National parks are institutions— “the prescriptions that humans use to organize all forms of repetitive and structured interactions” (Ostrom 2005, p. 3). As such, they change in accordance with human interactions and values, responding to economic drivers, visitor patterns, politics, development, and sometimes even scientific information. The idea of a national park seems to change more slowly, however, exhibiting a sort of inertia. This tension, between the ideals and expectations of a national park on one hand and the realities of operating a park on the other, provides the theme to Robert B. Keiter's book To Conserve Unimpaired: The Evolution of the National Park Idea.

Although Keiter holds these two perspectives up as controversy, the tension is a healthy one (at least for those not having to run the parks themselves), because it engages the idealists, the managers, the politicians, the visitors, and the neighboring communities in a dialogue that should result in compromise. The national park is said to be the United States's best idea (a phrase that has been credited to various people, according to the author), but Keiter argues that the national park project is not one idea but many—wilderness area, tourist destination, recreational playground, commercial commodity, ancestral homeland, natural laboratory, wildlife reserve, and ecological cornerstone. The lodestar for US national parks is the National Park Service Organic Act of 1916, which contained the following mandate:

Inherent in this mandate is the longstanding struggle between conservation and public enjoyment; it is an nternal conflict made greater by the dramatic increase in the use of national parks over the last century.

To Conserve Unimpaired details the major ideas that have shaped the American view of the national park. The book discusses several parks, using them as examples, then extends the argument to the national park system as a whole. It is a good book but a limited one—it neglects to address the influential roles, both positive and negative, that US national parks have played in the global effort to conserve protected areas. Perhaps this would be too much to expect from one book, but it would have been a powerful addition to this one. The chapters contain significant details about specific parks and key individuals, as well as arguments on the national park idea that are based on each park's needs and expectations. This approach leans toward the anecdotal and is frustrating in places. The author's previous work and experience skew his arguments toward a smaller geography than might have been desirable. In addition, there is a great deal of overlap between chapters, with some incidents and stories being repeated— and acknowledged as such by the author.

Keiter's decision to focus most of the book on individual parks and not on the whole system of parks is my biggest disappointment. The author states that individual park superintendents have great latitude in shaping what happens in their parks, but it is the national park system, both empowered and constrained by the Organic Act of 1916, that is the institution of most ortance—and of greatest interest. The system in toto is given attention only near the end of the book and in a way that is not well integrated with the rest. To explain the long-term success of individual parks, the dialogue needs to be focused on system-wide policies. The US National Park Service has been taking important steps toward creating management objectives for its portfolio of protected areas. It has consulted broadly on how to address its responsibility for migratory animals that spend part of their lives in the parks. It is also now considering how certain animals and plants will move out of and into parks in response to climate change. And it is looking at important system-wide issues, such as lead pollution in and around all national parks.

There was a time when the conservation community treated national parks as if they were holy relics, to be revered by all but not touched. That was before we learned, through rough and tumble debate, that the US view of parks was not shared by many others in the world—or even in the United States, itself. Today, the US National Park Service is a part of the gritty fabric of life—like politics and even religion. It is a value-based institution whose long-term persistence requires measured accommodation and nflinching dedication. This is the lesson from To Conserve Unimpaired: The work on parks is never done.