Manejo de eucalipto submetido a diferentes espaçamentos e pesos de desbastes visando multiprodutos

Abstract

Different spacing and the application of thinning are used for the production of larger and better-quality wood, allowing its destination for multi-products, being necessary the analysis of the economic viability to verify the economic return. Therefore, the objective of this research was to evaluate the production (diameter, height, volume and biomass of the bole) and the economic viability of plantations of the hybrid Eucalyptus urophylla × Eucalyptus grandis in different spacing and thinning weights with destination of wood for multi-products in the state of the Holy Spirit. For this, an experiment was installed under a randomized block design, with six treatments (spacing 3x3 m; 3x2 m; 2x2 m; and 2x2 m with 20; 40 and 60% thinning). To assess production, using forest inventory data, analysis of variance and the Scott Knott test were performed at the 5% probability level of the diameter variables at 1.30 m from the ground (DBH) and the total height (H), total volume and biomass of the individual shaft and per hectare, at 61 months of age. For the projection of the DAP and H, three adjustment models were tested, with the production projected for 72, 84, 96 and 108 months of age. The production of thinning was destined for two categories of fencepost and firewood and the production of the final cut was destined for sawmills, fencepost and firewood. All the costs inherent to the eucalyptus plantations were collected, as well as the revenues obtained from the sale of the multi-products. Net Present Value, Equivalent Uniform Annual Value, Internal Rate of Return and Cost Benefit Ratio were calculated, with a discount rate of 6% per year for the harvest at 84 months of age. Sensitivity analysis was carried out varying the production costs, the sales value of the multi-products, the quantity produced, the age of the harvest and the discount rates. Plantations with 3x3 m and 3x2 m spacing destined for cellulose at 72 and 84 months of age were also evaluated. Considering DAP, H, total volume and individual biomass, the 3x3 m spacing produced the highest averages. For the variables total volume and biomass per hectare, the highest averages were obtained by treatments with 2x2 m spacing with thinning 6 and 40%. For the projects analyzed at 84 months of age, no treatment was economically viable for the discount rate of 6% per year. By reducing production costs by 20%, 2x2 m treatments with 40 and 60% thinning showed economic viability. With the 20% increase in the sale value of multi-products, the 2x2 m spacing with 60% thinning also showed economic viability. As for the 1.9% discount rate, only the 2x2 m spacing was economically unfeasible. Plantations destined only for cellulose were economically unfeasible for all planning horizons considered. The smaller spacing combined with thinning has increased the final production in volume and biomass and, by reducing production costs or the discount rate, or increasing sales value, multi-products are a viable alternative for rural producers.