Spiders and harvestmen on large solitary trees along rural-to-urban gradients across Europe

The biodiversity and distribution of many groups of arthropods living on the trunk and in the canopy of large trees is still relatively little described at the European scale. Pan traps are commonly used to assess pollinators in various ecosystems but have been less used to monitor spiders and harvestmen in trees. Here, we report on the diversity and abundance of spiders and harvestmen caught using pan traps in large solitary trees. Sampling took place on Quercus robur, Fraxinus excelsior, and Tilia sp. along rural-to-urban gradients in nine European cities. Most spiders and harvestmen were caught in rural areas, but the total amount of collected specimens varied considerably across the sampled cities. Salticus zebraneus, a species that frequently inhabits old trees, was the most abundant spider, while Dicranopalpus ramosus was the most frequently recorded harvestman. Our results demonstrate that using pan traps for sampling treeinhabiting spiders and harvestmen can be a valuable low-cost and low-effort method.