Bioenergy is one of the alternatives to reduce the dependence of global energy on fossil fuels. The short rotation coppice (SRC) of eucalypt species appears as an interesting option for forest biomass production in a short time. However, the harvesting of whole trees (included the crown) in SRC systems has implications on sustainable land use. More information is required on the increase of biomass as renewable energy resource to achieve the sustainability of these crops. The main objective of this research was to evaluate the sustainable use of biomass from very high-density eucalypt plantations, managed at tropical conditions for bioenergy. To accomplish this objective, the tree was fractionated into three fractions: stem, branches, and leaves, and there was determination of the dry matter, energy yield, and nutrients export. This experiment used a short rotation coppice, a hybrid clone of Eucalyptus urophylla  Eucalyptus grandis, of 2 years old. According to the results obtained, the density planting and fertilization levels have a greater influence on the dry matter yield, energy yield, and nutrient exports. The higher density planting reaches mean values of 30.9 tonnes of dry matter per hectare (t DM ha À1) and 743.3 GJ ha À1. Considering the biomass yield and nutrients export of short rotation coppice of eucalypt, the higher density planting with the lower dose of fertilization is more indicative of sustainable use. The leaves have an important participation in nutrients export and should be retained in the soil of forest.

In Brazil, after the cycle of latex extraction, rubber plantations are reformulated and the wood of these plantings are traditionally used as a cheap source for energy purposes. Rubberwood has other uses based on the consolidated experience in Asian countries. The aim of this article was to evaluate the technological potential of the wood of two main commercial clones of Hevea brasiliensis in Brazil, RRIM600 and GT1, after the period of latex extraction. To accomplish this objective, some physical and mechanical properties of wood were analyzed. The clones had a basic density greater than 0.540 g cm -3 , low volumetric shrinkage (\10 %), and medium to high strength in compression parallel to grain ([40 MPa). According to the results obtained, rubberwood has applications in small and secondary structures, lightweight construction, and furniture industry and it can be an alternative in the Brazilian market to reduce the timber demand from native forest species.

RESUMO -Os sistemas florestais de curta rotação possuem elevada produtividade em reduzido espaço de tempo e área, entretanto poucos trabalhos enfocam a qualidade da biomassa florestal produzida nessas condições. De fato, a qualidade da matéria-prima é muito importante para alto rendimento nos sistemas energéticos. Dessa forma, este trabalho teve como objetivo estudar a madeira com casca proveniente de diferentes sistemas florestais adensados, por meio do conhecimento do poder calorífico superior e dos principais componentes químicos da madeira -lignina insolúvel, extrativos e cinzas. Adicionalmente, estudou-se o acúmulo desses componentes por árvore ao longo do tempo. As florestas clonais de Eucalyptus urophylla x Eucalyptus grandis foram plantadas em cinco espaçamentos de plantio e três níveis de adubação. Aos 18, 24 e 30 meses após o plantio, coletaram-se árvores-amostra, das quais foram separados discos da região do DAP para análises químicas. No geral, os teores de lignina insolúvel, extrativos totais e cinzas obtidos nos diferentes tratamentos estão de acordo com os encontrados na literatura e assemelham-se aos das árvores mais velhas da mesma espécie. O acúmulo dos componentes químicos por árvore foi maior em florestas menos adensadas (espaçamentos mais amplos).Palavras-chave: Madeira com casca; Eucalyptus sp.; Energia florestal. CHEMICAL ANALYSIS OF WOOD WITH BARK IN SHORT ROTATION FORESTRY SYSTEMSABSTRACT -The short rotation forestry systems have high productivity in short period of time and area, however, few studies focused on the quality of forest biomass produced in these conditions. In fact, the quality of the raw material is very important for high performance of energy systems. Thus, the present work aimed to study the wood with bark from different dense forest systems, through knowledge of the gross calorific value and the main chemical components of wood -insoluble lignin, extractives and ash. Additionally, we studied the accumulation of these components in the tree over time. Clonal forestry of Eucalyptus urophylla x Eucalyptus grandis were planted in five planting spaces and three fertilization levels. At 18, 24 and 30 months after planting, sample trees was collected and disks from the DBH region were separated for the chemical analyses. Overall, the levels of insoluble lignin, extractives and ash obtained from the different treatments

The stem volume of commercial trees is an important variable that assists in decision making and economic analysis in forest management. Wood from forest plantations can be used for several purposes, which makes estimating multi-volumes for the same tree a necessary task. Defining its exploitation and use potential, such as the total and merchantable volumes (up to a minimum diameter of interest), with or without bark, is a possible work. The goal of this study was to use different strategies to model multi-volumes of the stem of eucalyptus trees. The data came from rigorous scaling of 460 felled trees stems from four eucalyptus clones in high forest and coppice regimes. The diameters were measured at different heights, with the volume of the sections obtained by the Smalian method. Data were randomly separated into fit and validation data. The single multi-volume model, volume-specific models, and the training of artificial neural networks (ANNs) were fitted. The evaluation criteria of the models were: coefficient of determination, root mean square error, mean absolute error, mean bias error, as well as graphical analysis of observed and estimated values and distribution of residuals. Additionally, the t-test (α = 0.05) was performed between the volume obtained in the rigorous scaling and estimated by each strategy with the validation data. Results showed that the strategies used to model different tree stem volumes are efficient. The actual and estimated volumes showed no differences. The multi-volume model had the most considerable advantage in volume estimation practicality, while the volumespecific models were more efficient in the accuracy of estimates. Given the conditions of this study, the ANNs are more suitable than the regression models in the estimation of multivolumes of eucalyptus trees, revealing greater accuracy and practicality.

Earlier experiments with young Eucalyptus short-rotation coppice (SRC) in tropical environment have not evaluated the quality of whole-tree biomass fractions, and as such their total energy potential is still unknown. As this system is managed with a higher planting density and fertilization level compared to conventional plantations, the quality of forest biomass needs to be assessed. Hence, the goal of this study was to analyze how the short-rotation coppice affected the quality of stem, branches, and leaves used for power generation. Samples were collected from high-density plantation of Eucalyptus at two years old, and the thermochemical properties were evaluated. Carbon and ash content were lower for the stem fraction in higher density of planting, although the higher heating value was not significantly different from each treatment. Overall, the fuel quality of whole-forest biomass was not influenced by management practices. Statistically significant differences were found only between the whole-tree fractions. Eucalyptus SRC provided biomass qualitatively close to that from conventional forest systems and has potential to be quickly and feasible energy option.