Decomposition and carbon cycling of dead trees in tropical forests of the central Amazon

Abstract

Decomposition rate constants were measured for boles of 155 large dead trees (>10 cm diameter) in central Amazon forests. Mortality data from 21 ha of permanent inventory plots, monitored for 10-15 years, were used to select dead trees for sampling. Measured rate constants varied by over 1.5 orders of magnitude (0.015-0.67 year-1), averaging 0.19 year-1 with predicted error of 0.026 year. Wood density and bole diameter were significantly and inversely correlated with rate constants. A tree of average biomass was predicted to decompose at 0.17 year-1. Based on mortality data, an average of 7.0 trees ha-1 year-1 died producing 3.6 Mg ha-1 year-1 of coarse litter (>10 cm: diameter). Mean coarse litter standing-stocks were predicted to be 21 Mg ha-1, with a mean residence time of 5.9 years, and a maximum mean carbon flux to the atmosphere of 1.8 Mg C ha-1 year-1. Total litter is estimated to be partitioned into 16% fine wood, 30% coarse wood, and 54% non-woody litter (e.g., leaves, fruits, flowers). Decomposition rate constants for coarse litter were compiled from 20 globally distributed studies. Rates were highly correlated with mean annual temperature, giving a respiration quotient (Q10) of 2.4 (10°C-1).