EQUATIONS TO ESTIMATE SHOOT AND ROOT SYSTEM BIOMASS IN Eucalyptus grandis STANDS AT SITES WITH DIFFERENT PRODUCTIVITIES

The main objective of this work was to adjust equations to estimate biomass of shoot and root system in 11-year-old Eucalyptus grandis stands growing in two sites with different productivities. Loamy soil (more productivity site) was classified as a Typic Hapludox (RED) and sandy soil (less productivity site) as a Typic Quartzipsamment (QTZ). Biomass inventory was carried out using ten sample-trees in each site including shoot (stem, bark, leaves and branches) and root system (fine and coarse roots) tree components. Two logarithmic regression equations were adjusted to estimate tree biomass, with diameter at breast height (DBH) and height (H) or (DBHH)-H-2 being used as independent variables. The adjusted models were significant at 95% of probability by the t Student test. The best-fit equations were found with (DBHH)-H-2. Validation of common equations for the two sites was based in the combined analyses of coefficient of determination (R-2), stand error of estimate (S-y.x) and graphic analysis of residues. Adjusted equations had highest precision for estimate of stem biomass (R-2 = 0.99; S-y.x = 0.12) and bark biomass (R-2 = 0.97; S-y.x = 0.24). In spite of R-2 > 0.70, equation for leaf and branch biomass had low accuracy. Thus, it was suggested the inclusion of other variables related to size of trees. Specific equations for biomass estimation by each site for fine [RED (R-2 = 0.97; S-y.x = 0.30); QTZ (R-2 = 0.96; S-y.x = 0.15)] and coarse roots [LVd (R-2 = 0.98; S-y.x = 0.19); RQ (R-2 = 0.99; S-y.x = 0.15)] were more accurate than common equations, since that there was more root biomass allocation in sandy soil (QTZ).