ENCLOSING DECOMPOSER FOOD-WEB - IMPLICATIONS FOR COMMUNITY STRUCTURE AND FUNCTION

We designed a field experiment to evaluate how restriction of soil fau nal movements affects decomposer community structure, food web archite cture, and decomposition of organic matter. Intact soil cores (3 cm th ick, diameter 16 cm) were placed either in ''open'' (mesh size 1mm, al lowing all meso- and microfauna to move through) or ''closed'' (27 mu m, animal movement prevented except for the smallest microfauna) mesh bags in early May. Before being buried in the forest floor of a mixed spruce stand, hay litter was placed in the mesh bags in separate litte r bags. The samplings took place 2 and 6 months after establishing the experiment. Additional ''field samples'' were taken from the adjacent soil to determine possible side effects of the mesh-bags. Physicochem ical conditions, decomposition rate of hay litter, and total respirati on of soil cores were identical in the two bag treatments. Enchytraeid s increased significantly in the closed treatment, while macrofauna, s uch Coleoptera larvae and dipteran larvae, went close to extinction in the closed bags. The elevated enchytraeid number is in accordance wit h the findings of closed microcosm studies, and is best explained by r educed predation by macrofauna. Although a set of 14 mite taxa was fou nd to distinctively reflect the degree of isolation, neither the total number of individuals nor the number of microarthropod taxa differed between the bag treatments, or between the bags and the field samples. It is concluded that in the time-span of one growing season, reductio n in the spatial scale does not necessarily reduce the diversity of fa una but can significantly change the decomposer food-web architecture.