We have sampled more than 75 sites across N.A. and have determined the control of proportional production by C 3 and C 4 species from the isotopic composition. With long-term climate data for the Great Plains we can describe the modern distribution of C 4 production and its theoretical response to a 2XCO 2 GCM simulation. C 4 is strongly predicted by high summer temperature and late growing season precipitation. Early season temperaure increases favor C 3 species. Students can also study soil organic matter changes and document the advance of forest into modern grasslands as is occurring at Newton Hills.
Students can also use isotopic tracers in dietary studies.
The project with The Nature Conservancy is testing hypotheses about the role of grazing in determining fire patterns and frequency in the Great Plains. Monthly assessments of diet from feces, hair samples, bone, or horn sheaths show that there is substantial dependence on C 3 grasses at Konza and that this pattern is quite different at Tallgrass Prairie Preserve in Oklahoma. The bison data show a clear latitudinal trend in isotopic composition suggesting their value in climate reconstruction as well. Similar procedures have documented dietary utilization by humans in North America as well as in the very dry Atacama Desert near Arica Chile and in the Canary Islands. The mummified samples from the Atacama desert include both the oldest known mummies and a near continuous record of coastal inhabitation for 10,000 to 12,000 years with diets ranging from highly dependent on marine resources to those dependent on material from the Andean Highlands.