Holocene regional and local vegetation history and lake-level changes in the Tornetrask area, northern Sweden

A combination of pollen and macrofossil analyses from six lakes at altitude s between 370 and 999 m above sea level (a.s.l.) in the Tornetrask area ref lect the Holocene vegetation history. The main field study area has been th e Abisko valley at altitudes around 400 m a.s.l. The largest lake, Vuolep N jakajaure has annually laminated (varved) sediments. The chronology and sed imentation rates in the pollen-influx calculations are based on varve yrs i n this lake and on radiocarbon dated terrestrial plant macrofossils in the other lakes. A strong increase of mountain birch (Betula pubescens ssp. tor tuosa) during the early Holocene with a tree-line c. 300 m above the presen t, indicates that the summer temperature was c. 1.5 degrees C higher than t oday, assuming that the land uplift has been 100 m since then. Scattered st ands of pine (Pinus sylvestris) may have been growing in the area immediate ly after the deglaciation but a forest consisting of pine and mountain birc h expanded first at low elevations and reached the eastern parts of the Tor netrask area at c. 8300 cal BP and the western parts at c. 7600 cal BP. The highest pine-birch forest limit was not reached until 6300 cal BP (110 m a bove present pine limit). Warm and dry conditions during the pine forest ma ximum led to lowering of the water level documented in Lake Badsjon in the Abisko valley about 1-1.5 m lower than today. Pine and mountain birch were growing at the maximum altitude until c. 4500 cal BP. Assuming that land up lift has been in the range of 20-40 m since the mid-Holocene, this implies that the temperature was then c. 1.5-2 degrees C higher than today. Rising lake-levels and lowering limits of pine and mountain birch since c. 4500 ca l BP indicate a more humid and cool climate during the late Holocene.