Spider communities in the aboveground oak forests of central Europe are determined by vertical scale: An important missing link for biodiversity conservation

Spiders are generalist predators able to respond very well to environmental conditions. Therefore, they are good bioindicators for forest management practices. The vertical distribution of spiders in forest stands has very rarely been studied. Thus, we investigated patterns in species richness, diversity, life-history traits and functional diversity of spiders within the aboveground vertical stratification of oak dominated forests and their response to the canopy cover gradient. There were three localities sampled during four growing seasons (2008–2011, Southern Moravia, Czech Republic). Spiders were sampled monthly by flight intercept traps, which were placed in three stratigraphical levels of oak stands. Altogether, 3592 spiders, representing 18 families, and 112 distinguishable species were collected during the study. We found that species richness, total abundance the abundance of ambush hunters, other hunters and scarce, rare and very rare species of spiders increased from ground level to the canopy, and that species composition changed across the vertical gradient. Some of these characteristics were significantly influenced by interaction with canopy cover. Less common ballooning species preferred the ground part of forest stratification. Canopy cover evaluation showed that the abundance of orb web weavers and less common ballooning species was highest in the more closed canopies. The opposite trend was found for sheet web weavers, very abundant species and open habitat species. Space web weavers, other hunters and very common ballooning species showed increased abundance in the higher layers under conditions of more open canopy cover. Our results suggest that sampling spiders across the vertical gradient of forest stands might be important for a proper biodiversity and management practice evaluation, although most recent assessments were conducted on ground-dwelling spiders obtained from pitfall traps.