Rapid responses of high‐mountain vegetation to early Holocene environmental changes in the Swiss Alps

Abstract

Summary 1The Early Holocene sediment of a lake at tree line (Gouillé Rion, 2343 m a.s.l.) in the Swiss Central Alps was sampled for plant macrofossils. Thin (0.5 cm) slices, representing time intervals of c . 50 years each from 11 800 to 7800 cal. year  , were analysed and the data compared with independent palaeoclimatic proxies to study vegetational responses to environmental change. 2 Alpine plant communities (e.g. with Salix herbacea ) were established at 11 600-11 500 cal. year  , when oxygen-isotope records showed that temperatures increased by c . 3-4 ° C within decades. Larix decidua trees reached the site at c . 11 350 cal. year  , probably in response to further warming by 1-2 ° C. Forests dominated by L. decidua persisted until 9600 cal. year  , when Pinus cembra became more important. 3 The dominance of Larix decidua for two millennia is explained by dry summer conditions, and possibly low winter temperatures, which favoured it over the late-successional Pinus cembra . Environmental conditions were a result of variations in the earth's orbit, leading to a maximum of summer and a minimum of winter solar radiation. Other heliophilous and drought-adapted species, such as Dryas octopetala and Juniperus nana , could persist in the open L. decidua forests, but were out-competed when the shade-tolerant P. cembra expanded. 4 The relative importance of Larix decidua decreased during periods of diminished solar radiation at 11 100, 10 100 and 9400 cal. year  . Stable concentrations of L. decidua indicate that these percentage oscillations were caused by temporary increases of Pinus cembra , Dryas octopetala and Juniperus nana that can be explained by increases in moisture and/or decreases in summer temperature. 5 The final collapse of Larix decidua at 8400 cal. year  was possibly related to abrupt climatic cooling as a consequence of a large meltwater input to the North Atlantic. Similarly, the temporary exclusion of Pinus cembra from tree line at 10 600-10 200 cal. year  may be related to slowing down of thermohaline circulation at 10 700-10 300 cal. year  . 6 Our results show that tree line vegetation was in dynamic equilibrium with climate, even during periods of extraordinarily rapid climatic change. They also imply that forecasted global warming may trigger rapid upslope movements of the tree line of up to 800 m within a few decades or centuries at most, probably inducing large-scale displacements of plant species as well as irrecoverable biodiversity losses.

Interactions between climate and vegetation during the Lateglacial period as recorded by lake and mire sediment archives in Northern Italy and Southern Switzerland

“…Despite these uncertainties, our paleorecords unambiguously underscore the high sensitivity of subalpine, treeline, and alpine vegetation to climatic changes, a finding that is in agreement with previous studies (e.g. Tinner and Kaltenrieder, 2005) emphasizing that global warming may trigger rapid vegetational reorganizations of Alpine vegetation within centuries at most.…”

“…However, forest adjustment dynamics to climatic change were very rapid at the beginning of the Holocene. For instance, treeline moved 800 m upwards in only 200 years in the adjacent inner section of the central Alps (Tinner and Kaltenrieder, 2005).…”

Ecological conditions and the distribution of alpine juniper (Juniperus communis subsp. alpina) in the Hrubý Jeseník Mts

“…However, the low number of juniper close to other woody species might indicate such a negative relationship. Juniper distribution could therefore be limited mainly to sites in the alpine belt without large stands of taller tree species (Jeník 1973;Jeník & Hampel 1991;van der Merwe et al 2000;Tinner & Kaltenrieder 2005).…”

New Aspects of High-Mountain Palaeobiogeography: A Synthesis of Data from Forefields of Receding Glaciers and Ice Patches in the Tärna and Kebnekaise Mountains, Swedish Lapland

“…Karlén 1976;Tinner and Kaltenrieder, 2005;Kirdyanov et al, 2012;Kullman, 2013), drawing on a conventional temperature lapse rate of 0.6˚C per 100 m in elevation (Laaksonen, 1976). Given these assumptions, the Holocene tree-line peaks, at 9500 cal yr BP and about 700 m higher than present, may imply summer temperatures 4.2˚C warmer than the first decade of the present century.…”