Carbon cycling boreal forests

Several studies, based on models, examined the effects of land-use change on the global carbon cycle and conclude that there is a net release of carbon due to land clearing. However, the results and conclusions of these studies are based on assumed sizes of vegetation carbon pools which are inputs to the models. For example, Melillo et al. 24) concluded that boreal and temperate deciduous forests of the northern hemisphere are net sources of atmospheric carbon. Their analysis used values for carbon density derived by Whittaker and Likens 19) from work by Rodin and Bazilevich (27). Rodin and Bazilevich extrapolated results of small, unrelated studies in Europe and the USSR to estimate total biomass of Eurasian boreal and temperate deciduous forests. Their estimates have since been extrapolated to forests worldwide and are used often today. 

Lindahl, B. O., Taylor, A. F. S. Finlay, R. D. (2002). Defining nutritional constraints on carbon cycling in boreal forests-towards a less phytocentric perspective. Plant and Soil, 242, 123-35. 

Kasischke E. S. and Stocks B. J. (eds.) (2000) Fire, Climate Change, and Carbon Cycling in the Boreal Forest. Springer Ecological Studies, New York, vol. 138, 461pp. 

Levine J. S. and Cofer W. R. (2000) Boreal forest fire emissions and the chemistry of the atmosphere. In Fire, Climate Change and Carbon Cycling in the North American Boreal Forests, Ecological Studies Series (eds. E. S. Kasischke and B. J. Stocks). Springer, New York. 

Flanagan L. B., Brooks J. R., Varney G. T., Berry S. C., and Ehleringer . R. (1996) Carbon isotope discrimination during photosynthesis and the isotope ratio of respired CO2 in boreal forest ecosystems. Global Biogeochem. Cycles 10(4), 629-640. 

But the dogma also has it that tropical forests are usually found on heavily weathered soils that are low in nutrients, particularly phosphorus. In a manner similar to possible interactions between the nitrogen and carbon cycles in temperate and boreal forests (McGuire et al., 1995) it has thus been suggested that low P availability may limit the extent to which tropical forests are able to increase their productivity in response to increases in atmospheric CO2 concentrations (Friedlingstein et al, 1995 McKane et al., 1995). 

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