Climatic warming in northern latitudes will undoubtedly create new ecological opportunities for vegetation advance as ice sheets retreat and permanent snow cover is reduced and the climate extremes are reduced with a great degree of oceanicity (Fig. 5.27). For some species, however, particularly those that show a preference for continental climates there may be disadvantages from warmer winters, which are a marked feature of the current warming trend. Examination of potential changes in distribution for Pinus sylvestris (Fig. 5.27) has shown that winter warming is likely to cause a retreat from western oceanic areas. Similar trends have been found in woody scrub species, for example Cassiope hypnoides, Vaccinium myrtillus, Calluna vulgaris and Salix polaris (Crawford & Jeffree, 2007). Such a trend mirrors the existing tendency for certain species to retreat from maritime habitats in response to increases in oceanicity. Other explanations are also possible. Patho
genic organisms may also play a role. It is frequently observed that Scots pine can be damaged by snow blight, e.g. Phacidium infestans, due to long-lasting cover of wet snow with temperatures close to zero in late winter as has been observed in the Alps (Senn, 1999) and also Lapland (Holtmeier, 2003). How different winter and summer warming scenarios will affect the various woody plants that inhabit the tundra-taiga interface is far from certain. The ability of species such as Pinus pumila to reach a latitude of 71° N (Fig. 5.28) in one of the coldest and most continental regions of Eurasia shows that they are highly adapted to cold winters and short growing seasons which would suggest that warmer winters may eventually prove less favourable to this species. In the more oceanic areas Alnus fruticosa replaces Pinus pumila as the dominant woody species (Fig. 5.28). Woody plants have come and gone from the Arctic during the Holocene as can be seen in examinations of the pollen record in the Taymyr Peninsula. A shrubby tundra with dwarf birch species and willow scrub together with alder (Alnus fruticosa) persisted from the Late Pleistocene/Holocene transition, c. 10 300-10 000 BP, and then disappeared by
3500-3000 BP (Andreev et al., 2003). It is probable therefore that these shrubby communities which are already adapted to more oceanic conditions will advance northwards more readily if winters are warmer than the more continental forest species (Fig. 5.27). In North America, the black spruce (Picea mariana), with its outstanding morphological plasticity, appears to be the tree species that is best adapted to expand its range and replace the tundra. Whether or not the forest tundra (Russian lesotundra) will also develop into a forest vegetation at high latitudes will depend on the degree of disturbance that will be inflicted on these regions in the years ahead. In many regions the tundra-taiga zone is not only a natural ecotone, but also a unique fringe zone with particular socioeconomic properties. In Russia, there is at present much evidence of deforestation and ecosystem degradation in different regions of the forest-tundra zone. Industrial activity has accelerated and despite a protection declared in 1959 for the lesotundra, there are now regions where the northern limit of the zone has been displaced southwards by 40-100 km (Fig. 5.29). In regions such as this it cannot be predicted with any certainty that climatic warming will lead to a northward movement of the boreal forest treeline (Vlassova, 2002). The manner of destruction with large-scale pollution is not only destroying the vegetation but is also causing a drastic reduction in the population of the indigenous peoples as well as reducing the life expectancy of the immigrant industrial population. The very considerable natural resources of the Arctic worldwide for timber, pulp and paper industries, as well as mining, oil and gas extraction, will have to be managed with great care if the environmental health of the region as a whole is to be preserved.
Fig. 6.1 Habitat heterogeneity in the Arctic at Hornsund, Spitsbergen (77° N). The close juxtaposition of contrasting sites (early and late, wet and dry), creates habitats with plants that will differ in their reactions to climatic warming. (Little auk, Alle alle, on boulder in foreground.)
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