Heartwood variation of Eucalyptus urophylla is influenced by climatic conditions

Abstract 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.