Future forest aboveground carbon dynamics in the central United States: the importance of forest demographic processes

The Central Hardwood Forest (CHF) in the United States is currently a major carbon sink. There are uncertainties in how long the current carbon sink will persist and whether the CHF will eventually become a carbon source. We used a multi-model ensemble approach to investigating aboveground carbon density of the CHF from 2010 to 2300 under current climates. Simulations were done using one representative model for each of the simple, intermediate, and complex demographic approaches (ED2, LANDIS PRO, and LINKAGES, respectively). All approaches agreed that the current carbon sink would persist at least to 2100 under current climates. However, carbon dynamics during the following 200 years of simulation differed among three demographic modelling approaches. Both the simple and the complex demographic approaches predicted prolonged periods of relatively stable carbon sink after 2100, with minor declines, until the end of simulations in year 2300. In contrast, the intermediate demographic approach predicted the CHF would become a carbon source between 2110 and 2260, followed by another carbon sink period. The disagreement between these patterns can be partly explained by differences in the ability of models to simulate gross growth (both birth and subsequent growth) and mortality of short-lived, relatively shade-intolerant tree species.