Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/27/2004
Publication Date: 11/1/2004
Citation: Gilmanov, T.G., Johnson, D.A., Saliendra, N.Z., Angell, R.F., Svejcar, A.J., Clawson, K.L. 2004. Winter CO2 fluxes above sagebrush-steppe ecosystems in Idaho and Oregon. Agricultural and Forest Meteorology. 126(2004):73-88. Interpretive Summary: Concerns over increasing atmospheric CO2 and potential effects on climate have stimulated research on CO2 fluxes of native ecosystems. In the western U.S., the largest intact native ecosystem is the sagebrush steppe at almost 100 million acres. Measuring CO2 uptake or release of ecosystems can be very difficult during the winter in the northern part of the U.S. We used a combination of Bowen ratio/energy balance technology and modeling with environmental variables to predict CO2 losses to respiration during the winter at three sites in Idaho and Oregon. Our results are comparable to short-term studies on similar ecosystems. This research in conjunction with ongoing measurements will provide a means of estimating whether the sagebrush steppe is likely to be a source or sink for atmoshperic CO2.
Technical Abstract: Sagebrush-steppe ecosystems cover more than 36 million ha in North America and represent an important economic and ecological resource. These ecosystems have a climate with an extended cold period that can last more than five months. The CO2 fluxes during this protracted cold period likely play an important role in determining annual fluxes in these ecosystems; however, few studies have measured continuous CO2 fluxes in sagebrush-steppe ecosystems during the winter. The objective of our study was to obtain continuous measurements of CO2 fluxes during the winter at representative sagebrush-steppe sites in the western USA. Measurements of CO2 fluxes were obtained using Bowen ratio/energy balance (BREB) techniques during the winter at two locations in Idaho and one location in Oregon. Average daily ecosystem respiration during the winter period (November 1 to March 15) was 1.31 ± 0.80 g CO2 m-2 d-1 and 1.23 ± 1.19 g CO2 m-2 d-1 at the two Idaho sites and 0.68 ± 0.56 g CO2 m-2 d-1 at the Oregon site. These values are well within the range of previously published results for similar ecosystems. Multivariate analyses showed that soil temperature, wind speed, and snow depth were the environmental factors most closely related to winter CO2 effluxes. Based on testing of empirical flux models, additional research will be required to develop predictive models that reliably predict winter CO2 effluxes across a wide range of sagebrush-steppe site.