What was done
Noting that "aerated forest soils are a significant sink for atmospheric methane (CH4)," the authors conducted a two-year study of a deciduous mixed forest in the Hainich National Park, Thuringia, Germany, where they established eighteen sub-plots spread throughout three different types of forest, and, where using dark closed chambers from September 2005 to September 2007, they measured net fluxes of CH4 every two weeks. Stand A, as they describe it, "was a single-species stand covered with European beech as the predominant tree specie," while stand B "was a three-species stand with beech, ash and lime as predominant species, and stand C was covered with beech, ash, lime, hornbeam and maple as predominant species."

What was learned
Guckland et al. report that "the variation of CH4 uptake over time could be explained to a large extent by changes in soil moisture in the upper five centimeters of the mineral soil," such that "the CH4 uptake during the main growing period (May-September) increased considerably with decreasing precipitation rate," which finding, as they describe it, is "in accordance with the general observation that soil moisture is the primary environmental control on CH4 uptake in soils because it regulates methane flux into the soil through diffusion (Smith et al., 2000; Butterbach-Bahl and Papen, 2002; Borken et al., 2006)." They also report that the methane flux response to soil moisture content was linear, as has been found to be the case in still other studies (Dobbie and Smith, 1996; Bradford et al., 2001; Price et al., 2003). In addition, they observed that "low CH4 uptake activity during winter was further reduced by periods with soil frost and snow cover."

What it means
"The results suggest," in the words of the three researchers, "that climate change [in this case, global warming] will result in increasing CH4 uptake rates in this region because of the trend to drier summers and warmer winters." And this response represents a negative feedback that should help to temper predicted increases in CO2-induced global warming.

References
Borken, W., Davidson, E.A., Savage, K., Sundquist, E.T. and Steudler, P. 2006. Effect of summer throughfall exclusion, summer drought, and winter snow cover on methane fluxes in a temperate forest soil. Soil Biology & Biochemistry 38: 1388-1395.

Bradford, M.A., Ineson, P., Wookey, P.A. and Lappin-Scott, H.M. 2001. Role of CH4 oxidation, production and transport in forest soil CH4 flux. Soil Biology & Biochemistry 33: 1625-1631.

Butterbach-Bahl, K. and Papen, H. 2002. Four years continuous record of CH4-exchange between the atmosphere and untreated and limed soil of an N-saturated spruce and beech forest ecosystem in Germany. Plant and Soil 240: 77-90.

Dobbie, K.E. and Smith, K.A. 1996. Comparison of CH4 oxidation rates in woodland, arable and set aside soils. Soil Biology & Biochemistry 28: 1357-1365.

Price, S.J., Sherlock, R.R., Kelliher, F.M., McSeveny, T.M., Tate, K.R. and Condron, L.M. 2003. Pristine New Zealand forest soil is a strong methane sink. Global Change Biology 10: 16-26.

Smith, K.A., Dobbie, K.E., Ball, B.C., Bakken, L.R., Sitaula, B.K., Hansen, S., Brumme, R., Borken, W., Christensen, S., Prieme, A., Fowler, D., MacDonald, J.A., Skiba, U., Klemedtsson, L., Kasimir-Klemedtsson, A., Degorrska, A. and Orlanski, P. 2000. Oxidation of atmospheric methane in Northern European soils, comparison with other ecosystems, and uncertainties in the global terrestrial sink. Global Change Biology 6: 791-803.