Switzerland revealed that _re has had a prominent role in changing the woodland composition of this area for more than 6999 years[

Fluctuations in the D 14 C curve and subsequent gaps of archaeological findings at 800-650 and 400-100 BC in western and central Europe may indicate major climate-driven land-abandonment phases. To address this hypothesis radiocarbon-dated sediments from four lakes in Switzerland were studied palynologically. Pollen analysis indicates contemporaneous phases of forest clearances and of intensified land-use at 1450-1250 BC, 650-450 BC, 50 BC-100 AD and around 700 AD. These land-use expansions coincided with periods of warm climate as recorded by the Alpine dendroclimatic and Greenland oxygen isotope records. Our results suggest that harvest yields would have increased synchronously over wide areas of central and southern Europe during periods of warm and dry climate. Combined interpretation of palaeoecological and archaeological findings suggests that higher food production led to increased human populations. Positive long-term trends in pollen values of Cerealia and Plantago lanceolata indicate that technical innovations during the Bronze and Iron Age (e.g. metal ploughs, scythes, hay production, fertilising methods) gradually increased agricultural productivity. The successful adoption of yield-increasing advances cannot be explained by climatic determinism alone. Combined with archaeological evidence, our results suggest that despite considerable cycles of spatial and demographic reorganisation (repeated land abandonments and expansions, as well as large-scale migrations and population decreases), human societies were able to shift to lower subsistence levels without dramatic ruptures in material culture. However, our data imply that human societies were not able to compensate rapidly for harvest failures when climate deteriorated. Agriculture in marginal areas was abandoned, and spontaneous reforestations took place on abandoned land south and north of the Alps. Only when the climate changed again to drier and warmer conditions did a new wide-spread phase of forest clearances and field extensions occur, allowing the reoccupation of previously abandoned areas. Spatial distribution of cereal cultivation and growth requirements of Cerealia species suggest that increases in precipitation were far more decisive in driving crop failures over central and southern Europe than temperature decreases. r

Using pollen percentages and charcoal influx to reconstruct the Holocene vegetation and fire history, we differentiate six possible responses of plants to fire of medium and high frequency: fire-intolerant, fire damaged, fire-sensitive, fire-indifferent, fire-enhanced and fire-adapted. The fire sensitivity of 17 pollen types, representing 20 woody species in the southern Alps, is validated by comparison with today's ecological studies of plant chronosequences. A surprising coincidence of species reaction to fire of medium frequency is character istic for completely different vegetation types, such as woodlands dominated by Abies alba (7000 years ago) and Castanea sativa (today). The temporal persistence of post-fire behaviour of plant taxa up to thousands of years suggests a generally valid species-related fire sensitivity that may be influenced only in part by changing external conditions. A non-analogous behaviour of woody taxa after fire is documented for high fire frequencies. Divergent behaviour patterns of plant taxa in response to medium and high fire frequencies (e.g., increases and decreases of Alnus glutinosa) also indicate that post-fire plant reactions may change with increasing fire fre quency.

Abstract. Vegetation history for the study region is reconstructed on the basis of pollen, charcoal and AMS ~4C investigations of lake sediments from Lago del Segrino (calcareous bedrock) and Lago di Muzzano (siliceous bedrock). Late-glacial forests were characterised by Betula and Pinus sylvestris. At the beginning of the Holocene they were replaced by temperate continental forest and shrub communities. A special type of temperate lowland forest, with Abies alba as the most important tree, was present in the period 8300 to 4500 B.P. Subsequently, Fagus, Quercus and Alnus glutinosa were the main forest components and A. aIba ceased to be of importance. Casmnea sativa and Juglans regia were probabIy introduced after forest clearance by fire during the first century A.D. On soils derived from siliceous bedrock, C. sativa was already dominant at ca. A.D. 200 (A.D. dates are in calendar years). In limestone areas, however, C. sativa failed to achieve a dominant role. After the introduction of C. sativa, the main trees were initially oak (Quercus spp.) and later the walnut (Juglans regia). Ostrya carpinifolia became the dominant tree around Lago del Segrino only in the last 100-200 years though it had spread into the area at ca. 5000 cal. B.C. This recent expansion of Ostrya is confirmed at other sites and appears to be controlled by human disturbances involving especially clearance. It is argued that these forests should not be regarded as climax communities. It is suggested that under undisturbed succession they would develop into mixed deciduous forests consisting of Fraxinus excelsior, Tilia, Ulmus, Quercus and Acer.

