Volumetric models and form factors for estimating wood stock in sustainable forest management: A study based on commercial species from Southern Amazonia

• Geometric variations in stems hinder standardized form factor use. • Average form factors underestimate timber stock compared to volumetric models. • The 0.7 form factor in legislation is inaccurate for timber stock estimates. • Using volumetric models from the first harvest year reduces forest management errors. • Reviewing CONAMA resolution 406/2009 aids sustainable forest management in the Amazon. Determining commercial wood stocks is essential for planning sustainable forest management, allowing for efficient production planning. The aim of this study was to evaluate the use of volumetric models and form factors in estimating the commercial wood stocks of ten native forest species in the southern Amazon. The data was obtained by rigorously cubing 128 trees, using the Smalian method, in an area of 4187.6 hectares in the municipality of Porto dos Gaúchos, Mato Grosso. Four single-input and seven double-input volumetric models were analyzed, using diameter and commercial height as variables. The different form factors calculated included averages per species and the standard factor of 0.7, adopted by Brazilian legislation in the first year of exploitation in forest management plans. The analysis revealed that the selection of trees provided model adjustments with low sampling errors, with the Spurr, Husch and Meyer equations presenting a standard error of <10 %. The results showed a wide variation in stem shape between species and individuals, making it difficult to adopt a standardized form factor. Using the average form factor, without considering genetic and environmental diversity, can result in significant underestimates of wood stocks. It is recommended that CONAMA resolution 406/2009 be revised to include the requirement to develop volumetric equations from the first year of exploitation in sustainable forest management.