HEIGHT-DIAMETER RELATIONSHIPS FOR Eucalyptus grandis HILL EX. MAIDEN IN MOZAMBIQUE: USING MIXED-EFFECTS MODELING APPROACH

Abstract

HIGHLIGHTS Height-diameter model using mixed-effects was developed for Eucalyptus grandis in Mozambique. Four dominant trees and one tree randomly selected in plot were sufficient to calibrate the model. The perspective is to increase accuracy, practicality, precision of height estimations and decrease of sampling effort in forest inventories in Mozambique ABSTRACT Equations express that height-diameter relationships are used to estimate tree heights that were not measured in the plots, as well as to calculate their volumes. In this study, we modelled height for Eucalyptus grandis Hill ex. Maiden stands using nonlinear mixed effect models in Mocuba District, Central Mozambique. Models were tested from 1414 trees measured, in 40 plots with dimensions of 20 x 20 m. Model one (M1) was the best in relation to the others according to the evaluated criteria (R 2 = 0.9183; RMSE = 0.558; AIC =-1234.8; BIC =-1224.9). The inclusion of the variables dominant height (h 100 , m), basal area (G, m 2. ha-1) and mean basal area diameter (dg, m) in model 1 (M1) within the scope of mixed effect model structures that involved both fixed and random effect parameters (Model 7) provides better fitting and more precise predictions. For calibration of random effects according to plot, height measurement of at least five trees is required (four dominant trees + one tree randomly selected in plot). Our model is site-specific and its application should therefore be limited to the stands with characteristics that were the basis of this study. Further works on recalibration, validation, and verification of our model using a larger dataset collected from a wider range of species distribution will be more interesting.

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“…In contrast, Hofiҫo et al (2020) reported higher R 2 values (0.9183) and similar values in the SRME (0.558) for Eucalyptus grandis Hill ex. Maiden, when they incorporated basal area and quadratic diameter as covariates in a height-diameter model fitted with the mixed-effects modelling approach.…”

“…Given its utility for forest management, the height-diameter relationship of trees has been extensively studied under different statistical approaches, and height-diameter models have been generated for various species and growth conditions in both natural forests and plantations (Corral-Rivas et al 2014, Ercanli 2015, Corral et al 2019, Hofiҫo et al 2020, Ordaz-Ruíz et al 2020. From a silvicultural point of view, these relationships are fundamental when estimating stand growth and yield (Ferraz et al 2018).…”