Nonlinear mixed-effects modeling of variable-exponent taper equations for lodgepole pine in Alberta,Canada |
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Authors: | Yuqing Yang Shongming Huang Guillermo Trincado Shawn X. Meng |
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Affiliation: | (1) Biometrics Unit, Forest Management Branch, Alberta Department of Sustainable Resource Development, 8th Floor, 9920-108 Street, Edmonton, AB, T5K 2M4, Canada;(2) Instituto de Manejo Forestal, Universidad Austral de Chile, Box 567, Valdivia, Chile |
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Abstract: | Four variable-exponent taper equations and their modified forms were evaluated for lodgepole pine (Pinus contorta var. latifolia Engelm.) trees in Alberta, Canada. A nonlinear mixed-effects modeling approach was applied to account for within- and between-tree variations in stem form. Even though a direct modeling of within-tree autocorrelation by a variance–covariance structure failed to achieve convergence, most of the autocorrelation was accounted for when random-effects parameters were included in the models. Using an independent data set, the best taper equation with two random-effects parameters was chosen based on its ability to predict diameter inside bark, whole tree volume, and sectioned log volume. Diameter measurements from various stem locations were evaluated for tree-specific calibrations by predicting random-effects parameters using an approximate Bayesian estimator. It was found that an upper stem diameter at 5.3 m above ground was best suited for calibrating tree-specific predictions of diameter inside bark, whole tree volume, and sectioned log volume. |
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Keywords: | Kozak’ s variable-exponent taper model Mixed-effects models Lodgepole pine Model calibration |
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