Wylie, Bruce (SAIC, USGS National Center, EROS Sioux Falls, SD, 57198; Phone: 605-594-6078; Fax: 605-594-6529; Email: wylie@usgs.gov)

Rangeland Carbon Fluxes in the Northern Great Plains

B. K. Wylie *, T. G. Gilmanov, A. B. Frank, J. A. Morgan, M. R. Haferkamp, T. P. Meyers, E. A. Fosnight, L. Zhang

Rangeland Carbon fluxes are highly variable in both space and time. In the Northern Great Plains, rainfall is an important determinant of whether this ecosystem will be a carbon sink or source. Given the large areas of rangelands and their significant soil organic matter stocks, understanding how they respond to climatic variation is important for making future predictions. Rangeland carbon fluxes associated with Net Ecosystem Exchange (NEE), gross primary productivity (Pg), total ecosystem respiration (Re) were quantified from multiple year data sets from five flux tower locations in the Northern Great Plains. Light response curve analysis was used to partition net fluxes into Pg, and Re. These flux tower measurements were then combined with 1 km2 spatial data sets of photosynthetically active radiation (PAR), Normalized Difference Vegetation Index (NDVI), temperature, precipitation, start of growing season, and soil derived data sets. Regression tree models were developed by removing infrequently variables or variables that had limited impact on model prediction. Cross validation and jackknifing approaches quantified model prediction accuracies. Maps of 10-day carbon dynamics of NEE, Pg, and Re were produced for each growing season from 1998 to 2001. Growing season carbon fluxes were combined with estimates of winter fluxes to estimate annual carbon budgets. Carbon sinks and sources were mapped and regional averages were calculated.