To assess how different tree species contribute to overall diversity and system function, we sampled 99 trees by fogging in Elbe floodplain forests and collected 182,179 arthropods, of which 25,861 (14.2%) were beetles. Ninety percent of all beetle individuals and 65% of the beetle species were associated with the canopy. Beetles of the herb and soil layer contributed 35% to canopy richness, but represented only 8% of all individuals. Beetle communities differed significantly in diversity, structure and functional composition between tree species, suggesting different roles in maintaining diversity. Two types of communities could be distinguished: 1) those with high proportions of specialists that formed a predictable framework, characterised by high alpha diversity and low within-beta diversity such as those on Quercus robur and Ulmus laevis, and 2) those on Fraxinus excelsior with predominantly non-specific beetles, characterised by high alpha and high beta diversity. We found that the distribution of the most abundant zoophagous and second most abundant phytophagous guilds in the beetle- and ordinal communities was similar for all trees but differed significantly between tree species. This suggests strong top-down control of herbivore populations. These results indicate that a comprehensive assessment of tree canopy diversity is necessary and overdue to understand the ecological processes that ensure the functioning of forest ecosystems and the provision of ecological services.