Paths and rates of recolonization of Pinus sylvestris L. and Picea species in Scandinavia in the Holocene Period

Abstract

Recolonization of Scandinavia by populations of Pinus sylvestris, on the one side, and of Picea abie and P. obovata on the other in the Holocene Period is analyzed: its paths, rates, and delays are compared. The dispersal rate of the populations, beginning from 12000 years BP, is evaluated by the published data of radiometric method of pollen dating. It has been revealed that P. sylvestris migrated into central Scandinavia from the Alps via the Denmark Isthmus at the rate of 500–1250 km/ka about 8200 years BP. The fast dispersal may be mainly explained by the hydrochory of pine seeds, which is by an order of magnitude quicker than anemochory. The rate of P. sylvestris expansion to Fennoskandia from the Russian Plain was lower (520 km/ka). Populations of Picea species dispersed from the same regions at a rate three to ten times lower (131–164 km/ka). That is why the invasion of Picea abies from the Alps to Scandinavia via the Denmark Isthmus did not take place before the formation of the Kattegat Strait. The populations of both Picea species reached the northern areas of Scandinavia 3500 years BP, its central part 2000 years BP, and the southern area 1500 years BP by a roundabout route via Karelia. In general, they reached Scandinavia by 4000, 6200, and 8500 years later than P. sylvestris, respectively. This is obviously related to the fact that pine trees begin to seed two times earlier than the spruce, and pine seedlings were more tolerant to the extreme climatic conditions of the periglacial habitats of the Mid-Holocene Period.