The Response of Tropical Rainforest Dead Wood Respiration to Seasonal Drought

Coarse woody debris (CWD, dead wood sections ≥10 cm diameter) represents a large store of carbon in tropical forests; however, estimates of the flux of carbon from CWD in these forests remain poorly constrained. The objective of this study was to resolve the dry/wet season response of respiration in CWD (R_cwd), and investigate the importance of biotic and abiotic factors for predicting the seasonal change of R_cwd at the ecosystem level. This study presents a 4-month time series of R_cwd measurements conducted on 42 dead trees (26 species) at the Paracou Research Station in French Guiana. R_cwd measurements were repeated 13 times on each CWD sample from July to November 2011, spanning the transition from wet to dry season, and then from dry season to the following wet season. Seasonal drought caused monthly R_cwd to drop by 20.5 ± 5.1% over the wet-dry transition. Changes in woody tissue moisture content explained 41.9% of the measured seasonal variability in R_cwd, but 60% of the seasonal variability in mean forest R_cwd rates could be modelled using surface soil water content. We estimate that R_cwd is approximately 5% of annual ecosystem respiration (R_eco) and that seasonal variations in R_cwd contribute appreciably to seasonal variations of R_eco, and should be included in functional models simulating the response of tropical rainforest ecosystems to current and future climate.