Effect of wood density and water permeability on wood decomposition rates of 32 Bornean rainforest trees

A better understanding of wood litter decomposition is essential for predicting responses of forest ecosystems to global climate change. Recent studies suggest that chemical properties of wood litters, rather than physical ones such as wood density, are more important for interspecific differences in wood decomposition rates. However, empirical data are still limited, especially for tropical trees. In addition, decomposition rate of wood litter often varies with time, which makes interspecific comparison difficult. We studied the wood decomposition of 32 rainforest trees to elucidate (i) the degree of interspecific variation in wood decomposition rate of a given size and configuration and (ii) if initial wood density and water permeability are consistent predictors of the overall decomposition rate and its pattern over time. A common garden decomposition experiment was conducted in a tropical rainforest in Malaysian Borneo for 32 native tree species. Small wood sticks were set on the forest floor and the weight loss was monitored monthly for 2.7 years. We found large variation in the wood decomposition rate (a 49-fold range), suggesting that we need to consider this variation when calculating community-level carbon dynamics of tropical rain forests. The physical traits of wood, i.e. wood density and water permeability, were related to wood decomposition rate and its pattern over time. Decomposition half-time related positively and negatively to initial wood density and water permeability, respectively. The time-dependent-rate model fitted better for 18 species (56% of the study species) that had higher water permeabilities than the others, suggesting that micelle porosity in wood relates to temporal changes in decomposition rate.