Evapotranspiration assessment of a mixed temperate forest by four methods: Eddy covariance, soil water budget, analytical and model

摘要

In forest ecosystems, assessment of evapotranspiration fluxes (ET) and distinction of its components, i.e. tree transpiration (T), rainfall interception (I), and soil plus understory evapotranspiration (ETu), are a major issue. At the Vielsalm Terrestrial Observatory in Belgium (VTO, Integrated Carbon Observation System network, ICOS), covered by a mixed forest of broadleaved (mainly Fagus sylvatica L.) and coniferous species (mainly Pseudotsuga menziesii [Mirb.] Franco), the water vapor fluxes have been continuously measured by eddy covariance since 1996, without distinction of its components. Widely validated for CO2 fluxes, water vapor fluxes measured by eddy covariance still lack validation, particularly in mixed and/or heterogeneous stands. During 2010-2011, three other methods to assess ET were implemented, in order to inter-validate them and to disentangle species specific ET into its components. These methods were: (i) the analytical method which relies on measurement of each elementary flux, i.e. tree transpiration, interception loss and evapotranspiration of soil plus understory (ETA); (ii) the soil water budget method (ETS) and (iii) modeling of stand ET (ETM).