Ciclagem de nutrientes em um trecho de Floresta Ombrófila Densa Aluvial em regeneração, Guaraqueçaba, PR

Abstract

The focus of the study was a nutrient cycling evaluation in an alluvial Atlantic Rain Forest in natural regeneration during the 9th and 10th years after Asian buffalo grazing was abandoned. The return of nutrients through total fine litterfall and the fractions (branches, fruits and flowers, miscellaneous and leaves of Myrsine coriacea, Alchornea glandulosa, Psidium guajava, Senna multijuga, Cecropia pachystachya, Tibouchina pulchra, Citharexylum myrianthum and leaves of the other species of the community) was estimated for two distinct areas in an initial sucessional stage “capoeira”. The leaf decomposition and nutrient release and retention were also studied. Rainfall and throughfall contribution to nutrient deposition in the most developed area of the “capoeira” and in a secondary forest were also estimated. Litterfall was higher (6.4 ± 1.2 ton ha-1y-1; 95% confidence limits) in the most developed area than in the least developed one (3.0 ± 1.0 ton ha-1y-1). The highest leaf litter production occurred in spring. The majority of the correlations between litterfall fractions and meteorological variables indicate a time interval pattern among the peaks of these events. Total amount of macronutrients in litterfall annually reached 237 kg ha-1y-1 in the most developed area, an average value as compared to other Brazilian forests. In the less developed “capoeira” total amount of nutrient deposition was only 97 kg ha-1y-1. The greater value can be considered average comparing to other studies in Brazilian Forests. The pattern of elements concentration in litterfall was: N > Ca > K > Mg > Al > P > Mn > Fe > Zn > Cu. Half of the leaf litter disappeared in one year. Weigh loss was higher in the earlier stages of the decomposition process. Calculated rate was lower than in other tropical forests of the world, although similar to other Atlantic forests in Brazil. There was a tendency of increasing element concentration during the decomposition process, except for K. The most developed area of the “capoeira” and the advanced secondary forest showed interception rainfall values around 14%; considered low comparing with other studies. The sequence of element concentration in throughfall in both areas was Na > K > Ca > Mg. The Na value was very high, reaching in average 96 kg ha-1y-1 in the “capoeira”. An annual return of 52 kg ha-1 of K, 5 kg ha-1 of Ca and 2.9 kg ha-1 of Mg was estimated for this process. These values contributed respectively to 65%, 5% e 15% of the total nutrient deposition (litterfall + throughfall).