Feedback Effects of Soil Carbon Cycling in Northern Ecosystems Essay

Feedback Effects of Soil Carbon Cycling in Northern Ecosystems Global warming will be greatest in mid-continental North America and Eurasia, where temperatures are predicted to increase 4 - 12_C during the winter and 2 - 6_ C in summer (Kasischke et. al, 1995). This warming will shift the boreal forest, bog, and tundra biomes that dominate these areas northward as much as 500 km in the first hundred years of warming (Toward...1988, qtd. in Varallyay, 1990). Alaskan studies indicate that these changes are already influencing ecosystem function and carbon balance in northern ecosystems (Grulke et al. 1990; Ochel and Billings 1992; Oechel et al. 1993; qtd. in Oechel et al. 1995). Alterations in carbon cycling in these soils are of particular concern, since soils of northern ecosystems store from 350-455 Pg of carbon, or from 22.5 to 29.4% of the world soil carbon pool (Billings, 1987; Post, et al., 1990: Oechel and Vourlitis, 1993; qtd. in Lal et al.1995). This sink is an important part of the global carbon cycle; soil carbon losses from changes in land use account for 40% of the increase in atmospheric CO2 to date (Tinker and Ineson 1990). Smith and Shugart (1993) have projected that the vegetation/soil system will eventually become a carbon sink when global warming occurs. However, the initial loss of soil organic matter and delayed response of ecosystems to range shifts are expected to cause an initial pulse of carbon to the atmosphere, representing a temporary positive feedback to climate change. The amount of organic carbon stored in the soil depends on the net primary productivity (NPP) of the ecosystem and the speed of humic decomposition. Rates of soil organic matter decay are partially temperature dependent; Jenkinson... ...niversity Press, 1995. Smith, T. M. and H. H. Shugart, 1993, The transient response of terrestrial carbon storage to a perturbed climate: Nature, 361, pp. 523-526. Stevenson, F. J. Cycles of Soil: Carbon, Nitrogen, Phosphorus, Sulfur, Micronutrients.: New York, John Wiley & Sons, Inc. 1986. Tinker, P. B., and P. Ineson, 1990. Soil organic matter and biology in relation to climate change: in Soils on a Warmer Earth, H. W. Scharpenseel, M. Schomaker and A. Ayoub, eds.: New York, Elsevier, 1990. Varallyay, G. Y., 1990, Influence of climatic change on soil moisture regime, texture, structure and erosion: in Soils on a Warmer Earth, H. W. Scharpenseel, M. Schomaker and A. Ayoub, eds.: New York, Elsevier, 1990. Whalen, S. C., W. S. Reeburgh, and K. S. Kizer, 1991. Methane consumption and emission by taiga: Global Biogeochemical Cycles, 5(3), pp. 261-273.