Importance of nitrogen controls on carbon sequestration in regrowing forests of the Mid-west and Northeast United States

Abstract:

Nitrogen (N) exerts strong control on carbon storage in the forests of the United States. Human activities have been altering nitrogen availability in forests for many decades. Some activities decrease N availability associated with forest harvest including biomass removal and leaching of nitrogen, especially nitrate, to river networks with potential pollution impacts downstream. Other activities increase N availability such as increased atmospheric N deposition from fossil fuel. In this study, we use process-based land surface models, the Terrestrial Ecosystem Model (TEM) and the Integrated Science Assessment Model (ISAM), to compare how various environmental factors (e.g., climate, atmospheric chemistry, land-use and land cover change) affecting N availability influence carbon sequestration in contemporary forests for two regions in the United States (511,734 km² in the Mid-west and 426,304 km² in the Northeast). These regions experience different climate, atmospheric chemistry, land cover (e.g., forests cover 36% of the Mid-west and 67% of the Northeast), land-use histories (e.g., secondary forests represent 63% of Mid-west and 94% of Northeast forests), and land management (e.g., N fertilizer applications, irrigation). Our simulations for a baseline period from 1980 to 2009 explore how changes in climate, including climate shocks such as drought events, together with other environmental changes such as land-use change, interact with nitrogen inputs to affect carbon sequestration in the forests of these two regions. This effort is part of an interdisciplinary research project funded by NSF to increase understanding of how climate-related shocks move through the food, energy and water systems of the two regions with special attention to the effects on engineered infrastructure (e.g., dams, irrigation, water treatment plants), natural infrastructure (e.g., land, aquatic systems), and their combination.