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The heartwood formation process is little known in fast growing plantation woods. Therefore, the aims of this study were to determine how planting spacing and tree age affect the formation and proportion of heartwood and sapwood, as well as the density of eucalyptus wood. Trees from a eucalyptus clonal plantation (Eucalyptus grandis × E. urophylla hybrid) cultivated in three spacings (3 × 1, 3 × 2 and 3 × 3 m) were sampled at 14, 27, 32, 53, 64 and 76 months of age. Heartwood percentage was quantified with Dimethyl yellow indicator, while the wood density was determined by X-ray densitometry. The heartwood percentage, wood volume, heartwood density and wood density were correlated with the different growth rates. The heartwood formation process started between 32 and 53 months, regardless of spacing. The heartwood proportion doubled with increasing age in the widest spacing and increased about four times in 3 × 1 and 3 × 2 m spacing. The planting spacing influenced the growth rates of the trees, but did not affect the heartwood and sapwood percentage or density. The greatest increase in density values occurred between the first year of growth (14 months) and the beginning of heartwood formation (53 months).

The increase in global temperature results in changes in rainfall patterns and can cause structural and functional changes in trees. Each plant is forced to face hydraulic safety limits and adopt a behavior to regulate its water status. The objective of this work was to evaluate the changes in the hydraulic architecture of the xylem of commercial eucalyptus clones in order to distinguish the hydraulic adjustments in a wide gradient of water availability. Eucalyptus urophylla (A1) and E. grandis × E. camaldulensis (C3) clones at six years old at 4 sites in Brazil distributed in a rainfall gradient and in two water conditions were analyzed: control (100% of total local rainfall) and rainfall reduction (RR). Xylem traits were evaluated at annual intervals and averaged over the entire growth period of the seven trees sampled at each site and water condition. The sites influenced the clones, with the greatest effect being the rainfall reduction treatment in C3 on the vessel wall diameter, area and thickness, double wall thickness, conduction area, vessel composition index, theoretical and potential hydraulic conductivities, vessel implosion resistance and vulnerability. The rainfall reduction provided an increase of 12% in vessel density, 8% in the double vessel wall, and 27% in theoretical hydraulic conductivity in the drought-tolerant C3 clone. The vessel wall thickness in the A1 clone was more responsive with a 3% increase in rainfall reduction, with an effect on double-wall thickness and vessel implosion resistance. Other hydraulic adjustment strategies were observed, such as the highest occurrence of tylose and a tradeoff between vessel diameter and frequency for the C3 clone. The greater variation in wood density was explained by variations in the lumen area of the xylem vessels and by vessel implosion resistance.

Neutral sulphite semichemical pulping (NSSC) of Schizolobium amazonicum (Paricá), a fast-growing Amazonian tree, was compared with that of Eucalyptus grandis (eucalypt), one of the most important wood sources for the Brazilian pulp industry, and with mixtures of both woods in different proportions (mix). Wood chips prepared from 7-year old trees were steamed, cooked using the NSSC process and defibered in a 12” disc refiner in three stages. The paricá wood produced pulp of lower yield (75 %) than eucalypt (77 %) at 16 % sulfite/150 min/170 °C. The paricá and eucalypt pulps were bleached to about 68 and 74 % ISO brightness, respectively, by the QPFAS sequence. Paricá consumed more energy for refining in comparison with the eucalypt wood. The wood mix produced lower yield and brightness than the single species processed separately.

The intensity of climate changes demands studies on the adaptability of the most planted eucalyptus genetic materials in the world, such as E. urophylla and E. grandis × E. camaldulensis which were evaluated in this study. The objective of this work was to evaluate wood traits and to relate it to the meteorological variables for each year of growth of the trees that grew in four sites with different climatic conditions and 33% rainfall exclusion. The wood traits evaluated were: wood density, vessel density, diameter and area, vessel wall thickness, total vessel wall thickness between adjacent cells, theoretical hydraulic conductivity, potential hydraulic conductivity, lumen conductivity area, vessel composition within space, vessel implosion resistance and vulnerability index to drought. Pearson’s correlations between the evaluated variables were estimated and the results expressed graphically through the correlation network. Multiple regression analysis with adjustment by the Exhaustive Search method was used to estimate the vessel wall thickness in order to isolate this characteristic and identify the explanation intensity of the meteorological variables. Pearson’s correlations between meteorological factors and wood traits show different interactions in the behavior of the clones and in the water availability conditions. Air temperature was present in all the vessel wall thickness estimation equations. The 33% rainfall exclusion provided the best equation adjustments with meteorological variables, explaining up to 84% of the variation in the vessel wall thickness. The rainfall exclusion intensified the effects of the interrelations between climate and hydraulic architecture in E. grandis × E. camaldulensis, with implosion resistance and vessel wall thickness having a strong relationship between climate and wood. The results of rain reduction in the dynamics between wood and climate have implications for indirect selection in breeding programs.

