Evapotranspiration from the understory of a tropical dry deciduous forest in Cambodia.

• 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]