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Tree transpiration can cause a rapid decrease of moisture content(MC)in the tree trunk when tree is felled.In this study,eight poplar trees(Populus alba L.var.pyramidalis)were felled and laid in vertical,45o slant and horizontal position on the ground.MCs were measured at the various locations and different times during the drying period.The transpirational rate and stomatal conductance to vapor were measured using leaf gas-exchange method.The transpiration rate of trees in 45o slant position was relative higher as well as a relative high decrease of MC.The accumulated transpiration rate was a cubic function of MC changes of trees,which existed an inflection point for all trees in the MC of about 42%.Stomatal transpiration in a positive correlation with the moisture loss was the major way for losing water at the first 3 to 5 days after trees were felled.Moisture reducing rate of fell trees were affected by air conditions.It had a positively correlated to air RH.However,it was negatively related to air temperature.When the transpirational drying occurred,the temperature difference between air temperature and leaf surface temperature was around 1 to 3 ℃.