|Milchunas, Daniel - COLORADO STATE UNIVERSITY|
|Pendall, Elise - UNIVERSITY OF WYOMING|
|Parton, William - COLORADO STATE UNIVERSITY|
Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: August 22, 2006
Publication Date: February 9, 2007
Citation: Morgan, J.A., Milchunas, D., Pendall, E., Parton, W.J., Derner, J.D. 2007. Management implications of rising atmospheric CO2 for semi-arid rangelands. Society for Range Management Meeting Abstracts. CDROM Traditions and Transitions. Abstract #300. Technical Abstract: While rising atmospheric carbon dioxide (CO2) is known to be an important contributor to radiative forcing of Earth’s climate and is projected to be leading to global warming, more direct effects of this gas on photosynthesis and plant water relations have been underway for more than a century, and likely have already contributed to important changes in rangelands. Experiments conducted in native and semi-natural grasslands in which ambient CO2 concentrations have been artificially increased have shown that increasing CO2 often increases photosynthesis, results in higher soil and plant water content, and can enhance plant water use efficiency. While these responses may appear beneficial, CO2-induced plant production has also been shown to result in a lowering of forage quality, in part due to the inability of soil N mineralization to keep pace with increased plant productivity, resulting in lowered plant N concentration. Furthermore, plant species differ in their sensitivities to CO2, with winners and losers emerging in studies designed to evaluate species responses to CO2; this suggests that rising atmospheric CO2 over the past hundred years may have already led to species shifts in native plant communities. Globally, C3 shrubs are expanding into C4 grasslands, a community change that has been hypothesized to be partly linked to increases in atmospheric CO2. New results from an experiment conducted in the Colorado shortgrasss steppe, which indicate a strong productivity response of the sub-shrub Artemesia frigida (fringed sage) to 5 years exposure to elevated CO2, support this CO2-induced shrub expansion hypothesis. While we know that grazing management and weather can alter plant community productivity and species composition, little progress has been made integrating this knowledge with more recent global change experiments. Herein we discuss these and related phenomena and speculate on the implications of rising atmospheric CO2 for rangeland ecology and management.