Modeling Stem Diameter Increment in Individual Pinus occidentalis Sw. trees in La Sierra, Dominican Republic

Abstract

One of the most common and important tree characteristics used in forest management decision-making is tree diameter-at-breast height (DBH). This paper presents results on an evaluation of two growth functions developed to model stem diameter increases in individual Pinus occidentalis Sw. trees in La Sierra, Dominican Republic. The first model was developed in order to predict future DBH (FDM) at different intervals of time and the other for predicting growth, that is, periodic annual diameter increment (PADIM). Each model employed two statistical techniques for fitting model parameters: stepwise ordinary least squares (OLS) regression, and mixed models. The two statistical approaches varied in how they accounted for the repeated measurements on individual trees over time, affecting standard error estimates and statistical inference of model parameters. Each approach was evaluated based on six goodnessof-fit statistics, using both calibration and validation data sets. The objectives were 1) to determine the best model for predicting future tree DBH; 2) to determine the best model for predicting periodic annual diameter increment, both models using tree size, age, site index and different indices of competitive status; and 3) compare which of these two modeling approaches predicts better the future DBH.OLS provided a better fit for both of the growth functions, especially in regards to bias. Both models showed advantages and disadvantages when they were used to predict growth and future diameter. For the prediction of future diameter with FDM, accuracy of predictions were within one centimeter for a five-year projection interval. The PADIM presented negligible bias in estimating future diameter, although there was a small increase in bias as time of prediction increased. As expected, each model was the best in estimating the response variable it was developed for.. However, a closer examination of the distribution of errors showed a slight advantage of the FDM against the PADIM. Based on this, it is proposed that the FDM model is used to estimate future diameter and periodic diameter increment (growth) of P. occidentalis.Additional key words: diameter growth, repeated measures, mixed models, OLS, site index, indices of competitive status. Resumen Modelando el incremento en diámetro del fuste en árboles individuales de Pinus occidentalis Sw. en La Sierra, República DominicanaUna de las características más empleadas e importantes utilizada en la toma de decisiones en el manejo forestal es el diámetro normal -DBH-de los árboles. En este artículo se presentan los resultados de la evaluación de dos funciones de crecimiento utilizadas para predecir el incremento futuro en diámetro normal (FDM) en intervalos de tiempo diferentes, y el crecimiento o incremento periódico anual en diámetro normal (PADIM) en árboles individuales de Pinus occidentalis, en La Sierra, República Dominicana. Se emplearon dos técnicas estadísticas para el ajuste de los parámetros: cuadrados mínimos ordinarios (OLS) por etapas de regresión...

Individual tree growth models for eucalyptus in northern Brazil

“…For diameter, the RMSE was less than 1 cm in all three productivity classes, a result similar to those reported by Bueno and Bevilacqua (2010). Nevertheless, the simulation of height was less accurate than the simulation of diameter, reflecting the difficulty found in fitting an ideal model to the variable height.…”

“…Bueno and Bevilacqua (2010) compared the two approaches in modeling the diameter growth of Pinus occidentalis and found that the estimates of future diameters (as used in this study) showed lower errors if directly projected by the model than those resulting from estimates using the increment in diameter. A possible justification is that the periodic increment varies significantly as a function of the environmental conditions of the study site (Garcia, 1988), which are extremely variable in northern Brazil.…”

“…However, modeling the diameter and height increment is not the only alternative for predicting tree growth, and other variables have been modeled, including future diameter and height (Bueno and Bevilacqua, 2010). All are alternative approaches to estimating the increase in stem and height size.…”

“…All are alternative approaches to estimating the increase in stem and height size. They are mathematically related, and few differences in the outcome of the modeling process are expected (Vanclay, 1994) if the assumptions regarding the error term are met (Bueno and Bevilacqua, 2010;Zhang et al, 2004).…”

Diameter Increment Modeling in an Araucaria Forest Fragment Using Cluster Analysis

“…Diameter Increment Modeling in an Araucaria Forest... Floresta e Ambiente 2018; 25(3): e20170625 presented in this research, with low coefficient of determination and high standard errors of estimation Palahí & Grau, 2003;Phillips et al, 2004;Della-Flora et al, 2004;Nebel & Meilby, 2005;Bueno & Bevilacqua, 2010;Stepka et al, 2012).…”