A systematic survey of regional multitaxon biodiversity: evaluating strategies and coverage

Abstract Background: In light of the biodiversity crisis and our limited ability to explain variation in biodiversity, it is time to rethink the way we study biodiversity and its causes. Inspired by the recently published ecospace framework, we developed a protocol for environmental and biotic mapping that is scalable to habitats, ecosystems and biomes. We applied our protocol as part of a comprehensive biodiversity study in Denmark. We selected study sites (40 x 40 m) using stratified random sampling along the major environmental gradients underlying biotic variation. Using standard methods, we collected vascular plant, bryophyte, macrofungi, lichen, gastropod and arthropod species lists for each site. To evaluate sampling efficiency, we calculated regional coverage (relative to the number of species known from Denmark per taxonomic group), and project scale coverage (i.e., based on the sample coverage per taxonomic groups). To cover eukaryotic organisms that are less easily targeted by classical inventories (e.g., nematodes, 9non-fruiting9 fungi) we collected soil samples for environmental DNA analyses. Finally, to assess site conditions, we conducted a comprehensive mapping of abiotic conditions (position), biotic resources (expansion of organic carbon) and habitat continuity (spatial and temporal). Results: The 130 study sites covered 0.0005% of the Danish terrestrial area (~42,500 km2). We found 2040 species of macrofungi (62% of the Danish fungal pool), 663 vascular plant species (42%), 254 bryophyte species (41%) and 202 lichen species (20%). For invertebrates, we observed 334 spider species (59%), 126 carabid beetle species (38%) and 105 hoverfly species (36%). Overall, sample coverage was high across taxonomic groups, indicating that 130 sites were sufficient to represent the variation in biodiversity across Denmark. This inventory is unprecedented in detail and resulted in the discovery of 150 species with no previous record for Denmark. Comparison of soil DNA with observed plants was both strong and confirmative for a recovery of plant biota by soil-derived DNA. Conclusions: We successfully covered the majority of targeted biodiversity across Denmark using an approach that includes habitat coverage, multi-taxon biodiversity assessment, and ecospace mapping. Our approach can be readily applied to assess biodiversity for other ecoregions.