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

Cesar Augusto Guimarães Finger,Frederico Dimas Fleig,Noé Dos Santos Ananias Hofiço,Emanuel Arnoni Costa,André Felipe Hess

doi:10.1590/01047760202026022677

Cesar Augusto Guimarães Finger, Frederico Dimas Fleig + Show 3 more

Open Access

https://doi.org/10.1590/01047760202026022677

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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 (R2 = 0.9183; RMSE = 0.558; AIC = -1234.8; BIC = -1224.9). The inclusion of the variables dominant height (h100, m), basal area (G, m2.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.

Highlights

The forest sector in Mozambique figures among the most important economic activities in the country, representing around 3.8% of the Gross Domestic Product (GDP) originated in the primary production, corresponding to 570 million US dollars in 2019 (WORLD BANK, 2020)
Forest plantings are concentrated mainly in Eucalyptus spp. and Pinus spp. with various purposes including cellulose, timber, lampposts, demand of vegetable energetic biomass, which has grown over the years (Bila and Issufo, 1994; FAO, 2001; Coetzee and Alves, 2005; MINAG, 2009; Overbreek et al, 2012; MITADER, 2016)
Maiden, which has been largely cultivated by the forest industry and small rural owners throughout the country, associated to the good performance of plantings, easy adaptation to the environment, quick growth in different sites and good timber quality (Willan, 1981; Chitará, 2003; Shimizu, 2006; MINAG, 2009; MaússeSitoe et al, 2016; Guedes et al, 2016)

Summary

Introduction

The forest sector in Mozambique figures among the most important economic activities in the country, representing around 3.8% of the Gross Domestic Product (GDP) originated in the primary production, corresponding to 570 million US dollars in 2019 (WORLD BANK, 2020). In order to promote the growth and investment of the forest sector in the country, the government of Mozambique has created and approved the National Strategy for Reforesting, whose objective was to develop silviculture aiming to encourage the increase of cost-effective commercial and industrial plantings, on a competitive and sustainable basis from the economic, social and environmental perspective (MINAG, 2009). The government expectation is to increase the areas of commercial forest planting from the current 64,000 ha to 1,000,000 ha in 2030 For this implementation, investments around 50 million US dollars will be necessary (Chitará, 2003; Nhantumbo and Salomão, 2010; Nhantumbo et al, 2013; MITADER, 2016), which need to be properly managed with an adequate longterm planning (MITADER, 2018)

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