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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Biomass additivity is a desirable characteristic of a system of equations for predicting components and total biomass, since equations independently adjusted generate biologically inconsistent results. The aim of this study was to fit and compare three methods for modelling biomass: (i) total biomass individual regression, (ii) total biomass regression function calculated as the sum of separate biomass components, and (iii) simultaneous equations of biomass components based on Nonlinear Seemingly Unrelated Regression. A total of 208 trees of Eucalyptus dunnii and Eucalyptus grandis were harvested and destructively sampled to record above-ground biomass. Results indicate that a system of equations adjusted by simultaneous equations provides accurate biomass estimations, guaranteeing additivity. This model system showed good fit and good prediction performance, given that the correlation coefficient was higher than 97 % for total above-ground biomass, for both species; whereas root mean square error was 23.9 kg and 30.2 kg for E. grandis and E. dunnii, respectively. A system of biomass equations was developed for each eucalyptus species, such that the sum of the estimations of the biomass components equaled the estimate of above-ground biomass. Results showed that the systems of equations have high potential for improving the accuracy of individual tree above-ground biomass estimates for both species.

SUMMARYThe aim of this study was to compare the accuracy of Weibull, reverse Weibull, S B Johnson, Gamma and Beta distributions, fitted with the method of moments and maximum likelihood, for describing diameter distributions in stands of Pinus taeda, Eucalyptus globulus, and Eucalyptus dunnii in Uruguay. Data from 429 permanent plots of P. taeda, 185 plots of E. globulus and 271 plots of E. dunnii were used. To compare the quality of fit for the probability distribution function (pdf), the Kolmogorov-Smirnov and Reynolds error indices were used. The function S B Johnson presented a better fit on the plots of P. taeda, while the inverted Weibull function was more accurate for Eucalyptus species. The method of moments was more accurate than maximum likelihood.Key words: pdf, distribution, Weibull, S B de Johnson. RESUMENEl objetivo de este estudio fue comparar la precisión de las distribuciones de Weibull, Weibull reversa, S B de Johnson, Gamma y Beta, ajustadas por método de los momentos y máxima verosimilitud, para describir distribuciones diamétricas de Pinus taeda, Eucalyptus globulus y Eucalyptus dunnii en Uruguay. Se utilizaron datos de un total de 429 parcelas permanentes de P. taeda, 185 parcelas de E. globulus y 271 parcelas de E. dunnii. Para compararla calidad del ajuste de las funciones de densidad de probabilidad (fdp) se utilizaron la prueba de Kolmogorov-Smirnov y el índice de error de Reynolds. La función S B de Johnson presentó un mejor ajuste en las parcelas de P. taeda, mientras la función Weibull reversa fue más precisa para las especies de Eucalyptus. El método de los momentos resultó con mayor precisión que el método de máxima verosimilitud.Palabras clave: fdp, distribución, Weibull, S B de Johnson. INTRODUCCIÓNConocer el número de árboles correspondiente a cada clase diamétrica de un rodal es de gran utilidad para el planeamiento y manejo de plantaciones, ya que permite estimar la variabilidad entre individuos, los posibles productos a obtener y, por lo tanto, el valor de la plantación. Las funciones de densidad de probabilidad (fdp) son utilizadas en el ámbito forestal para estimar la probabilidad de ocurrencia de un número de individuos y la probable distribución que presentará según sus diámetros, describiendo en términos matemáticos la estructura del rodal (Vallejos et al. 2004).Dentro de las fdp más utilizadas se destacan las funciones de S B de Johnson, Weibull, Weibull reversa, Beta y Gamma, siendo las distribuciones de Weibull y S B de Johnson las más empleadas debido a una mejor calidad de ajuste (Vanclay 1994). Sanquetta et al. (2014) trabajaron con las funciones Gamma, Log Normal, Normal y Weibull (dos y tres parámetros), para describir las distribuciones diamétricas de Acacia mearnsii De Wild.. La función de Weibull es ampliamente utilizada en el ámbito forestal, su versión reversa (Kuru et al. 1992, Xu et al. 1992, en la cual el origen de la curva de distribución diamétrica se cambia del diámetro a la altura del pecho (DAP) mínimo al máxi-mo, presenta como ventajas: a) mayor fac...

