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

Abstract

ABSTRACT. Recent recession of high-mountain glacier ice and perennial snow and ice patches has exposed megafossil and macrofossil tree remnants and peat, offering a new source of Holocene high alpine vegetation history in the Scandes. Radiocarbon dates of 90 tree megafossils from Swedish Lapland, 29 of which had not previously been published, range from 11 980 to 1950 cal yr BP. During the interval 9500 -8500 cal yr BP, mountain birch (Betula pubescens ssp. czerepanovii) and Scots pine (Pinus sylvestris) grew 600 -700 m higher upslope than they do today, which is a new and remarkable discovery. Subsequently, tree density gradually declined at higher elevations, and as the tree line moved downslope, the ratio of Betula to Pinus increased. Tree growth ceased around 4500 cal yr BP, presumably in response to the return of perennial ice and snow. A short episode of resumed tree growth of Betula indicates conditions warmer than present around 2000 years ago. Between c. 8500 and 7300 cal yr BP, Picea abies, Larix sibirica, Populus tremula, Sorbus aucuparia and Alnus incana were subordinate species on a forest floor dominated by plant species characteristic of prealpine or subalpine woodlands. Growth of trees as much as 700 m higher upslope than today around 9500 cal yr BP implies that summer temperatures at that time may have been 3.0˚C warmer than today's temperatures (corrected for land uplift). This inferred temperature difference between the early Holocene and the present concurs with changes in the Earth's orbital parameters.Key words: glaciers; tree growth; megafossils; macrofossils; Holocene; radiocarbon dating; climate change; Swedish Scandes RÉSUMÉ. Le recul récent de la glace de glacier, de la neige pérenne et des bancs de glace en haute montagne a permis de découvrir des mégafossiles et des macrofossiles de restes d'arbres et de tourbe, ce qui offre une nouvelle source d'histoire de la végétation alpine des Scandes en haute altitude pendant l'Holocène. La datation au carbone 14 de 90 mégafossiles d'arbres en provenance de la Laponie suédoise, dont 29 n'avaient jamais fait l'objet d'une publication, donne des résultats variant de 11 980 à 1 950 années cal. BP. Au cours de l'intervalle allant de 9 500 à 8 500 années cal. BP, le bouleau de montagne (Betula pubescens ssp. czerepanovii) et le pin sylvestre (Pinus sylvestris) poussaient à une hauteur de 600 à 700 m plus élevée qu'aujourd'hui, ce qui représente une découverte à la fois nouvelle et remarquable. Subséquemment, la densité des arbres a diminué graduellement en haute altitude, et au fur et à mesure que la limite forestière s'est mise à descendre, le rapport entre Betula et Pinus s'est accru. La croissance des arbres a cessé vers 4 500 années cal. BP, probablement en raison du retour de la glace et de la neige pérennes. Un bref épisode de reprise de la croissance des arbres de Betula indique la présence de conditions plus chaudes qu'à présent il y a environ 2 000 ans. Entre 8 500 et 7 300 années cal. BP environ, Picea abies, Larix sibirica, Populus tremu...

Further Details on Holocene Treeline, Glacier/Ice Patch and Climate History in Swedish Lapland

“…This study adds seven new dates of megafossil tree remnants (4 Betula, 2 Pinus, 1 Picea) to a previous sample of 21 specimens from the same glacier (12 Betula, 9 Pinus) (Kullman & Öberg 2015). Individual dates are given in Table 1 and the samples are depicted in Figures 5-7.…”

“…In the Swedish Scandes, however, important findings of megafossil trees under above-mentioned circumstances, high above current treelines, have been reported and discussed in some studies (Kullman 2004;Öberg & Kullman 2011a; Kullman & Öberg 2013Kullman & Öberg , 2015Kullman 2017a). These resultshave proven accuracy in time, space and species composition, going far beyond the resolution of pollen analysis and other microfossil approaches (cf.…”

“…Some exceptional outlying records of 500-700m higher than present treeline, support an even higher elevational origin as a more general pattern. The possible generality of this supposition needs to be further elucidated in perspective of its implications for Holocene vegetation history and paleoclimate (Öberg & Kullman 2011a,b;Kullman & Öberg 2013Kullman & Öberg , 2015. With this background, the present study reports efforts to sustain and further approach the uppermost limit of megafossil trees within an area previously well researched with respects to megafossil tree remnants (debris wood) occurring at glacier forefields at relatively modest levels above the present-day treelines (Öberg & Kullman 2011a;Kullman & Öberg 2013Kullman & Öberg , 2015.…”

Holocene development and permafrost history in sub‐arctic peatlands in Tavvavuoma, northern Sweden

“…10 000–9600 cal. a BP) the climatic conditions in the region were favourable for plant productivity with around 3 °C warmer summer temperatures compared to today (Kullman & Öberg ), resulting in relatively rapid peat and net carbon accumulation rates during the early Holocene.…”

Climate Change and Primary Birch Forest (Betula pubescensssp. czerepanovii) Succession in the Treeline Ecotone of the Swedish Scandes

“…4, 5), variations in winter temperature are reasonably of relatively small importance for the birch vegetation evolution, although the timing of snow melt needs to be considered in that connection. Relevant aspects of Holocene landscape and tree line history are provided by Lundqvist (1969Lundqvist ( , 2012, Kullman (1995Kullman ( , 2005Kullman ( , 2013Kullman ( , 2015, Bergman et al (2005)…”