A Model for Predicting the Vertical Distribution of Cross-sectional Area Increments in Hinoki Cypress Stems

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概要

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• To confirm that the vertical distribution of stem cross-sectional area increment (CSAI) for Hinoki cypress can be described by two straight lines derived from three tree attributes: sunny crown length (CL), stem volume increment (SVI), and CSAI at the base of the sunny crown (CSAI_<(CL)>), two model were constructed and compared. One is the unrestricted model for describing the vertical distribution of CSAI by two straight lines (CSAI_<(z)>=az and CSAI_<(z)>=b+cz where CSAI_<(z)> is the CSAI at a distance z from the apex, and a, b, and c are parameters), and the other is the restricted model imposed two restrictions on the unrestricted model: (i) the two straight lines intersect at the coordinates (CL, CSAI_<(CL)>, (ii) the area of the diagram formed from the two straight lines is equal to the SVI. AKAIKE's information criterion (AIC) and root mean square error (RMSE) were used to identify the better model. Data were obtained from 112 sample trees selected in six pure stands of even-aged Hinoki cypress. Parameters in the unrestricted model were estimated from CSAI dataset using least-squares method, and those in the restricted model were calculated from measurements of CL, SVI, and CSAI_<(CL)> for each sample tree. The unrestricted model fit well to CSAI observations, indicating that the vertical distribution of CSAI can be described by two straight lines. The AIC value for the restricted model was smaller than that for the unrestricted model, indicating that the restricted model is superior to the unrestricted model in describing the vertical distribution of CSAI. Although the restricted model returned a larger RMSE value than the unrestricted model did, the difference in RMSE was small. In conclusion, the vertical distribution of CSAI for Hinoki cypress can be described by two straight lines derived from CL, SVI, and CSAI_<(CL)>.

著者

• Waguchi Yoshiaki

  Nara Forest Res. Inst. Nara Jpn

• Ueda Masafumi

  Laboratory Of Forest Ecology Graduate School Of Agriculture Kyoto Prefectural University

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• A Model for Predicting the Vertical Distribution of Cross-sectional Area Increments in Hinoki Cypress Stems
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