Interannual variation in forest carbon exchange as affected by spring storms in coastal eastern US

Interannual variation in C sequestration by forest ecosystems contributes to uncertainties about global carbon balance. Feedback mechanisms between ecosystem properties and climate may cause variability either through environmental or biological modulation.

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.