This is Section 10.2.4 of the Arctic Climate Impact Assessment
Lead Author: Michael B. Usher; Contributing Authors:Terry V. Callaghan, Grant Gilchrist, Bill Heal, Glenn P. Juday, Harald Loeng, Magdalena A. K. Muir, Pål Prestrud
The Arctic encompasses the northern edge of the boreal forest and the woody communities, often containing shrubby trees, that are associated with the northern tree line. These northern forests are often dominated by four coniferous genera: the pines (Pinus spp. ), spruces (Picea spp. ), larches (Larix spp. ), and firs (Abies spp. ), as well as by two broadleaved genera, the birches (Betula spp. ) and the aspens (Populus spp. ), most of which have transcontinental distributions across Eurasia or North America. An example of a pine-dominated forest near Inari, Finland (about 69° N) is shown in Fig. 10. 2. This is typical of the near natural forest, with slow-growing trees, dead wood, and natural regeneration in gaps where the dead and moribund trees allow sufficient light to penetrate to the forest floor. The forests frequently give way to mires and small lakes leading to a mosaic structure of forest and wetland. Figure 10. 3, also near Inari in Finland, shows this transition, with both pine trees and birch woodland in the distance. The boreal forest region has a distinctive set of biodiversity characteristics at each of the three levels of biodiversity – genetic diversity, species diversity, and ecological communities. These are the key to assessing vulnerability of the boreal forest biodiversity to climate change.
When two or more distinct ecological communities or habitats are adjacent, there is a unique opportunity for organisms to live and reproduce in a diverse landscape. Landscape diversity is controlled by the physical arrangement of ecological communities. Climate change, by influencing the distribution of forest species, communities, and conditions, is a major factor controlling landscape diversity.
The extensive ecotone between boreal forest and tundra (a tree line 13500 km long) is a prominent feature of the northern boreal region (some of the major climate-related fluctuations of the tree line are discussed in Chapter 14). The juxtaposition of trees and tundra increases the diversity of species that can exploit or inhabit the tundra. For example, insectivorous ground-dwelling birds that feed in the tundra but nest in trees are able to survive because of the mixture of habitats. Local human inhabitants can obtain shelter and make useful items for outdoor activities at this interface. The probability of climate warming causing the development of new tree line communities is described in Chapter 14. During recent decades of warming, the white spruce (Picea glauca) limit in Alaska (and almost certainly in western Canada) has developed two populations with opposite growth responses to the warming. Under extreme levels of projected warming, white spruce with negative growth responses would be likely to disappear from the dry central part of the northern boreal forest. In moister habitats, white spruce with positive growth responses to warming would expand in distribution. It is possible that part of the southern tundra boundary in North America would no longer border spruce forest but would border aspen (Populus tremuloides) parkland instead.
The changes in boreal forests caused by fire and insect disturbance produce higher order effects due to the patterns and timing of the habitat conditions that they create at larger scales. Microtine rodents, birds, and hares (Lepus timidus) in the Fennoscandian boreal region undergo cyclic population fluctuations, generally on a three-to-four-year cycle. Many factors contribute to these population cycles, including predator numbers, food plant quantity and/or quality, pathogens, parasites, and habitat heterogeneity. Some weather and climatic factors, such as snow depth, also directly influence animal numbers. In the future, population cycles of boreal animals are likely to remain primarily under the control of predators, although overall numbers of animals will respond to the overall amount of suitable habitat produced by events, such as forest fires, that are in turn related to climate warming. A ten-year study of trophic structure in the boreal forest in the Kluane area of southwest Yukon Territory, Canada, examined the ten-year animal population cycle. In this region the boreal community is a top-down system driven by the predators, and snowshoe hare (Lepus americanus) is a keystone species without which much of the community would collapse. Hares influence all other cycles, and hare cycles are themselves controlled by the interaction of predator effect and food supply with little or no climate or fire effect detected. However, by the end of the study, 30% of the white spruce forest in the study area had been killed by spruce bark beetle (Dendroctonus rufipennis), which was probably related to climate warming (see Chapter 14). The change in habitat condition in the Kluane study area is one of the largest disturbances resulting from climate warming in the region over the last few centuries.
