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32nd Annual Arctic Workshop Abstracts
March 14-16, 2002
INSTAAR, University of Colorado at Boulder

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LANGDON, CATHERINE T. University of Exeter.
Dumayne-Peaty, Lisa . University of Birmingham.
Matthews, John A. university of Wales, Swansea.

The tree-line is a sensitive ecotone that consists of trees that grow at their climatic limit and previous studies have shown that the tree-line has responded substantially to climatic change (e.g. Aas and Faarlund, 1996; Gunnarsdottir, 1996; Torske, 1996). There are, however several debates surrounding the exact effect of climatic change on the tree-line. For example, there is contention over whether an early Holocene sub-alpine birch belt occurred above the pine tree-line (Aas and Faarlund, 1988, 1996), whether it established as the result of a mid-Holocene climatic deterioration (Gunnarsdottir, 1996) or later Holocene climatic instability (Kullman, 1981). Furthermore, recent palaeoenvironmental and palaeoecological research, notably in Scandinavia, has focused on the nature and extent of the Finse event (a cooler, wetter period c. 8,200 cal. years B.P. that caused glaciers to advance (Nesje and Dahl, 2001; Tinner and Lotter, 2001) and its effect on vegetation. The LIA is also an important event in Scandinavian climatic history but there is little palynological evidence for its effect on vegetation due to the deposition of predominately inorganic sediments and difficulties in distinguishing the effect of climatic change from the effects of human activity.

Traditionally megafossil evidence has been used to elucidate the position of past tree-lines but this evidence is often spatially and temporally discontinuous, and therefore pollen and macrofossil studies can supplement information based on past tree-lines from megafossil data. As such, this poster presents the results of pollen analysis of a small mire to provide evidence for long term changes in forest composition and extent at and around the present day altitudinal tree-line in the Leirdalen valley, south central Norway. The results presented are part of a wider study carried out into tree-line fluctuations in the area (Barnett et al., 2001). The palynological data indicates that following deglaciation c. 10115 cal. years B.P., dense pine forest migrated into the area replacing vegetation that was dominated formerly by birch. It is probable that the pine forest-limit subsequently increased in altitude significantly in response to a warmer climate with average summer temperatures higher than at present. This climatic optimum is thought to have been interrupted by a climatic deterioration dated to c. 8,380 cal. years B.P. (the Finse event) that caused the woodland around the site to diminish and allowed the emergence of a light demanding vegetation assemblage. A sudden shift from dense pine forest to birch woodland with pine and alder in conjunction with the development of a sub-alpine birch belt is postulated to have occurred c. 6870 cal. years B.P. Further deterioration of climate with neoglacial episodes led to the suppression of the tree-line c. 3930 cal. years B.P. However, after c. 1900 cal. years B.P. the trends in the pollen profiles imply that there was a retreat in the tree-line due to the Little Ice Age and/or human impact on the landscape.

The study has been refined through the collection of modern pollen data derived from Tauber traps in order to create a modern pollen analogue with which to relate the fossil pollen assemblages. Furthermore, models developed through the NorFA-POLLANDCAL network (Gaillard et al. 2002) have been used to predict the quantitative relationship between suggested landscape scenarios at the tree-line and pollen percentages. Through the use of these techniques it has also been possible to consider the spatial scale of the landscapes represented by pollen deposited in the different sizes of sampling site used in this study.

Barnett, C., Dumayne-Peaty, L. and Matthews, J.A. (2001). Holocene climatic change and tree-line response in Leirdalen, central Jotunheimen, south central Norway. Review of Palaeobotany and Palynology. 117, 119-137.

Torske, N. (1996). Holocene vegetation, climate and glacier histories in the Jostedalsbreen region, western Norway - palaeoecological interpretations from an alpine peat deposit. In: Frenzel, B. (ed), Holocene Treeline Oscillations, Dendrochronology and Palaeoclimate. Vol 20 European Palaeoclimate and Man, 13. Gustav Fischer Verlag, Stuttgart. 215-232.

Gunnarsdottir, H. (1996). Holocene vegetation history and forest-limit fluctuations in Smadalen, eastern Jotunheimen, south Norway. In: Frenzel, B. (ed), Holocene Treeline Oscillations, Dendrochronology and Palaeoclimate. Vol 20 European Palaeoclimate and Man, 13. Gustav Fischer Verlag, Stuttgart. 233-255.

Aas, B. and Faarlund, T. (1996). The present and Holocene sub-alpine Betula spp. Belt in Norway. In: Frenzel, B. (ed), Holocene Treeline Oscillations, Dendrochronology and Palaeoclimate. Vol 20 European Palaeoclimate and Man, 13. Gustav Fischer Verlag, Stuttgart. 19-42.

Nesje, A. and Dahl, S.-O. (2001). The Greenland 8200 cal. Yr BP event detected in loss-on-ignition profiles in Norwegian lacustrine sediment sequences. Journal of Quaternary Science, 16 (2), 155-166.

Tinner, W. and Lotter, A.F. (2001). Central European vegetation response to abrupt climate change at 8.2 ka. Geology, 29 (6), 551-554.

Gaillard, M.-J. and POLLANDCAL members (2002). The pollen/landscape calibration (POLLANDCAL) network of the Nordic council of Ministers (NorFA).


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