Community structure of saprophagous arthropods in forestcanopies and their status in a decomposer system

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Decomposer microarthropods such as oribatid mites and springtails in forest soils play important roles in the nutrient cycle offorest ecosystems. It is known that they inhabit not only in soils but also on canopies, and it is thus suggested that ; decomposition processes may start at forest canopies. Because Japanese cedar (Cryptomeria japonica D. Don), in particular, keeps dead leaves and dead branches attached on the canopies for several years, their decomposition processes on canopies I are more important than on those of other tree species. The objective of this study is to clarify the community structure of decomposer microarthropods in dead leaves and dead branches on canopies of Japanese cedar trees.This study was carried out in the Nagoya University Experimental Forest at Inabu, located 55 km east of Nagoya, Aichi Prefecture, Japan. Sampling was carried out from May to September 1999 at intervals of about a month. Attached dead leaves and branches were sampled from the canopies … More of three trees selected on each sampling occasion at a 29 years-old : plantation of Japanese cedar. In the laboratory, dead-leaf and dead-branch samples were separated and washed in NaOH solution to extract microarthropods from them. Microarthropods were counted and identified at the order level, while those sampled on May at the family level. The dead leaves and branches were weighed on a microbalance before and after drying in a convection oven.Acari, Collembola and dipteran larvae were sampled from attached dead leaves and blanches on canopies of Japanese cedar. In terms of the number of individuals, Acari occupied more than 50% ofthe total arthropods, followed by Collembola and dipteran larvae. Nine families of Acari and five families of Collembola were recorded. Because all Acari were Oribatida, most of which were detritivorous or fungivorous, the species composition of oribatid mites from attached dead leaves and branches differed from that previously reported for the whole canopy. The taxonomic compositions of the microarthropods differed between dead leaves and dead branches, which may reflect a difference in the characteristics as habitats between them. The density of Acari per dry mass of dead parts (number g^<-1> d.wt) increased from May to September. This tendency also differed from that previously reported for the whole canopy. These results suggest that attached dead leaves and branches may have a specific feature as habitattin the whole canopy. The relative abundance of Acari to all microarthropods was high from May to September, while those of Collembola and dipteran larvae tended to increase in July and August under warm and dry conditions. Their densities, however, were almost constant during the survey period, suggesting that they have relatively stable population densities. Less