|Bradford, James - Jim|
Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Proceedings
Publication Acceptance Date: 8/9/2005
Publication Date: 11/7/2005
Citation: Morgan, J.A., Baron, V.S., Bradford, J.A., Haferkamp, M.R., Sims, P.L., Skinner, H. 2005. Managing grassland as a co2 sink. ASA-CSSA-SSSA Annual Meeting Abstracts. Interpretive Summary:
Technical Abstract: Although net ecosystem CO2 exchange (NEE) rates tend to be low in most grasslands, especially native grasslands, these regions occupy a large portion of Earth’s terrestrial surface and thus represent a potentially large and significant sink or source for C. Herein we report on findings from several experiments conducted in native grasslands and improved pastures in which micrometeorological or static chambers were used to evaluate the impact of grazing practices on NEE. In three native grasslands of the Great Plains, recommended grazing practices enhanced NEE compared to non-grazed and heavily-grazed pastures, although under severe drought, grazed pastures became net sources of CO2. Although grazing temporarily removes a portion of the photosynthetic surface, and over a long period of time can alter plant community species composition and thus affect seasonal CO2 dynamics, the long-term effects of current recommended grazing on NEE in these grasslands appears to be minor. In contrast, year-to-year differences in weather appear to exert a much stronger effect on NEE in these native grasslands compared to management. In an improved pasture experiment in Pennsylvania, NEE rates were greater in alfalfa than grass pastures, were affected by whether the pastures were grazed vs. hayed, although year-to-year differences in NEE again dwarfed management effects. However, timing of forage harvesting appeared to be an important factor explaining the variable year-to-year NEE dynamics in Pennsylvania. Finally, in Alberta, conversion of cropland to perennial forage indicates the system may respond as a CO2 source the first one or two years after establishment, followed by modest net CO2 assimilation in the third (second production) year. On balance, results from these different experiments suggest that while recommended grazing practices may sometimes encourage CO2 uptake, the grazing effect on NEE is variable, and year-to-year variation in CO2 flux dynamics complicates our ability to predict the net effect of these practices.