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Models for Tree Taper Form: The Gompertz and Vasicek Diffusion Processes Framework

Agriculture Academy, Vytautas Magnus University, Universiteto g. 20-214, Akademija, Kaunas 53361, Lithuania
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Symmetry 2020, 12(1), 80; https://doi.org/10.3390/sym12010080
Received: 4 December 2019 / Revised: 23 December 2019 / Accepted: 29 December 2019 / Published: 2 January 2020
In this work, we employ stochastic differential equations (SDEs) to model tree stem taper. SDE stem taper models have some theoretical advantages over the commonly employed regression-based stem taper modeling techniques, as SDE models have both simple analytic forms and a high level of accuracy. We perform fixed- and mixed-effect parameters estimation for the stem taper models by developing an approximated maximum likelihood procedure and using a data set of longitudinal measurements from 319 mountain pine trees. The symmetric Vasicek- and asymmetric Gompertz-type diffusion processes used adequately describe stem taper evolution. The proposed SDE stem taper models are compared to four regression stem taper equations and four volume equations. Overall, the best goodness-of-fit statistics are produced by the mixed-effect parameters SDEs stem taper models. All results are obtained in the Maple computer algebra system.
Keywords: asymmetric Gompertz process; symmetric Vasicek process; tree stem taper; mountain pine asymmetric Gompertz process; symmetric Vasicek process; tree stem taper; mountain pine
MDPI and ACS Style

Narmontas, M.; Rupšys, P.; Petrauskas, E. Models for Tree Taper Form: The Gompertz and Vasicek Diffusion Processes Framework. Symmetry 2020, 12, 80.

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