First post-glacial establishment of forest trees: early Holocene vegetation, mollusc settlement and climate dynamics in central Troms, North Norway

Sediments from two limnic basins in a sub-continental region of northern Norway are investigated for pollen, plant macrofossils and bivalves at a high stratigraphical resolution. The basins are located at 280 and 400 m a.s.l. on the S-SW slope of Mt. Skrubben (848 m a.s.l.). The bio- and lithostratigraphical records are interpreted in terms of immigration and establishment of forest tree species and climate. The mountain was deglaciated at both sites at c. 9200-9100 BP (c. 10200-10100 cal. BP). Betula pubescens forest stands established at c. 8900 BP (c. 9900 cal. BP). The first Pinus sylvestris individuals may have established at or near the lowermost investigation site at c. 8700-8600 BP (c. 9700-9600 cal. BP), while P. sylvestris forest stands were present at 400 m a.s.l. c. 7700 BP (c. 8500 cal. BP) and expanded in area and/or density from c. 7200 BP. Macrofossils of P. sylvestris occur in strata with a pine pollen influx as low as c. 200 grains cm(-2) yr(-1). The immigration of P. sylvestris to the western part of northern Fennoscandia may thus have happened earlier than formerly interpreted from pollen analyses alone, where influx values as low as c. 200 grains cm(-2) yr(-1) would not be considered as indicative of local presence. Alnus incana established at approximately the same time as P. sylvestris. During the period from deglaciation to c. 6600 BP (c. 7300 cal. BP), calcareous limnic sediments were deposited in the basins, with Chara species and a Sphaeriidae fauna consisting of Pisidium hibernicum, P. lilljeborgii, P. milium, P. nitidum, P. waldeni and P. casertanum. During the period c. 8800-8500 BP, P. nitidum prevailed, and almost pure CaCO3 sediments were formed. We interpret the environment as dry with a low influx of both minerogenic particles and humic substances. The period 8800-8500 BP (9800-9500 cal. yr BP) is interpreted as a period with warm and dry summers and cold and dry winters.