A temperature reconstruction using chironomids was attempted at Egelsee, Switzerland, a site where pollen and macrofossil records showed a correspondence between vegetation and climatic changes inferred by other proxies in Europe. The general pattern of temperature changes inferred from chironomids during the Late Glacial [i.e. cold temperatures between ca. 16,500 and 14,800 cal BP, close to present-day temperature between 15,000 and 13,000 cal BP and colder temperatures during the Younger Dryas (YD)], and the major temperature changes of the Holocene (i.e. the Younger Dryas-Holocene transition and the Late Holocene cooling trend) at Egelsee, were mirrored in other European climate reconstructions using various proxies. However, the amplitude of temperature changes during the YD was smaller than reconstructed by other proxies at various sites, and the 8,200 years BP event was not apparent. These differences between records were probably due to the dominance of Corynocera ambigua, with percentages reaching 60% in parts of the Egelsee sequence. This taxon was not present in any of the 103 lakes used for the transfer function and its absence may have yielded less accurate inferences. Its presence in samples only associated with cold inferences at Egelsee suggests that this taxon is a cold indicator. However, it was also found in warm Danish lakes and the factors that determine the presence of C. ambigua remain unexplained. Most samples had a poor fit to temperature and instead, dissolved organic carbon seemed to be a factor influencing the chironomid assemblages during the Holocene. These results illustrate the need to better understand the ecology of chironomids and to disentangle the various factors that affect chironomid communities through time. Ultimately, such information will lead to more accurate temperature reconstructions. Keywords Temperature reconstruction Á Chironomid-inferred temperature Á Swiss training set Á Ecology of Corynocera ambigua

The montane belt is regarded as unattractive for prehistoric land use (Aerni, 1991). The key evidence for this hypothesis is the existence of very few archaeological finds. This 'absencebased' evidence, however, may be checked with palaeoecological methods. The key question is what exactly would make the montane belt unattractive. Is it the remoteness, the poor accessibility and/or the climate? Thus, the second aim is to compare the results of our study with local archaeological evidence and welldated palaeoecological records from the central Swiss Plateau. The most important sites are Abstract: Past vegetation dynamics and human impact from the Lateglacial to the present are reconstructed by pollen analysis of a core 12 m long from the raised bog Egelsee, central Switzerland (770 m a.s.l.). The depth-age model of the core is based on 29 AMS 14 C dates. The oldest dated macrofossil has an age of 13 080 ± 105 radiocarbon yr BP (15 370 cal. yr BP); extrapolation leads to a basal age of the core of 16 200 cal. yr BP. The biostratigraphy shows a typical vegetation development for Central Europe from open pioneer vegetation to Betula-Pinus forests in the Lateglacial, thermophilous mixed deciduous forests in the early Holocene, then mesophilous Abies-Fagus forests, and finally to the present cultural landscape. The initial population expansion of Abies alba may have coincided with climatic change at c. 8500 cal. yr BP. The mass expansion of Abies alba at 8100 cal. yr BP may have been triggered by the 8.2-ka event and coincided with the empirical limit of Fagus silvatica, indicating initial population expansions. The succession of ecosystems with different plant composition is confirmed by detrended correspondence analysis (DCA): the main changes in the DCA axis 1 and 2 correspond to the transition phases between the different ecosystems. DCA axis 1 has an eigenvalue of λ 1 = 0.46 and is significantly correlated (r = 0.82) to the non-arboreal pollen percentage curve. Rarefaction analysis shows a high pollen diversity in the Lateglacial, lower pollen diversity in the Holocene before human impact, and increasing pollen diversity correlated with increasing human impact. Very little is known about the archaeology of the montane belt in central Switzerland. This study provides new data concerning human impact and settlement history in this area. Human activities are indicated by cereal pollen (earliest Hordeum/Triticum type at 4700 cal. yr BP). Distinct pulses of anthropogenic forest clearances can be observed from the Neolithic period onwards.

A massive tufa complex in the lower Lorze Valley (550 m a.s.l., north-central Switzerland) formed between 9000 and 5000 cal. yr BP. In the plain 4 km southeast of the complex lies Neugrundmoor (830 m a.s.l.), a mire in the hydrologic recharge area of the springs responsible for the tufa formation. Here we address an earlier, untested hypothesis that the transition of Neugrundmoor from fen to raised bog caused the end of the tufa formation, by means of pollen and testate amoebae analyses on a peat section. The chronology of the section is based on ten AMS 14C-dates of terrestrial plant macrofossils. Our results suggest that until 7100 cal. yr BP the plain had shallow ponds, which gradually developed into fens. Starting 5350 cal. yr BP, large raised bogs developed in the fens in a few centuries. This agrees with the hypothesis that the end of tufa formation coincided with the transition from fen to raised bog. It also coincided with the end of the mid-Holocene temperature optimum, when climate became cooler and wetter. We suggest that the main factor causing the end of tufa formation at 5500—5000 cal. yr BP was declining air temperatures, which on the one hand led to diminished calcium precipitation, on the other to enhanced bog formation. Peat has a low hydraulic conductivity, so we suggest that less water became available for tufa formation because of increased thickness of peat layers, exacerbating the direct effect of cooling on calcium precipitation. Noticeable human influence in the surroundings did presumably not start before c. 3500 cal. yr BP and was then very weak, so this was not responsible for the end of the tufa formation. Extrapolation of our results suggests that climatic cooling alone is sufficient to explain the widespread termination of tufa formation after the mid Holocene.

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