Tree-ring samples from Scots pine have been collected from living trees, dead standing logs, old buildings, and subfossil wood from small lakes. A large number of trunks and stumps have preserved in muddy lakes, in both current tree-line area and beyond it.
With its 7641 years, this tree-ring chronology is the longest unbroken conifer tree-ring chronology in Eurasia and the second longest in the world. A longer one, over 8800 years, is built from living and dead Bristlecone pines found in the White Mountains of California.
Long tree-ring chronologies have proved to be are very useful in estimating the past climate. The characteristics of the Finnish chronology, the distribution of the samples and the strong June-July temperature connection have provided exceptional tools for dendroclimatic analysis and reconstructions.
The existence of this chronology and data have enabled reconstructing models for past tree-lines in Finnish Lapland. The area is located beyond the Arctic circle, between 68° and 70° Northern latitude, and 20° and 30° Eastern latitude.
Pine tree-line reached higher altitudes and more northern locations in Finnish Lapland during warmer times for thousands of years ago. Based on the sample locations beyond the present timberline, Kultti et al¹ calculated at 2006 that early summers (June-July) were during the Holocene Optimum ca 6000 years ago 2,6 oC warmer than today. The data also showed 0,5C warmer temperatures during the Medieval Warm Period and 0,5 oC cooler temperatures during the last Ice age. Today’s timberline pines do not show any specific warming in their growth. The result is comparable with the temperatures observed in the Sodankylä climate station.
Finnish timberline region is close to both Arctic and Atlantic Oceans. Due to this geographical location and prevailing southwestern winds the timberline pine is sensitive to climate patterns occurring in the North Atlantic. This characteristic allows to make some conclusions concerning the large-scale climate of the northern hemisphere. This concerns especially a phenomenon called climatic cyclicity. The most recent research has focused on analyzing the cyclicity of the supra-long chronology.
¹Past changes in the Scots pine forest line and climate in Finnish Lapland: a study based on megafossils, lake sediments, and GIS-based vegetation and climate data. Seija Kultti, Kari Mikkola, Tarmo Virtanen, Mauri Timonen and Matti Eronen. The Holocene 16,3 (2006) pp. 381/391
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Comments: Sanna Kettunen, Firstname.lastname @ metla.fi