Changes in biodiversity and vegetation composition in the central Swiss Alps during the transition from pristine forest to first farming

Aim: We investigate the response of vegetation composition and plant diversity to increasing land clearance, burning and agriculture at the Mesolithic–Neolithic transition (c. 6400–5000 bc) when first farming was introduced. Location: The Valais, a dry alpine valley in Switzerland. Methods: We combine high-resolution pollen, microscopic charcoal and sedimentological data to reconstruct past vegetation, fire and land use. Pollen evenness, rarefaction-based and accumulation-based palynological richness analyses were used to reconstruct past trends in plant diversity. Results: Our results show that from c. 5500 cal. yr bc, slash-and-burn activities created a more open landscape for agriculture, at the expense of Pinus and Betula forests. Land clearance by slash-and-burn promoted diverse grassland ecosystems, while on the long term it reduced woodland and forest diversity, affecting important tree species such as Ulmus and Tilia. Main conclusions: Understanding the resilience of Alpine ecosystems to past disturbance variability is relevant for future nature conservation plans. Our study suggests that forecasted land abandonment in the Alps will lead to pre-Neolithic conditions, with significant biodiversity losses in abandoned grassland ecosystems. Thus, management measures for biodiversity, such as ecological compensation areas, are needed in agricultural landscapes with a millennial history of human impact, such as the non-boreal European lowlands. Our study supports the hypothesis that species coexistence is maximized at an intermediate level of disturbances. For instance, species richness decreased when fire exceeded the quasi-natural variability observed during the Mesolithic times. Under a more natural disturbance regime, rather closed Pinus sylvestris and mixed oak forests would prevail.

Climatic and human impacts on mountain vegetation at Lauenensee (Bernese Alps, Switzerland) during the last 14,000 years

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.

The role of peat decomposition in patterned mires: a case study from the central Swiss Alps

A number of hydrological, botanical, macro- and micro-climatological processes are involved in the formation of patterned peatlands. La Grande Tsa at 2336 m a.s.l. is probably the highest bog in the central Swiss Alps and is unique in its pattern. In two of five pools there is in the contact zone between the basal peat and the overlying gyttja an unconformity in the depth-age models based on radiocarbon dates. Palynostratigraphies of cores from a ridge and a pool confirm the occurrence of an unconformity in the contact zone. We conclude that deepening of the pools results from decomposition of peat. The fact that the dated unconformities in the two pools and the unconformity in the ridge-core all fall within the Bronze Age suggest they were caused by events external to the bog. We hypothesize that early transhumance resulted in anthropogenic lowering of the timberline, which resulted in a reduction in the leaf-area index and evapotranspiration, and in higher water levels and thus pool formation.

Cold-season temperatures in the European Alps during the past millennium: variability, seasonality and recent trends

This study presents a proxy-based, quantitative reconstruction of cold-season (mean October to May, TOct–May) air temperatures covering nearly the entire last millennium (AD 1060–2003, some hiatuses). The reconstruction was based on subfossil chrysophyte stomatocyst remains in the varved sediments of high-Alpine Lake Silvaplana, eastern Swiss Alps (46°27’N, 9°48′W, 1791 m a.s.l.). Previous studies have demonstrated the reliability of this proxy by comparison to meteorological data. Cold-season air temperatures could therefore be reconstructed quantitatively, at a high resolution (5-yr) and with high chronological accuracy. Spatial correlation analysis suggests that the reconstruction reflects cold season climate variability over the high- Alpine region and substantial parts of central and western Europe. Cold-season temperatures were characterized by a relatively stable first part of the millennium until AD 1440 (2σ of 5-yr mean values = 0.7 °C) and highly variable TOct–May after that (AD 1440–1900, 2σ of 5-yr mean values = 1.3 °C). Recent decades (AD, 1991-present) were unusually warm in the context of the last millennium (exceeding the 2σ-range of the mean decadal TOct–May) but this warmth was not unprecedented. The coolest decades occurred from AD 1510–1520 and AD 1880–1890. The timing of extremely warm and cold decades is generally in good agreement with documentary data representing Switzerland and central European lowlands. The transition from relatively stable to highly variable TOct–May coincided with large changes in atmospheric circulation patterns in the North Atlantic region. Comparison of reconstructed cold season temperatures to the North Atlantic Oscillation index (NAO) during the past 1000 years showed that the relatively stable and warm conditions at the study site until AD 1440 coincided with a persistent positive mode of the NAO. We propose that the transition to large TOct–May variability around AD 1440 was linked to the subsequent absence of this persistent zonal flow pattern, which would allow other climatic drivers to gain importance in the study area. From AD 1440–1900, the similarity of reconstructed TOct–May to reconstructed air pressure in the Siberian High suggests a relatively strong influence of continental anticyclonic systems on Alpine cold season climate parameters during periods when westerly airflow was subdued. A more continental type of atmospheric circulation thus seems to be characteristic for the Little Ice Age in Europe. Comparison of Toct–May to summer temperature reconstructions from the same study site shows that, as expected, summer and cold season temperature trends and variability differed completely throughout nearly the entire last 1000 years. Since AD 1980, however, summer and cold season temperatures show a simultaneous, strong increase, which is unprecedented in the context of the last millennium. We suggest that the most likely explanation for this recent trend is anthropogenic greenhouse gas (GHG) forcing.