Specific areas of the boreal region are more species-rich than others. Areas that have not been glaciated or which were deglaciated earliest are generally more species rich than more recently deglaciated areas, suggesting that risks of major migrations of the boreal forest increase the probability of species loss. Boreal regions with a diversity of geological and soil substrates, such as Far East Russia, the Scandes Mountains, and the northern Rocky Mountains of North America, are relatively species-rich compared to more uniform areas such as the Canadian Shield or the Ob Basin. Boreal areas that have experienced interchange between the ecosystems (Asian Steppes, North American Plains) or continents (Beringia) are relatively species-rich.
Total species richness in the boreal region is greater than in the tundra to the north and less than in the temperate deciduous forest to the south, in line with levels of total ecosystem productivity. The southern boreal region contains more species than the northern boreal region, and one effect of climate warming is likely to be the addition of species to what is now the northern boreal region. A global summary of changes in phenology (the distribution and timing of events) across a number of organism groups already indicates the existence of a coherent signal of warming (i. e., poleward and upward migration, earlier activity in spring). However, the processes that eliminate boreal species (fire, insects, and drought) operate quickly, while those that add species (migration) operate more slowly. This raises the possibility that climate warming, in certain areas, could result in reduced species richness in the short term followed later by species gains as long as migratory barriers were not limiting. However, intensive forest management in Fennoscandia is one of the main causes of decline in the most rare or endangered boreal forest species there and managed forest landscapes do pose movement and connection barriers to the species in them.
The conservation of certain boreal forest habitats is particularly important for maintaining species diversity, and climate change can bring serious challenges in this respect. Of the major ecological regions of the earth, boreal forest is distinctive for being conifer dominated. Older conifer forests on productive sites are the focal habitats of biodiversity conservation across the boreal region for several reasons. They are particularly rich in canopy lichens, mosses, and bryophytes; in the fungi responsible for decomposing wood; and in specialized insects, for woodpeckers and other cavity nesting animals, and for insectivorous songbirds.
The reason that old-growth (or natural) forests are so important for the conservation of biodiversity lies in the holistic approach to nature conservation. Natural forests, with their J-shaped stem-number curve (a few old, large trees and many small, young trees) provide a range of habitats that support a range of different species of plants and animals. Old trees provide nesting holes for some bird species, diseased and moribund trees provide a substrate for many species of fungi, dead wood provides a resource for saproxylic (wood-feeding) insects, and some moth species will only lay their eggs on the foliage of young trees, etc. Wood-feeding arthropods form a diverse taxonomic group that is under pressure throughout Europe and elsewhere. In contrast, managed forests of younger trees tend to have little dead wood, few nesting holes for birds, and less light reaching the forest floor and thus a less well developed dwarf shrub, herbaceous, moss, and lichen flora, which in turn supports fewer invertebrates. A focus on the beetles of the northern forests has demonstrated both that these semi-natural forests contain a relatively large number of rare species and that there are difficulties in making accurate inventories.
Owing to the natural rate of stand-replacing disturbances (fire and insects) in the boreal forest, old-growth conifer stands are not necessarily abundant even in landscapes with little direct human impact. Human modification of the boreal forest landscape typically makes these old forests rarer because management for wood products is usually based on the good returns from cutting large conifers. In parts of the boreal region, where commercial forest management is established or expanding, productive stands of mature and old conifers are already rare (eastern Canada, northern Fennoscandia) or the target for early harvest (Siberia). One of the major effects of climate warming on boreal forests is to increase tree death from fire and insects, and conifer stands are more flammable and often more susceptible to insect-caused tree death than broadleaved forests. Thus the ecosystem of greatest conservation interest, old conifer forest, is the one at most risk of decline due to climate warming.
Fire is a natural and recurrent feature of boreal forests, aiding the maintenance of biodiversity in these northern forests. Fire is expected to pass through a forest every 100 to 200 years. Some species are adapted to using the resources of burnt forests – charred trees which are still standing, trees which have started to decay, and the early stages of ecological succession following fire. Because fires in managed forests are usually extinguished quickly, burnt forest habitats have become rare and the species that depend on them are increasingly threatened and even locally extinct. In Finland, 14 species, mostly beetles (Coleoptera) and bugs (Hemiptera), associated with burnt areas in forests are threatened with extinction.
