Slow litter decomposition in a Cecropia-dominated secondary forest of central Amazonia

Different proportions of tree canopy cover in a second-growth forest were removed to determine the effect of canopy opening on the carbon cycle of a 10-y-old tropical rain forest dominated by Cecropia species. Understorey vegetation was left intact. Mean maximum monthly temperature increased in the 50 and 100% cut areas relative to 0% canopy removal plots. Plots with a 100% canopy removal had slightly higher soil moisture than 50 and 0% removal plots. Annual fine litter input was 6.9±0.3 t ha−1 in the 0% cut plots with two separate peaks during the year. There was less litter input and a tendency toward slower decomposition of leaf litter in more open plots than in the plots with greater canopy cover. Percent lignin, carbon and nitrogen did not differ between the kinds of plant material used in the decomposition experiment. Quantity of tannins, however, related directly to decomposition rates. The annual decay rate (k) determined at 560 d from three kinds of litter in bags ranged from −0.39 to −0.61. There was no significant difference in decay rates associated with percent canopy removal. Decay rate estimates, using annual input of litter divided by standing mass of fine litter (the average of dry and wet season estimates, 10.3 t ha−1), resulted in a k value of −0.7 in the 0% plots, and was higher than any estimate obtained using litterbags. Decomposition rates determined in these second-growth plots are lower than any reported for primary forests in Amazonia.