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The fragile forest-tundra

Between the northern edge of the boreal forest, where trees actively regenerate, and the treeless tundra is a dynamic transition zone known as 'forest-tundra'. This zone can range from a few kilometres in North America to more than 200 kilometres in Europe (Stonehouse 1989). It is naturally fragmented and contains patches of relatively heavy forest cover punctuated by areas of lichen-heath as well as areas of very sparse tree growth. It supports more species than either the boreal or the tundra systems since it contains species from both systems (CAFF 2001). The trees of the forest-tundra are often poorly formed and stunted, and regeneration is slow. Traditionally, this has made commercial exploitation of timber impractical although the ecosystem has provided indigenous peoples over the centuries with wood for fuel and construction (CAFF 2001). As world pressure on resources escalates, however, the tundra-forest could become a larger commodity producer. In fact logging operations in Fennoscandia and northwest Russia crept close to the forest-tundra in the 1960s and 1990s (CAFF 2001).

In winter, the forest-tundra provides important habitat for some populations of North American caribou and for European reindeer, in turn supporting the traditional reindeer husbandry activities of indigenous peoples such as the Saami of Scandinavia. The zone also supports sheep farming, fishing and harvesting of non-timber products. Important physical functions of the forest-tundra system are to stabilize and protect fragile soils and nutrients, to prevent erosion, to conserve water resources and watershed capability, to filter pollutants, to act as an indicator of climate change and, together with the boreal forest proper, to act as a carbon store (see box).

Arctic forests and climate change

Any significant change in the area of boreal forests could have a considerable effect on the level of CO2 in the atmosphere. With 26 per cent of total carbon stocks, boreal forests account for more carbon than any other terrestrial ecosystem - 323 gigatonnes (Gt, 109 tonnes) in the Russian Federation, 223 Gt in Canada and 13 Gt in Alaska (Dixon and others 1994).

Conversely, it has been calculated that boreal forests will experience greater temperature increases from climate change than any other forest type. The warming, which is expected to be greater in winter than in summer, will shift climate zones north by as much as 5 km a year. Boreal forests will advance northwards while their southern edges will experience die back or replacement by temperate species. During summer, soils will be drier, and fires and drought more frequent. Local species loss may be significant although few tree species are expected to become extinct (UNEP-WCMC 2002).

Models used to predict the long-term changes in vegetation distribution have not conclusively shown whether the overall area of boreal forest will expand or decrease. However, one of the most comprehensive models of climate change forecasts that the northward expansion of forest will reduce the area of tundra by about 50 per cent by 2100 (White, Cannell and Friend 2000).