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28. Estimating tree growth parameters from existing height-diameter models by K.O. Obisesana and O.J Odewole Transactions Vol. 6 (Jan., 2018), pp. 247{ 262
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Estimating tree growth parameters from existing height-diameter

models

K.O. Obisesana and O.J Odewoleb

Department of Statistics, University of Ibadan, Nigeria

Abstract. 

Diameter at breast height is one of the easily measured variables with much lesser error of

measurement when compared to tree height. This study presents ve set of existing height-diameter equa-

tions for two species of tree. These species are the gmelina, also called white beech, and the pine specie.

189 tree stands of the latter and 130 tree stands of the former were considered. A non-linear least squares

approach was adopted in estimating the growth parameters from the selected models. Curtis (1967) H-D

model performed best among the ve selected models in estimating tree growth parameters for pine specie.

This was determined by the values of RSE and AIC. The Curtis(1967) model had RSE= 2.76 and AIC=

924.29 which are the least among others. Also, the Michaelis-Menten model performed very well next to the

Curtis model for gmelina specie because both models had very close RSE and AIC. From the exploratory

data analysis carried out, it was observed that height of pine tree species increases even when the diam-

eter remains unchanged at a point. A series of tests was carried out to check if errors generated by the

selected models were normally distributed. Shapiro-Wilk and Kolmogorov-Smirnov statistic established

the normality of the residuals.

Keywords: gmelina, pine, diameter, least squares, RSE, AIC, model.

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