CARBON DYNAMICS OF DISTURBANCE IN THE EASTERN U.S. TEMPERATE FORESTS

Most temperate forests in the eastern U.S. are currently recovering from disturbance. These disturbances include both human disturbances of agricultural abandonment or timber harvest, as well as natural disturbances such as storms and fire. Both croplands and pasturelands have increased at the expense of forests since 1700, with croplands reaching a maximum in the 1950s. Fires were more prevalent prior to 1920 due fire suppression in the 20^th century. Along the coast, tropical storms and hurricanes in the south are common. We use the Hurtt et al. (2006) land use transition datasets to model agricultural conversion, agricultural abandonment, and timber harvest since 1700 at the half degree resolution. We also have developed half degree resolution datasets of tropical storm and hurricane return frequencies based on the Zeng et al. (2009) data and fire return intervals for pre-1920 and the 20^th century based on LANDFIRE Rapid Assessment Vegetation Models and vegetation types from Nowacki and Abrams (2008). These data are used within the TEM-Hydro model to determine the carbon dynamics of the temperate forest ecosystem as a result of these disturbances. The human disturbances are based on the actual historical record, while the fire and storm data are applied stochastically based on return frequencies. Disturbances result in carbon release to the atmosphere by volatilization, slash directly to the soil, standing dead material which decays slowly, and products that decay at different rates. I will present results for present-day U.S. forests to determine how past disturbance affects current Net Ecosystem Productivity as well as net carbon sequestration rates.