My research has focused on the physiological ecology of grasses with an emphasis on photosynthesis and production of C₃ and C₄ grasses. This led to significant involvement in major ecosystem level studies in grassland systems ranging from tundra regions to temperate zone prairies to the tropics. The ability to distinguish and quantify carbon from these two photosynthetic systems became apparent in 1975 and led to the development of our Isotope Ratio Mass Spectrometry laboratory.

Current research focuses on the use of isotopic fractionation to quantify carbon fluxes and to: 1.) evaluate the control of C₃ and C₄ production by climate and their resonses to climate change, 2.) examine the effects of land use on soil carbon, 3.) evaluate diets and subsistence strategies of ancient people and modern animals, 4.) incorporate remote sensing as a tool to integrate grassland performance over large spatial scales. Support is provided by the Department of Energy (NIGEC), The Nature Conservancy, the USDA, and the NSF. We have also been selected as a NASA Space Grant Institution and provide two student internships for work with remote sensing at the EROS Data Center.

More detailed data are being used to study the way in which bison and fire determine landscape patterns on the major grassland preserves of The Nature Conservancy.

2. The soil organic matter retains an isotopic record of past and current vegetation thereby allowing us to reconstruct C₃and C₄composition and to assess its response to climate change. We have sampled more than 75 sites across N.A. and have determined the control of proportional production by C₃ and C₄ species from the isotopic composition. C₄ percent of total grass production is estimated by the following equation:

With long-term climate data for the Great Plains we can describe the modern distribution of C₄ production

and its theoretical response to a 2XCO₂ GCM simulation.
Students can also examine the STATSGO soil data base now available at the EROS Data Center where we have identified the C₃ and C₄ grasses and have aggregated the production by C₄ species across the Great Plains of N.A.

The control of production from either the isotope data or STATSGO derived estimates are similar. C₄ is strongly predicted by high summer temperature and late growing season precipitation. Early season temperaure increases favor C₃ species.
Students can also study soil organic matter changes and document the advance of forest into modern grasslands as is occurring at Newton Hills.