||Understanding the role of belowground processes in the carbon cycle under disturbance regimes such as increased CO2 will lead to more accurate prediction of global carbon uptake and storage. Several studies have demonstrated that roots are the primary sinks for new carbon in some ecosystems, but methodological limitations have made it difficult to accurately quantify belowground carbon pools, especially through time. Newer technologies must be thoroughly explored, refined and tested prior to their use in testing hypotheses in long-term experiments. Coarse roots, unlike their aboveground counterparts, often persist for long periods after tree harvest or disturbances such as fire. The recent application of ground-penetrating radar (GPR) to imaging belowground plant structures provides a potential means to address major deficiencies quantifying belowground carbon sinks. The goal of the proposed research is to advance the application of ground-penetrating radar (GPR) in quantifying belowground carbon pools with special focus on the sensitivity of GPR in detecting change through time (roots as C sinks), live versus dead belowground structures (critical in evaluating the dynamics of belowground C pools), and legacy effects of vegetation loss and CO2 fertilization on root C pools. Results of the proposed research will contribute to the Long Term Performance Measure of DOE‟s climate change research by providing improved methods for obtaining critical quantitative measures of the largest and least understood carbon sink in forested ecosystems. Quantification of roots with GPR will refine carbon budgets and estimates of belowground C- sequestration in temperate ecosystems, enhance understanding of the role of forested ecosystems in the global carbon cycle, and improve the accuracy of global carbon models. The first year of the proposed research will be devoted to experiments and tests conducted at Blackwater Ecologic Preserve in Virginia to further shape and refine GPR applications. Experiments conducted in one-meter square pits excavated to a depth of 60-cm will include tests on sensitivity of GPR for detecting change in root mass over time, the capability for detecting live versus dead roots, the effects of soil moisture levels, the impact of potential object shadowing and detection of roots of varied size and water content, and the capability to accurately portray the spatial distribution of root mass. In year two, the protocols and thresholds established in year one will be tested on independent sites in Florida – a former DOE sponsored elevated CO2 experiment site at Kennedy Space Center and a large scale evaluation of carbon pools and climate change in the Everglades watershed (Disney Wilderness Preserve NEON Satellite Site).