Produção de serapilheira e retorno de macronutrientes em três grupos florísticos de uma floresta ombrófila mista, RS

Abstract

The aim of the current study was to evaluate the production of litter and the return of macronutrients in three floristic groups which occur in the Araucaria Forest, located in the National Forest of São Francisco de Paula, RS state. For this purpose, we selected three permanent conglomerates of 1ha (100x 100m) each one, where the vegetation was previously classified, by cluster analysis, in three different floristic groups: FG1 - hillside environment; FG2 - typical araucaria forest; and FG3- humid environment. For litter fall collection, 16 litter traps of 1m 2 of area were distributed, systematically, by floristic group. The material was collected monthly during one year and separated in the following fractions: leaves, araucaria needles, branches, miscellaneous and seeds. For the chemical analysis of the macronutrients - nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) - returned in litter, we considered the floristic groups, the fractions and the climatic seasons. The annual production of litter was 8.354,4 kg.ha -1.yr -1, 7.929,5 kg.ha -1.yr -1 and kg.ha -1.yr-1 in the groups FG2, FG1 and FG3, respectively. For the FG1 and FG3 groups, spring was the season that presented the highest litter deposition, followed by summer, winter and autumn. The FG2 group showed the highest litter deposition in summer, followed by spring, autumn and winter. The fractions of leaves and araucaria needles formed the main litter component, responding also by a higher return of macronutrients. The estimated litter return of macronutrients were of 358,57 kg.ha -1.yr -1 and 256,80 kg.ha -1.yr -1 for the groups FG2, FG3 and FG1, respectively. The order of transference of those macronutrients present in the deposited litter was: N>Ca>K>Mg>S>P, for the groups FG1 and FG2; and Ca>N> K>Mg>S>P, for the GF3.