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Calibrated pollen accumulation rates as a basis for quantitative tree biomass reconstructions

Department of Geology, P.O. Box 64, FI-00014, University of Helsinki, Finland, heikki.seppa{at}helsinki.fi

Teija Alenius

Department of Geology, P.O. Box 64, FI-00014, University of Helsinki, Finland

Petteri Muukkonen

Finnish Forest Research Institute, P.O. Box 18, FI-01301 Vantaa, Finland

Thomas Giesecke

Department of Palynology and Climate Dynamics, Albrecht-von-Haller-Institute for Plant Sciences, University of Göttingen, Untere Karspule 2, Göttingen, Germany

Paul A. Miller

Geobiosphere Science Centre, Department of Physical Geography & Ecosystem Analysis, Lund University, Sölvegatan 12, 223 62 Lund, Sweden

Antti E.K. Ojala

Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland

Recent investigations show that the pollen accumulation rate (PAR) of the common tree taxa is directly related to the biomass and, by inference, to the population size of the taxa around the study site. Fossil PAR records preserved in lakes provide therefore a potential proxy for quantitative biomass and population reconstructions. We use the high-resolution PAR records obtained from two accurately dated lake sediment cores in Finland to generate quantitative Holocene biomass records for Pinus, Picea and Betula, the most common tree taxa of the European Boreal forest. PAR values were calibrated to biomass values by comparing the modern PAR values with the modern biomass values and assuming a linear relationship between the past PAR and biomass values. The obtained PAR and biomass values and trends are remarkably coherent between the two records. Pinus has a stable Holocene biomass size and its modern biomass, about 20 t/ha, corresponds with the natural Pinus biomass in the study regions. In contrast, Picea immigrated from the East during the mid Holocene, had a maximum biomass, 50—60 t/ha, at 3500—1000 cal. yr BP, and declined strongly during the last 1500—1000 years as a result of increased human activity and related rise of fire frequency. Thus, the modern Picea biomass in the study regions, about 22 t/ha, is only 35—40% of the natural Picea biomass. The results of this pilot study demonstrate the potential of the calibrated PAR data in quantitative biomass and population reconstructions. Such reconstructions can provide fresh insights into the structure of past plant communities and, when combined with records reflecting palaeoclimates, natural disturbances, and human activity, can help to disentangle the long-term importance of different enviromental drivers to changes in plants populations and ecosystems.

Key Words: Pollen accumulation rate • Holocene • Boreal forest • biomass • population • climate • competitive interactions • disturbances.

The Holocene, Vol. 19, No. 2, 209-220 (2009)
DOI: 10.1177/0959683608100565


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