Dr. Leavitt’s research centers on past, present and future global change, variously using light stable-isotope analysis of tree rings, native plant leaves, crop plants, soils and geological materials. Leavitt has used carbon isotope analysis in multiple FACE (Free-Air CO2 Enrichment) experiments conducted at the Maricopa Agricultural Center (Arizona), including cotton, wheat and sorghum, to understand more about impact of CO2 fertilization on crop production and soil organic carbon pools. He has further pursued use of carbon isotopes in tree rings to investigate environmental moisture, drought, and water-use efficiency of pinyon pine, ponderosa pine and Douglas-fir trees in networks of sites around the US Southwest and Baja. Much of Leavitt’s recent efforts have involved ongoing investigation of wood from ancient buried forests from around the Great Lakes area spanning the period from about 4,000 to 15,000 years ago, for tree-ring and isotope analysis to better understand the environment of that time. Additionally, several recent and ongoing studies have involved investigation of tree rings and tree-ring isotopes in China with respect to climate and ecological questions.