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 (E-t) 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 (F-d) were measured using thermal dissipation (Granier-type) sensors in a 156-m(2) plot before and after thinning. The canopy conductance (G(c)) was calculated on the basis of E-t values. The results revealed that the F-d at the outer xylem (0-20 mm) increased remarkably, whereas the F-d at the inner xylem (20-40 mm) had no significant change after thinning. Mean stand sap flow density (Is) 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 E-t increased, particularly in the small tree class. Unlike the daily tree E-t, the daily stand E-t 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 E-t 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. G, decreased after thinning, which implies lower stand E-t and photosynthesis. G, was primarily related to the VPD and would be an effective model to predict E-t from these Japanese cypress plantations. This study provides useful information for understanding the E-t 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. (C) 2014 Elsevier B.V. All rights reserved.