Increased arthropod biomass, abundance and species richness in an agricultural landscape after 32 years

Recent studies reporting widespread declines in arthropod biomass, abundance and species diversity raised wide concerns in research and conservation. However, repeated arthropod surveys over long periods are rare, even though they are key for assessing the causes of the decline and for developing measures to halt the losses. We repeatedly sampled arthropod fauna in a representative Swiss agricultural landscape over 32 years (1987, 1997, 2019). Sampling included eight study sites in four different semi-natural and agricultural habitat types and different trap types (pitfall, window, yellow bucket) over an annual period of 10 weeks to capture flying and ground dwelling arthropod taxa. In total, we analyzed 58,448 individuals from 1343 different species. Mean arthropod biomass, abundance and species richness per trap was significantly higher in 2019 than in the prior years. Also, species diversity of the study area was highest in 2019. Three main factors likely have contributed to the observed positive or at least stable development. First, the implementation of agri-environmental schemes has improved habitat quality since 1993, 6 years after the first sampling. Second, landscape composition remained stable, and pesticide and fertilizer was constant over the study period. Third, climate warming might have favored the immigration and increase of warm adapted species. Our results support the idea that changes in arthropod communities over time is highly context-dependent and complex. Implications for insect conservation We conclude that the integration and long-term management of ecological compensation patches into a heterogenous agricultural landscape supports insect conservation and can contribute to stable or even increased arthropod abundance, biomass and diversity. Future studies are needed to clarify interdepending effects between agricultural management and climate change on insect communities.

Automated summary

Recent studies have shown declines in arthropod biomass, abundance, and species diversity, raising concerns for research and conservation. However, long-term repeated surveys of arthropods are rare. In this study, arthropod fauna was sampled over 32 years in a Swiss agricultural landscape, and the results showed an increase in biomass, abundance, and species richness in 2019 compared to previous years. Factors such as improved habitat quality, stable landscape composition, and climate warming likely contributed to these positive trends. The findings highlight the context-dependency and complexity of arthropod community changes over time.