Comparative studies on turbulent fluxes measured over burned and unburned sites of a sagebrush-dominated mountain Ayodeji B. Arogundade, 1 * Wenguang Zhao 2 and Russell J. Qualls 1 1 Department of Biological and Agricultural Engineering, University of Idaho, Moscow, ID 83844, USA 2 Kimberly Research and extension Center, University of Idaho, Kimberly, ID 83341, USA ABSTRACT Fire is a major disturbance that causes rangeland change. In this study, we compared the turbulent fluxes of carbon dioxide and sensible and latent heat, measured over burned and unburned sites of a sagebrush-dominated mountain in southern Idaho during the late summer of 2006. The outcome of the investigation shows that fire altered the horizontal components of turbulence intensity (i u and i v ) as well as the partitioning of radiant energy between latent and sensible heat fluxes. Average daytime Bowen ratios (b) at the burned and unburned sites were 2.03 and 1.87. On the basis of Bowen ratios determined from eddy covariance measurements of sensible and latent heat fluxes, the sensible heat fluxes were relatively more significant at the burned site than at the unburned site most of the time, and the converse was true of the latent heat fluxes. The exception to this was for the few days following heavy rainfall, when near-surface soil moisture increased the evapotranspiration at the burned site more than at the unburned site until the shallow moisture supply was depleted. By means of ratios of CO 2 /(H + LE), fluxes, carbon sequestration was found to be more significant at the unburned site, declining at both sites as summer progressed but declining more rapidly at the burned site than at the unburned site. Copyright © 2012 John Wiley & Sons, Ltd. KEY WORDS turbulent fluxes; evapotranspiration; turbulence intensity; carbon sequestration; energy budget closure; eddy covariance; sagebrush; fire Received 23 December 2011; Revised 12 October 2012; Accepted 16 October 2012 INTRODUCTION Sagebrush ecosystems occupy over 62 million ha of the western US (Rich et al., 2005) or 25% of the total rangeland in the USA (Glimanov et al., 2003), and they provide important habitat for several ungulate and vertebrate species (Sivanpillai et al., 2009). In fact, more than 10% of the world’s temperate and semi-deserts are located in North America, and more than 50% of the total North American desert land area is classified as Western intermountain sagebrush steppe ecosystems (Angell et al., 2001). These extensive areas are important as watersheds, wildlife habitat and animal forage (Angell et al., 2001). From the management position, according to Glimanov et al. (2003), rangelands are essential because they provide opportunities to facilitate carbon sequestration in a shorter time and at lower costs than afforestation. Wildlife biologists recognize sagebrush as important browse for deer, elk and pronghorn antelope (Knight, 1994). It also provides an important habitat for sage grouse and other birds (Knight, 1994; Connelly et al., 2004). However, these ecosystems have been degraded by frequent wild fires, overgrazing by domestic animals and other anthropogenic disturbances (Johansen et al., 1993; Rich et al., 2005). These disturbances not only affect the fauna that are dependent on this vegetation for forage (Sawyer et al., 2006) but also influence the microclimate of the environment. In fact, fire continues to be a major environmental factor in sagebrush communities (Prater et al., 2006). Fire, drought and burrowing animals are common disturbances in sagebrush ecosystems, and removing these ecosystems could lead to reduced total water availability and net primary productivity compared with when grasslands are removed (Harniss and Murray, 1973; Knight, 1994). The effects of anthropogenic disturbances, especially fire, on energy fluxes measured over forested regions have also been widely studied (Bonan, 2008; Amiro, 2001; Amiro et al., 1999; Montes-Helu et al., 2009). It has been observed that changes in land cover, such as caused by fire, can act as climate-forcing events by modifying the vegetation type, surface colour, albedo and the partitioning of energy fluxes (Feddema et al., 2005; Montes-Helu et al., 2009). In addition, fire influences the turbulence structure in the surface layer that provides information on the diffusivity of air pollutants (Park and Park, 2006) and also drives scalar exchange between vegetation and the atmosphere (Finnigan, 2000). However, lack of data for most vegetation types limits our understanding of how disturbances modify the components of the energy balance (Montes-Helu et al., 2009). Few studies have been conducted on the impacts of fire on energy fluxes over sagebrush-dominated mountains, even though sagebrush ecosystems have the potential to play an important role in the global carbon cycle because of their extensive coverage (Glimanov et al., 2003). Quantitative estimates of CO 2 *Correspondence to: Ayodeji B. Arogundade, Department of Biological and Agricultural Engineering, University of Idaho, P.O. Box 440904, Moscow, ID 83844, USA. E-mail: arog5831@vandals.uidaho.edu ECOHYDROLOGY Ecohydrol. (2012) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/eco.1346 Copyright © 2012 John Wiley & Sons, Ltd.