Climate Change

Warming affects marine, aquatic, and terrestrial ecosystems. There is strong evidence from a variety of sources that a warming trend unprecedented in historic, and perhaps even in prehistoric, times is already under way. For example, earlier melting and delayed freezing of sea ice on Canada's Hudson Bay is affecting the health of the region's historically large polar bear population. Bears now have a shorter time to build necessary fat reserves by hunting their main prey (ringed seals) via breathing holes in the ice. The warming and melting of permafrost has also been well documented in Alaska and Russia. Alpine glaciers in the Northern Hemisphere, and virtually throughout the world, are in rapid retreat. It is estimated that in another 30 years, the fabled snows of Mt Kilimanjaro in Africa will cease to exist.

In terms of tundra vegetation, a warming Arctic climate may offer both opportunities for revegetation efforts, and risks from migrating exotics. With or without climatic change, we cannot expect the chorologies of ruderal plants, or even whole plant communities, to remain static. Expansion of corridors and increasing human relocation from southern regions will likely continue to provide a ready source of introduced species. Several of the disturbances discussed above may assure the availability of a variety of habitat conditions favorable to colonizing species. Evidence from current climatic conditions indicates that such disturbances may favor the establishment, maintenance, and spread of nascent satellite plant populations in the Arctic.

Several factors, including the long photoperiod, short growing season, low temperature, and low soil nutrient and water content, help explain why European weeds are not likely to assume importance in the Arctic. However, the latter four factors would be directly or indirectly affected by a warming climate. Furthermore, the number of successful introductions to date in places as far north as Svalbard and southern Greenland suggests that photoperiod is not an effective barrier for many species. The example of southern ruderals, establishing first in villages and then spreading with disturbance, is not uncommon and illustrates the potential importance of remote founder populations. Once established beyond the treeline, populations of potentially invasive plants are literally a step or two ahead of more southerly and ostensibly northward migrating plants. A soil development lag may favor site capture by more ecologically plastic southern exotics over migrating elements of the endemic flora. The question of vegetation composition is not simply anesthetic concern as the survival of terrestrial herbivores, and the humans who depend on them, will ultimately depend on what forage is available.

In addition to climate change, the thinning of the ozone layer in polar regions has increased the amount of ultraviolet radiation received at the earth's surface. Experiments in the Subarctic and Antarctic have found plants to be affected by both UV-B and warming. In Antarctica, warming improved sexual reproduction in the only vascular species occurring there, whereas growth of the same two species was improved when UV-B was reduced. In Arctic tundra, growth and regeneration of several species is also known to be affected by enhanced UV-B and warming.

Bruce Forbes

See also Climate Change; Contaminants; Exxon Valdez; Hydrocarbon Contamination; Local and Transboundary Pollution; Ozone Depletion

Further Reading

AMAP, Arctic Pollution Issues: A State of The Arctic Environment Report, Oslo: Arctic Monitoring and Assessment Programme, 1997 Bliss, Lawrence C., "Arctic Ecosystems: Patterns of Change in Response to Disturbance." In The Earth in Transition: Patterns and Processes of Biotic Impoverishment, edited by George M. Woodwell, Cambridge and New York: Cambridge University Press, 1990, 347-366 Callaghan, Terry V. & Sven Jonasson, "Arctic terrestrial ecosystems and environmental change," Philosophical Transactions of the Royal Society of London, A352 (1995): 259-276 Crawford, Robert M.M. (editor), Disturbance and Recovery in Arctic Lands: An Ecological Perspective, Dordrecht: Kluwer, 1997

Durner, George M. & Trent L. McDonald, "Estimating the impacts of oils spills on polar bears." Arctic Research of the United States, 14 (2000): 33-37 Forbes, Bruce C. & Gary Kofinas (editors), "The human role in reindeer and caribou grazing systems." Polar Research, 19(1) (2000): 1-142 Forbes, Bruce C., James J. Ebersole & Beate Strandberg, Anthropogenic disturbance and patch dynamics in circumpolar arctic ecosystems," Conservation Biology, 15 (2001): 954-969

Heal, O. William et al. (editors), Global Change in Europe's Cold Regions, Ecosystems Research Report 27, Brussels: European Commission, 1998 Kankaanpaa, Paula et al. (editors), Arctic Flora and Fauna:

Status and Conservation, Helsinki: Edita, 2001 Komarkova, Vera & Frans-Emil Wielgolaski, "Stress and Disturbance in Cold Region Ecosystems." In Ecosystems of Disturbed Ground, edited by Lawrence R. Walker, Amsterdam: Elsevier Science, 1999: pp. 39-122 Nelson, Frederick E., Oleg A. Anisimov & Nikolay I. Shiklomanov, "Subsidence risk from thawing permafrost," Nature, 410 (2001): 889-890 Oechel, Walter C. et al. (editors), Global Change and Arctic

Terrestrial Ecosystems, Berlin: Springer, 1997 Polunin, N., Botany of the Canadian Eastern Arctic, Part. III, Vegetation and Ecology. Bulletin No. 104, Ottawa: National Museum of Canada, 1948 Post, Roger A., Effects of Petroleum Operations in Alaskan Wetlands: A Critique, Technical Report 90-3, Juneau: Alaska Department of Fish and Game, 1990 Reynolds, James F. & John D. Tenhunen (editors), Landscape Function and Disturbance in Arctic Tundra, Berlin: Springer, 1996

Starfield, Anthony M. & F. Stuart Chapin III, "Model of transient Arctic and boreal vegetation in response to climate and land-use change." Ecological Applications, 6 (1996): 842-864 Sumina, Olga Ivanovna (editor), Research on Anthropogenic Impacts in the Russian Arctic, Arctic Centre Reports 29, Rovaniemi: University of Lapland, 2000 Truett, Joe C. & Stephen R. Johnson, The Natural History of an Arctic Oil Field: Development and the Biota, San Diego: Academic Press, 2000

0 0

Post a comment