Different patterns, but no temporal decline in temperate forest soil meso‐ and macrofauna over the last decade

Global biodiversity loss is threatening ecosystem functioning and human well-being. Arthropods above the ground have substantially decreased in abundance and diversity during the last 15-20 years. However, changes in belowground biodiversity, particularly in forests, received little attention. Here, we analyzed a comprehensive dataset of soil-living meso- and macrofauna in forests differing in land-use intensity within the framework of the open research platform "Biodiversity Exploratories" in Germany. The abundance of soil animal species was analyzed at 3-year intervals, covering 12 years from 2008 to 2020. Neither species richness nor γ-diversity of both soil meso- and macrofauna declined, suggesting contrasting dynamics of biodiversity above and below the ground. The density and diversity of soil mesofauna varied significantly between years within regions. These variations were closely related to the precipitation levels in the previous winter and during the sampling period. However, there was no consistent long-term downward trend, as declines in some years were offset by full recoveries. Temporal trends of soil macrofauna taxa densities were inconsistent and depended on regions and forest management intensity. The stability of many soil taxa was related to effective diversity and asynchrony of species fluctuations, supporting the portfolio effect. However, variance ratios not different from null communities and a negative impact of temporal species turnover on stability suggest a minor influence of compensatory dynamics as predicted by the insurance hypothesis. Instead, strong abiotic control resulted in synchronous species dynamics. Species densities, particularly those of soil mesofauna, depended heavily on abiotic conditions, such as soil moisture. While influencing the density and richness of soil fauna and modulating the effects of precipitation, forest management did not directly affect the stability of soil fauna communities. While our findings demonstrate a remarkable resilience of soil animal communities in temperate German forests amidst ongoing biodiversity decline, they are based on a limited temporal window and forests in central Europe. As such, caution is needed when extrapolating these results to longer timescales or wider spatial scales. Nonetheless, our study provides valuable insights into the temporal dynamics of soil faunal density and diversity, and the key drivers underlying their community stability.