Late Weichselian vegetation, climate and floral migration at Eigebakken, South Rogaland, Southwestern Norway

Abstract

The Eigebakken, Jæren, pollen diagram shows a tripartite division of the Late Weichselian into three main climatic periods. The pleniglacial, from local deglaciation c. 14,000 B.P. to c. 13,000 B.P., reflects an Artemisia-dominated pioneer vegetation on disturbed mineral-soil, prevented from further development by cold winters and katabatic winds. The Bøilling amelioration opens the Late Weichselian Interstadial (13,000–11,000 B.P.) and initiates soil development and vegetational closure into a Salix-shrub consolidation phase (to c. 12,650 B.P.). Thereafter an open birch vegetation phase (to c. 12,200 B.P.) follows. The subsequent birch-forest phase (c. 12,200-11,000 B.P.) reflects the interstadial vegetational and edaphical optimum. In this phase July mean temperature reached at least 14°C. In contrast to late-glacial studies from N Rogaland, the Eigebakken diagram gives no biostratigraphical indications of climatic deteriorations such as “Older Dryas” within the interstadial. This is probably explained by denser local birch forests with higher ecological inertia on Jæren. Furthermore, no traces of Fægri's “Brøndymyra interstadial” are recorded. The Younger Dryas Stadial (11,000-c. 10,500 B.P.) shows a two-step regressional succession. In the first step (to 10,600 B.P.) the birch forests degraded into open birch woodland. The second phase (10,600– c. 10,500 B.P.) involved the maximum extent of open-ground vegetation and possibly temporary local deforestation. Critical climatic factors included cold winters and strong winds. The first vegetational responses of the Holoecene climatic amelioration are recorded locally as early as c. 10,500 B.P. Tree-birches re-established, finally developing into dense forests c. 10,000 B.P. Boreal-circumpolar, eurasiatic and arctic-alpine plants dominated the late-glacial flora. For the majority of the late-glacial taxa a northward migration into SW Norway is suggested.