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

Abstract

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.

Pollen from accurately dated speleothems supports alpine glacier low-stands during the early Holocene

“…The absence of this taxon in the younger samples is attributed to the lower pollen count, underlining the potential statistical bias. Also Picea and Fagus emerge at Milchbach between 7476 ± 50 and 7312 ± 51 yr, anticipating their main regional expansion of this taxon after 6500 cal yr BP (Heiri et al, 2003;Wick et al, 2003;Rey et al, 2013). Nonetheless, our data are consistent with the recurrence of several Picea and Fagus pollen grains reported from the nearby S€ agistalsee (10 km) since 7500 cal yr BP (Wick et al, 2003).…”

“…Abies pollen is first detected in Milchbach speleothems between 7601 ± 236 and 7272 ± 158 yr (sample MB5-D), in good agreement with the onset of the Abies expansion identified between 7400 and 7500 cal yr BP at Hinterburgersee (10 km to the north; Heiri et al, 2003) and Lauenensee (60 km to the west; Rey et al, 2013). The absence of this taxon in the younger samples is attributed to the lower pollen count, underlining the potential statistical bias.…”

“…This result is consistent with the statistically robust MB5-D pollen assemblage and more generally with early Holocene pollen records from the northern Swiss Alps and foreland located in the same altitudinal range as the Grindelwald valley (600e1900 m asl). The latter imply a deciduous forest dominated by Pinus, Corylus, Ulmus (Lotter, 1999;Heiri et al, 2003;Wick et al, 2003;Rey et al, 2013. ), with Quercus and Tilia occurring at the lower altitudes (Lotter, 1999) and P. cembra at the higher sites (Heiri et al, 2003;Wick et al, 2003).…”

Palaeoclimate records 60–8 ka in the Austrian and Swiss Alps and their forelands

“…Decreases in treeline elevations were apparently relatively minor in the northern Alps (e.g. Bachalpsee (2265m) Sanetsch (2288m) Iffigsee (2065m) Sägistalsee (1935m) Hinterburgsee (1515m) Lauenensee (1388m) Soppensee (596m) Lobsigensee (514m) Feld (2130m) Leysin ( Welten, 1982;Ammann and Tobolski, 1985;Gaillard, 1985;Lotter, 1999;Tobolski and Ammann, 2000;Heiri et al, 2003b;Wick et al, 2003;Lotter et al, 2006;Berthel et al, 2012;Rey et al, 2013;Schw€ orer et al, 2013a). The black lines provide an interpretation of the minimum and maximum altitude of the Alpine treeline based on the presented plant macrofossil records.…”

Análisis De La Dinámica Espacio-Temporal (1948-2003) Del Límite Altitudinal Del Bosque (Tree Line) en Andorra Mediante Fotografía Aérea

“…Sin embargo existe un elevado consenso en que durante las últimas décadas se ha observado que la tree line ha incrementado su límite altitudinal aunque la magnitud varíe según la zona estudiada (Harsch et al, 2009;Rey et al, 2013;Schwörer et al, 2014;Améztegui et al, 2016) y los factores topoclimáticos (por. ej., zonas resguardadas de los vientos o con cubierta nival) tal y como apunta Kullman, L. (2001).…”