The geometry of global protected lands

Expanding protected areas (PAs) is a worldwide endeavour aimed at addressing the biodiversity crisis and harnessing the benefits that natural ecosystems provide to humanity. However, conservation agendas often overlook the spatial geometry of PAs—shape and size—and its implications for critical issues such as agricultural encroachment, poaching, biological invasion or the contact between wildlife, domestic animals and humans. Here we show how the global PA expansion has added predominantly small and complex-shaped PAs. Consequently, one-third of protected lands are located within 2 km of unprotected areas, while only 0.6% extend beyond 100 km. Developed countries tend to have smaller, dispersed, perforated and fragmented PAs, while less-affluent nations host larger, more-compact units. Relatively smaller and less-compact PAs were also found within the world’s most critically endangered biomes. The results highlight overlooked threats for the long-term conservation of nature and global environmental sustainability. As countries continue to expand their PA networks, the consideration of the spatial geometry of protected lands becomes urgent.