Protected areas on international borders show uneven conservation outcomes

Border protected areas (BPAs) are national protected areas that are immediately adjacent to a country's border or span two or more countries; they are characterized by distinctive opportunities and pressures. They play a critical role in protecting carbon-rich ecosystems, conserving endangered biodiversity, reducing cross-border environmental threats, and promoting peace and cooperation. At the same time, compared with other protected areas within the same country, BPAs may be particularly vulnerable to asymmetric enforcement, cross-border leakage, conflict, and weak institutional coordination. Using a pixel-level propensity score matching approach, we conducted the first global assessment of forest loss in BPAs relative to counterfactuals in nonborder protected areas within the same country. We found that compared with nonborder protected areas, most BPAs (81%) experienced lower or similar forest loss rates, preventing the loss of 112,036 ha of forest and ∼3.69 MtCO₂e/year in emissions between 2013 and 2022. However, the remaining 19% of BPAs experienced significantly higher forest loss than their counterfactuals, resulting in the loss of 87,657 ha and additional emissions of ∼2.85 MtCO₂e/year. Importantly, BPA underperformance was not driven solely by lower border protection feasibility as larger reserve size and closer proximity to urban centers were also associated with higher forest loss. Drivers of forest loss in underperforming BPAs varied regionally: agriculture expansion dominated in Africa and Asia; regulatory mismatches in timber regulations were most important in Europe; and wildfire risk was a key factor in North America. We further identified mainland Southeast Asia and the Congo Basin as urgent border conservation hotspots, where high deforestation pressure threatens both endangered species and carbon-rich forests. Thus, BPA underperformance is geographically concentrated and not pervasive. Targeted regional interventions would enhance cross-border cooperation, mobilize sustainable financing, and strengthen governance structures, while also facilitating the effective integration of BPAs into global biodiversity and climate policy frameworks.