Influence of evaporation from the forest floor on evapotranspiration from the dry canopy

Evaporation from the forest floor ( Ef ) of a secondary broad‐leaved forest was monitored for 1 year at 30 min intervals using a closed chamber system. The diurnal and seasonal variation of Ef and forest structure were analysed for days undisturbed by rainfall. The diurnal change in Ef reached a maximum at about 14:00 and gradually decreased towards midnight along with the vapour pressure deficit ( D ). Although Ef comprised about 20% of evapotranspiration from the dry canopy ( Et ), it had only a small influence on diurnal evaporation efficiency (β) characteristics above the canopy because its diurnal range was much smaller than that of Et . Although leaf emergence and leaf fall clearly affected available energy ( Ae ) beneath the canopy, the influence was not clear with Ef . In contrast, seasonal variation in Ef was strongly correlated with D and Ae above the canopy, and the determination coefficient ( R 2 ) changed with the Bowen ratio ( B ). At night, Et was almost equal to Ef when the friction velocity ( u *) ranged between 0·2 and 0·4 m s −1 . The ratio of Ef to Et was exponentially correlated with leaf area index ( LAI ) when the soil was not dry. The ratio of Ef to Et was mainly influenced by LAI and soil moisture, but the existence of understory vegetation did not have a strong influence. Copyright © 2008 John Wiley & Sons, Ltd.