Snow variability in the Swiss Alps 1864-2009

We present a climate analysis of nine unique Swiss Alpine new snow series that have been newly digitized. The stations cover different altitudes (450–1860 m asl) and all time series cover more than 100 years (one from 1864 to 2009). In addition, data from 71 stations for the last 50–80 years for new snow and snow depth are analysed to get a more complete picture of the Swiss Alpine snow variability. Important snow climate indicators such as new snow sums (NSS), maximum new snow (MAXNS) and days with snowfall (DWSF) are calculated and variability and trends analysed. Series of days with snow pack (DWSP) ≥ 1 cm are reconstructed with useful quality for six stations using the daily new snow, local temperature and precipitation data. Our results reveal large decadal variability with phases of low and high values for NSS, DWSF and DWSP. For most stations NSS, DWSF and DWSP show the lowest values recorded and unprecedented negative trends in the late 1980s and 1990s. For MAXNS, however, no clear trends and smaller decadal variability are found but very large MAXNS values (>60 cm) are missing since the year 2000. The fraction of NSS and DWSP in different seasons (autumn, winter and spring) has changed only slightly over the ∼150 year record. Some decreases most likely attributable to temperature changes in the last 50 years are found for spring, especially for NSS at low stations. Both the NSS and DWSP snow indicators show a trend reversal in most recent years (since 2000), especially at low and medium altitudes. This is consistent with the recent ‘plateauing’ (i.e. slight relative decrease) of mean winter temperature in Switzerland and illustrates how important decadal variability is in understanding the trends in key snow indicators.

Exploring Water Governance Arrangements in the Swiss Alps From the Perspective of Adaptive Capacity

In times of increasing uncertainty because of climate and socioeconomic changes, the ability to deal with uncertainty and surprise is an essential requirement for the sustainability of alpine water governance. This article aims to contribute to the understanding of the adaptive capacity of water governance arrangements in the Swiss Alps and to propose options for reforms. To this purpose, we evaluated the current arrangements and the ways the actors have dealt with water shortages in the past, based on qualitative interviews and a document review. The research revealed that the adaptive capacity of the investigated arrangements is rather high with regard to reactive ways of responding to water shortage problems. However, there is limited capacity to proactively anticipate possible changes and to find prospective solutions on a regional scale. We conclude that with increased environmental and social pressures, forms of proactive water resource governance should be introduced, taking into account the welfare of people in both upstream and downstream areas.

Differences between recent and historical records of upperspecies limits in the northern European Alps

Are there differences in historical and recent upper range limits of vascular plants and are such differences more pronounced in individual species groups? The limits of 1103 plants of the Northern Alps are compared to range limits in the mid-19th century. The comparison is based on two surveys. The first survey was conducted by Otto Sendtner in 1848–1853, the second in 1991–2008 during a habitat inventory. To our knowledge this is the first comparative studies reaching back to the end of the “Little Ice Age” and comprising an almost entire regional flora covering the complete range of habitats. During the recent survey, most species were found at higher elevations. Even though the differences fit well with the expected shifts due to climate warming we cannot exclude effects of sampling bias. However, we assume that the relative differences between species groups can be safely interpreted. The differences in upper limits between both surveys were significantly larger among forest species. The most important reason is probably discontinued pasture and mowing, which may have amplified possible warming effects. Nitrogen deposits may have contributed to this effect by placing competitive species in a more advantageous position.

Archaeological Discoveries on Schnidejoch and at Other Ice Sites in the European Alps

Only a few sites in the Alps have produced archaeological finds from melting ice. To date, prehistoric finds from four sites dating from the Neolithic period, the Bronze Age, and the Iron Age have been recovered from small ice patches (Schnidejoch, Lötschenpass, Tisenjoch, and Gemsbichl/Rieserferner). Glaciers, on the other hand, have yielded historic finds and frozen human remains that are not more than a few hundred years old (three glacier mummies from the 16th to the 19th century and military finds from World Wars I and II). Between 2003 and 2010, numerous archaeological finds were recovered from a melting ice patch on the Schnidejoch in the Bernese Alps (Cantons of Berne and Valais, Switzerland). These finds date from the Neolithic period, the Early Bronze Age, the Iron Age, Roman times, and the Middle Ages, spanning a period of 6000 years. The Schnidejoch, at an altitude of 2756 m asl, is a pass in the Wildhorn region of the western Bernese Alps. It has yielded some of the earliest evidence of Neolithic human activity at high altitude in the Alps. The abundant assemblage of finds contains a number of unique artifacts, mainly from organic materials like leather, wood, bark, and fibers. The site clearly proves access to high-mountain areas as early as the 5th millennium BC, and the chronological distribution of the finds indicates that the Schnidejoch pass was used mainly during periods when glaciers were retreating.