ECOHYDROLOGY Ecohydrol. 2, 462–471 (2009) Published online 28 July 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/eco.74 Evapotranspiration in intermediate-aged and mature fens and upland black spruce boreal forests Corinne A. Barker, 1 Brian D. Amiro, 1 * Hyojung Kwon, 2 Brent E. Ewers, 2,3 and Julia L. Angstmann 2,3 1 Department of Soil Science, University of Manitoba, Winnipeg, MB, Canada 2 Department of Botany, University of Wyoming, Laramie, WY, USA 3 Program in Ecology, University of Wyoming, Laramie, WY, USA ABSTRACT The Canadian boreal forest consists of a mosaic of landscapes of varying soil drainage and forest age driven by wildfire. The hydrological consequences are complicated by plant responses to soil moisture and forest age, both potentially influencing evapotranspiration. Evapotranspiration was measured using the energy balance residual technique in 2006 and 2007 at forested upland and fen sites that originated following fire in 1964, 1930 and about 1850, near Thompson, Manitoba, Canada. Both net radiation and sensible heat flux density were greater at the older sites than those at the younger sites. Evapotranspiration was also greater at the older sites by between 4 and 19% for the 1930–1964 comparison, and 15% for the 1930–1850 comparison. There was no difference in net radiation between upland and fen sites of the same age, although upland sites had a higher sensible heat flux density. Albedo was greater at the fen sites. Evapotranspiration was greater at the upland sites by 11–20%, likely driven by greater leaf area at the upland sites. These intermediate to mature boreal forest sites still show the persistence of the impact of fire, and it is clear that changes in drainage and local hydrology will also have an impact on local evapotranspiration. The implication is that even these small changes in evapotranspiration can have a great regional and global effect because of the large land area of the boreal forest. Copyright  2009 John Wiley & Sons, Ltd. KEY WORDS boreal forest; energy balance; eddy covariance; fire; drainage; wetlands Received 9 March 2009; Accepted 31 May 2009 INTRODUCTION The circumpolar boreal forest has a large impact on global cycling of carbon and water (Dixon et al., 1994; Chapin et al., 2000). Within this large area, the forest is continuously being renewed by fire, insects, disease and human disturbance, such as harvesting. This creates a multi-aged forest mosaic that is determined by the current and past disturbance regime. Fire is one of the main disturbances in the North American and Siberian boreal forest, and any shift in the frequency or extent in area burned will change the age structure of the forest. For example, Flannigan et al. (2005) estimated that Canadian forests could experience a doubling of area burned with a warming climate, expected to occur near the end of the current century. These potential shifts in age structure could cause changes to the water balance of the forest if younger forests have different hydrological characteristics than older forests. The boreal forest also has topographic variation, resulting in differences in vegetation, soil moisture content and drainage. Across this landscape, large fires usually burn both the lowland and upland communities during the same event (Turetsky et al., 2004), creating a mosaic of various ages. * Correspondence to: Brian D. Amiro, Department of Soil Science, University of Manitoba, Winnipeg, Manitoba, R3T 2N2 Canada. E-mail: Brian Amiro@umanitoba.ca The water balance of these boreal ecosystems is likely determined by forest age, topographic position and soil drainage for a given climate regime. In particular, upland, relatively well-drained forests contrast with low-lying areas dominated by fens. However, it is not clear if evapotranspiration (ET) differs among these areas. For example, Mackay et al. (2007) found that the drivers of ET were fundamentally different within and across seasons between wetland and upland forests in northern Wisconsin. Current models of boreal ET predict smaller fluxes from poorly drained forests than well-drained ones; however, these results have not been tested against ET data from poorly drained sites (Bond-Lamberty et al., 2009). A comparison of previous studies of boreal forest ET showed that broad-leaved deciduous forests gener- ally have greater ET than coniferous evergreen forests (Baldocchi et al., 2000). In addition, ET decreased imme- diately following a fire, increasing to a maximum at about 20–25 years of age, then decreasing and remain- ing approximately constant for many years (Amiro et al., 2006a). This general relationship was based on com- parisons among geographically widespread forests from Alaska, USA, to Manitoba, Canada, and exhibited quite a bit of variability among sites. The area near Thompson, Manitoba, Canada, has been one of the focal points for northern boreal forest research since the BOREAS experiment in the early 1990s (Sell- ers et al., 1997). Since the intensive campaigns during Copyright  2009 John Wiley & Sons, Ltd.