Highly protected areas buffer against aridity thresholds in global drylands.

Drylands are highly vulnerable to global-scale aridity thresholds that cause drastic reductions in their productivity. While protected areas may help buffer against the impact of aridification, their effectiveness in mitigating the aridity thresholds across global drylands remains virtually unknown. Here we assembled a global dataset of drylands and found that highly protected areas, which include national parks and wilderness areas, can buffer the emergence of aridity thresholds in ecosystem productivity by up to 0.15 units of aridity. This suggests that, in highly protected regions, drylands must become substantially drier before reaching an aridity-induced threshold in ecosystem productivity. The importance of highly protected area for supporting drylands was consistent across 23 years of study, in woody and non-woody ecosystems and after accounting for rangelands. Notably, only 3.3% of all drylands were under The International Union for Conservation of Nature (IUCN) category I high levels of protection such as wilderness areas, with 3.8% being protected under IUCN category II (for example, national parks). Overall, our findings highlight the crucial role of highly protected areas in maintaining productive dryland ecosystem in the face of global aridity thresholds, and further stress the need for increasing the level of protection to ensure the conservation of drylands under predicted climate changes.