A model of litterfall, litter layer losses and mass transfer in a humid tropical forest at Pernambuco, Brazil

Data on litterfall, litter layers accumulated on top of the mineral soil and layer mineralization collected for three years in a tropical rain forest at Pernambuco, Brazil, were implemented on a simulation model. Litterfall was collected biweekly using 11 collectors 1 × 1 m. Every three months, 20 litter mat samples, 0.5 × 0.5 m, were collected, divided into the L, F and H layers and the CO2 evolution from each litter layer was determined in the laboratory. Litterfall, in the three years, averaged 7.8, 8.3 and 8.2 Mg ha-1 y-1, most of it leaves. Litter mat masses varied widely from place to place (15–90 Mg ha-1) and the overall averages were 5.6, 7.6 and 26.1 Mg ha-1 for the L, F and H layers, with CO2 evolution averages of 2.27, 0.507 and 0.123 mgC g litter C-1 day-1. According to the model, the L layer had a high turnover rate, losing 4.7 Mg ha-1 y-1 through mineralization and 3.4 Mg ha-1 y-1 transferred to the F layer. Values for the F and H layers were 1.4 and 1.2 mineralized and 2.0 and 0.8 Mg ha-1 y-1 transferred. Thus, it would take 2.1, 6.7 and 39 years for newly fallen leaves to be mostly fragments, to be transformed to humus and to be incorporated to the soil organic matter, respectively. Variations of litterfall throughout the three years would have little effect on the system which was not very sensitive to litterfall changes, except for the top layer.