NET EFFECTS OF DISTURBANCE: SPATIAL, TEMPORAL, AND SOCIETAL DIMENSIONS OF FOREST DISTURBANCE AND RECOVERY ON TERRESTRIAL CARBON BALANCE

This dissertation investigates the role of forest disturbance and recovery on terrestrial carbon balance over a range of spatial scales from local to global, time periods from the past 150 years to the upcoming century, and across ecological and societal dimensions. The research addresses how spatial and temporal variations in disturbance patterns impact regional forest carbon balance, how data density, resolution and uncertainty impact the ability to initialize models to represent the complex history of disturbance, and how improved representation of disturbance and recovery associated with land-use change can inform projections of climate mitigation strategies. The net impacts of tropical cyclones - including both disturbance and recovery - on the U.S. forest carbon balance was simulated using an advanced ecosystem model for the period 1851-2000. The net effect of tropical cyclones was shown to depend strongly on the spatial and temporal scales of analysis. There was large interannual variation in the net carbon balance - with individual years ranging from a net carbon source of approximately 30 Tg C yr-1 to a net carbon sink of approximately 20 Tg C yr-1. Overall, tropical cyclones provided a net carbon source during the latter half of the 19th century, but contributed a net carbon sink over much of the 20th century from periods of forest recovery exceeding new damage. Forest canopy height data from spaceborne remote sensing was used to establish present-day model initial conditions representing the complex history of disturbances at continental scales, focusing on how data density, resolution and initialization data uncertainty propagate to model prediction errors. Incomplete data coverage in currently available spaceborne lidar data resulted in prediction uncertainties larger than the total estimated continental flux. Coarse resolution averaging of height initialization data or environmental inputs resulted in prediction errors of 25% to 120% of the total estimated flux. And uncertainties in currently available gap-filled canopy height products propagated to greater than 35% uncertainties in flux predictions. A coupled model framework was developed, linking a state-of-the-art socioeconomic model with a mechanistic ecosystem model, to increase process detail within integrated assessments of climate mitigation. Comparison of results from the coupled model to previous studies suggests a high sensitivity of mitigation scenarios to model representation of disturbance and recovery associated with land-use and land-use change. In particular, slower forest growth rates in the coupled model reduces the potential to offset future carbon emissions through policies that promote afforestation. This propagates to ~40% higher policy cost necessary to meet a mitigation target of 500ppm atmospheric CO2-equivalent