Holocene vegetation change at Grosssee, eastern Swiss Alps: effects of climate and human impact

Vegetation History and Archaeobotany https://doi.org/10.1007/s00334-024-01014-7 ORIGINAL ARTICLE Holocene vegetation change at Grosssee, eastern Swiss Alps: effects of climate and human impact Allison R. Dwileski1 · Fabian Rey1 · Marina A. Morlock2 · Nicole Glaus3 · Sönke Szidat4 · Hendrik Vogel3 · Flavio S. Anselmetti3 · Oliver Heiri1 Received: 17 April 2024 / Accepted: 30 August 2024 © The Author(s) 2024 Abstract Pollen, spores, and microscopic charcoal from the sediments of Grosssee (1,619 m a.s.l.), a small lake in the lower subalpine vegetation zone of the Glarus Alps, Switzerland, were analysed to reconstruct vegetation patterns and land use over the past ca. 12,300 calibrated 14C years bp (cal bp). Pollen data revealed an open landscape covered with grasses and herbs such as Artemisia during the Late Glacial Period. The catchment was likely initially afforested with Betula and Pinus cembra or Pinus sylvestris during the Early Holocene. Thermophilous taxa such as Ulmus, Tilia, and Alnus glutinosa-type expanded from ca. 11,000–9,200 cal bp, and mesophyllic Picea abies and Fagus sylvatica followed, and expanded beginning from ca. 8,000–7,600 cal bp. Interestingly, Alnus viridis (synonym: A. alnobetula) expanded about 2,000 years earlier than at comparable sites in the northern Swiss Alps. Its expansion was profound and persistent, and percentages > 15% were already achieved by ca. 7,000 cal bp. Local erosion events that followed are well explained by vegetation changes and inferred human land use activities at Grosssee. In particular, this led to a more open landscape, and land uses (e.g. grazing) intensified from the Mid- to Late Holocene. Indicators of environmental disturbance including persistently high levels of A. viridis, monolete fern spores, and microscopic charcoal were pronounced after ca. 4,000 cal bp. At that time, high influxes of spores from coprophilous fungi and the consistent presence of cultural indicators (Cerealia-type, Plantago lanceolata) indicate increased grazing and high levels of human impact. Land use and grazing activities seemed to have been particularly pronounced and to have promoted diversity in the vegetation over the past 1,000 years. Keywords Pollen · Vegetation change · Erosion · Alnus viridis · Alnus alnobetula · Human impact Introduction Communicated by F. Bittmann. Oliver Heiri 1 Geoecology, Department of Environmental Sciences, University of Basel, Basel, Switzerland 2 Department of Ecology and Environmental Sciences, Umeå University, Umeå, Sweden 3 Institute of Geological Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland 4 Department of Chemistry, Biochemistry and Pharamaceutical Sciences & Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland Lake sediments serve as valuable archives to better understand patterns of regional environmental development and change over the course of a lake’s history (Bennett and Willis 2001; Smol et al. 2001). Investigations using multiple proxies from a single site can be overlapped to form a valuable picture of environmental dynamics (Birks and Birks 2006). For example, lithological and geochemical studies of sediments as well as their structures and chronostratigraphy can be used to better understand soil and hydrological patterns in watersheds, trends in sediment deposition, and to identify large-scale events including floods and landslides (Koinig et al. 2003; Gilli et al. 2013; Glur et al. 2013; Wirth et al. 2013; Perret-Gentil et al. 2024). Plant macrofossils, pollen, and spores, on the other hand, can be used to reconstruct the history of terrestrial vegetation of a region, looking at patterns of plant migration and succession (Rey et al. 2019), shifts 13 Vegetation History and Archaeobotany between open tundra and open pasture to shrubland and forest communities, and signs of human-associated land-use from agriculture to grazing to large-scale clearing (Moore et al. 1991). In addition, charcoal can be used to reconstruct fire histories (Tinner and Hu 2003; Conedera et al. 2009). It is when different types of proxies are combined that a clearer picture of the abiotic and biotic environment over the course of time can be made, and ideas about future environmental responses to climatic and land-use changes can be developed (Rull et al. 2018). Montane to alpine environments are locations of high diversity (e.g. habitats, species) (Garcés-Pastor et al. 2022). They are fragile and fragmented, often steep and exposed, affected by extremes (i.e. in temperature), and susceptible (with increasing altitude) to low growing season temperatures limiting tree growth (Körner 1999, 2004; Paulsen and Körner 2014). They are also highly sensitive to change (Körner 1999). It is the combination of these aspects that places high-altitude environments as suitable locations for the study of climatic and vegetation patterns during the Late Glacial period and the Holocene. Grosssee, a subalpine lake in the Walensee region of the Glarus Alps of eastern Switzerland, is suitable for the use of pollen to reconstruct vegetation history and to look for connections between patterns of vegetation, climate change, and land use. The first pollen-based studies of the greater region have investigated the eastern central Swiss Alps (e.g. Müller 1972; Perret 1993; Perret and Burga 1994) using a combination of the Russian borer and Dachnowsky sampler to retrieve cores from peats and near-shore lake sediments. One of these studies (Seebenalp) is located very close to Grosssee (Perret 1993). These studies are highly valuable in that they investigated multiple nearby sites in parallel, however, the aspect of the sampling technique (littoral lake sediments) resulted in very local signals for use in vegetation reconstruction compared to cores retrieved from the centre of lake basins (Bennett and Willis 2001). Recent advances in coring technology now allow sampling of sediment records from the centre of lakes, where sediments better integrate the extra-local to regional pollen deposition. Furthermore, recent developments of accelerator mass spectrometry (AMS) 14C analysis now allow the development of more highly resolved and constrained radiocarbon chronologies than was possible for many of these earlier studies (e.g. Rey et al. 2023; Heiri et al. 2024). Several recent pollen studies of the upper montane and subalpine vegetation belts of the central Swiss Alps have focused on lakes in western and southwestern (Wick et al. 2003, Sägistalsee; Rey et al. 2013, Lauenensee; Schwörer et al. 2014, Iffigsee; Thöle et al. 2016, Lac de Bretaye; Rey et al. 2022, Lac de Champex) and southeastern (Gobet et al. 2003) Switzerland. Such studies have identified the 13 development of Holocene vegetation and patterns of change in the Alps and have connected them to variations in climate as well as human-driven impacts such as land clearance by logging and (...truncated)