Dynamics of coarse woody debris and decomposition rates in an old-growth forest in lower tropical China

The biomass and decomposition of coarse woody debris (CWD, ≥10 cm in diameter) were studied in a monsoon evergreen broad-leaved old-growth forest in Dinghushan Nature Reserve, Southern China. The study examined the biomass of CWD from 1992 to 2008 and decomposition of three dominant tree species CWD (Castanopsis chinensis, Cryptocarya concinna, Schima superba) from 1999 to 2008. Changes in the wood density of three tree species’ CWD were used to estimate the decay rates with a single exponential model. The results showed that the biomass of CWD in the old-growth forest was increasing from 17.41 tonnes ha⁻¹ (t ha⁻¹) in 1992 to 38.54 t ha⁻¹ in 2008, and a higher decay constant was observed for C. concinna (0.1570 – 19 years for 95% mass loss); the decay rates of S. superba and C. chinensis were 0.1486 (20 years for 95% mass loss) and 0.1095 (27 years for 95% mass loss), respectively. The difference in decay constant rates may be due to their substrate quality and decomposers. The content of carbon (C) in three species declined after 9 years of decay. Nitrogen (N) content increased in all species with decay. The C/N ratio in the three species declined during the decay process.