In a tropical rainforest, 3D structure is formed by the mixture of various tree species and organisms at different growth stages. Therefore, leaf litter locates in many positions not only forest floor but also aboveground, such as at the base of palms and on the branches. It is expected these above ground litter will remain in respective locations and decompose there. However, most previous studies on litter decomposition have been conducted on the forest floor, and little studies on aboveground parts. Furthermore, soil animals have a significant effect on leaf litter decomposition in tropical rainforests, but it’s not clear whether they influence the decomposition of aboveground litter. At the regional scale, environmental conditions such as temperature and humidity are also limitation factors on the decomposition rate. At the local scale, however, the relationship between the micro environment and the decomposition at different locations is unknown. The aim of this study was to assess the decomposition characteristics of leaf litter along the spatial distribution of litter in tropical rainforests. We evaluated decomposition rates at various locations, in addition with the effects of soil animals and the influence of environmental factors.
Litterbag experiments were conducted in Lambir Hills National Park, Sarawak, Malaysia, at following five locations: on soil (SL), on litter (LL), on fallen trees (FT), at the base of palms (PL), and on the branches in the air (AL). We used leaf litter randomly collected from the forest floor. Two types of litterbags with different mesh sizes, fine and coarse, were used at each location to evaluate the effects of soil animals. Litterbags were collected at 6, 12, and 18 months after installation. Temperature and volumetric humidity (VH) were measured at each location for two months.
We found the decomposition rate at 6months varied greatly among the locations. It was particularly fast at SL and LL. After 18 months, however, there were no significant differences in the remaining litter mass among the four locations except AL. Decomposition in AL was the slowest during whole periods. Additionally, the effects of soil animals were observed in the aboveground litter as those in the forest floor. Mean temperature was not the factor of the changes in the decomposition rate, but the higher changes of temperature during a day caused a lower rates of the decomposition. Mean VH had a positive effect on the decomposition rate, and the higher change of VH during a day decreased the decomposition rate.