Long‐term restoration outcomes in biodiversity offsetting: evaluating 20 years of habitat development and target attainment

Introduction Biodiversity offsetting aims to achieve no net loss of ecosystem functions by compensating unavoidable impacts. Germany has enforced a legally binding impact mitigation regulation (Eingriffsregelung) since 1976 using numerical eco‐point scoring systems, yet its long‐term ecological effectiveness remains poorly understood. We evaluated long‐term restoration outcomes of compensation measures in North Rhine–Westphalia across complementary indicators of target habitat attainment, numerical target‐value achievement, and restoration progress. Methods Combining archival reconstruction with field mapping following official assessment frameworks, we analysed 74 compensation measures (>20 years old, comprising 661 habitat units, 408.9 ha) in the Lower Rhine Lowlands. We assessed target habitat attainment, numerical target‐value achievement, numerical target deviation (ΔTarget), and an adapted Achieved Restoration index AR) using mixed‐effects models. Results Overall, 64% of habitat units achieved their numerical target score, whereas only 17% attained their intended target habitat type. Forests showed favourable outcomes, while grasslands showed low target attainment and restoration performance. Larger habitat units performed generally better. Although restoration age positively correlated with AR, older sites did not show progressive convergence toward intended target habitat states. Discussion Numerical target‐value achievement occurred far more frequently than target habitat‐type attainment, demonstrating that standardized eco‐point scoring metrics can mask major structural and compositional divergence. Long‐term outcomes were heavily influenced by habitat‐specific successional dynamics, site conditions, and management histories, with grassland habitats particularly prone to target failure due to unmanaged forest succession.