Search

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.

This study investigated Holocene tree-line history and climatic change in the pre-Polar Urals, northeast European Russia. A sediment core from Mezhgornoe Lake situated at the present-day alpine tree-line was studied for pollen, plant macrofossils, Cladocera and diatoms. A peat section from Vangyr Mire in the nearby mixed mountain taiga zone was analysed for pollen. The results suggest that the study area experienced a climatic optimum in the early Holocene and that summer temperatures were at least 2°C warmer than today. Tree birch immigrated to the Mezhgornoe Lake area at the onset of the Holocene. Mixed spruce forests followed at ca. 9500-9000 14C yr BP. Climate was moist and the water level of Mezhgornoe Lake rose rapidly. The hypsithermal phase lasted until ca. 5500-4500 14C yr BP, after which the mixed forest withdrew from the Mezhgornoe catchment as a result of the climate cooling. The gradual altitudinal downward shift of vegetation zones resulted in the present situation, with larch forming the tree-line. European Commission - Tundra Degredation in the Russian Arctic project; Grant Number: ENV4-CT97-0522