Holocene climate, fire and vegetation dynamics at the treeline in the Northwestern Swiss Alps

Abstract

Treelines are expected to rise to higher elevations with climate warming; the rate and extent however are still largely unknown. Here we present the first multi-proxy palaeoecological study from the treeline in the Northwestern Swiss Alps that covers the entire Holocene. We reconstructed climate, fire and vegetation dynamics at Iffigsee, an alpine lake at 2,065 m a.s.l., by using seismic sedimentary surveys, loss on ignition, visible spectrum reflectance spectroscopy, pollen, spore, macrofossil and charcoal analyses. Afforestation with Larix decidua and tree Betula (probably B. pendula) started at *9,800 cal. B.P., more than 1,000 years later than at similar elevations in the Central and Southern Alps, indicating cooler temperatures and/or a high seasonality. Highest biomass production and forest position of *2,100-2,300 m a.s.l. are inferred during the Holocene Thermal Maximum from 7,000 to 5,000 cal. B.P. With the onset of pastoralism and transhumance at 6,800-6,500 cal. B.P., human impact became an important factor in the vegetation dynamics at Iffigsee. This early evidence of pastoralism is documented by the presence of grazing indicators (pollen, spores), as well as a wealth of archaeological finds at the nearby mountain pass of Schnidejoch. Human and fire impact during the Neolithic and Bronze Ages led to the establishment of pastures and facilitated the expansion of Picea abies and Alnus viridis. We expect that in mountain areas with land abandonment, the treeline will react quickly to future climate warming by shifting to higher elevations, causing drastic changes in species distribution and composition as well as severe biodiversity losses.

From pristine forests to high‐altitude pastures: an ecological approach to prehistoric human impact on vegetation and landscapes in the western Italian Alps

“…A temporary timberline depression has been related to the 8·2 ka cal bp climate oscillation (Schwörer et al . ), but maximum timberline altitudes were reached after that (Tinner ), still without signs of human impact. Overall, no human interference is recorded in the high‐elevation ecological scenario at the onset of farming activities in the lowlands.…”

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.…”

Holocene treeline and timberline changes in the South Carpathians (Romania): Climatic and anthropogenic drivers on the southern slopes of the Retezat Mountains

“…In the treeline ecotone, the density of trees decreases upwards, and the highest elevation reached by single tree individuals taller than 2-3 m defines the treeline (Arno and Hammerly, 1984;Schwörer et al, 2013;Tinner and Theurillat, 2003).…”

“…Several long-term multi-proxy records from the Alps illustrate the effects of past climate and land-use changes on treeline ecology (Berthel et al, 2012;Finsinger and Tinner, 2007;Gobet et al, 2003Gobet et al, , 2005Lang and Tobolski, 1985;Rey et al, 2013;Schwörer et al, 2013Schwörer et al, , 2014Tinner et al, 1996;Tinner and Kaltenrieder, 2005;Tinner and Theurillat, 2003;Wick et al, 2003;Wick and Tinner, 1997). The use of plant macrofossil and stomata analysis in many of these studies provides a detailed picture of local vegetation dynamics around the treeline ecotone (Tinner, 2007), because of the lower dispersal distance of plant remains compared with pollen (Ammann et al, 2014;Birks and Bjune, 2010).…”