Volumetric modeling for bracatinga (Mimosa scabrella) in bracatinga stands in Curitiba metropolitan region

Abstract

The objectives of this research were: to develop equations to estimate the stem and firewood volume of bracatinga (Mimosa scabrella Benth.); to evaluate the accuracy of the estimates having as a  comparator the true volumes obtained by the xylometer method; to  test the validity of Ahrens' (1981) published equation. In bracatinga stands, 384 trees were measured until a minimum diameter of 4 cm at the small end. The validation set was composed by 55 trees measured by the xylometer. The ² (chi-square), aggregated difference test, standard error of estimation, average error and graphical distribution  of the residuals were used on validation process. The best equation obtained for the stem was provided by Schumacher-Hall model. For  firewood, data were stratified, forming one set of trees with DBH < 6 cm and other with DBH 6 cm. The first set was best modeled using Parabolic model, while the second one performed better applying  Schumacher-Hall model. The validated equations resulted in ² values not significant at the level of 5% and no visible tendencies along the collected DBH extent. Ahrens' (1981) equation also had a not significant ² value at 5%, but presented a strong underestimate along all its DBH extent.