Sustentabilidade da produtividade de madeira de Pinus taeda com base no estoque, na exportação e na ciclagem de nutrientes

Abstract

The impacts of intensive management on the sustainability of forest production depends on the maintenance of soil fertility. The contribution of forest residues and nutrient cycling in this process are crucial. The objectives of this study were: (i) quantify the biomass and nutrient stocks in the shoot above and belowground and root system of a stand of 16-years-old Pinus taeda, (ii) characterize the potential release of nutrients from primary and secondary minerals, and the stock of nutrients in a Humic Cambisol (iii) quantify the export of nutrients through wood harvesting and forest components, (iv) evaluate the potential of sustainability in wood based on the balance of nutrients under different forest management scenarios. We evaluated a 16-years-old plantation of Pinus taeda in a Humic Cambisol, undulating relief in the middle-south of Santa Catarina. Ten trees were sampled from five diameter classes according to the distribution of diameter at breast height. Biomass of the needles, twigs, bark, wood and roots were measured for each tree. Besides the biomass and litter soil samples were collected from the layers 0-20, 20-40, 40-60, 60-100, 100- 140, 140-180 and 180-190 cm. Equations which has the sectional area of 1.30 m as independent variable and the biomass of each component as the dependent variable were adjusted to estimate the biomass of the entire studied forest. Furthermore, equations which has the nutrient content of the component as the dependent variable and the biomass as independent variable were adjusted to estimate the amount of each nutrient in all parts of the tree.The concentration and stock of nutrient were determined from the soil sample collected. In addition, a mineralogical characterization was performed for the soil and litters. Three scenarios simulated forest management, removal of wood (A), the wood and bark (B) and wood + bark + cup (C) of the forest system. The sum of all components of biomass was 313 mg h-1 being the most representative of the wood (62%). The stock of nutrients in the tree was N> Ca> K> S> Mg> P. The wood was the largest exporter of nutrients (210 N, 33 P, 85 K, 91 Ca, 31 Mg and 65 S, kg ha-1). The mineralogy of the Cambisol showed the predominance of quartz sand, silt and clay, with small traces of vermiculite in the silt fraction. Clay is the main fraction which contributes to the weathering of the soil due to the transformation of illite-vermiculite, releasing K. The depletion of nutrients from the soil-biomass was: P> S> N> K> Mg> Ca and S. The P and S remained as the most limiting at the scenario A due to its low inventories in the soil. At the scenario B, the number of rotations forest changed to N, K, S. The scenario C resulted in the greatest reduction in productivity, allowing for P two rotation and for Mg 14. It was evident by the number of potential crop rotations, the different management scenarios in the short term may jeopardize the sustainability of P. taeda.