To evaluate an interactive effect of snow on energy exchange between the forest and atmosphere, the energy balance above a forest was measured continuously between February and April of 1997 in the Hitsujigaoka Experimental Forest, Sapporo, northern Japan. The forest was a dense, 23-year-old, coniferous plantation. The study site had frequent snowfalls and the canopy was frequently covered with snow during the study period. Snow-cover on the canopy was monitored daily using a photo-camera mounted above the canopy, and the fraction of the snow-covered area on the canopy was determined as an index of the canopy-snow condition. Turbulent energy fluxes above the canopy were measured using the eddy and band-pass covariance method. The diurnal courses of the measurements showed that turbulent fluxes were sensitive to the snow on the canopy. Latent heat fluxes dominated above the snow-covered canopy and sensible heat flux prevailed above the snow-free canopy. The effect of the canopy-snow on turbulent energy exchange was examined using the evaporative efficiency for the canopy-layer in an energy balance model composed of two sources of vapor fluxes. The evaporative efficiency changed dynamically according to the canopy-snow condition in the short terms and could be positively related to the extension of the snow-covered area on the canopy. A quantitative relationship was empirically determined between the evaporative efficiency and the fraction of the canopy-snow area. The snowcover season in the study site can be classified into the following two types of turbulent flux composition: (1) in mid-winter, when the canopy was snow-covered, latent heat flux dominated and the Bowen ratio was positive and low; (2) during the snowmelt season, sensible heat flux from the dry canopy prevailed and the Bowen ratio was much larger than in mid-winter. Copyright (C) 1999 John Wiley & Sons, Ltd.