Climate impacts on vegetation and fire dynamics since the last deglaciation at Moossee (Switzerland)

Abstract

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.

14,500 years of vegetation and land use history in the upper continental montane zone at Lac de Champex (Valais, Switzerland)

“…In addition, regional archaeology shows the highest density of finds (Fig. 1), indicating that the valleys were important pathways for crossing the Alps and rather densely populated, which is supported by palaeoecological evidence from the lowlands Rey et al 2020). In agreement, the rather remote site Lac de Fully (2,135 m a.sl., Finsinger and Tinner 2007) indicates the first substantial opening of the forests during this period and other subalpine sites point to an intensified land use (Tinner and Theurillat 2003).…”

“…The spread of mesophilous A. alba and F. sylvatica at lower elevations was caused by a climatic shift towards more oceanic conditions with higher precipitation after the 8.2 ka event Lotter 2001, 2006), which is recorded as lake level rises on the western Swiss Plateau, in eastern France and in the Jura Mountains (Magny et al 2011;Magny 2013). The expansion of Abies alba at higher altitudes after 7,500 cal bp is well-documented across the Western and Northern Alps (Heiri et al 2003;Tinner and Kaltenrieder 2005;Rey et al 2013;Schwörer et al 2014;Thöle et al 2016) and the lowlands north of the Alps (Lotter 1999;Becker et al 2006;Wehrli et al 2007;Gobet and Tinner 2012;Gobet et al 2017;Rey et al 2017Rey et al , 2020. Based on macrofossil data, the highest regional tree line was located at ca.…”

“…Tree line and forest dynamics during the last 14,500 years Lac de Champex became ice-free shortly after the onset of the Bølling warming (14,600 cal bp, van Raden et al 2013), which is confirmed by high Juniperus values (> 40%) in the pollen record. The massive expansion of juniper scrublands around 14,600-14,500 cal bp is typical for the Central European lowlands (Lotter 1999;Rey et al 2017Rey et al , 2020 and was caused by a rapid ca. 4-5 °C warming (Heiri et al 2014(Heiri et al , 2015Bolland et al 2020).…”

“…are lacking. The forests around many sites in the central alpine valleys and in the lowlands south and north of the Alps became rather open again (Welten 1982a, b;Vescovi et al 2007;Rey et al 2017Rey et al , 2020. In the Southern Alps, trees were present at Pian di Gembro (1,350 m a.s.l., Pini 2002) whereas treeless tundra vegetation was re-expanding at Foppe (1,470 m a.s.l., Vescovi et al 2018), setting the tree line somewhere around 1,400 m a.s.l.…”

Impact of Pleistocene–Holocene climate shifts on vegetation and fire dynamics and its implications for Prearchaic humans in the central Great Basin, USA

“…The expanding wetlands in response to periods of increased moisture possibly served as attractive habitats for large herbivores. The microfossil record tentatively indicates the presence of such herbivores by finds of dung fungal spores at ~13.4 and ~11.0–10.5k cal a bp that are commonly associated with herbivore presence (Gill et al ., 2012; Rey et al ., 2017, 2020). Elston et al .…”