|Bradford, James - Jim|
|Mayeux Jr, Herman|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2008
Publication Date: 9/5/2008
Citation: Svejcar, A.J., Angell, R.F., Bradford, J., Dugas, W., Emmerich, W.E., Frank, A.B., Gilmanov, T., Haferkamp, M.R., Johnson, D.A., Mayeux Jr, H.S., Mielnick, P., Morgan, J.A., Saliendra, N., Schuman, G.E., Sims, P.L., Snyder, K.A. 2008. Carbon fluxes on north american rangelands. Rangeland Ecology and Management. 61:465-474. Interpretive Summary: There is increasing interest in understanding the role of vegetation in carbon cycles. Rangelands cover about half the Earth's land surface, yet have received much less attention than forests with regard to uptake and release of CO2. We studied the pattern of growing season CO2 uptake on eleven rangeland sites over a six-year period. There were several seasonal patterns that emerged when we compared the various types of rangeland. It was also evident that brief periods can be very important in determining whether a rangland site sequesters or releases carbon on an annual basis. This information should be valuable to scientists and managers seeking to improve carbon sequestratoin on rangelands.
Technical Abstract: Seasonal patterns of growth and thus carbon uptake are relevant to both scientists who study ecosystem properties and managers who strive to maintain rangeland productivity. We studied seasonal patterns of net ecosystem exchange of carbon (NEE) on 11 US rangelands over a 6-year period. All sites were in good ecological condition and were not grazed during the study period. Sites were distributed among the Great Plains (6), Southwestern hot desert (3), and Northwestern sagebrush steppe (2). We used the Bowen ration-energy balance system (model 023/CO2 Bowen Ratio, Campbell Scientific Inc, Logan, UT) for continuous measurements of energy, water vapor, and CO2 fluxes at each study site during the measurement period (1996 to 2001 for most sites). Data were processed and screened using standardized procedures, which facilitated across location comparisons. In this analysis we focused on patterns of growing season NEE. We fitted curves to weekly 6-year average NEE for each site. The sites could be grouped based on peak weekly NEE and duration of positive NEE (net uptake of CO2). Peak weekly NEE occurred in mid-June for most Great Plains and sagebrush steppe sites. The exception was Texas where the weekly peak NEE occurred in mid-May. Our analysis also indicates that NEE during brief periods (as short as 2 weeks) may be critical in determining whether a rangeland site is a net sink or source for CO2 on an annual basis.