Measuring what matters: operationalising biodiversity indicators for results-based CAP monitoring

In this viewpoint article we address the challenge of monitoring biodiversity impacts of the EU’s Common Agricultural Policy (CAP) in agricultural landscapes, where ecological complexity and fragmented instruments have limited effectiveness. We review biodiversity indicators applied to soils, insects, birds, and habitats and assess their alignment with Essential Biodiversity Variables (EBVs) and policy-oriented RACER criteria (Relevance, Acceptance, Credibility, Ease of use, and Robustness). Using a systematic literature review of 3440 articles and expert evaluation, we identify 130 indicators and rank them according to relevance, scalability, temporal sensitivity, data availability, and standardization which indicate their scientific quality. We highlight advanced indicator systems - such as remote sensing (fAPAR), eDNA-based soil indices (eBII), meta-barcoding of insect diversity (MIDI), and avian acoustic diversity (AADI) - that demonstrate high potential for operational use in biodiversity monitoring within CAP. We show how these indicators can deliver reliable, scalable, and cost-effective biodiversity assessments while meeting both scientific quality standards and policy requirements. By integrating EBVs with the RACER framework, we propose a conceptual pathway to harmonize scientific robustness with policy relevance. We argue that adopting such indicators is essential for implementation of the results-based agri-environmental schemes, improving the accountability, transparency, and effectiveness of CAP measures, aligned with the EU Biodiversity Strategy 2030 and the Nature Restoration Law.