However, can extensive fires be tolerated in managed forests when the trees are required for extraction and as the raw material for the timber industry? Growth rates of trees near the transition from forest to tundra are extremely slow, which makes management of these far northern forests uneconomic (except for the initial exploitation of the few trees large enough to be used in timber mills, etc. ). However, with climate change (and eutrophication by nitrogen deposition) productivity is likely to increase, and so the management of these northern forests becomes a potentially more viable economic activity, with consequent effects on forest biodiversity.
Fire itself is not the risk factor for the maintenance of boreal forest species diversity, but rather the altered characteristics of fire that can result from climate warming, especially amount, frequency, and severity. Conifer dominance itself promotes the occurrence of large, landscape scale fires through characteristics such as flammable foliage and ladder fuels (defined by Helms as “combustible material that provides vertical continuity between vegetation strata and allows fire to climb into the crowns of trees or shrubs with relative ease”). Many boreal trees and other plants show adaptations to fire such as seed dormancy until fire, serotinous cones, fire-resistant bark, and sprouting habit. Many under story plant species of the boreal forest have means of persistence from underground structures following fire or are effective re-colonizers. Fire in the boreal forest sustains a set of species in early post-fire communities that are distinct from later successional species. These include species from a range of groups, including birds, beetles, spiders, and vascular and non-vascular plants. Changes in natural fire regimes by human management interacting with climate warming can disrupt the specific fire regimes that sustain these species. For example, in some circumstances climate warming combined with human fire suppression results in less frequent but more intense fire. This change can kill species adapted to periodic light ground fires.
The boreal landscape also includes areas that never burn. These fire-free areas are important for the persistence of fire-sensitive species. Fire-free refuges occur across most of Fennoscandia; in the southeast Yukon Territory such an area contains an exceptionally rich flora. With the more frequent, more extensive, and more intense fires projected to result from climate warming, current fire refuges are likely to burn for the first time in recent history, thus reducing or locally eliminating fire-sensitive species.
After a sustained period of enhanced burning caused by climate warming, some boreal forests are likely to undergo type conversion from conifer to broadleaf tree dominance as a result of the depletion of fuels (see Chapter 14). An abrupt shift in forest composition of that type would significantly decrease the amount of old conifer habitat present at a given time from the large landscape perspective, possibly decreasing populations of some dependent organisms to critically low levels.
The boreal forest is characterized by large numbers of individuals of the few tree species with wide ecological amplitude, in contrast to tropical forests that sustain a small number of individuals of many species. Genetic diversity in any species is in part the result of opportunity for gene recombinations and so follows the laws of probability. In the boreal forest, probability favors the survival of large numbers of different gene combinations because of the characteristically large populations of each species. To the degree that these genotypes reflect specific adaptations to local environments, they promote the survival and success of the species. For example, foresters have developed seed transfer guidelines in order to define areas in which it is safe to collect seed for planting in a given site, based on their practical experience of failures in tree plantations from seed collected outside the local environment; boreal Alaska includes several hundred seed transfer zones, suggesting that a high degree of local adaptation maybe typical.
The optimum growth and survival of the major boreal tree species across their large and varied natural distributions requires the survival of a large proportion of current genes, including genes that are rare today but would help survival of the species under future environmental conditions. One of the main risks for boreal forest from climate change is that major areas of the current distribution of boreal tree species might become climatically unsuitable for their survival faster than populations of the species could migrate, resulting in the loss of many adaptive genes. Fire and insect outbreaks are known to be triggered by warm weather (see Chapter 14), and gene loss would be likely to result from larger areas of more complete tree death. Gene survival in a changing climate becomes even more difficult if the native gene diversity is already diminished, as is usually the case in a managed forest and where human activities have reduced forests to remnants. In human-dominated landscapes the appropriate genes for an adaptive response of boreal forest plants to some aspects of climate change may already be rare if the trait was not associated with traits selected for in the forest management program. In addition, when the landscape is fragmented by human activities (for example by roads, pipelines, power lines, industrial and agricultural development, and excessive grazing), even the plant species with adaptive genes are very unlikely to migrate effectively under future climate change.
Nearly all the boreal forest tree species are open wind pollinated, which facilitates a wide distribution of genes. The present boreal forest is the product of major periods of global warming and cooling that forced the boreal organisms to migrate far to the south of current limits and back several times. These climatic displacements imply that today’s plants have considerable adaptive abilities as they have survived past climate changes. Even so, some loss of genes is almost inevitable in populations of trees and other plants coping with the major and rapid environmental changes that have been projected (see Chapter 4).
