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This study presents a yield model for aboveground biomass production from three species the Eucalyptus in northern and western regions of Uruguay, based on sampling records from intensive crop plantations. High-density eucalyptus plantations represent a forestry alternative for the production of forest biomass. This work assessed the survival and growth of three eucalyptus species (Eucalyptus benthamii Maiden & Cambage, E. dunnii Maiden and E. grandis Hill ex Maiden) planted at densities of 2220, 3330, 4440 and 6660 trees ha−1, for a period of 57 months in northern (Tacuarembó) and western (Paysandú) regions of Uruguay. Linear and logarithmic equations of individual volume were fitted by site and species. The survival of E. grandis, E. benthamii and E. dunnii was not related to planting density, and the highest mortality values occurred in Tacuarembó. The effects of competition among trees were more evident at the highest planting density for E. grandis. In all species, the reduction in diameter was more marked than that of height, as planting density increased. Tree volume showed the same trend, and this was higher with higher planting densities. At Tacuarembó, the volume was the highest with E. benthamii at 6660 trees ha−1 (416.4 m3 ha−1), and, at Paysandú, the highest production was obtained with E. grandis (370.7 m3 ha−1) and with the densities of 4440 and 6660 trees ha−1 (305.9 and 315.3 m3 ha−1, respectively). With all species and planting densities, there was an increase in the accumulated volume during the 57-month study period; however, growth curves indicate that the maximum production per unit time and, therefore, the optimum harvest time occurred at 48 months. In this work, it has been shown that the use of intensive short-rotation plantations of eucalyptus for the production of biomass in Uruguay is suitable in soils prioritized for forestry.

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Biogeosciences and Forestry Biogeosciences and Forestry Using soil-based and physiographic variables to improve stand growth equations in Uruguayan forest plantations Cecilia Rachid-Casnati (1) , Euan G Mason (2) , Richard C Woollons (2) Information provided by traditional growth models is an essential input in decision making processes for managing planted forests. They are generally fitted using inventory data guaranteeing robustness and simplicity. The introduction of explanatory factors affecting tree development in age-based sigmoidal growth and yield equations attempts not only to improve the quality of predictions, but also to add useful information underpinning forest management decisions. This study aimed to assess the use of the following soil-based and physiographic predictors: potentially available soil water (PASW), elevation (Elev), aspect (α) and slope (β) in a system of empirical stand equations comprising: dominant height (hdom), basal area (G), maximum diameter at breast height (dmax), and standard deviation of diameters (SDd). Augmented models were compared with the base models through precision and bias of estimations for two contrasting species: Pinus taeda (L.), and Eucalyptus grandis (Hill ex. Maiden), planted commercially in Uruguay. Soil-based and physiographic information significantly improved predictions of all the state variables fitted for E. grandis, but just hdom and G for P. taeda. Only PASW was consistently significant for the augmented models in P. taeda and E. grandis, while the contribution of other predictors varied between species. From a physiological point of view, predictors on the augmented models showed consistency. Models with such augmentation produced decrease of errors between 3 to 10.5%, however decreases in the prediction errors calculated with the independent dataset were lower. Results from this study contributed to add information to the decision-making process of plantations' management.

Se compararon diferentes ecuaciones de volumen y ahusamiento, evaluando en especial el uso de ecuaciones compatibles, con el objetivo de ser utilizadas en inventarios forestales o sistemas de apoyo a la toma de decisiones. Utilizamos datos de 863 y 932 árboles correspondientes a las especies Pinus taeda y Eucalyptus grandis respectivamente, provenientes de plantaciones situadas en los departamentos de Rivera, Tacuarembó, Paysandú y Río Negro en Uruguay. En general, los rankings de ecuaciones fueron consistentes para ambas especies; para la estimación de volúmenes las ecuaciones con mayor ajuste fueron aquellas presentadas por Clutter et al. (1983) y Schumacher y Hall (1933) para P. taeda y E. grandis respectivamente, mientras que para la descripción de perfiles el modelo que mejor se ajustó fue la ecuación de exponente variable presentada por Muhairwe (1999) y modificada por Methol (2001). La mejor ecuación de ahusamiento tipo compatible rankeó en posiciones intermedias para ambas especies, representando igualmente una opción satisfactoria para aquellos productores forestales que deseen usufructuar las ventajas de este tipo de ecuaciones.