Absorption and emission of water vapor from the bark of teak (Tectona grandis), a deciduous tree, in a tropical region during the dry season

: Changes in stem circumference (SC) were observed in teak ( Tectona grandis ) in a tropical region during the dry season after tree-ring formation had stopped. We hypothe‐ sized that these SC changes were caused by water absorp‐ tion and emission from the outer bark surface. To test this hypothesis, we measured SC, heat pulse velocity (HPV), and leaf number using time series images in a teak tree plantation in northern Thailand. We also performed labora‐ tory experiments to observe changes in the weight and thickness of teak bark blocks under various vapor pressure conditions. Increases in teak tree SC were observed after rainfall during the dry season, when defoliation was almost complete and HPV was low. The weight and thickness of the bark blocks, on which all surfaces other than the outer bark were sealed, varied with water vapor content. These results suggest that water vapor absorption and emission through the outer bark surface can affect SC during the dry season. However, SC continued to increase after the vapor pressure deficit increased, and decreased more rapidly in the tree with higher HPV, suggesting that water exchange between the xylem and inner bark also contributes to changes in SC.