|Title||Carbon fluxes on North American rangelands|
|Publication Type||Journal Article|
|Year of Publication||2008|
|Authors||Svejcar T, Angell R, Bradford JA, Dugas W, Emmerich W, Frank AB, Gilmanov T, Haferkamp M, Johnson DA, Mayeux H, Mielnick P, Morgan J, Saliendra NZ, Schuman GE, Sims PL, Snyder K|
|Journal||Rangeland Ecology and Management|
|Keywords||article, climatic variability, desert, grassland, journal, leaf area, method, Bowen ratio, NEE, net ecosystem exchange of CO2, precipitation, respiration, shrubland|
Rangelands account for almost half of the earth's land surface and may play an important role in the global carbon (C) cycle. We studies net ecosystem exchange (NEE) of C on eight North American rangeland sites over a 6-yr period. Management practices sand disturbance regimes can influence NEE; for consistency, we compared ungrazed and undisturbed rangelands including four Great Plains sites from Texas to North Dakota, two Southwestern hot desert sites in New Mexico and Arizona, and two Northwestern sagebrush steppe sites in Idaho and Oregon. We used the Bowen ratio-energy balance system for continuous measurements of energy, water vapor, and carbon dioxide (CO2) fluxes at each study site during the measurement period (1996 to 2001 fore most sites). Data were processed and screened using standardized procedures, which facilitated across-location comparisons. Although almost any site could be either a sink or source for C depending on yearly weather patterns, five of the eight native rangelands typically were sinks for atmospheric CO2 during the study period. Both sagebrush steppe sites were sinks and three of four Great Plains grasslands were sinks, but the two Southwest hot desert sites were sources of C on an annual basis. Most rangelands were characterized by short periods of high C uptake (2 mo to 32 mo) and long periods of C balance or small respiratory losses of C. Weather patterns during the measurement period strongly influenced conclusions about NEE on any given rangeland site. Droughts tended to limit periods of high C uptake and thus cause even the most productive sites to become sources of C on an annual basis. Our results show that native rangelands are a potentially important terrestrial sink for atmospheric CO2, and maintaining the period of active C uptake will be critical if we are to manage rangeland for C sequestration.