The wood production potential that a site presents is largely represented by its climatic condition and by the affinity of its genetic material. An issue which concerns all wood producers is climate change and how it will influence wood production and wood characteristics, as they can be decisive in industrial applications. Therefore, this study aimed to: (i) verify the wood volume (WV), stem biomass (SB) and the basic wood density (BWD) behavior against different climatic scenarios; and (ii) verify the potential of estimating the BWD through meteorological variables. The WV, BWD and SB of four different Eucalyptus spp. clones as to their climate of origin and species were analyzed. The cultivation was from 2012 to 2015 (four years) with planting in 11 locations in Brazil, representing a wide range of climatic characteristics with average precipitation from 649 mm y−1 to 1618 mm y−1. Precipitation, maximum vapor-pressure deficit, water deficit in the soil, temperature and precipitation seasonality were used to characterize the regions during the growth period. Hierarchical grouping was carried out for the sites, and the WV, BWD and SB behavior within the groups were analyzed. Thus, a linear regression equation between the most influential meteorological variables in the BWD were adjusted in order to identify the potential of the estimative BWD. Four groups were formed between the sites, and the variation in WV, BWD and SB for each clone between the wet and dry groups were respectively: C3: −68.3%, +8.7% and −65.0%; K2: −77.5%, +8.3% and −74.3%, A1: −40.3%, −9.21% and −39.9%; and Q8 – −31.6%, +8.4% and −34.1%. The drier locations generally showed lower WV and SB, and higher BWD associated to a decrease in the growth rate. This behavior is intrinsic to each clone and does not establish a defined proportion. Humid locations did not show clear patterns in changing density. The maximum vapor-pressure deficit and the water deficit in the soil were the most significant variables and had the best potential to estimate the basic wood density of the wood. Basic wood density is a resource which can be strongly influenced by genetics, and above all there is a significant influence of climate on the sites.

One of the forms used to differentiate wood is heartwood and sapwood classifications, as variations in the proportions influence wood use. The aim of this study was to compare the heartwood percentage (H%) and wood density (WD) of eucalyptus in plantations along a climatic gradient, and to estimate these characteristics using meteorological variables and tree growth rate. E. urophyla clones at 6 years old were analyzed in 12 sites distributed across a wide geographic variation in Brazil. Seven trees from each site were sampled, and a disc was taken from the DBH position. H% was determined by image analysis, while heartwood density (HD), sapwood density (SD) and wood density (WD) by X-ray densitometry. H%, HD, SD and WD data were submitted to analysis of individual variance and the sites means were compared. WD and H% were correlated with the following variables: temperature (T), precipitation (P), soil water deficit (SWD), water use index (W), water use efficiency (WUE) and mean annual increment (MAI); these variables were also used in the multiple regression analysis in the adjustment of equations. The differentiation between heartwood and sapwood by color was possible in all sites. The sites located in higher and more humid latitudes presented the highest H% values (between 61 and 67%). In general, HD was lower than SD, with the sites with the lowest MAI values showing the lowest SD values, and wet sites with higher MAI and the highest densities. H% showed strong and significant correlations with T, P, SWD, W and MAI, whereas HD only showed moderate and significant correlations with T, MAI and WUE. The best equation for estimating H% used the P and MAI variables, which managed to explain 79% of the variation. In the WD estimation, the best equation only used the WUE variable and obtained an explanation power of 53%. In addition to the strong relationship between heartwood percentage and growth, it was found that the climate also influences heartwood formation. Use the equation obtained for clone A1 in other clones confirmed that the response variability for wood properties is also influenced by genetic. No relationship was observed between the Huber value and climatic conditions, however, the factors influencing SA:LA ratio behavior are complex and requires considering other components. H% was shown to be more correlated with climate than density, and the observed variability between sites suggests the inclusion of heartwood content assessments in this species in management and breeding programs.