Carbon dynamics of prescribed fire in pine- and oak-dominated forests on the mid-Atlantic coastal plain, USA

The use of prescribed fire to reduce the risk of wildfires and maintain or enhance desired ecological conditions is increasing in forests of the Mid-Atlantic region. Accurate estimates of forest carbon (C) dynamics associated with prescribed burning, including net ecosystem productivity (NEP) and time to accumulate the C lost during burns, termed neutral net ecosystem C balance (NECB), as a function of fire intensity and burn intervals would assist fire managers optimize treatment timing while balancing other ecosystem services provided by forests. We quantified forest C dynamics and evapotranspiration in two pine-and oak-dominated forests in the Pinelands National Reserve of southern New Jersey that have been managed using prescribed fire over two decades. Using long-term C flux data, we found that NEP, ecosystem respiration (RE) and gross ecosystem production (GEP) were similar among stands during undisturbed years. Estimated C loss during three prescribed burns at the pine-dominated stand averaged 4.3 +/- 0.9 Mg C ha-1, which is equivalent to 2-3 years of NEP during undisturbed years, and consistent with fuel consumption during prescribed burns throughout the Pinelands. Only annual NEP was lower during years when burns were conducted compared to unburned years, while annual RE, GEP, evapotranspi-ration and ecosystem water use efficiency were similar. Over a two-decade period, NEP totaled 28.3 Mg C ha-1 and NECB was 15.5 Mg C ha-1, indicating that stands managed using repeated prescribed burns still sequester moderate amounts of C. At an oak-dominated stand, a prescribed burn released lower amounts of C (1.7 Mg C ha -1), and annual NEP was greater over the following 3-year period compared to a decade of low annual NEP following severe spongy moth defoliation and associated tree mortality, suggesting that prescribed fires could play a role in the restoration of ecosystem functioning in insect-damaged stands. Patterns of forest C dynamics during and following prescribed burns in these mid-Atlantic forests are similar to intermediate age pine -dominated stands throughout the southeastern USA, which also sequester moderate amounts of C through repeated prescribed burning regimes.