Abstract
Measurements of energy, carbon dioxide and water vapour fluxes and supporting meteorological variables were made from 1 September 2003 to 31 August 2004 in a 74โyearโold mixedwood forest in northern Ontario, Canada, using the eddy covariance technique. Land surface cover data analysis showed that although this forest is comprised of deciduous and coniferous species, their proportion throughout the forest was almost equal, resulting in a homogeneously mixedwood stand. The seasonal pattern of albedo showed a distinct pattern as a result of mixed deciduous and coniferous species with the first low radiation reflection period in early spring (between snowmelt and deciduous leafโout), and the second low reflection period in late autumn (between senescence and snowfall). Root zone soil water content remained above 0ยท32 throughout the growing season, which is characteristic of wet soil conditions. The evaporative flux exceeded the sensible heat flux during most of the growing season. Daily mean evapotranspiration values during the peak growing season were about 2โ2ยท5 mm day^โ1^ with maximum values reaching up to 4โ5 mm day^โ1^ on sunny days. The total water loss over the 12โmonth measurement period was 480 ยฑ 30 mm, while the total precipitation was 835 mm. Despite high soil water content, bulk surface conductance calculated using the inverted PenmanโMonteith formulation, showed a strong correlation with vapour pressure deficit (VPD), indicating stomatal control on water loss during the afternoons with high atmospheric demand and during occasional dry periods. Bulk surface conductance values in this mixedwood forest were relatively higher than those in other boreal coniferous forests and were more similar to values observed in the southern boreal deciduous forests. The PriestleyโTaylor ฮฑ values showed a wide range but during most of the growing season its values were close to unity, indicating that water stress does not play a major role in the overall water loss from this boreal forest ecosystem, while energy supply has a strong control on evapotranspiration. These results will help parameterize accurately energy and water exchanges for the moist mixedwood forests in land surfaceโatmosphere interaction and hydrologic models. Copyright ยฉ 2006 John Wiley & Sons, Ltd.