SUMMARYThe increasing forested area in Uruguay facilitates the establishment of exotic bark and ambrosia beetles. In 2009, the first infestation of bark beetles was officially recorded. The outbreak included Hylurgus ligniperda, Cyrtogenius luteus and Orthotomicus erosus. The objective of this study was to describe and compare the seasonal flight activity and development time of bark beetles in Pinus taeda commercial stands. Flight activity was monitored by placing interception traps from July 2012 to July 2013. Every 15 days, beetles were collected. Development time was assessed with sets of trap logs from June 2013 to June 2014 during every season. A fortnight after the presence of colonization signs was verified, trap logs were taken to the lab to be incubated. Among the three species of bark beetles captured, H. ligniperda was the most abundant, representing 57 % of the total captures, followed by O. erosus (30 %) and C. luteus (12 %). Hylurgus ligniperda was captured throughout the monitoring period, showing flight peaks during fall and winter. On the other hand, captures of O. erosus were recorded mostly during spring and summer. Cyrtogenius luteus was captured exclusively during high temperature periods. For all species recorded, log colonization date varied through seasons matching the flight period. Incubation time was strongly influenced by temperature, with shorter generations in high temperature periods. Correspondingly, differences in the duration of the subcortical phase were observed for the three species. Our study provided valuable information that can be used to adjust pruning and thinning schedules by forestry companies.Key words: bark beetles, flight phenology, commercial pine tree, Uruguay. RESUMENEl incremento de área forestada en Uruguay facilita el establecimiento de escarabajos de corteza y de ambrosia exóticos. En 2009 se reportó el primer brote de escarabajos de corteza, que incluyó a Hylurgus ligniperda, Cyrtogenius luteus y Orthotomicus erosus. El objetivo del trabajo fue describir y comparar la actividad estacional de vuelo y el tiempo de desarrollo de estos insectos en plantaciones comerciales de Pinus taeda. La actividad de vuelo fue monitoreada mediante trampas de intercepción (julio 2012 a julio 2013) y recolección cada 15 días. El tiempo de desarrollo se evaluó utilizando trozas cebo durante cada estación (junio 2013 a junio 2014). Quince días después de observados los signos de colonización, las trozas cebo fueron llevadas al laboratorio para incubación. Hylurgus ligniperda fue la especie más abundante (57 % de las capturas), seguida por O. erosus (30 %) y C. luteus (12 %). Hylurgus ligniperda fue capturado durante todo el período de monitoreo, con picos de vuelo durante otoño e invierno. Orthotomicus erosus fue registrado mayormente durante primavera y verano. Cyrtogenius luteus fue capturado exclusivamente durante períodos de alta temperatura. Para estas especies, la fecha de colonización de trozas varió entre estaciones, concordando con el período de vuelo. El tiempo de inc...

Native grasslands are the main source of food for livestock in the Campos region of South America. These forage resources are heterogeneous in species composition, grazing management, and soil fertility within a context of variable climate, all of which are factors that affect forage crude protein content over time and space. Despite the importance of protein in livestock nutrition, there is a gap in the knowledge of how fertilisation, sward height, and soil water availability influence the crude protein content of these grasslands. We used data from a long-term fertilisation experiment to construct a structural model aiming to identify the main factors influencing forage crude protein content of a basaltic native grassland in northern Uruguay. The structural model revealed that both fertilisation and the increase in soil water availability (through the improvement of the nitrogen content of green leaves) are the main pathways by which forage crude protein content increases. This new approach (which identifies and quantifies the main factors that drive forage crude protein content of native grasslands) could be used to support prediction models for forage protein content in order to improve grazing livestock nutrition of Campos native grasslands.

The risk assessment of urban trees is a challenge that must be addressed by many cities, in consideration of their climatology, management and spatial heterogeneity. Since these trees are in stages of aging, added to bad practices, inadequate selection and establishment, amongst others, their early elimination, and hence the loss of the ecosystem services they provide, is being promoted. For this reason, two tree risk assessment methods were developed to be applied in a complementary manner in urban parks, one basic visual (BV) and the other detailed visual (DV), both structured with the components of likelihood of failure, likelihood of impact, consequence and risk rating, being analyzed qualitatively and semi quantitatively. The methods were applied in 24 trees of Eucalyptus and Tipuana genus by two groups of assessors, experienced and inexperienced, totaling 192 assessments. Results were analyzed with a linear mixed model (LMM), which showed differences between both methods for the likelihood of failure, where the assessment of branches turned out to be the attribute with the highest impact. The methods proved to be suitable to be used in a complementary manner, since BV turns out to be efficient when it is necessary to assess a large number of trees. DV turned out to be more effective, since it was able to identify more precisely the attributes of the tree that must be considered for adequate risk mitigation and management. Therefore, their combined use is recommended for risk assessment in trees established in parks.