Arctic terrestrial ecosystems and environmental change

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Abstract
The impacts of environmental change on Arctic terrestrial ecosystems are complex and difficult to predict because of the many interactions which exist within ecosystems and between several concurrently changing environmental variables. However, some general predictions can be made. (i) In the sub-Arctic, subtle shifts in plant community composition with occasional losses of plant species are more likely than immigration of exotic species. In the high Arctic, colonization of bare ground can proceed and there are likely to be shifts in ecotypes. Major shifts in vegetation zones, such as the advance of the boreal forest, are likely to be slow and species specific responses will result in different assemblages of species in plant communities in the longer term. All changes in community structure, apart from species removal by direct extreme weather conditions (e.g. drought) will be slow because of the slow growth, low levels of fecundity and slow migration rates of plant species over large latitudinal ranges. (ii) Mobile mammals and birds can probably adjust to changes in the distribution of their food plants or prey in the Arctic, but vertebrate and invertebrate herbivores may face problems with changes in the quality of their food plants. Non-migratory animals could be severely affected by altered winter snow conditions which affect availability of food and shelter. (iii) Increases in primary production are uncertain and depend mainly upon the responses of soil microbial decomposer activity to changes in soil temperature, moisture and plant litter quality. Assumptions that climate warming will lead to warmer soils and increased nutrient availability to sustain higher productivity are uncertain as greater biomass may lead to reduced soil temperatures through insulation effects and increased nutrients released may be immobilized by soil microorganisms. (iv) Changes in environmental conditions are themselves often uncertain. There is particular doubt about changes in precipitation, growing season length, cloudiness and UV-B radiation levels while such environmental changes are likely to vary in magnitude and direction between different regions of the Arctic. (v) The large populations and circumpolar distributions typical of Arctic biota lead to a strong buffering of changes in biodiversity. Perhaps the greatest threats to Arctic biota will be imposed by the degradation of permafrost which may lead to either waterlogging or drought depending upon precipitation regimes.