Protected areas are a key tool in the conservation of global biodiversity and carbon stores. We conducted a global test of the degree to which more than 18,000 terrestrial protected areas (totalling 5,293,217 km²) reduce deforestation in relation to unprotected areas. We also derived indices that quantify how well countries’ forests are protected, both in terms of forested area protected and effectiveness of protected areas at reducing deforestation, in relation to vertebrate species richness, aboveground forest carbon biomass and background deforestation rates. Overall, protected areas did not eliminate deforestation, but reduced deforestation rates by 41%. Protected area deforestation rates were lowest in small reserves with low background deforestation rates. Critically, we found that after adjusting for effectiveness, only 6.5%—rather than 15.7%—of the world’s forests are protected, well below the Aichi Convention on Biological Diversity’s 2020 Target of 17%. We propose that global targets for protected areas should include quantitative goals for effectiveness in addition to spatial extent.

保护区是保护全球生物多样性和碳储存的重要工具。我们对 18,000 多个陆地保护区（总计 5,293,217 平方公里²) 减少未受保护地区的森林砍伐。我们还得出量化国家森林保护程度的指标，包括受保护的森林面积和保护区减少毁林的有效性，以及与脊椎动物物种丰富度、地上森林碳生物量和背景毁林率相关的指标。总体而言，保护区并没有消除森林砍伐，而是将森林砍伐率降低了 41%。背景森林砍伐率较低的小型保护区的保护区森林砍伐率最低。至关重要的是，我们发现在调整有效性后，世界上只有 6.5%（而不是 15.7%）的森林受到保护，远低于《爱知生物多样性公约》2020 年 17% 的目标。