The effect of strip thinning on tree transpiration in a Japanese cypress (Chamaecyparis obtusa Endl.) plantation.

This study analyzes the effect of strip thinning on tree transpiration (Et) in a dense and mature Japanese cypress (Chamaecyparis obtusa Endl.) plantation in central Japan. Strip thinning, which removed 50% of stems, was conducted in a headwater basin in October 2011. Xylem sap flow densities (Fd) were measured using thermal dissipation (Granier-type) sensors in a 156-m² plot before and after thinning. The canopy conductance (Gc) was calculated on the basis of Et values. The results revealed that the Fd at the outer xylem (0-20 mm) increased remarkably, whereas the Fd at the inner xylem (20-40 mm) had no significant change after thinning. Mean stand sap flow density (JS) values were higher in the post-thinning period than in the pre-thinning period, and the differences significantly increased with increasing vapor pressure deficit (VPD) values. Furthermore, the daily single tree Et increased, particularly in the small tree class. Unlike the daily tree Et, the daily stand Et decreased from 1.29 ± 0.60 to 1.00 ± 0.40 mm d-1 during the growing season or decreased from 1.23 ± 0.48 to 0.74 ± 0.42 mm d-1 on the annual scale. The total stand Et decreased by 23.0%, from 214.9 to 165.5 mm, during the growing season or decreased by 38.3%, from 441.0 to 272.1 mm, on the annual scale. Gc decreased after thinning, which implies lower stand Et and photosynthesis. Gc was primarily related to the VPD and would be an effective model to predict Et from these Japanese cypress plantations. This study provides useful information for understanding the Et responses at individual tree and stand levels to strip thinning and contributes to obtaining a thorough understanding of the change in tree water use under different management strategies. [ABSTRACT FROM AUTHOR]