In the Brazilian planted forest sector, most of the species used are from the genus Eucalyptus. Even though Southern Brazil has a suitable climate for species of the genus Pinus, the planting of frost-resistant Eucalyptus species has been increasing annually. The objective of this study was to evaluate the basic density, fiber dimensions, and chemical composition of Eucalyptus benthamii, Eucalyptus dunnii, Eucalyptus saligna, and Eucalyptus cloeziana woods. The trees used were from a six-year-old experimental plantation located in Canoinhas, state of Santa Catarina. For each species, three trees were selected, and discs were removed from each tree at 0%, 25%, 50%, 75%, and 100% of the commercial stem height. To evaluate the quality of the wood, the basic wood density, fiber dimensions, and chemical composition of the wood were determined by comparing the values between species and between the heights in the stem. The highest basic density was that of the wood of E. cloeziana; this species also had the greatest length and width of fibers. E. dunnii had the lowest levels of lignin and the highest levels of holocellulose. The highest lignin content was found in the wood of E. benthamii, E. saligna, and E. cloeziana. The relationship between wood properties and stem height was not relevant. The results highlight the tendency for higher extractives to be found at taller heights (100%), and holocellulose and lignin content are similar at all heights.

Limited information exists on how small changes in soil water affect the physiological responses of eucalyptus and their relationship with productivity. This experiment evaluated physiological traits during decreased soil water and compared them with growth and water stress integral (WSI) of 22 eucalyptus genotypes with 1.5 years old. The experiment was conducted in sandy soil with low water holding capacity in Chile. Selected genotypes were Eucalyptus globulus, E. nitens, and E. nitens × E. globulus hybrids (E. gloni). Seasonal predawn leaf water potential (Ψ_pd) was evaluated under well-irrigated conditions and after 40 days without irrigation. Subsequently, two sampling instances were considered for analysis, well- irrigated conditions M₀ (470 days after planting) and 40 days without irrigation M_final (510 days after planting). During that period, we measured midday leaf water potential (Ψ_md), leaf area index (LAI), diurnal changes in photosynthesis (A_n) and stomatal conductance (g_s). The broad range of WSI among genotypes indicated contrasting levels of accumulated water stress during early development. In fact, E. globulus presented 30% more water stress than E. nitens, and genotypes with the highest WSI showed the lowest growth. Between M₀ and M_final, there was a reduction in A_n and g_s in the morning and midday with small changes in the afternoon, and consequently, values of the intrinsic water use efficiency (iWUE) increased. The Ψ_md showed small changes and we observed a large LAI increment for all genotypes. Changes in iWUE were more pronounced for genotypes with lower WSI, which suggested that these genotypes with lower accumulated water stress were more sensitive to changes in soil water, such as E. gloni genotypes allowing them to maintain high productivity.

The Mixed Ombrophilous Forest is one of the most threatened ecosystems in Brazil. It is thus necessary to understand its dynamics of growth over time so that sustainable use and conservation management strategies be proposed. The objective of this study is to evaluate the behavior of the diametric distribution of two pioneer and non-pioneer ecological groups in a fragment of Mixed Ombrophilous Forest considering four years of evaluations: from 2002 to 2017. Exponential, Gamma, Weber and Weibull 3P density probability functions were adjusted. The diametric behavior of the forest and the ecological groups analyzed remained negative exponentially, being a characteristic of natural forests. The distributions that best adjusted were Weibull 3P for the forest as a whole and for the group of pioneers, and Weber for non-pioneers. We concluded that ecological groups have the same pattern of diametric distribution as the forest as a whole. However, different forest management strategies are necessary considering the intrinsic characteristics of each group.

Accurate forest biomass estimates require the selection of appropriate models of individual trees. Thus, two properties are required in tree biomass modeling: (1) additivity of biomass components and (2) estimator efficiency. This study aimed to develop a system of equations to estimate young eucalyptus aboveground biomass and guarantee additivity and estimator efficiency. Aboveground eucalyptus biomass models were calibrated using four methods: generalized least squares (GLS), weighted least squares (WLS), seemingly unrelated regression (SUR), and weighted seemingly unrelated regression (WSUR). The approaches were compared with regard to performance, additivity, and estimator efficiency. The methods did not differ with regard to the mean biomass estimation; therefore, their performance was similar. The GLS and WLS approaches did not satisfy the additivity principle, as the sum of the biomass components was not equal to total biomass. However, this was not observed with the SUR and WSUR approaches. With regard to estimator efficiency, the WSUR approach resulted in narrow confidence intervals and an efficiency gain of over 20%. The WSUR approach should be used in forest biomass modeling as it resulted in effective estimators while ensuring equation additivity, thus providing an easy and accurate alternative to estimate the initial biomass of eucalyptus stands in ecophysiological models.