HOLIVAR2006 Abstracts
Which climate variables caused changes in vegetation composition?
Thomas Giesecke1,2 and Heikki Seppä3
1Department of Geography, The University of Liverpool, Roxby Building,
Liverpool, L69 7ZT, UK
2Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen K, Denmark
3Department of Geology, University of Helsinki, Gustaf Hällstöminkatu 2, Finland
Contact: Thomas Giesecke (tg@geus.net)
In Scandinavia, Holocene climate reconstructions from pollen data generally show a rise in temperature at the beginning of the Holocene, maximum warmth during the Mid-Holocene, and a subsequent decline in temperatures towards the present day. This trend is also visible in the pollen-based climate reconstructions from two small central Swedish lakes. Pollen diagrams from both lakes show a shift in tree composition during the Mid-Holocene from Corylus, Ulmus and Alnus to Tilia and Quercus. These species are temperate trees that today mainly grow south of the two lakes. At present, the distribution of Corylus reaches much further north in maritime areas of Norway, while Tilia has its northern-most distribution in Finland and to the east. The observed change in vegetation composition during the Mid-Holocene could therefore be explained by a shift from a long growing season with cool temperatures to a shortening of the growing season with higher maximum summer temperatures. The general trend that is obtained from pollen-based temperature reconstructions on the other hand may reflect shifts of large vegetation belts at the biome level.
Thomas Giesecke is interested in the long-term processes of forest ecosystems and the drivers of past vegetation changes.