Volumetria e qualidade da madeira de Swietenia macrophylla king proveniente de plantio na Amazônia Central

Abstract

The objective of this work was to adjust volumetric models, generate a form factor, determine the physical and mechanical properties and compare these properties of Swietenia macrophylla King in different diametric classes in pure plantations from Fazenda Sakai, located in Itacoatiara - AM, in 20 years-old. To obtain the volumetric estimate, rigorous cubing of 29 trees was carried out, 5 trees for rigorous cubication (destructive) and 24 by the non-destructive method using a retractable ladder. Eleven models were adjusted to estimate the commercial volume with shell and selected by means of the statistical criteria adjusted determination coefficient (R²aj), residual standard error (Syx), Akaike Information Criterion (AIC) and graphic distribution of the residues. To analyze the quality of the wood, the physical properties were evaluated: humidity and density, and the mechanical properties of shear, static bending, parallel compression of the fibers and janka hardness, in 5 trees of the plantation, according to ABNT 7190 (1997) and ASTM D 143-94 (200). The variables were evaluated by applying the t test (p <0.05) to find statistical differences between the diameter classes for the technological properties of wood and by descriptive statistics. The equations with the best adjustments for volumetric estimates were Husch (log) for single entry and Spurr (log) for double entry, which presented adjusted coefficients of determination (R2aj.) of 0.80 and 0.86%, residual standard error (Syx) of 0.08 and 0.06 and Akaike Information criterion (AIC) of 7.73 and 11.66 respectively. The average form factor obtained for plantations was 0.93, which demonstrates that this species has stem with a lower degree of taper, which is essential for greater use of the stem in industrial processing for wood production. The wood moisture averages obtained for the diameter classes ranged from 33.9 to 50.4%, while the density averages varied between 0.46 and 0.55 g / cm³ (Table 1). For both variables, significant differences were found between the diameter classes, where the first diameter class had a lower density value, while the intermediate classes had a higher density and lower humidity, demonstrating that, from the 26 cm class on, it is already it is possible to obtain an optimum density of wood and the intermediate classes have a better response to drying. The intermediate classes also presented higher values of TFM compression, MOE flexion and MOR flexion, which demonstrates that the intermediate classes presented greater resistance capacity and flexibility to deformation, while the upper classes presented higher values of tangential and transversal hardness and higher values of shear, which shows greater density and probably a higher percentage of late wood.