Healthy natural systems within America's 58 national parks depend, in large part, on the definition of one word: "unimpaired." That is the only word in the National Park Service Organic Act of 1916 "that sets any kind of standard," said Richard West Sellars. His 1997 book Preserving Nature in the National Parks: A History "really revolves around the struggle for the control of the definition of that word."

According to the Organic Act, which created the Park Service, the parks must be managed "to conserve the scenery and the natural and historic objects and the wild life therein and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations."

At issue is whether the mandate applies to all organisms, great and small — what we now understand collectively as an ecosystem — or merely to the most obvious "stars" like bears, forests, and rivers. "The incredible beauty of the national parks has always given the impression that scenery alone is what makes them worthwhile and deserving of protection," Sellars writes in the book's introduction.

The result is that the real focus of the National Park Service, historically, was on what the author calls "facade" management. And with that priority, landscape architects have had the lion's share of the say-so in park management.

"Landscape architecture very naturally was important in the parks, because it held the keys to maintaining the beauty of the parks while developing them with roads and visitor facilities," Sellars said in an interview at his Santa Fe home. Strong wildlife management is a key but less visible component of leaving parklands "unimpaired," he added.

"My whole book deals with the resistance to science," he said. "It just seemed in many peoples' minds to be unnecessary. In the late 1930s, there were 400 people employed as landscape architects, and I think there were nine in the biology programs. Beginning in the mid-1950s, when the service's Mission 66 program was spending about $100 million annually for park development, the budget for scientific research projects amounted to less than $30,000 a year.

"What I was looking at [in Preserving Nature] was the management of natural resources in the parks and the bureaucracy and what was behind the parks being managed a certain way. I looked at the corporate psyche of the service, as much as anything else."

Sellars retired from the National Park Service in 2008 after 35 years as an NPS historian. He first worked as a seasonal naturalist at Grand Teton National Park in the 1960s. He started his employment in 1973 in Santa Fe; six years later, he was appointed chief of the Southwest Cultural Resources Center at the NPS Southwest Regional Office on Old Santa Fe Trail. While there, he directed programs by the center's historians, archaeologists, historical architects, and underwater archaeologists. He served as a member of Santa Fe's Historic Design Review Board and was president of the George Wright Society, an organization dedicated to excellence in resource management in the parks.

This year, Yale University Press released a new edition of Preserving Nature, with a new preface and epilogue by Sellars. Still there, and still relevant, is the meat of the book, which stimulated the U.S. Congress to increase the focus on natural-resource management and science in the national parks shortly after its publication.

While lamenting that the Park Service brass treated the idea of wildlife science as anathema for most of the 20th century, Sellars acknowledges that "had the parks been managed then in the way that many are calling for today, finely attuned to ecological matters and perhaps paying less attention to public enjoyment, probably the whole national park idea would have collapsed. The founders realized they had to create a constituency in order to support the idea of the national parks."

Similarly, the establishment of Yellowstone National Park in 1872 — the first national park — likely would never have happened if not for the support of the Northern Pacific Railroad. The railroads and the American Automobile Association backed the Organic Act, foreseeing a lucrative tourist industry.

Conservation issues in U.S. parklands became more important in the 1960s and 1970s, in step with changing public concerns evidenced by the release of Rachel Carson's Silent Spring in 1962 and Stewart Udall's The Quiet Crisis in 1963, passage of the Wilderness Act of 1964, the National Environmental Policy Act of 1969, and the Endangered Species Act of 1973.

A biological, ecological perspective may yet be given much greater priority in the National Park Service. Jon Jarvis, who is currently awaiting confirmation as the agency's new director, would be the first with a biology background, Sellars said. "That is a good sign, but one of the things missing is rhetorical leadership. There's a good deal of energy and interest out in the country, and I don't see that Obama has fire in his belly on environmental matters. The Bush administration left such a plate of nasty stuff on his doorstep, but Obama doesn't seem to be strongly inclined toward the environment. I would say that his concerns fall into the category of the 'new environmentalism,' which focuses on cities and pollution and environmental justice."

Our national parks had their halcyon days during the first half of the 20th century. By perhaps the 1970s, some of their wonderful qualities seemed to have disappeared with overuse, with too many people in the parks. Sellars writes that, today, too often the parks are blighted by "teeming, noisy crowds," commercial enterprises, and "bland, unattractive modern structures" replacing the original structures built in the National Park Service Rustic mode.

Now, apathy is a problem. "It's difficult to say exactly what are the causes," Sellars said. "A lot of things caused a rise in interest in the parks after World War II: the mobility of people after going through the Great Depression and World War II and gas rationing; it just kind of exploded.

"In the earlier days, parks didn't have as much competition as they do today. They were the preeminent places to visit, and in some ways they still are, but today we have the digital world and Disneyland and Disney World, and the recreational opportunities on state lands and in the national forests and BLM lands have been improved. BLM now manages perhaps 10 big national monuments [including Kasha-Katuwe Tent Rocks National Monument] created by President Clinton."

Visitor numbers in the national parks are up about 4 percent this year, Sellars said. He presumes that's because many people don't have the money for trips to more distant locations. But he fears that, over the long haul, the national parks may be losing their distinctiveness.

For one thing, there is a push to allow gasoline-powered outdoor recreation in the parks. In the new edition's epilogue, Sellars writes of a secret revision of NPS management policies, authorized by Interior Department Secretary Gale Norton during the Bush administration, which the Coalition of National Park Service Retirees warned would open the parks to "almost unlimited use by off-road vehicles."

Then there is the new law that will allow people to carry loaded guns in the parks. And an NPS proposal to involve hunters in an elk-reduction program at Theodore Roosevelt National Park in North Dakota has been submitted for public comment.

"The parks have always been like a sanctuary: you just don't expect people to be packing heat in the national parks," Sellars said. "The more these things are successful, the more the national parks lose their distinctiveness and become somewhat obscure in the public mind."

That is most unfortunate, because those who find their way to Sequoia, Yellowstone, Carlsbad, Acadia, Yosemite, or any of the other national parks (not to mention the national historic parks, national seashores, national monuments, trails, and historic battlefields managed by the Park Service) realize significant rewards — not just in the splendor of scenery and wildlife, but in perspective.

"In the Grand Tetons, when I was doing campfire talks and nature walks, I always encouraged people to appreciate what they saw there but also to appreciate what they had back home," Sellars said. "Appreciation can lead to curiosity and understanding and greater care of the land — not just in the parks, but everywhere."