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.

RESUMO: O sucesso da implantação de florestas depende da disponibilidade e da qualidade de mudas. O objetivo desta pesquisa é avaliar a possibilidade do uso de mudas de toco e mudas de raiz nua de Cedrela fissilis obtidas de regeneração natural para plantio à campo. Nós usamos Modelos Lineares Generalizados para avaliar sobrevivência e Modelos Hierárquicos para avaliar crescimento em altura durante um ano após o plantio. O diâmetro do colo (DC) inicial e tratamento (mudas de raiz nua ou de toco) afetaram a sobrevivência e o crescimento. Mudas de toco e mudas com maior DC inicial apresentaram maiores probabilidades de sobrevivência e maior crescimento. A melhor qualidade de mudas no tratamento de mudas de toco é devido à maior tolerância ao stress hídrico. Mudas de toco com DC inicial maior que 1 cm tiveram probabilidade de sobrevivência acima de 80%, enquanto mudas de raiz nua pequenas tiveram probabilidade de sobrevivência média de 20%. As mudas de toco cresceram quatro vezes mais que mudas de raiz nua. A utilização da regeneração natural de C. fissilis como fonte de mudas de toco pode ser uma alternativa barata para projetos de restauração florestal e plantios de enriquecimento.

ABSTRACT The success of forest creation relies on seedling availability and quality. The aim of this research is to assess the possible use of rootstock and bare-root seedlings of Cedrela fissilis obtained from natural regeneration for direct field planting. We used Generalized Linear models to assess survival and Hierarchical Models to assess height growth over one year after planting. Initial root-collar diameter (RCD) and treatment (rootstock or bare-root) affected survival and growth. Rootstock and larger seedlings presented higher levels of survival and growth. Higher seedling quality in the rootstock treatment is due to higher water stress tolerance. Rootstock seedlings with more than 1 cm of initial RCD had over 80% of survival probability, while small bare-root seedlings had mean survival probability as low as 20%. Rootstock seedlings grew as much as fourfold more than bare-root. Using natural regeneration of C. fissilis as a source of rootstock seedlings may be a cheap alternative for forest restoration and enrichment planting projects.

Existem basicamente três diferentes métodos de estimativa de volume de árvore individuais: uso de fator de forma, modelos de volume e funções de afilamento, que apresentam resultados diferentes quanto à precisão de variáveis. A comparação entre os métodos foi o objetivo desta pesquisa e, para tal, foram medidas 45 árvores de Eucalyptus grandis provenientes de primeiro desbaste. Os métodos foram submetidos a testes para verificar a robustez das estimativas geradas. Os fatores de forma não se mostraram robustos em suas estimativas. A função de afilamento testada precisou de métodos de regressão especiais para que suas estimativas fossem robustas. A utilização de equação de dupla entrada foi o método mais eficiente para a determinação de volume.

Essentially, there are three contrasting methods for volume estimation of single trees: the use of a form quotient, volume equations, and taper functions, which produce different results in estimative precision. The aim of this study was to compare these methods. To this end, 45 trees of Eucalyptus grandis from a first thinning were measured. The methods estimates were subjected to robustness tests. Form quotients were not robust estimators of total volume. The taper function tested needed special regression methods to achieve robustness. The use of volume equations of two independent variables was the most effective method for volume estimation.