At a time when conservationists are calling for 30 percent of the world to be protected for nature, and when the E.O. Wilson Foundation warns, “the world’s incredible biodiversity is shrinking fast,” existing national parks – and potential parks -- can play a key role in preserving nature and slowing the sixth mass extinction. But it could be a hard won goal, as national parks and lands worthy of national park designation are being hemmed in by development and resource extraction. These are some of the battlegrounds that are key to nature’s future.