Did tree‐Betula, Pinus and Picea survive the last glaciation along the west coast of Norway? A review of the evidence, in light of Kullman (2002)

Abstract

AbstractAim We discuss the hypotheses proposed by Kullman [Geo‐Öko21 (2000) 141; Nordic Journal of Botany21 (2001) 39; Journal of Biogeography29 (2002) 1117] on the basis of radiocarbon‐dated megafossils of late‐glacial age from the central Swedish mountains that boreal trees survived the glaciation along the south‐west coast of Norway and subsequently migrated eastward early in the late‐glacial to early deglaciated parts of the central Swedish Scandes mountains.Methods We assess these hypotheses on the basis of glacial geological evidence and four lines of palaeoecological evidence, namely macrofossil records of the tree species, vegetation and climate reconstructions from plant evidence, independent climate reconstructions from other proxies for the late‐glacial environment of south‐west Norway, and the patterns of post‐glacial spread of the tree species.Location South and west Norway, central Swedish Scandes mountains (Jämtland).Results and conclusions South‐west Norway and the adjacent continental shelf were under ice at the last‐glacial maximum (LGM). The late‐glacial vegetation of south‐west Norway was treeless and summer temperatures were below the thermal limits for Betula pubescens Ehrh., Pinus sylvestris L. and Picea abies (L.) Karst. Instead of spreading immediately after the onset of Holocene warming, as might have been expected if local populations were surviving, B. pubescens showed a lag of local arrival of 600 to > 1000 years, Pinus lagged by 1500 to > 2000 years, and Picea only reached southern Norway c. 1500 years ago and has not colonized most of south‐west Norway west of the watershed. Glacial geological evidence shows the presence of an ice sheet in the Scandes at the LGM and in the Younger Dryas, which was cold‐based near or at the area where the late‐glacial‐dated megafossils were recovered by Kullman. We conclude that the samples dated by Kullman (2002) should be evaluated carefully for possible sources of contamination. All the available evidence shows that the biogeographical hypotheses, based on these radiocarbon dates taken at face value, of late‐glacial tree survival at the Norwegian coast and subsequent eastwards spread to the mountains, are unsupportable.