Arthropod assemblages in Norway spruce monocultures during a forest cycle - A multi-taxa approach

In an effort to understand processes accompanying aging of forest stands and to support management of commercial forests, population characteristics of epigeic arthropod assemblages (spiders, ground beetles, centipedes, millipedes and woodlice - suborder Oniscidea) were studied in spruce monoculture stands and compared with local environmental factors (litter, coarse and fine woody debris, canopy closure, and moss, herb and shrub cover). Arthropod sampling was conducted in 15 differently aged stands using pitfall traps, with environmental variables monitored concurrently. A total of 66 spider, 29 ground beetle, 12 centipede, 8 millipede and 3 woodlice species were determined. In general, litter depth, herb cover, canopy closure and the amount of coarse woody debris had the greatest influence on assemblage composition in all groups. Spider community composition, being more stenotopic than other arthropod groups, was affected by the highest number of factors. A closer association with site conditions in spiders and ground beetles was manifested by a marked differentiation in the occurrence of forest and open-habitat species in the youngest (open) and oldest (closed) stands, though neither the total species number nor abundance differed significantly throughout stand development. Contrary to arthropod assemblages, significant relationships between ecological groups and environmental variables were identified only in several cases. Centipede diversity (as defined by biodiversity indices) was significantly higher in 30-35-year-old stands. Appropriate intervention in homogenous spruce stands may help increase habitat availability for most epigeic arthropods, thus enhancing, or at least maintaining, biodiversity within such habitats.