Late Weichselian vegetation,climate, and floral migration at Liastemmen,North Rogaland,south-western Norway

Palynological results from Liastemmen indicate a tripartite division of the Late Weichselian. In the pleniglacial period, from deglaciation ca. 14000 BP to ca. 13000 BP, Artemisia-dominated pioneer vegetation on disturbed, mineral-soil was strongly influenced by cold winters and katabatic winds. The Late Weichselian Interstadial (ca. 13000 BP-ca. 11000 BP) comprises a Salix-shrub consolidation phase, and from ca. 12700 BP a tree-birch phase. In the last 500 years of this period July and January means are estimated to about 16°C and between ?2°C and ?6°C, respectively. In the Younger Dryas Stadial (ca. 11000 BP-ca. 10200 BP) Artemisia-dominated vegetation returns. Three brief climatic deteriorations (ca. 12 250 BP, 11 700 BP, and 11 300 BP), unfavourable to woody vegetation on humus soils, are demonstrated within the interstadial. Critical climatic factors include cool winters and strong winds, exposing vegetation and soil to frost, drought, and erosion. The oldest and strongest oscillation, probably involving local deforestation, is correlated with the ‘Older Dryas deterioration’. Boreal-circumpolar, eurasiatic, and arctic-alpine plants dominated the late-glacial flora. For the majority of the late-glacial taxa a northward migration is demonstrated. This may also apply for Papaver radicatum, Pinguicula alpina, and Primula scandinavica, all with bicentric distributions in Norway today.