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The sub-arctic birch forest ecosystem

In Fennoscandia, the mountain birch (Betula pubescens) forms the ecotone between the boreal coniferous forest and the alpine areas, and between the northern taiga and the coast and tundra. These sub-arctic mountain birch forests, characterised by a climate that that has both oceanic and continental elements, are almost exclusively a Fennoscandian phenomenon, with a midpoint in northern Norway. Important features of this ecosystem are that (1) it is naturally large-scale fragmented. The sub-arctic birch forests occur in Map showing the distribution of birch and mixed birch forest in northern Fennoscandiaform of narrow belts and isolated areas cut off by mountain/tundra areas and exposed coast lines. (2) It has a special regime of natural disturbance factors. The dominating, natural disturbance factor is biotic, composed of massive outbreaks of herbivorous insects, especially the two geometrid moth species Epirrita autumnata (autumnal moth) and Operophtera brumata (winter moth).

Figure 1. The distribution of birch and mixed birch forest (light green) versus coniferous forest (dark green) in northern Fennoscandia. Vegetation map by Bernt Johansen, Norut, Tromsø.

 

Our study sites

Our study sites are located in Troms and Finnmark counties in Northern Norway, approx. 69-70°N, 18-30 °E. Most of our sites experience an oceanic climate with mild and snow-rich winters and cool summers. Tromsø (69°40’N, 19° E) has a mean temperatures of -4.4°C in January and 9.1°C in July and an annual precipitation of just above 1000 mm.

The location of our main study sites on the west coast of Norway:


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