Regional carbon dynamics in the southeastern U.S. coastal plain: Balancing land cover type, timber harvesting, fire, and environmental variation

Understanding regional carbon budgets is a leading issue in carbon cycling research, but issues of measurement difficulty, scale, boundaries, and logistics compromise estimates at areas larger than stands or research plots. We studied four 15 x 15 km sample areas to examine land management and wildfire effects on carbon storage dynamics in the forested southeastern U.S. coastal plain region from 1975 to 2001. Carbon exchange and storage rates were estimated using satellite remote-sensing methods coupled with micrometeorological and biomass measurements. Carbon losses occurred by timber harvesting and fire, and carbon release continued for four years following clearing, suppressing landscape carbon gain proportional to the cleared area. Carbon accumulated at an average rate of 90,000 t C yr(-1) in the landscape (total area 900 km(2)) from 1975-2000, or similar to 1 t C ha(-1) yr(-1). Interannual variation was related mainly to the magnitude of annual plantation timber harvesting. Wildfires were rare and their effects on carbon balances consequently small, despite having large local impact. Previous studies in the area demonstrated that environmental fluctuations had little direct effect on the net landscape exchange of carbon, although indirect effects included higher probability of fire during droughts and shifts in harvesting to drier sites during wet periods. Although this study was a simple aggregation of carbon cycle components from fine spatial scale (Landsat images) to the landscape, the extrapolation incorporated important spatial and temporal environmental heterogeneities and led to the unexpected suggestion that the industrial forests of the southeast U. S. Coastal plain are a long-term carbon sink. The analysis also revealed specific uncertainties in our scaling efforts that point to future research needs.