Spatial and temporal variability of soil CO2 efflux in southeastern forests

The combination of biotic and abiotic factors that contribute to soil CO2 efflux can lead to large variability across spatial and temporal scales. This variability can result in uncertainty in respiration estimates; however, it can also provide insight into the primary processes affecting CO2 emissions from soil. In order to quantify the magnitude and identify the sources of variability in soil CO2 efflux across spatial and temporal scales, we deployed several automated, multi-chamber sampling systems in forest stands in the southeastern U.S. We measured fluxes from a medium-age loblolly pine stand for 10 years (2001-2010), which spanned two severe droughts and one very wet year. During this time period, we also operated three systems in additional plots within the pine stand for 5 years, one system in an adjacent mixed-species broadleaf deciduous stand for 4 years, and one system in a nearby mature loblolly pine stand for 2 years. The high frequency of measurements (~2 hours per chamber) allows us to examine diurnal trends and precipitation responses while longevity of this study provides information on interannual variability and effects of stand age. Additionally, we quantify spatial variability at the scale of plot-level (1-10 m), stand-level (~100 m), and regionally (1-50 km) to examine the effects of local heterogeneity, species composition, and soil type. Chamber-based measurements are compared with leaf litter fall, trenched plot data, and eddy covariance measurements.