From the geological record, Spicer and Chapman considered that climate change is most strongly expressed at the poles. There is a dynamic equilibrium between the climate, the soils, and the vegetation. Arctic soils are crucial to the functioning of the terrestrial ecosystems. Heal considered that "soil biology has changed dramatically since. . . the 1970s" and "the emphasis and approach has changed from descriptive to predictive, structure to function, organism to process, local to global". Much of the descriptive data collected in the 1970s were summarized by Swift et al., where the soils of the tundra and taiga were compared with those of temperate and tropical areas. However, these shifts in emphasis highlight that scientific knowledge of arctic soils is out of date, and is particularly weak because the information gained during the International Biological Programme (the first international collaborative research program of the International Council of Scientific Unions, running from 1964 to 1974, with a focus on "the biological basis of productivity and human welfare" –see Clapham and Bliss et al.) in the 1970s lacks experimental evidence relevant to the current issues of climate change. Evidence for the change in ecological thinking is evident in the studies by Robinson and Wookey on Svalbard, in which the emphasis was on decomposition and nutrient cycling.
Soils have frequently been neglected when biodiversity and its conservation are considered. However, soils often contain the most species-rich communities in the Arctic, and so need to be considered in any planning or action for conserving biodiversity. However, many fundamental questions remain. What are the physical drivers of change? How will the ecological processes that occur within soil respond to climate change? How will the populations and communities of soil organisms adapt to climate change? It is known that environmental perturbations can change the dominance and trophic structure of the nematode community in the subarctic soils of northern Sweden, and that such changes can have a large impact on microbial biomass and microbial turnover rates. In the boreal forest, there appears to be little correlation between taxonomic diversity and the process rates within the soils, but it is not known whether this is typical of other arctic soils.
It is widely held that diversity promotes ecosystem function, and so that biodiversity loss threatens to disrupt the functioning of ecosystems. More research is needed on arctic soils to determine whether the many species in these soils are all required, or whether there is some "redundancy" whereby the ecosystem could function efficiently with far fewer species. Also, with climate change, it becomes increasingly important to understand the carbon fluxes through arctic and subarctic soils – will there be net accumulations of soil carbon or net losses of carbon in the form of CO2 or CH4 to the atmosphere? Such knowledge is critical for the development of conservation policies and for the management of arctic ecosystems and their biodiversity.
Chapter 10: Principles of Conserving the Arctic’s Biodiversity
10.2 Conservation of arctic ecosystems and species
10.2.1 Marine environments
10.2.2 Freshwater environments
10.2.3 Environments north of the treeline
10.2.4 Arctic boreal forest environments
10.2.5 Human-modified habitats
10.2.6 Conservation of arctic species
10.2.7 Incorporating traditional knowledge
10.2.8 Implications for biodiversity conservation
10.3 Human impacts on the biodiversity of the Arctic
10.4 Effects of climate change on the biodiversity of the Arctic
10.5 Managing biodiversity conservation in a changing environment
- ^Nikolov, N. and H. Helmisaari, 1992. Silvics of the circumpolar boreal forest tree species. In: H.H. Shugart, R. Leemans and G.B. Bonan (eds.). A Systems Analysis of the Global Boreal Forest, pp 13–84. Cambridge University Press.
- ^Hogg, E.H. and P.A. Hurdle, 1995.The aspen parkland in western Canada: a dry-climate analogue for the future boreal forest? Water, Air and Soil Pollution, 82:391–400.
- ^Angelstam, P., E. Lindstrom and P.Widen, 1985. Synchronous short term population fluctuations of some birds and mammals in Fennoscandia – occurrence and distribution. Holarctic Ecology, 8:285–298.
- ^Krebs, C.J., R. Boonstra, S. Boutin and A.R.E. Sinclair, 2001. Conclusions and future directions. In: C.J. Krebs, S. Boutin and R. Boonstra (eds.). Ecosystem Dynamics of the Boreal Forest. The Kluane Project, pp. 492–501. Oxford University Press.
- ^Komonen, A., 2003. Hotspots of insect diversity in boreal forests. Conservation Biology, 17:976–981.
