Power
People rarely use "powerful" and "park ranger" in the same sentence—unless the sentence was something like, "The park ranger saved us from the powerful bear." As far as we know, there's never been a park ranger who reshaped the face of all human society with his or her incredible ranging.
Still, park rangers do have a lot of power over guests in the park. The types of rangers who are in charge of law enforcement are kinda like nature cops. They make sure the rules of the park are enforced; these guys can even give you a speeding ticket.
You can also move up in the ranks of park ranger-dom (hopefully not through Lady Macbeth-like ruthlessness). Being the superintendent of a heavily visited park, like the Great Smokies or the Grand Canyon, is a huge job, and you might have to rule with an iron fist to keep it all in check.