Carbon Dynamics Along A Chronosequence Of Slash Pine Plantations In North Florida

To determine factors controlling the carbon dynamics of an intensively managed landscape, we measured net CO₂ exchange with the atmosphere using eddy covariance and soil CO₂ fluxes using static chambers along a chronosequence of slash pine (Pinus elliottii var. elliottii) plantations consisting of a recent clearcut, a mid-rotation (10-yr-old) stand, and a rotation-aged (24-yr-old) stand. Daytime net ecosystem exchange of CO₂ (NEE_day) at the clearcut was not significantly different than zero during the growing season of the first year following harvest and reached levels that were ∼40% of those at the older stands during the second growing season. NEE_day was similar at the mid-rotation and rotation-aged sites, reflecting the similar leaf areas of these stands. Nighttime net ecosystem exchange of CO₂ (NEE_night) was an exponential function of air or soil temperature at all sites. However, low decomposition rates of litter and flooding of the site following harvest likely constrained NEE_night at the clearcut, and drought affected rates at the mid-rotation site. Annual net ecosystem exchange of CO₂ (NEE_yr) was estimated at −1269 and −882 g C·m⁻²·yr⁻¹ at the clearcut, and 576 and 603 g C·m⁻²·yr⁻¹ at the mid-rotation stand in 1998 and 1999, respectively. For comparison, NEE_yr was 741 and 610 g C·m⁻²·yr⁻¹ at the rotation-aged stand in 1996 and 1997, respectively. In contrast, annual ecosystem respiration (R_eco) was similar in magnitude at all sites during all years. Although R_eco is similar in magnitude, NEE_yr is highly dynamic across this intensively managed landscape, with a maximum range of ∼2000 g C·m⁻²·yr⁻¹. This range exceeds that across all the sites in both the Ameriflux and Euroflux networks and illustrates the need to include the range of stand ages and disturbance histories in landscape- to regional-scale flux estimates.