First insights into soil fauna mapping across Europe using data from multiple data sources for three different taxa

Soil fauna is one of the most important components of the soil ecosystem. It is highly diverse and abundant, supporting essential ecosystem services. However, its use in management decisions has been limited by now. This is partly a result of missing data and knowledge for large-scale mapping and application. In this study, our objective was to shed light on these aspects by mapping the spatial distribution of representative groups of macro- and mesofauna. Specifically, we used publicly available data for Earthworms, Millipedes, and Springtails and mapped their abundance, richness, and diversity across Europe. We applied machine learning techniques to understand the spatial configuration of these soil fauna taxa as influenced by topography, climate, vegetation, land use, and soil properties. Springtail abundance ranged from 1000 to 15,000 individuals per m2, while rarefied species richness ranged from 2 to 7 species per sample, with higher values in mountainous regions compared to plains. Earthworm abundance ranged from 20 to 300 individuals per m2, while richness ranged from 2 to 6 species, with higher values in Scandinavia compared to central and eastern Europe. Millipede abundance ranged from 20 to 400 individuals per m2, while species richness ranged from 1 to 6 species, with the highest values in central Europe and the lowest in northern Europe. Although the three taxonomic groups displayed marked differences in spatial patterns, in general, the diversity values were higher in northern and central Europe compared to South Europe. In the case of the latter, however, the data available were less, which might have led to underestimations of diversity in this area. Our results showed further that for Springtails, Earthworms and Millipedes, altitude, climate, vegetation, and land use were among the strongest predictors of species richness and diversity patterns, while abundance was mainly influenced by vegetation and soil properties. Our results indicate that climate changes, particularly rising temperatures, might impact on the evolution of soil fauna communities in the coming decades, especially in the mountain areas. Although mapping provides a visual presentation of soil ecosystems and conservation trends, as well as soil biodiversity hotspots, we also found that soil mapping has a high degree of uncertainty (e.g. in areas of low data availability, such in the case of Southern Europe), largely underestimated due to the highly endemic and patchy nature of soil fauna, with significant disparities in current data, including historical differences in methodologies, sampling efforts and scope of studies. Our mapping methodology can be applied at regional, national or European scale, providing actionable management and policy implementation pathways. Our study highlights the need to continue soil biodiversity monitoring efforts, especially in areas with less data, promote data sharing and conduct further research on soil biodiversity conservation and management.