Seasonal Decomposition Rates of Broadleaf and Conifer Wood Litter in Far Eastern Tropical Forest Communities

Studies on wood litter decomposition sometimes show conflicting results. While low temperatures and humidity during winter in temperate climates are reported to halt the activity of decomposing agents, in the warmest and wettest tropical regions of the Far East, peat accumulates on the forest floor, indicating that the decomposition process is not proceeding well. In this study, we compared the inter-seasonal and inter-forest communities’ decomposition rate constant (k) of jabon (Anthocephalus macrophyllus (Roxb.) Havil.) and tusam (Pinus merkusii Jungh. & de Vriese) woods in three forest communities (Karst, Lowland, and Pine) on the Indonesian island of Sulawesi. We placed 1,200 wooden planks (600 jabon logs and 600 tusam logs) measuring 10 cm × 10 cm × 1.5 cm on the ground in each forest community during different seasons: dry season and wet season. k was observed seasonally. We also observed the decomposing agent diversity, soil properties, and chemical content of the wood sample to examine factors affecting k values. The results showed the tendency of jabon wood k to be higher in the dry season than in the wet season, and the opposite trend was noted for tusam wood. k of both wood samples was highest in Karst, followed by Lowland and Pine forests. However, except for bacterial diversity and abundance of Odontotermes sp., there was no clear correlation between k and the diversity and abundance of decomposing agents. The k values varied distinctly, even among samples within the same forest community in the same season, causing the data not to be normally distributed. These findings indicate that decomposition processes in tropical forests vary at the microsite scale due to the high diversity of decomposing agents and their complex reciprocal association.