Monitoramento ambiental florestal: fluxo de nutrientes em povoamento de Eucalyptus dunnii, no sul do Brasil

Abstract

The biogeochemical cycling of nutrients is a dynamic process and consists of the transfer of nutrients between the soil-plant-soil. This transfer can occur in several ways, the deposition of litter is the most significant and consists in the return to the soil of leaves, twigs and thick branches, bark and miscellaneous, representing source of organic matter and nutrients. Through the atmospheric deposition we have the contribution of ions that can be as much by dust and aerosols as by the rain. Part of the precipitation is intercepted by the tree canopy and returned to the atmosphere by evapotranspiration, the portion that crosses the forest canopy is called throughfall and the one that descends through the trunk is called stemflown. The objective of the study was to quantify the litterfall, the partition of rainfall and its nutrients in Eucalyptus dunnii stands in southern Brazil. The experiment consisted of the delimitation of 4 plots of 20 m x 21 m. In each one of them 4 litter collectors were arranged in line, between line, diagonal and tree positions, with an area of 0.5 m². Four useful areas of the trees were also demarcated for collecting thick branches> 0.5 cm in diameter. For rainfall, 3 collectors were installed in an open area. The throughfall consisted in the installation of 3 collectors in each plot, in the line, interlining and diagonal positions of the trees. The stemflow through the trunk occurred with the installation of a hose around the trunk of the tree in the form of a spiral, leading the water to a reservoir near the base of the same The total litter production was 8,48 Mg ha-1, 59% composed of the leaf fraction. The return of macro and micronutrients via litter was 215 kg ha-1 and 8 kg ha-1 respectively. The rainfall during the 12 months was 1903 mm, with an average interception by the canopy of 8,9%. In the rainfall, 28 kg ha-1 of nutrients were supplied. When we considered the sum of throughfall and stemflow, the amount of nutrients contributed was 76.6 kg ha-1. The climatic variables of temperature, solar radiation and evapotranspiration have a strong influence on the pattern of litter deposition, showing that it has a seasonal character. In addition, it is an important source of organic matter and nutrients to the soil, with the most representative leaf fraction in terms of amount of biomass and nutrients to the soil. The interaction with the canopy of the Eucalyptus dunnii trees enriches the net precipitation with nutrients.