A new approach to investigate arthropod biodiversity in forest ecosystems, using meta‐barcoding on trap combinations

Abstract Autonomous monitoring of arthropod biodiversity is regularly based on a single trap type. However, the taxonomic composition of samples strongly depends on the trap type, and even the most widely used systems catch very different subsets of species from a local species pool. Metabarcoding of Malaise trap samples is a widely used approach. However, it is known that this trap type is strongly biased on dipterans and hymenopterans. We developed a combination of three trap types to show how the representativeness of local samples is improved and used them in 101 strict forest reserves (SFRs) in Germany for an overall survey. Separate analyses were conducted in two oak‐dominated and three beech‐dominated SFRs to show the different species composition of each trap type. COI sequences with high similarity were clustered into OTUs that can be assigned to BINs corresponding to taxonomic species. In the overall survey, we found 10 K OTUs that could be assigned to 2.4K species. In the oak forests, 400 species from 31 orders and, in the beech forests, 538 species from 27 orders could be identified. The four most important orders (Coleoptera, Diptera, Hymenoptera and Lepidoptera) together accounted for 85.5%–88.9% of all (BINs). The results confirm the dominance of Diptera and Hymenoptera in Malaise traps and of beetles in window and pitfall traps. The detection rate of our trap combination increased by 2.5% to 0.78% compared to the Malaise traps. We, therefore, estimate that about 12.8 K species live in German forests. The number of BINs increased by more than 29% in our combined traps compared to the Malaise‐only traps. With limited additional fieldwork, our trap combination reduced the taxonomic bias in the local samples compared to other studies relying only on Malaise traps, with the orders of the local fauna better represented. As the combined traps take about twice as long as the Malaise trap to set, we recommend the use of additional trap types in biodiversity monitoring and research to obtain a broader taxonomic and functional overview of changes in arthropod diversity.