Soil Respiration at Harvard Forest HEM and LPH Towers 1996-2007

Soil respiration, including both CO2 produced during decomposition of organic matter in soil and surface litter, and CO2 produced during respiration of living roots, is a major component of forest-atmosphere carbon exchange, typically comprising 60 to 80% of whole-forest respiration. Soil respiration data can explain a major part of a forest ecosystem’s response to changing climate, and help in evaluating the accuracy of nighttime eddy flux data as estimates of whole-ecosystem respiration measurements. Soil respiration in the footprint areas of the Harvard Forest Hemlock and Little Prospect Hill eddy flux towers has shown generally similar responses to soil temperature and precipitation as soil respiration near the EMS flux tower (see data set HF006), but also some differences. Soil respiration at the Hemlock tower site has been lower than at the other tower sites during very wet summer weather, but higher during dry summer periods. Average estimated annual total soil respiration has been close to the same for all three tower footprint areas, however. There has been some evidence of lower soil respiration in the parts of the Little Prospect Hill tower footprint with lowest soil moisture (those with a high slope position, 100 m from the tower), as compared with other sites during very dry summer periods, but such periods have been very rare during the period of data collection. Soil respiration measured near the Little Prospect Hill tower in summer has also been higher than ecosystem respiration as estimated from nighttime carbon flux measured by an eddy covariance system. This indicates that during some nighttime periods, CO2 is being removed from the volume of air below the eddy flux system by a route other than through the top of the forest canopy near the flux tower, possibly by downslope advection, even under conditions when it initially appeared that atmospheric turbulence was high enough to prevent removal of CO2 by these other mechanisms.