DYNAMICS AND STRATIFICATION OF FUNCTIONAL-GROUPS OF MICROARTHROPOD AND MESOARTHROPOD IN THE ORGANIC LAYER OF A SCOTS PINE FOREST

This paper addresses the abundance, biomass and microstratification of functional groups of micro-and mesoarthropods inhabiting the organic layers of a Scots pine forest (Pinus sylvestris L.). An experiment usi ng stratified litterbags, containing organic material of four degradat ion stages, i.e., freshly fallen litter, litter, fragmented litter and humus, was performed over a period of 2.5 years. Statistical data ana lysis revealed that each organic layer had a different, characteristic species composition that changed with time following successive degra dation stages. Species of Acari, Araneae and Collembola were assigned to different functional groups based on taxonomy, microstratification, food type or feeding mode. The abundance and biomass carbon of functi onal groups were dependent on the organic layer and most functional gr oups showed a particular preference for one of the upper organic layer s. Temporal and spatial differences in density and biomass carbon of f unctional groups could partly be related to fluctuations in the soil c limate, although effects of trophic interactions could not be ruled ou t. A general decline in abundance and biomass, especially in populatio ns of fungal feeders, during the last year of the study could not be e xplained by a reduction in litterbag volume, changed litter chemistry or soil climate, but was attributed to an indirect effect of a remarka ble increase in soil coverage by wavy hair grass, Deschampsia flexuosa (L). The analysis demonstrated that species diversity, microhabitat s pecification, soil fauna succession, and degradation stages of organic material are interrelated. The results obtained indicate that both th e chemistry of organic matter and decomposition rates have an importan t effect on trophic relationships and community structure.