A 7500-year pine tree-ring chronology for northern Finnish Lapland
by
Matti Eronen
Department of Geology, P.O. Box 11 (Snellmaninkatu 3), FIN-00014 University of Helsinki, Finland
Coauthors: Markus Lindholm (Saima Centre for Environmental Sciences, University of Joensuu, Linnankatu 11, FIN-57130 Savonlinna, Finland), Mauri Timonen (Finnish Forest Research Institute, P. O. Box 16, FIN-96301 Rovaniemi, Finland)

Subfossil trunks of pine (Pinus sylvestris, L.) are preserved in large numbers in many lakes in northern Fennoscandia and these constitute an extremely valuable source for studies on past climatic variability, especially variations in summer temperatures. The forest-tundra ecotone of northern Fennoscandia is a sensitive marginal zone which is easily affected by climatic variations. Many different proxy data indicate changes in the northern natural systems, which are caused by climatic shifts during the Holocene. Subfossil pine logs found in situ beyond the present coniferous treeline show conclusively that favourable climatic conditions prevailed in the middle part of the Holocene. In the mid-Holocene time 5000-3800 calB.C. temperatures were generally 2 EC or more higher than at present. At that time pine reached its widest Holocene distribution in northern Fennoscandia, but in the latter part of the Holocene the limit of pine has gradually retreated along with cooling temperatures The subfossil pines are highly suitable material for dendrochronological research. In the forest-tundra ecotone region of northern Finnish Lapland a very large from living Scots pines (Pinus sylvestris, L.) and over 1700 samples of subfossil pines have been collected for dendrochronological studies. In addition to this, more than1400 pine subfossils have been sampled from the forested area of Finnish Lapland. The goal in this long-lasting work was to build a more than 7000 years long continuous pine ring-width chronology. The construction of the chronology is now completed. The major part of the Finnish Lapland master curve was constructed several years ago, but it was extremely difficult to bridge the gap about 300 years long, prior to 165 B.C, between the "absolute" younger part of the chronology and the "floating" older part. The crucial samples were identified and assembled into the chronology in early 1999. The unbroken pine chronology extends from the present to 5520 B.C. The one-year accuracy of the chronology makes it possible to analyse in detail past variations in summer temperature, which clearly is the decisive climatic forcing factor for the radial growth of pine in Lapland. The mathematical-statistical analyses and correlations with other proxy data are underway. There are temporal variations in the growth pattern, but is difficult to extract any clear long-term trends in the data and the tests have not revealed any distinct cyclicity. The most conspicuous event indicated by tree rings occurred 330 B.C. In that year the radial growth of pines suddenly dropped close to zero and the recovery from this catastrophe took 20-30 years. The reason for this event is still unknown.

Date received: March 23, 2001

Copyright © 2001 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cagc-24.