Relationship between Sunny Crown Volume Increment and Stem Cross-Sectional Area Increment at Sunny Crown Base for Hinoki Cypress, and its Application

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Vertical distribution of stem cross-sectional area increment (CSAI) for hinoki cypress can be described by combination of two linear equations derived from three tree attributes: sunny crown length (SCL), stem volume increment (SVI), and CSAI at the base of sunny crown (CSAI_<SCB>). In this study, to propose a method for estimating CSAI_<SCB>, a relationship between CSAI_<SCB> and sunny crown volume increment (SCVI) was investigated. Data were obtained from 112 sample trees selected in six stands of even-aged hinoki cypress. The proportional relation can be assumed between SCVI and CSAI_<SCB>, and the relationship could be expressed by the regression equation: CSAI_<SCB>=2.88×10^<-4>SCVI. For each sampled tree, two vertical distributions of CSAI were obtained: one is the distribution obtained by using CSAI_<SCB> estimated from the regression equation, and both of SCL and SVI observations, and the other is the distribution obtained by using observations of SCL, SVI, and CSAI_<SCB>. The two distributions were compared using root mean squared error (RMSE). Although the vertical distribution obtained by using CSAI_<SCB> estimate produced a larger RMSE value than that by using CSAI_<SCB> observation did, the difference in RMSE was small. In conclusion, the assumption of the proportional relationship between SCVI and CSAI_<SCB> provides a useful approach for predicting vertical distribution of CSAI for hinoki cypress.
森林計画学会の論文