Seasonal variation in the energy and water exchanges above and below a larch forest in eastern Siberia

The water and energy exchanges in forests form one of the most important hy dro-meteorological systems. There have been far fewer investigations of the water and heat exchange in high latitude forests than of those in warm. hu mid regions. There have been few observations of this system in Siberia for an entire growing season, including the snowmelt and leaf-fall seasons. In this study, the characteristics of the energy and water budgets in an east ern Siberian larch forest were investigated from the snowmelt season to the leaf-fall season. The latent heat flux was strongly affected by the transp iration activity of the larch trees and increased quickly as the larch stan d began to foliate. The sensible heat dropped at that time, although the ne t all wave radiation increased. Consequently, the seasonal variation in the Bowen ratio was clearly 'U'-shaped. and the minimum value (1.0) occurred i n June and July. The Bowen ratio was very high (10-25) in early spring, jus t before leaf opening. The canopy resistance for a big leaf model far excee ded the aerodynamic resistance and fluctuated over a much wider range. The canopy resistance was strongly restricted by the saturation deficit, and it s minimum value was 100 s m(-1) (10 mm s(-1) in conductance). This minimum canopy resistance is higher than values obtained for forests in warm, humid regions, but is similar to those measured in other boreal conifer forests. It has been suggested that the senescence of Leaves also affects the canop y resistance, which was higher in the leaf-fall season than in the foliated season. The mean evapotranspiration rate from 21 April 1998 to 7 September 1998 was 1.16 mm day(-1). and the maximum rate, 2.9 mm day(-1), occurred a t the beginning of July. For the growing season from 1 June to 31 August, t his rate was 1.5 mm day(-1). The total evapotranspiration from the forest ( 151 mm) exceeded the amount of precipitation (106 mm) and was equal to 73% of the total water input (211 mm), including the snow water equivalent. The understory evapotranspiration reached 35% of the total evapotranspiration, and the interception evaporation was 15% of the gross precipitation. The u nderstory evapotranspiration was high and the interception evaporation was low because the canopy was sparse and the leaf area index was low. Copyrigh t (C) 2001 John Wiley & Sons, Ltd.