- ^Komonen, A., J. Ikävalko and W. Weiyung, 2003. Diversity patterns of fungivorous insects: comparison between glaciated vs. refugial boreal forests. Journal of Biogeography, 30:1873–1881.
- ^Waide R.B., M.R. Willig, G. Mittelbach, C. Steiner, L. Gough, S.I. Dodson, G.P. Juday and R. Parmenter, 1999.The relationship between productivity and species richness. Annual Review of Ecology and Systematics, 30:257–300.
- ^Root, T.L., J.T. Price, K.R. Hall, S.H. Schneider, C. Rosenzweig and J.A. Pounds, 2003. Fingerprints of global warming on wild animals and plants. Nature, 421:57–60.
- ^Nilsson, S.G. and L. Ericson, 1992. Conservation of plant and animal populations in theory and practice. In: L. Hansson (ed.). Ecological Principles of Nature Conservation. Applications in temperate and Boreal Environments, pp. 71–112. Elsevier Applied Science.
- ^Hanski, I. and O. Ovaskainen, 2000.The metapopulation capacity of a fragmented landscape. Nature, 404:755–758.
- ^Juday, G.P., 1997. Boreal forests (taiga). In: The Biosphere and Concepts of Ecology, pp. 1210–1216.Volume 14 Encyclopedia Britannica, 15th edition.
^Berg, A., B. Ehnstrom, L. Gustafsson, T. Hallingback, M. Jonsell and J. Weslien, 1994. Threatened plant, animal, and fungus species in Swedish forests: distributions and habitat associations. Conservation Biology, 8, 718–731.
–Essen, P.A., B. Ehnstrom, L. Eriscon and K. Sjoberg, 1992. Boreal forests – the focal habitats of Fennoscandia. In: L. Hansson (ed.). Ecological Principles of Nature Conservation. Applications in Temperate and Boreal Environments, pp 252–325. Elsevier Applied Science.
^Pavan, M., 1986. A European Cultural Revolution: The Council of Europe’s "Charter on Invertebrates". Council of Europe, Strasbourg.
–Speight, M.C.D., 1986. Saproxylic Invertebrates and their Conservation. Council of Europe.
- ^Martikainen, P. and J. Kouki, 2003. Sampling the rarest: threatened beetles in boreal forest biodiversity inventories. Biodiversity and Conservation, 12:1815–1831.
- ^Linder, P. and Ostlund, L., 1992. Changes in the boreal forests of Sweden 1870–1991. Svensk Bot.Tidskr., 86:199–215. (In Swedish)
- ^Rosencranz, A. and A. Scott, 1992. Siberia’s threatened forests. Nature, 335:293–294.
- ^Korhonen, K.-M., R. Laamanen and S. Savonmäki (eds), 1998. Environmental Guidelines to Practical Forest Management. Metsähallitus, Helsinki.
- ^Helms, J.A. (ed.), 1998.The Dictionary of Forestry. The Society of American Foresters, Bethesda.
^Gorshkov, V. V. and I. J. Bakkal, 1996. Species richness and structure variations of Scots pine forest communities during the period from 5 to 210 years after fire. Silva Fennica, 30:329–340.
–Grime, J.P., 1979. Plant Strategies and Vegetation Processes. Wiley.
–Grubb, P.J., 1977. The maintenance of species-richness in plant communities: the importance of the regeneration niche. Biological Reviews, 52:107–145.
–Rees, D.C. and G.P. Juday, 2002. Plant species diversity and forest structure on logged and burned sites in central Alaska. Forest Ecology and Management, 155:291–302.
^Essen, P.A., B. Ehnstrom, L. Eriscon and K. Sjoberg, 1992. Boreal forests – the focal habitats of Fennoscandia. In: L. Hansson (ed.). Ecological Principles of Nature Conservation. Applications in Temperate and Boreal Environments, pp 252–325. Elsevier Applied Science.
–Haeussler, S. and Kneeshaw, D., 2003. Comparing forest management to natural processes. In: P.J. Burton, C. Messier, D.W. Smith and W.L. Adamowicz (eds.). Towards Sustainable Management of the Boreal Forest, pp. 307–368. NRC Research Press.
–Rees, D.C. and G.P. Juday, 2002. Plant species diversity and forest structure on logged and burned sites in central Alaska. Forest Ecology and Management, 155:291–302.
