Carbon dioxide exchange and early old-field succession

Old-field succession is a widespread process active in shaping landscapes in the eastern United States, contributing significantly to the terrestrial sink of atmospheric carbon dioxide, particularly at midlatitudes. However, few studies document ecosystem-scale carbon dioxide exchange during the early years of old-field succession, particularly during the temporal transition from cultivation to abandonment. Rates of carbon dioxide exchange were measured for 20 months over a field in Virginia during the transition from an actively cultivated crop field to an unmanaged old field, including one season of crop growth and two seasons of successional growth. Ecosystem carbon respiration exceeded carbon assimilation during growing seasons and dormant periods, resulting in a net flux of carbon dioxide from the biosphere to the atmosphere of between 1.27 and 1.85 kg C m(-2) for the entire 20-month period (an average loss to the atmosphere of 2.07 to 3.01 g C m(-2) day(-1)). Crop growth (from 10 January 2001 to 6 June 2001) resulted in a net loss of between 0.22 and 0.32 kg C m(-2) to the atmosphere (an average daily loss of 1.5 to 2.2 g C m(-2)), whereas the two seasons of successional growth combined contributed an additional 1.05 to 1.53 kg C m(-2) to the atmosphere (an average daily loss of 2.2 to 3.3 g C m(-2)). Empirical modeling was used to demonstrate control of ecosystem carbon respiration by soil temperature, soil moisture status, and the status of vegetation growth activity. Tower-based estimates of carbon loss were compared at both short (half hourly) and long (seasonal) timescales to independent, ground-based measurements. Using estimates of carbon exchange from previously published studies, these results are placed in the context of a trajectory of old-field succession.