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ARS Home » Plains Area » Mandan, North Dakota » Northern Great Plains Research Laboratory » Research » Publications at this Location » Publication #157568
Title: SHRUBS EFFECTS ON CARBON DIOXIDE AND WATER VAPOR FLUXES OVER GRASSLANDS

Author
item Frank, Albert
item KARN, JAMES - USDA-ARS (RETIRED)

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2004
Publication Date: 1/1/2005
Citation: Frank, A.B., Karn, J.F. 2005. Shrubs effects on carbon dioxide and water vapor fluxes over grasslands. J. Range Manage. 58:20-26.

Interpretive Summary: Land use changes and increasing fossil fuel use have contributed to increased atmospheric carbon dioxide concentrations. Grasslands are a species rich ecosystem that may be important in mitigating these increases in atmospheric carbon dioxide. The effect of shrub invasion on carbon dioxide uptake in Northern Great Plains grasslands is not known. The Bowen ratio/energy balance technique was used to measure carbon dioxide uptake and evapotranspiration over a grazed mixed-grass prairie and a mixed-grass prairie that has extensive invasion of woody shrubs over a 4 year period. Peak biomass occurred during the July to early August period and averaged 1,763 kg per ha for the prairie and 1,808 kg per ha for the shrub prairie site. Carbon dioxide uptake was greater for the shrub prairie site during the period of increasing uptake during May and June, whereas, the prairie site had greater uptake during the period of decreasing uptake from August to mid-October. Total carbon dioxide uptake was similar for both sites averaging 349 g carbon dioxide per m2 per yr for the prairie and 350 g carbon dioxide per m2 for the shrub prairie. Evapotranspiration rates were higher in the prairie than the shrub prairie site. These results suggest that invasion of shrubs into a Northern Great Plains grassland ecosystems does not reduce carbon dioxide uptake. A small level of shrub invasion into grasslands may have advantages for wildlife population and for enhancing species diversity.

Technical Abstract: Temperate grasslands are a species rich ecosystem that may be important in mitigating the increase in atmospheric carbon dioxide. The effect of shrub invasion on carbon dioxide fluxes in Northern Great Plains grasslands is not known. The objectives of this research were to determine carbon dioxide and water vapor fluxes over a grazed mixed-grass prairie (prairie site) and a mixed-grass prairie that has extensive invasion of woody shrubs (shrub prairie site). The Bowen ratio/energy balance technique was used to determine carbon dioxide and water vapor (evapotranspiration) fluxes over a 4 year period from 1 May to 17 October in 1999, 2000, 2001, and 2002. Above-ground biomass and leaf area index were measured about every 21 days throughout the growing period. Peak biomass occurred during the July to early August period and averaged 1,763 kg per ha for the prairie and 1,808 kg per ha for the shrub prairie site. Carbon dioxide fluxes trended greater (positive flux is carbon dioxide uptake) for the shrub prairie site during the period of increasing fluxes during May and June, whereas, the prairie site had greater flux during the period of decreasing flux from August to mid-October. The flux was similar for both sites averaging 349 g carbon dioxide per m2 per yr for the prairie and 350 g carbon dioxide per m2 per yr for the shrub prairie. Evapotranspiration rates were higher in the prairie (521 mm) than the shrub prairie site (461 mm). These results suggest that shrub invasion on Northern Great Plains grasslands does not reduce the potential of grasslands to sequester atmospheric carbon dioxide.