A century ago Congress created the National Park Service (NPS) “to conserve the scenery and natural and historic objects and the wildlife therein…” Back then there were 35 national parks and monuments, now there are over 400. These include, of course, Yellowstone and Yosemite, the so-called “natural” parks where the NPS is sworn to safeguard biodiversity, wild rivers, and carbon sinks (a.k.a. forests). They are America’s environmental legacy.

The NPS also has under its wing other types of par...