Winter CO2 fluxes above sagebrush-steppe ecosystems in Idaho and Oregon

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 winter at representative sagebrush-steppe sites in the western USA and to study their relationships to environmental factors. 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–March 15) was 1.31 ± 0.80 g CO2 m−2 day−1 and 1.23 ± 1.19 g CO2 m−2 day−1 at the two Idaho sites and 0.68 ± 0.56 g CO2 m−2 day−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 mathematical models that reliably predict winter CO2 effluxes across a wide range of sagebrush-steppe sites.