SPATIAL AND TEMPORAL VARIATIONS IN TEMPERATE FOREST SOIL CARBON-DIOXIDE DURING THE NONGROWING SEASON

In the Whitehall Forest of Georgia during the 1985-86 non-growing season soil CO2 varied with soil depth, varied spatially at constant depth, and varied temporally with changing environmental conditions. Variations with depth in the upper 1.4 m of the soil were of greater magnitude than temporal variations and spatial differences at 30 cm depth were of lesser magnitude. Mean soil CO2 in evergreen forest was higher (0.207 per cent) than in deciduous and mixed forest (0.157 per cent). There were no trends in soil CO2 along hillslopes or with changes in soil texture, bulk density, moisture content, or temperature. Soil CO2 did increase near trees possibly due to increased root densities and/or more numerous pockets of microbial activity. For CO2 at 30 cm depth, two variables - the mean daily temperature range in the month before measurement and actual evapotranspiration in the week before measurement (AET7) - explained 76 per cent of the variation in mean soil CO2. At the profile site, where soil CO2 was measured at five depths, 66 per cent of the variability in CO2 was explained by soil depth, AET7, and the average daily temperature range in the two months before measurement.