- ^Essen, P.A., B. Ehnstrom, L. Eriscon and K. Sjoberg, 1992. Boreal forests – the focal habitats of Fennoscandia. In: L. Hansson (ed.). Ecological Principles of Nature Conservation. Applications in Temperate and Boreal Environments, pp 252–325. Elsevier Applied Science.
- ^Haeussler, S. and Kneeshaw, D., 2003. Comparing forest management to natural processes. In: P.J. Burton, C. Messier, D.W. Smith and W.L. Adamowicz (eds.). Towards Sustainable Management of the Boreal Forest, pp. 307–368. NRC Research Press.
- ^Widen, B. and L. Svensson, 1992. Conservation of genetic variation in lants – the importance of population size and gene flow. In: L. Hansson (ed.). Ecological Principles of Nature Conservation. Applications in Temperate and Boreal Environments, pp. 71–112. Elsevier Applied Science.
- ^Li, P., J. Beaulieu and J. Bousquet, 1997. Genetic structure and patterns of genetic variation among populations in eastern white spruce (Picea glauca). Canadian Journal of Forest Research, 27:189–198.
- ^Alden, J., 1991. Provisional tree seed zones and transfer guidelines for Alaska. USDA Forest Service, General Technical Report PNW 270.
- ^Lieffers,V.J., C. Messier, P.J. Burton, J.-C. Ruel and B.E. Grover, 2003. Nature-based silviculture for sustaining a variety of boreal forest values. In: P.J. Burton, C. Messier, D.W. Smith and W.L. Adamowicz (eds.).Towards Sustainable Management of the Boreal Forest, pp. 481–530. NRC Research Press.
- ^Widen, B. and L. Svensson, 1992. Conservation of genetic variation in lants – the importance of population size and gene flow. In: L. Hansson (ed.). Ecological Principles of Nature Conservation. Applications in Temperate and Boreal Environments, pp. 71–112.Elsevier Applied Science.
- ^Spicer, R.A. and J.L. Chapman, 1990. Climate change and the evolution of high-latitude terrestrial vegetation and floras. Trends in Ecology and Evolution, 5:279–284.
- ^Fitzpatrick, E.A., 1997. Arctic soils and permafrost. In: S.J.Woodin and M. Marquiss. Ecology of Arctic Environments, pp. 1–39. Blackwell.
- ^Heal, O.W., 1999. Looking north: current issues in Arctic soil ecology. Applied Soil Ecology, 11:107–109.
- ^Swift, M.J., O.W. Heal and J.M. Anderson, 1979. Decomposition in Terrestrial Ecosystems. Blackwell.
- ^Clapham, A.R. (ed.), 1980.The IBP Survey of Conservation Sites: an Experimental Study. Cambridge University Press.
- ^Bliss, L.C., O.W. Heal and J.J. Moore, 1981.Tundra Ecosystems: a Comparative Analysis. Cambridge University Press.
- ^Robinson, C.H. and P.A.Wookey, 1997. Microbial ecology, decomposition and nutrient cycling. In: S.J.Woodin and M. Marquiss (eds.). Ecology of Arctic Environments, pp. 41–68. Blackwell.
- ^Usher, M.B., in press. Soil biodiversity, nature conservation and sustainability. In: R.D. Bardgett, M.B. Usher and D.W. Hopkins (eds.). Biological Diversity and Function in Soils. Cambridge University Press.
- ^Heal, O.W., 1999. Looking north: current issues in Arctic soil ecology. Applied Soil Ecology, 11:107–109.
- ^Ruess, L., A. Michelsen and S. Jonasson, 1999a. Simulated climate change in subarctic soils: responses in nematode species composition and dominance structure. Nematology, 1:513–526.
^Ruess, L., A. Michelsen, I.K. Schmidt and S. Jonasson, 1999b. Simulated climate change affecting microorganisms, nematode density and biodiversity
in subarctic soils. Plant and Soil, 212:63–73.
- ^Huhta,V.,T. Persson and H. Setälä, 1998. Functional implications of soil faunal diversity in boreal forests. Applied Soil Ecology, 10:277–288.
- ^Luck, G.W., G.C. Daily and P.R. Ehrlich, 2003. Population diversity and ecosystem services.Trends in Ecology and Evolution, 18:331–336.
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