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Abstract: We measured evapotranspiration in an eastern Siberian boreal forest, in which the understory was cowberry and the overstory was larch, during the entire growing seasons of 2005 and 2006. We compared evapotranspiration from the understory vegetation above the forest floor E U with evapotranspiration from the whole ecosystem above the overstory canopy E O. The E U/E O ratio had a seasonal trend with a flat-bottomed U-shape during the growing season (4 May–30 September). High-E U/E O ratios at the beginning and end of the growing season were observed because larch, one of the two sources of E O, was a deciduous tree, while the understory was the evergreen cowberry. The mean daily E U values during the foliated period of larch (1 June–31 August) were 0.8 and 0.9mmday−1, or 51.4 and 51.8% of E O in 2005 and 2006, respectively. The understory vegetation was one of the most important components of the hydrologic cycle in this forest. A significant amount of E U was caused by plant physiological control, due to the aerodynamic conductance, which was much larger than the surface conductance, leading to a smaller decoupling coefficient. We found that 71% of E U was caused by the vapour pressure deficit above the forest floor. [Copyright &y& Elsevier]

• ET and its components were measured separately in a tropical dry deciduous forest. • Understory ET is important, contributing 35% to whole-ecosystem ET. • Overstory LAI strongly affects the proportion of understory ET relative to whole ET. • Underestimates of stand transpiration can be corrected with calibrated coefficients. The water balance of tropical dry deciduous forests is less well understood than some other forest ecosystems. To help close this knowledge gap, we separately measured the evapotranspiration from the whole ecosystem (ET W), transpiration (TR) and interception loss (IL) from overstory trees, and evapotranspiration from the understory vegetation (ET U) in a tropical dry deciduous forest in Cambodia. It was found that ET W was equivalent to 73.7% of rainfall (P) at the annual scale. In the dry season, ET W corresponded to 120.1% of P , which indicates the utilization of soil water replenished during the wet season. The sum of transpiration estimated by the thermal dissipation (TD) method with the original coefficient (TR G), IL , and ET U was smaller than ET W, except for the middle of the dry season, due to an underestimation of TR G. Although recently reported calibration coefficients can reasonably correct TR G , future calibrations of the TD method are highly recommended for the precise evaluation of single-tree-scale transpiration in tropical dry forests. The annual contribution of the understory vegetation to ET W (ET U / ET W) was 34.6%, leading to the conclusion that the understory vegetation cannot be ignored when trying to gain a comprehensive understanding of the hydrologic cycle in tropical dry forests. The seasonal variations in ET U / ET W were mainly controlled by the leaf area index (LAI) of overstory trees, resulting from the overall stability of ET W and decreasing trend of ET U with increasing LAI in the wet season, with the opposite holding true in the dry season, i.e., decreasing ET W with the decline of LAI and less variations of ET U. Thus, LAI influenced both the seasonality and the annual contribution in ET U / ET W , exerting a notable influence on hydrological cycling in this forest. [ABSTRACT FROM AUTHOR]

Abstract: We measured sensible and latent heat fluxes (H and λE) in five forests located in boreal, cool-temperate, and warm-temperate zones of the Far East concurrently over several years to clarify their energy-consumption characteristics and the variation in and factors controlling evapotranspiration. The consumption of energy for evapotranspiration was larger at the southern sites than at the northern sites, and evapotranspiration in summer (July–August) was larger (average 2.9mmday−1) for temperate forests than for boreal forests (average 1.7mmday−1). Differences in energy-consumption characteristics between the forest types (e.g., deciduous vs. coniferous) were not as distinct as those by location. This inter-locational difference resulted from differing evapotranspiration restrictions caused by land-surface characteristics, rather than differing atmospheric evaporation demand. [Copyright &y& Elsevier]

Abstract: The dependence of surface conductance G s on various variables in a forest environment is important for characterising the spatiotemporal variations of water, energy and CO2 exchange between the forest and the atmosphere. Using a Jarvis-type model, we examined the variation of G s in five different mature forests from three climate zones (boreal, cool- and warm-temperate) in the Far East. First, we applied the model using summertime G s data from each site separately (within-site analysis). We evaluated the maximum surface conductance G smax and parameters related to the response of G s to the environments. We found that these values differed among the locations. Second, we applied the model for pooled G s data from all the sites and calculated a common parameter set (pooled analysis). In the pooled model, the difference in the observed G smax among the sites was expressed as a function of soil water content and the leaf area index. In addition, the responses of G s to radiation, vapour pressure deficit and air temperature in different forests were also closely represented by common response functions. As a result, the pooled model could estimate the variation of G s at each site using one parameter set with similar precision to the within-site models. These results suggest that the surface conductance of the various mature forests had the same maximum value and response properties, although we were not able to verify this. Our new parameterisation concept for pooled G s data should be effective for simultaneous evaluations of the water, energy and CO2 exchanges of forests over wide regions. [Copyright &y& Elsevier]