The influence of logs on the spatial distribution of litter-dwelling invertebrates and forest floor processes in New Zealand forests

Logs have been recognized as being important components of forest ecosystems acting as a reservoir for Carbon, as sites for seedling establishment and as habitat for insects, birds and other wildlife. In this study, red beech (Nothofagus fusca) logs of a similar decay class were selected from an old-growth forest in the South Island of New Zealand, to investigate the influence of log proximity on invertebrate community composition and litter quality. Core samples were taken from the forest floor at 0 m (beneath logs), 1.5 and 2.5 m distances from the logs, and invertebrates were extracted from the litter and fermentation layer using Tullgren funnels. All invertebrates were identified to family level with the exception of Acari (mites), which were identified as recognizable taxonomic units (RTUs). The invertebrate fauna of the litter layer was more diverse than that of the fermentation layer and log proximity affected invertebrate family composition in both the litter and fermentation layers. Of the 79 invertebrate families and 41 RTUs extracted from all core samples, five families and three RTUs differed significantly among the three distances from the logs. In the litter layer Threvid larvae (Diptera) and Phlaeothripidae (Thysanura) significantly increased in abundance with increasing distance from the logs. While Dalodesmidae (Diplopoda), Neobisiidae (Arachnida), Amphinectidae (Arachnida) and mite RTUs O, AB, AM occupying the leaf litter and mite RTU AM occupying the fermentation layer significantly decreased in abundance with increasing distance from the log. The density of litter properties such as leaves, twigs, wood, roots, soil and fragments <2 mm differed significantly between the litter and fermentation layers. The density of wood in samples collected beneath logs was higher than that of samples taken at the other distances. At all distances, the C:N ratio was significantly higher in the litter layer compared with the fermentation layer. The C:N ratio beneath the logs in the fermentation layer was significantly higher than that at the other distances. The results indicate that red beech logs influence litter-dwelling invertebrate communities which has consequences for below-ground processes and has implications for CWD management in production forests. (C) 2003 Elsevier Science B.V. All rights reserved.