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Abstract

Total forest evaporation, E, understorey evaporation, E-u, and environmental variables were measured for 18 consecutive mid-summer days during July 1996 in a 215-year-old stand of Pious sylvestris L. trees located 40 km southwest of the village of Zotino in central siberia, Russia (61 degrees N, 89 degrees E, 160 m asl). Tree and lichen (Cladonia and Cladina spp.) understorey one sided leaf and surface-area indices were 1.5 and 6.0, respectively. Daily E, measured by eddy covariance, was 0.8-2.3 mm day(-1) which accounted for 15-67% of the available energy, R-a. Following 12 mm rainfall, daily E reached a maximum on the second day (the first clear day) but declined rapidly thereafter to reach minimum rates within one week. The sandy soil had a range of water content equivalent to only 4 mm water per 100 mm depth of soil. It was estimated that 38% of soil water was utilised before water deficit began to limit E. E-u, also measured by eddy covariance and by lysimeters, was 0.5 to 1.6 mm day(-1) or 33-92% of E. E-u was proportional to R-a, but in response to soil drying, the slope of this linear relation declined by a factor of three to a minimum value only three days after the rainfall. Based on the measurements and climatological data, including average annual precipitation of 600 mm year(-1) with half as rain during the nominal growing season (1 May to 30 September), water balance calculations suggested E was 265 mm per growing season. (C) 1998 Elsevier Science B.V. All rights reserved. [References: 44]