Seasonal and interannual litter dynamics of a tropical semideciduous forest of the southern Amazon Basin, Brazil

This study analyzed how seasonal and interannual variations in climate alter litter dynamics, including production, decomposition, and accumulation. Monthly measurements of leaf, stem, and reproductive ( flower plus fruit) litter and the forest floor litter mass were combined with a mass balance model to determine rates of litter decomposition for a semideciduous tropical forest located in the rain forest-savanna ecotone of the southern Amazon Basin for 2001-2007. Annual rates of litter production varied between 8 and 10.5 Mg ha(-1) a(-1), and leaf litter production accounted for the majority (similar to 70%) of the total litter production. Leaf litter production peaked at the end of the May - August dry season while stem litter production peaked during the wet season and reproductive litter production peaked during the dry-wet season transition. Forest floor litter mass ranged between 5 and 8 Mg ha(-1) over the study period and generally declined as litter inputs declined. Litter decomposition rates were remarkably stable from year-to-year and varied between 10.8 and 12.4 Mg ha(-1) a(-1). On average, rates of litter decomposition were highest during the dry-wet season transition. Overall, our results suggest that rainfall variability directly altered litter production dynamics and indirectly altered forest floor litter mass and decomposition kinetics through its effect on litter production. Future changes in seasonal and/or interannual rainfall patterns, whether in response to El Nino or to anthropogenic climate change, will likely have important consequences for the litter dynamics of Amazonian semideciduous forest.