Tian, Hanqin (Auburn Univ., School of Forestry and Wildlife Sciences, Auburn, AL, 36849; Phone: 334-844-1059; Fax: 334-844-1084; Email: tianhan@auburn.edu)

Carbon Sequestration in Southeast US: Ecosystem Responses to Multiple Stresses

H. Tian *, H. Chen, C. Zhang, M. Liu, S. Pan, J.M. Melillo, D.W. Kicklighter, B. Felzer

Land ecosystems in the southeast US are thought to be currently functioning as the largest carbon sink among the six major bioclimatic regions of the conterminous United States. Inverse-and inventory-based estimates on the carbon sink do not identify the mechanisms responsible for the carbon sink. Many of the major factors (and complex interactions) that affect this carbon sink are operating concurrently in the southeastern ecosystems. In this study, we intend to examine how ecosystem carbon storage has changed as a result of multiple stresses and interactions among those stresses including land-cover change, climate variability, atmospheric composition (carbon dioxide and tropospheric ozone), precipitation chemistry (nitrogen composition), and natural disturbances such as fire using estimates of carbon fluxes and storage from factorial simulation experiments with the Terrestrial Ecosystem Model (TEM) in conjunction with remotely sensed and field data. Our analysis suggests that the net carbon exchange of terrestrial ecosystems with the atmosphere in this region varied substantially from a source of 230gC/m² to a sink of 325 gC/m². Forest recovery after cropland abandonment and natural disturbances have resulted in an carbon uptake, but rapid urbanization and rising tropospheric ozone pollution have led to a significant reduction in carbon storage in the southeast.