Holocene forest history of the Pöyrisjärvi area of the coniferous tree line in western Finnish Lapland: a pollen stratigraphical study

Abstract

The evolution of the forests beyond the current coniferous tree line during the Holocene was studied by means of pollen analysis. Two closed-basin lakes, Jierstivaara and Isohattu, in western Finnish Lapland, were cored for the purpose. The rate of sedimentation proved to be uneven. After a slow initial rate a marked acceleration occurs between 6000 and 4000 BP. The last three millenia seem to have been a period of even sedimentation. A stage of raised pollen concentrations coincides with the accelerating rates of sediment growth. Fluctuations in the water table of the lakes are estimated to have contributed to the changes in the matrix sedimentation and in the pollen concentration. Pine arrived in the area 6000-6500 BP. Pure pine forest was never established. During the last 3000 years pine has almost totally disappeared from the vicinity of the sites. From the Jierstivaara core additional close-interval pollen and charcoal analyses were made which cover a period from about 8200 to 4500 BP. They show in more detail the spread of pine and the following time of low water lever which coincides with a period of high juniper values for about 600 radiocarbon years. Low charcoal values throughout the sequence point to a minor role of fires in the area.

Keywords

• pollen analysis
• tree line
• forest history
• pollen deposition rates
• Holocene
• northern Fennoscandia
• charcoal analysis
• forest fires