Response of ground-dwelling harvestman assemblages (Arachnida: Opiliones) to European beech forest canopy cover

We studied the effects of the overstory canopy cover on ground-dwelling harvestmen communities in European beech forests in the Western Carpathian Mts. We analyzed the differences in species richness, abundance and composition in two tree canopy cover categories (closed and open canopy). Overall, 1765 individuals belonging to 16 species were caught using pitfall traps. Repeated-measures ANOVA revealed that under both closed and open canopies a similar absolute and rarefied species richness and number of individuals (standardized to 100 pitfall trap days) were caught, and that both species richness and abundance were affected by the season (i.e., time of trap replacement); yet the total number of individuals trapped was more than two times greater under the open canopy than under the closed canopy. Despite the subtle differences in the taxonomic composition of the catches under the open and closed canopies revealed by DCA followed by RDA, the composition of ground-dwelling harvestmen assemblages differed under the two canopy covers. The open canopy was more suitable for heliophilic, xerothermic eurytopic harvestmen species typical for open and ecotonal habitats, such as Egaenus convexus (C.L.Koch) and Oligolophus tridens (C.L. Koch) but still suitable for hemihygrophilic Lophopilio palpinalis (Herbst). The closed canopy stands were preferred by shade-tolerant, hygrophilic eurytopic harvestmen species, such as Trogulus sp. Latreille, Dicranolasma scabrum (Herbst) and Platybunus bucephalus (C.L. Koch). Our results highlight the importance of intra-habitat heterogeneity of a harvestmen community.