Abstract
The growth of a tree or a forest settlement is of great value to a forest enterprise, because many decisions are directly dependent of this information, for instance, determining the optimal cutting age. This study aims to apply a new class of models to fit growth curves for diameter and height of Eucalyptus grandis X Eucalyptus urophylla seedling data. Data were collected from a trial conducted in a green house at the Natural Resources Department at School of Agriculture, Botucatu, S?o Paulo, Brazil. The experiment’s design was completely randomized with eight treatments and four replications. In this trial, the growth variables referring to the height and the diameter were evaluated, being measured five and four times, respectively. The methodology was carried in a mixed longitudinal model using a new approach based on Box-Cox Normal (BCN) distribution, and comparisons with this model were made assuming normality of the data. The results revealed that the BCN mixed model provided similar results to the standard model in order to estimate growth curves; however, the BCN model was the best result according to Akaike criterion, considering the slight asymmetry in the data set. This approach is of great interest in case of outliers and robust procedures for parameter estimation.
Highlights
The results revealed that the Box-Cox Normal (BCN) mixed model provided similar results to the standard model in order to estimate growth curves; the BCN model was the best result according to Akaike criterion, considering the slight asymmetry in the data set
The estimated means were smaller than the estimated median. This result was expected due to the slight asymmetry presented in the data
This paper presented a new approach based on the Box-Cox Normal distribution to analyse growth data
Summary
The survival, the establishment, the cultivation frequency and the early forest growth are necessary ratings for the forest enterprise success, which is directly related to the seedling quality at planting (Gomes, 2001). In this context, the height/diameter relation is one of the features used to evaluate the forest seedling quality, because it reflects the reserve accumulation, a greater resistance and better fixation in the soil (Carneiro, 1995). The average height and the base diameter are two parameters, which show the high plant quality considered relevant to forestry industry companies (Gomes et al, 1996)
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