Submitted to: USDA Symposium on Natural Resource Management to Offset Greenhouse Gas Emissions
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 2002
Publication Date: February 1, 2003
Citation: HAFERKAMP, M.R., HEITSCHMIDT, R.K., MACNEIL, M.D. MEASURING CO2 FLUX OVER NORTHERN GREAT PLAINS RANGELANDS. USDA SYMPOSIUM ON NATURAL RESOURCE MANAGEMENT TO OFFSET GREENHOUSE GAS EMISSIONS. 2003. Abstract #70. Technical Abstract: The role of rangelands in regulating atmospheric CO2 levels is a critical issue in global climate change research. Rangelands are complex systems occupying more than 40% of the land area in the world and USA. We studied the effects of seasonal grazing on CO2 flux on small plots located on a silty range site in the mixed-grass prairie with an Eapa fine loam soil. Treatments were: no grazing or intensively grazed in mid-May or mid-July applied during 1996, 1997, and 1998. Data were collected from mid-April to mid-October at about 30 day intervals to estimate standing crop, leaf area, soil organic matter, root mass to a 30-cm soil depth, and diurnal variation of CO2 flux (at 0800, 1200, 1600, and 2400 hours) above 1 m**2 of rangeland in a closed 1-m**3 chamber. Green standing crop on unclipped control plots ranged from 855 to 212 kg ha**-1 in 1996, 530 to 153 kg ha**-1 in 1997, and 371 to 158 kg ha**-1 in 1998. Perennial cool-season grasses and sedges generally made up more than 60% of the green standing crop during April through July each year. Perennial warm-season grasses and sage worts begin to increase in dominance during July. During grazing events an average of 68 to 78% of the green standing crop was removed. Reducing the green standing crop reduced the uptake of CO2 by an average of 175% in May and 109% in July. Fluxes were reduced only 19% on adjacent un-grazed plots. Uptake of CO2 was greatest during spring and early summer, peak periods of precipitation and green biomass. Grazing in May reduced CO2 uptake for 30 days in 2 of the 3 years. A 30-day reduction in CO2 flux from July grazing occurred only in 1998. Residual effects of grazing, however, declined in autumn with the onset of plant maturation. Thus weather, particularly precipitation appears to exert a primary control on CO2 exchange.