We measured carbon pools (standing biomass, coarse woody debris, and soil carbon) and fluxes (eddy covariance, and soil respiration) in two commercial loblolly pine plantations for two years. The older, closed-canopy stand consisted of trees of 14 years old, with mid-season LAI=3.0 m² m^-2, whereas the young stand had just been planted after clearcutting a native coastal hardwood stand, with mostly annual herbaceous canopy. The contrasting stand structure, disturbance history and the ratio of live-to-dead biomass makes for very different carbon exchange patterns at the two sites, but they responded very similarly to the seasonal dynamics of large precipitation events. Rainfall exceeding 5 mm d^-1, particularly during the first half of the growing season, triggered large increase in ecosystem respiration (ER), and suppressed gross ecosystem productivity (GEP). These responses lead to similar year-to-year differences in annual carbon budget in the two contrasting ecosystems.