Under natural conditions beech forest would be the most widespread habitat in Central Europe. Therefore the knowledge of this vegetation type, including the animal communities dwelling there, as well as the mechanisms forming these communities are of high interest for biodiversity research and conservation in Central Europe. However, historically, Central European beech forests were thought to harbor only relatively few species. Here, faunistic data of five beech forest reserves, which were generated as part of the Hessian strict forest reserves program, are analyzed to investigate diversity patterns of Hessian beech forests of low mountain ranges. We focus on species-level data from six organism groups: Aculeata, Araneae, Coleoptera, Heteroptera, Lumbricidae, and Macrolepidoptera. We show that with 2552 forest-dwelling species from these organism groups an unexpectedly high number of species was found in Hessian beech forests, and that a higher species richness can be expected in these groups. Observed species diversity ranges from 1245 to 1556 forest dwelling species in the five individual forest reserves. Overall, 36 % of the forest dwelling species of the considered species groups known from Germany were found with all applied methods in the forest reserves. Different forest reserves share 40-50 % of the species, representing 50-70 % of the species of the individual reserves, indicating high levels of regional and habitat-structure based differentiation. Only 21 % of the species are found in all five reserves. The low percentage of species found in all five reserves is, in addition to differing local conditions, probably a result of the communities being composed of few highly abundant and many rare species, leading to a high percentage of species only found by chance in our surveys. We also observe differences in community heterogeneity among the five reserves. Patterns differ between organism groups, clearly indicating that a focus on single taxa or a single indicator group falls short of revealing meaningful patterns. In spider communities, beta diversity is linked to the spatial distance between traps. In other organism groups community heterogeneity within reserves rather depends on structural heterogeneity. Species richness was associated with percentage of reserve area not covered with the most dominant habitat type, the deadwood amount, and with survey year. Being the potential natural vegetation of Germany and considering the unexpectedly high diversity of their associated fauna, beech forests bear a great conservation value. However, their widespread occurrence and dominance is likely to push them out of focus of conservation efforts. Yet protecting diverse and richly structured beech forests can contribute greatly to preserving the native arthropod fauna and should play a central role in biodiversity conservation efforts in Central Europe.