| Summary: | Changes in tree-line, mean July temperature (T-jul ) and mean annual precipitation (P-ann ) for the last 10 200 cal. yr BP are reconstructed on the basis of pollen and plant macrofossils preserved in lake sediments from two sites near the present-day tree-line in Troms, northern Norway. Quantitative climate reconstructions are performed using pollen-climate transfer functions based on WA-PLS regression. Early Holocene Betula pubescens forests were gradually replaced by Pinus sylvestris at Dalmutladdo (355 m a.s.l.) starting about 7000 cal. yr BP. The local presence of pine woodland at that time is supported by finds of stomata and plant macrofossils and by high pollen accumulation rates. Until about 4000 cal. yr BP the P. sylvestris tree-line was 250-300 m higher than today, suggesting T-jul about 2.0degreesC higher than at present. The later part of the Holocene has a cooler and moister climate and an increasing development of mires and fern-rich vegetation, as shown by increases of Sphagnum and fern spores and the re-establishment of B. pubescens woodland. The reconstructed T-jul from the two sites shows similar trends to previously published data, with T-jul 1-2degreesC warmer between 9500 cal. yr BP and 2000 cal. yr BP T-jul . Maximum T-jul values occur between 8500 and 4500 cal. yr BP, after which there is a gradual decrease in T-jul.
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