Filmmaker Ken Burns has explored baseball, jazz, the Civil War and more. Now, in a six-part series that premieres Sunday on PBS, he turns his lens on our national parks -- "America's best idea." He spoke to OnEarth about his motivation for the documentary, what he learned about wolves and other wildlife, and his concern that global warming could destroy some of America's treasures for future generations. The interview has been edited for brevity.

Why were you interested in telling the story of America's national parks?

I've always been interested in how my country ticks, and that's what I try to explore in my films. The national parks are the first time in human history that land has been set aside -- not for kings or noblemen or the very rich -- but for everybody, and for all time. We invented it. It's an utterly democratic idea. In a way, it's the Declaration of Independence applied to the landscape.

Did spending so much time in our national parks affect your thinking about preserving nature and the environment?

I think it can't help but do that. It's not so much that you suddenly wake up and think, "Now I'm for nature." It's just that your experience again and again and again transforms all levels of your being by spending time in our national parks. These things work on us in very special ways. There are so many paradoxes. You stand on the rim of the Grand Canyon, you look down and you see the patient work of the Colorado, and you feel instantly your insignificance in the face of the eons of time exhibited before you. But that has a strange way of making you feel bigger, connected to everything, a part of everything else.

You've said that you hope your film encourages more Americans to have that experience. But do you worry about the tension between encouraging more visitors and at the same time preserving the parks?

Absolutely, it's a huge tension -- and a wonderfully democratic one to have. It's built into the act that created the National Park Service in 1916, well after the parks themselves. It says that they're here for the benefit and the enjoyment of the people, but they should also be left unimpaired for future generations. So the great tension of course is that when people flock to the national parks, they are in danger, as one park service director said, of "wearing out the scenery," of "loving them to death." And yet this is an important problem for a democracy to have. Ninety-five percent of the people who visit a national park never go more than a few hundred yards from the road and don't see the vast tracts of wilderness in there. They remain pristine and protected. But if the parks don't have constituents, they run the danger that when the next development idea comes down the pike, they're not going to have someone standing up and saying, "No, you can't do that."

One of the things that obviously appeals to park visitors is the opportunity to see wildlife such as wolves and bears and bison -- many of which are threatened or endangered. Did your experience provide you any insight into efforts to preserve those animals?

During our filming and research, we "met," in a historical sense, a biologist named George Melendez Wright, who was the park service's first biologist and who insisted that the parks re-arrange their thinking about wildlife. In the early days, the parks were almost resorts. It was about recreation. The bears were fed, the predators were killed, park rangers were directed to the nests of pelicans to stop their eggs from hatching because they thought the pelicans denied fishermen of too many fish. We changed our ideas thanks to George Melendez Wright and evolved our relationship to nature and to wildlife. We no longer feed those bears, we no longer open the garbage dumps, we no longer kill the predators, we reintroduced wolves into Yellowstone. These are important benchmarks of progress of the national park ideal.

Speaking of wolves, I know you're aware that they were removed from the endangered species list recently in parts of the northern Rockies, and they're being hunted this month in Idaho and Montana. What are your thoughts about that?

As Wright and later Adolph Murie, another biologist, pointed out, the wolves were not responsible for the decline of other animal populations. They were in fact part of a very complex ecosystem that culled and strengthened other wildlife by weeding out the sick and elderly of, say, an elk or sheep population. So they're hugely important to the ecosystem, and therefore thank God that they are protected in our national parks so that we can offset whatever dilatory effect comes from these wolf kills, which to me are just inherited fear. We've hated the wolf for reasons mostly unfair through all of human history.

Are there other important insights about wildlife and wilderness preservation that you gained while working on this film?

If there had been no national parks, there would be no bison. The most magnificent symbol of our country would be a stuffed animal in a museum like a wooly mammoth -- something prehistoric and long gone. But we've got hundreds and hundreds of bison in Yellowstone and other places that are protected through the national park service. Without national parks, the Grand Canyon would be lined with mansions. Without national parks, the Everglades would have long ago been drained and replaced with track housing, and so one of the most diverse environments on the planet, the only place where alligators and crocodiles co-exist with thousands of wading birds, would all be gone. Yosemite and Zion would be gated communities. Yellowstone would be "Geyser World."

Do you think that if more Americans visited their national parks or connected with nature in other ways, there would be more concern about environmental issues?

Of course. Just as we say that we're shamed by the low turnout at elections and that we wished we had a more engaged citizenry, the same thing applies to our national parks. If more people go, you're building more park protectors, and you're encouraging Congress to give more money to the national parks, as they have at many times in our history when attendance has skyrocketed. The more people who come, the more good citizens you make. Thomas Jefferson didn't think you could be an authentic American unless you had a relationship with nature. He couldn't conceive of a national park, because he thought all of America was a park. But the continent he thought would take 100 generations to fill up was filled up in 100 years, so parks had to be created to offset the fact that we were about to lose it all.

Your film will delve into a number of challenges that the national parks have faced over the years. What do you see as the greatest challenges facing them today and in the future?

From the very creation of the parks, this is not a story of, "Let's watch Bambi frolic in the forest." This is a story of conflict and drama. Human beings, and Americans in particular, are by nature extractive, some would even say rapacious. It used to be said that American progress could be measured in how much land was "redeemed" from wilderness. So in the 19th century, and even today, we had to go against people who look at a river and think, "dam," or people who look at a beautiful canyon or valley and wonder what mineral wealth can be extracted from it. The history of the national parks is the history of that conflict, of people going against the momentum and tide of human affairs to stop that. As our national parks have grown, they've become much more sensitive bellwethers of the environment, recording even more precisely than other areas of our country the effects of climate change, the adverse effects of power plants and pollution, the introduction of non-native species, a whole host of things. They become laboratories for understanding issues that we're dealing with throughout our whole globe.

Are you concerned about the changes that global warming could bring to some of our national parks, such as Yellowstone, where scientists are worried that warmer temperatures could allow pine beetles to wipe out entire forests?

Tremendously concerned. I had the privilege, if that's even the right word, to witness first hand the impact of those pine beetles at work in Yellowstone. And I dread the fact that my children or my grandchildren might one day go visit an exquisite national park in northwestern Montana, and it will be called, "The Park Formerly Known as Glacier."

Learn More:
PBS: The National Parks: America's Best Idea
OnEarth article: Bear Versus Beetle 
Report: National Parks in Peril