Hiroyuki Matsunaga, Naoko Matsuo, Takahisa Nakai, Natsuko Yoshifuji, Nobuaki Tanaka, Katsunori Tanaka, Chatchai Tantasirin
Received 2021/04/19, Accepted 2021/05/20, Published 2021/07/20

Hiroyuki Matsunaga¹⁾, Naoko Matsuo¹⁾, Takahisa Nakai¹⁾, Natsuko Yoshifuji²⁾, Nobuaki Tanaka³⁾, Katsunori Tanaka⁴⁾, Chatchai Tantasirin⁵⁾

1) Graduate School of Bioresources, Mie University, Japan
2) Forestry and Forest Products Research Institute, Japan
3) The University of Tokyo Hokkaido Forest, The University of Tokyo Forests, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan
4) GRID INC., Japan
5) Faculty of Forestry, Kasetsart University, Thailand

TextChanges 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 hypothesized that these SC changes were caused by water absorption 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 laboratory 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.
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