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Enhanced Consumption of Methane by Soils May Slow Global Warming as Ranges of Hardwood Trees Expand
Menyailo, O.V. and Hungate, B.A.  2003.  Interactive effects of tree species and soil moisture on methane consumption.  Soil Biology & Biochemistry 35: 625-628.

Methane (CH4) is an important greenhouse gas, contributing roughly 20% of total non-H2O greenhouse radiative forcing; and, in the words of the authors of this intriguing paper, "boreal and temperate forest upland soils are important biological sinks for atmospheric CH4 (Wahlen and Reeburgh, 1996)."

What was done
The authors assessed the influence of six boreal forest species [spruce (Picea abies), birch (Betula pendula), Scots pine (Pinus sylvestris), aspen (Populus tremula), larch (Larix sibirica) and Arolla pine (Pinus cembra)] on soil CH4 consumption in the Siberian artificial afforestation experiment, in which the six common boreal tree species have been grown under common garden conditions for the past 30 years under the watchful eye of the staff of the Laboratory of Soil Science of the Institute of Forest, Siberian Branch of the Russian Academy of Sciences (Menyailo et al., 2002).

What was learned
It was determined, according to the authors of this important study, that "soils under hardwood species (aspen and birch) consumed CH4 at higher rates than soils under coniferous species and grassland."  Under low soil moisture conditions, for example, the soils under the two hardwood species consumed 35% more CH4 than the soils under the four conifers; while under high soil moisture conditions they consumed 65% more.

What it means
Pastor and Post (1988) have suggested, in the words of Menyailo and Hungate, that "changes in temperature and precipitation resulting from increasing atmospheric CO2 concentrations will cause a northward migration of the hardwood-conifer forest border in North America."  Consequently, if such a shifting of species does indeed occur, it will likely lead to an increase in methane consumption by soils and a reduction in methane-induced global warming potential, thereby providing yet another biologically-mediated negative feedback factor that has yet to be incorporated into models of global climate change.

Menyailo, O.V., Hungate, B.A. and Zech, W.  2002.  Tree species mediated soil chemical changes in a Siberian artificial afforestation experiment.  Plant and Soil 242: 171-182.

Pastor, J. and Post, W.M.  1988.  Response of northern forests to CO2-induced climate change.  Nature 334: 55-58.

Wahlen, S.C. and Reeburgh, W.S.  1996.  Moisture and temperature sensitivity of CH4 oxidation in boreal soils.  Soil Biology & Biochemistry 28: 1271-1281.

Reviewed 16 July 2003