Why do some protected areas prevent habitat loss better? Intrinsic and extrinsic factors shaping their individual effectiveness

Protected areas (PAs) are key instruments for reducing habitat loss. Yet, variability in their effectiveness at the individual level remains poorly understood, limiting our ability to assess their conservation impact. This study addresses this gap by applying a conceptual framework and methodological approach designed to assess differences in effectiveness among individual PAs within a network. We analyzed 85 terrestrial forested PAs decreed before 2000 in Mexico using spatial data, matching techniques, and machine learning methods to evaluate (1) overall network effectiveness, (2) effectiveness of individual PAs, (3) the intrinsic and extrinsic factors associated with variation in effectiveness, and (4) the specific contribution of these factors. At the network level, PAs reduced habitat loss by -3.74%. Individually, PAs reduced it by an average of -2.96% ± 5.1 SD. Most PAs (n = 80; 94%) contributed to forest conservation, either by significantly preventing habitat loss (n = 50; 59%) or by exhibiting low habitat loss rates due to extrinsic conditions limiting human activity (n = 30; 35%). Only five (6%) PAs showed higher habitat loss rates than unprotected areas. Interestingly, PAs facing higher habitat loss pressure —characterized by lower slopes and elevations, greater distance from roads, and neighboring communities reliant on primary-sector jobs—were the most effective in preventing habitat loss, although the influence of these variables varied widely among individual PAs. Our findings highlight the importance of considering intrinsic and extrinsic characteristics when evaluating and managing PAs. Our framework can be applied to other regions to strengthen conservation strategies aimed at mitigating habitat loss.