Synergistic effects of flower strips and landscape complexity buffer arthropods against warming and drought – A meta-analysis

Flower strips and areas ('flower strips’) have been introduced as agri-environment schemes to agricultural landscapes to counteract farmland biodiversity loss. Beetles and spiders have important regulatory functions in agroecosystems, such as predating crop pests. Although there are many case studies, the effects of flower strips on these organisms have not yet been synthesized quantitatively. Equally understudied are the potential mitigation effects of flower strips under projected climate change – particularly warmer and drier conditions – and how these effects may vary across different landscape contexts. Thus, we carried out a systematic review and identified 36 primary studies from 12 European countries that examined abundance and species richness of three beetle (Carabidae, Coccinellidae, Staphylinidae) and eight spider families (Araneidae, Clubionidae, Gnaphosidae, Linyphiidae, Lycosidae, Tetragnathidae, Theridiidae, Thomisidae) in flower strips from 1995 to 2024. Data on land use and climate were obtained from the Copernicus project and the CHELSA database. We conducted a meta-analysis to understand the effectiveness of flower strips for different beetle and spider families, as affected by flower strip characteristics (age, seed mixture richness), landscape complexity, annual and winter temperature and precipitation, and potential interactions. We found overall positive effects of flower strips on abundance and species richness of beetles and spiders, but also family-specific differences. Increasing winter temperatures affected beetles and spiders, with positive effects in homogeneous landscapes, and neutral to negative effects in more complex ones. Beetle abundance and richness increased with annual temperature and precipitation in complex landscapes but declined in homogenous ones. Spider abundance increased with winter precipitation in homogeneous but decreased in complex landscapes. Overall, flower strips are an effective conservation tool for beetle and spider populations and thus possibly sustain pest-control services. However, climate change is altering their effectiveness across Europe, underscoring the need for more resilient and landscape-integrated agroecosystems to sustain arthropod biodiversity and ecosystem functioning.