Evaporation from an eastern Siberian larch forest

Total forest evaporation (lambda E), understorey evaporation, and environmental variables were measured on nine summer days under different weather conditions in a 130-year-old stand of Larix gmelinii (Rupr.) Rupr. trees located 160km south of Yakutsk in eastern Siberia, Russia (61 degrees N, 128 degrees E, 300m above sea-level (a.s.l.)). Tree and broad-leaved understorey vegetation one-sided leaf area indices were 1.5 and 1.0, respectively. Agreement of lambda E and sensible heat flux (H), both measured by eddy covariance, and the available energy (R-a) was generally good: (H + lambda E) = 0.83R(a) + 9W m(-2) with r(2) = 0.92 for 364 half-hour periods and the mean +/- 95% confidence limit was 129 +/- 17 for(H + lambda E) and 144 +/- 19 for R-a. Daily E was 1.6-2.2mm, less than half of the potential evaporation rate and accounting for 31-50% of R-a, with the lowest percentage on clear days. A perusal of the sparse literature revealed that average daily E of boreal coniferous forest during the tree growing season (1.9 mm day(-1) for this study) is relatively conservative, suggesting that low evaporation rates are a feature of this biome's energy balance. Using the Penman-Monteith equation, the maximum bulk-surface conductance (G(smax)) was 10 mms(-1). E and G(s) were regulated by irradiance, air saturation deficit, and surface soil water content during a week-long dry period following 20 mm rainfall, From lysimeter measurements, 50% of E emanated from the understorey at a rate proportional to R-a. Based on the measurements and published climatological data, including average annual occurrence of a late summer-autumn soil water deficit, and annual runoff of 44 mm by snowmelt. (C) 1997 Elsevier Science B.V.