The results are based on pollen and plant macrofossil analysis of sediments from the lake Svanåvatnet close to Mo i Rana, Nordland County, in northern Norway.
Changes in the vegetation
The early Holocene vegetation was dominated by pioneerplants, but a rapid establishment of trees and shrubs are observed at the site. Pollen accumulation rates and the presence of macrofossils shows that tree birch (Betula pubescens) was present already 8500 years ago. Pine (Pinus sylvestris) established at around 8600 years ago and the landscape was dominated by trees until 3500 years ago when a reduction is observed in total tree pollen. The pollen analysis shows that spruce (Picea abies) was present in the region during the last 2500 years, but pollen accumulation rates suggests local presence at Svanåvatnet only the last 150 years.
Warmer and wetter climate
Quantitative reconstructions of past climate are performed by transfer functions and the relationship between modern climate and vegetation. A rapid increase is seen in mean July temperature as well as mean annual precipitation during the early Holocene (8700-7700 years before present). In the following period, when tree species abundance and diversity is high and tree line altitude is at its highest in the region, maximum mean July temperatures are reconstructed inferring about 2 ºC higher than at present. During the same period a wetter climate is inferred with mean annual precipitation 300-400 mm higher than today until about 3000 years before present. This is confirmed by the high amounts of fern spores present in the sediments. Mean January temperatures vary through the Holocene and is from 8000 – 3500 years before present reconstructed to be about 2 ºC higher than today. From 3500 years before present and until today a gradual decrease is observed in all reconstructed climate parameters, together with a reduction in tree abundance and the development of a more open landscape.
Conclusions
The climate history at Svanåvatnet indicates similarities with reconstructed climate parameters at other localities in northern and central parts of Scandinavia. Reconstructed annual precipitation shows larger discrepancies with these localities possibly due to regional differences in precipitation patterns during the Holocene.
Reference:
Bjune, A.E. & Birks, H.J.B. 2008. Holocene vegetation dynamics and inferred climate changes at Svanåvatnet, Mo i Rana, northern Norway. Boreas, 37, 146–156.