Norway spruce postglacial recolonization of Fennoscandia

Kevin Nota,Heikki Seppä,Stefan Bertilsson,Minna M Väliranta,Yoshihisa Suyama,Brita Svensson,Pascal Milesi,Richard Bindler,Jonatan Klaminder,Barbara Wohlfarth,Tamara Van Steijn,Shun K Hirota,Urban Gunnarsson,Ayumi Matsuo,Laura Parducci,Alessandro Nobile

doi:10.1038/s41467-022-28976-4

Abstract

Contrasting theories exist regarding how Norway spruce (Picea abies) recolonized Fennoscandia after the last glaciation and both early Holocene establishments from western microrefugia and late Holocene colonization from the east have been postulated. Here, we show that Norway spruce was present in southern Fennoscandia as early as 14.7 ± 0.1 cal. kyr BP and that the millennia-old clonal spruce trees present today in central Sweden likely arrived with an early Holocene migration from the east. Our findings are based on ancient sedimentary DNA from multiple European sites (N = 15) combined with nuclear and mitochondrial DNA analysis of ancient clonal (N = 135) and contemporary spruce forest trees (N = 129) from central Sweden. Our other findings imply that Norway spruce was present shortly after deglaciation at the margins of the Scandinavian Ice Sheet, and support previously disputed finds of pollen in southern Sweden claiming spruce establishment during the Lateglacial.

Highlights

Contrasting theories exist regarding how Norway spruce (Picea abies) recolonized Fennoscandia after the last glaciation and both early Holocene establishments from western microrefugia and late Holocene colonization from the east have been postulated
A migration route from the east means that spruce rapidly dispersed across a massive ice sheet that persisted in northern Fennoscandia until ca 10 cal. kyr BP19,20 or that spruce established from the south-east and moved toward the north to central Sweden, for which the palynological record is controversial[8,21,22]
The strongest evidence of early Holocene establishment of spruce trees in central Fennoscandia comes from still living and clonally regenerating spruce trees currently growing in the central Scandes several metres above the treeline, and where carbon-14 inferred ages suggest an onset of growth around 9.7–9.5 cal. kyr BP14

Summary

Introduction

Contrasting theories exist regarding how Norway spruce (Picea abies) recolonized Fennoscandia after the last glaciation and both early Holocene establishments from western microrefugia and late Holocene colonization from the east have been postulated. Findings of spruce megafossils dating back to glacial times[12–15], as well as ancient DNA fragments of P. abies in early Holocene sediments seem to support the theory that spruce was present in the central Scandinavian Mountains (the Scandes) already at 13 cal. The alternative hypothesis of an early colonization from the west where spruce survived on summits protruding the ice-sheet (the nunatak hypothesis) was first suggested based on early Holocene macrofossil findings of spruce in the alpine region of the southern Swedish Scandes[13] Later, this hypothesis was supported by the discovery of a P. abies mitochondrial DNA mutation (mh[05] haplotype A) dominant in contemporary forests from western Fennoscandia and present in ancient sediments from central Norway dated to 10.3 cal. Mitochondrial and nuclear DNA from contemporary spruce forests suggest a complex spread

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Conclusion