Late-glacial vegetational ecotones and climatic patterns in Western Norway

The mapping of Weichselian late-glacial interstadial (13-11 ka B.P.) and Younger Dryas stadial (11-10 ka B.P.) pollen percentages for selected taxa demonstrates vegetational and hence climatic differentiation in Western Norway during these times. In the south, early interstadial Salix dominance was replaced by Betula woodland development. During Younger Dryas time, Betula pollen declined to values consistent with a modern vegetational analogue of the vegetation at the upper forest limit. In the inner fjord areas north of Stavanger, the interstadial vegetation contained scattered birch trees, the density depending on local topography and soils. During the Younger Dryas, vegetation resembling the modern mid- and low-alpine vegetation developed. On the outer coast, the interstadial vegetation was probably treeless, and dominated by Salix spp., including S. herbacea, and herbs. The vegetation became even more open during the Younger Dryas, resembling that of the modern mid- and high-alpine zones. The spatial ecotones delimiting the three areas of different vegetation development during both the interstadial and the Younger Dryas can be placed north of Stavanger, separating the southern region, and between the outer coast and inner fjord areas to the north. The Younger Dryas drop in temperature in all areas was up to about 5°C, enough to pass ecotonal thresholds in time in all areas.