Measurement of carbon dioxide evolution from a Japanese cedar (Cryptomeria japonica D. Don) forest floor using an open-flow chamber method

Little information is available on the fluctuation of soil respiration in Japanese cedar forests (Cryptomeria japonica D. Don), a principal and highly productive plantation in Japan. We measured the seasonal change in soil respiration for three years in thinned and intact sections of a Japanese cedar forest to establish the relationship between soil respiration and environmental factors and to examine the effects of a common silvicultural practice, namely forest thinning. We measured soil respiration while regulating CO₂ concentration and wind speed in a chamber using a portable open-flow chamber system. Soil respiration rates, ranging from 2570 to 3060 (g CO₂) m^-2 year^-1 and 1830 to 2170 (g CO₂) m^-2 year^-1 in the thinned and intact sections, respectively, increased in summer and decreased in winter. Soil respiration rates (R(s)) significantly correlated with soil surface temperature (T(s)). The relationship was approximately In (R(s))= a + b(T(s)), where a and b are constant values, varying from 0.067 to 0.106 and from 3.30 to 4.62, respectively. The Q¹⁰ values were 2.0 and 2.5 in the thinned and intact sections, respectively. Soil surface CO₂ concentrations (0.8-3.9 g m^-3), calculated from the soil respiration rates, were higher than ambient atmospheric CO₂ concentrations. They tended to increase in summer and decrease in winter. Soil respiration rates in the thinned section were significantly higher than those of the intact section in the first and second years of the measurement, but not in the third year, namely the fifth year after thinning; an indication that thinning may have increased soil respiration from the forest floor temporarily.