Characteristics of Parameters in Power Equation Representing Sunny Crown Profile of Hinoki Cypress Tree

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Characteristics of parameters in power equation (r=azb where r is the crown radius (m) at a given distance z (m) from the tree apex, and a and b are parameters) for representing the sunny crown profile were examined for Hinoki cypress (Chamaecyparis obtusa ENDL.). Three hypothetical models were constructed; Model 1: the values of a and b are unique for each tree, Model 2: the value of b is common to all trees, Model 3: the values of a and b are common to all trees. The three models were compared using AKAIKE'S information criterion (AIC) and root mean squared error (RMSE). Data were obtained from 112 sample trees selected in six pure stands of even-aged Hinoki cypress. Model 3 was inferior to the other two models in terms of AIC and RMSE. Model 2 was superior to Model 1 in terms of AIC. Although Model 2 gave a larger value of RMSE than that of Model 1, the difference was only 0.006m. When the profile of the sunny crown of a Hinoki cypress tree is represented by the power equation, we can assume that parameter b is invariant between trees and that parameter a varies from tree-to-tree.