As the World Warms: Trees and Shrubs Proliferating in Sweden
Rundqvist, S., Hedenas, H., Sandstrom, A., Emanuelsson, U., Eriksson, H., Jonasson, C. and Callaghan, T.V. 2011. Tree and shrub expansion over the past 34 years at the tree-line near Abisko, Sweden. Ambio 40: 683-692.
Comparison between the two periods revealed "rapid and substantial increases in the abundance of prominent tree and shrub species near tree-line and forest-line in sub-Arctic Sweden," such that the authors "recorded an invasion by a thermophilic tree species not present in the plots 34 years ago."
In discussing their findings, the seven Swedish scientists describe how they mesh well with those of many other researchers, noting that "there is an indication that the shrub layer near the tree-line has expanded, since the 1930s, in the Abisko area (Enquist et al., 1933; Sandberg, 1963)," while "data from Canada, Fennoscandia, Alaska and Russia reveal that there is a Pan-Arctic expansion of shrubs and trees in progress (e.g. Kullman, 2002; Tommervik et al., 2004; ACIA, 2005; Tape et al., 2006; Karlsson et al., 2007; Olofsson et al., 2009; Hallinger et al., 2010; Hendenas et al., 2011)." And they state that the change in shrubs and small trees they observed is "consistent with anticipated changes due to climate change and reduced herbivory," which change in climate, in their words, "could be interpreted as an ongoing natural re-establishment of plants at higher altitudes due to a natural increase in the temperature since the 'Little Ice Age' (Kammer et al., 2007)."
ACIA. 2005. Arctic Climate Impact Assessment. Cambridge University Press, Cambridge, United Kingdom.
Hallinger, M., Manthey, M. and Wilmking, M. 2010. Establishing a missing link: warm summers and winter snow cover promote shrub expansion into alpine tundra in Scandinavia. New Phytologist 186: 890-899.
Hedenas, H., Olsson, H., Jonasson, C., Bergstedt, J., Dahlberg, U. and Callaghan, T.V. 2011. Changes in tree growth, biomass and vegetation over a 13-year period in the Swedish Sub-Arctic. Ambio 40: 672-682.
Kammer, P.M., Schob, C. and Choler, P. 2007. Increasing species richness on mountain summits: Upward migration due to anthropogenic climate change or re-colonization? Journal of Vegetation Science 18: 301-306.
Karlsson, H., Hornberg, G., Hannon, G. and Nordstrom, E.-M. 2007. Long-term vegetation changes in the northern Scandinavian forest limit: A human impact-climate synergy? The Holocene 17: 37-49.
Kullman, L. 2002. Rapid recent range-margin rise of tree and shrub species in the Swedish Scandes. Journal of Ecology 90: 68-77.
Olofsson, J., Oksanen, L., Callaghan, T., Hulme, E.P., Oksanen, T. and Suominen, O. 2009. Herbivores inhibit climate-driven shrub expansion on the tundra. Global Change Biology 15: 2681-2693.
Sandberg, G. 1963. Vaxtvarlden I Abisko nationalpark. In: Curry-Lindahl, K. (Ed.). Natur i Lappland, II. Bokforlaget Svensk Natur, Uppsala, Sweden.
Tape, K., Sturm, M. and Racine, C. 2006. The evidence for shrub expansion in Northern Alaska and the Pan-Arctic. Global Change Biology 12: 686-702.
Tommervik, H., Johansen, B., Tombre, I., Thannheiser, D., Hogda, K. and Gaare, E. 2004. Vegetation changes in the Nordic mountain birch forest: The influence of grazing and climate change. Arctic, Antarctic, and Alpine Research 36: 323-332.