Symmetrical local and spillover effectiveness of protected areas in anthropogenic mitigation and vegetation conservation

The Earth has exceeded six critical environmental boundaries, posing threats to sustainable development and the realization of human well-being. Protected areas (PAs) are the core global governance tool to address this challenge and need to be ensured to achieve effective conservation outcomes. The existence of spillover effect may either enhance or diminish the value of PAs, but the consistency between local and spillover effectiveness remains unclear. Here, we focused on 10768 PAs in six typical global regions to explore the consistency between local effectiveness and spillover intensity in two dimensions of anthropogenic mitigation and vegetation conservation. During this process, we employed a nonlinear method to quantify the extent of spillover effect and used the counterfactual method to evaluate the conservation effectiveness. Our analysis indicates that in different regions, the change in the proportion of ecological land varies nonlinearly with the distance from the PA boundary, and the spillover extent varies among regions. A small part of PAs exhibited a significant isolated phenomenon. The spillover intensity and local effectiveness were positive for more than half of the PAs. PAs have achieved consistent local and spillover effectiveness in both dimensions, while the spillover intensity was weaker. Precipitation, NPP and elevation were the dominant influencing factors for local effectiveness in both dimensions. Our results showed that merely designating PAs is not sufficient for success. Effective management measures are also needed. The assessment of PA effectiveness should not be limited to the designated boundaries, but also consider the indirect impact of spillover effect. Indicators of multiple dimensions should be taken to quantify the effectiveness comprehensively.