Roads imperil South American protected areas

• 830,000 km of roads (∼20× Earth’s circumference) run through 3,837 protected areas in South America. • 83% of protected land is roadless but fragmented into ∼25,500 patches; half <1 km² and only 6% >100 km². • Roads are widespread across regions and IUCN categories; in most biomes, median interior distance to roads is ≤3 km. • Mitigation requires restoring connectivity, roadless cores, road regulation, and biodiversity-sensitive planning. Protected areas (PAs) in South America play a crucial role in safeguarding biodiversity and ecosystem services. However, the widespread presence of roads within PAs poses a major, yet largely overlooked, threat to their ecological integrity. In this study, we used the most recent version of OpenStreetMap to assess the extent and spatial distribution of road networks within South American PAs. We identified approximately 830,500 km of roads, a length equivalent to 20 times the Earth’s circumference, within 3,837 PAs (24% of the continent’s land area). By applying a 1-km buffer around all roads, we found that although about 83% of the protected land area remains technically roadless, it is dissected into nearly 25,500 discrete patches, more than half of which are smaller than 1 km², and only 6% exceed 100 km². Consequently, in six out of nine terrestrial biomes, the median distance from protected interiors to the nearest road is less than 3 km. Only remote regions, such as flooded grasslands and savannas, sub-Antarctic forests, and large portions of the Amazon basin, exhibit low road presence within PAs. Immediate conservation action is essential, with a focus on transparent road monitoring and management to preserve the ecological functions of these critical landscapes and ensure the long-term conservation of nature.