Nine months before the discovery of the largest oil field in North America at Prudhoe Bay in Alaska, the executive director of the Sierra Club sent a team of three of us north to Alaska, on a premonition. It was clear by then, summer of 1967, that a big strike on the North Slope was likely. Our assignment was to gather materials for a large-format photographic book defending the nation鈥檚 last great wilderness against Big Oil.

I was 22, the writer. My two photographer companions and I flew in by bush plane to Last Lake on the Sheenjek River, then walked for five weeks across the Brooks Range and out to the Arctic Ocean.聽

Near the shore of Last Lake, before we departed, I found the cache of a native Alaskan聽Gwich鈥檌n hunter, a tiny shake聽cabin elevated atop peeled spruce poles. No wolverine or grizzly had figured how to climb the poles. The door remained intact. Inside I found the hunter's聽draft card; his name was Ambrose William. We left William's cache behind us聽and walked north in perpetual daylight for more than a month without seeing another sign of human being鈥攏ot a blaze on a tree, not a corroded tin can, not a dropped penny, nothing. We had entered a perfect traillessness.聽

In our , and in a follow-up book I co-authored on the Trans Alaska Pipeline southward from Prudhoe Bay, we laid out all the threats: disruption of caribou migration by the pipe; the thawing of permafrost underneath it; the slow biodegradation of any leaks, marine or terrestrial; the seismic terrain traversed; the narrow waterways that supertankers would have to negotiate with Prudhoe oil. (We predicted the wreck of the Exxon Valdez 15 years before that ship was built.) But nothing about the pipeline itself worried us, and other environmentalists, more than did the service roads for pipeline maintenance. There is nothing more fatal to wilderness than a road. Roads open up the country to vehicles, prospectors, recreational hunters, the occasional arsonist. Roads have 鈥渆dge effects鈥� from which wilderness unravels to either side. The trail is a primitive road on a much smaller scale, but with similar dynamics.

The advantage of a trail in wilderness is that it concentrates human foot traffic. Its disadvantage is the same. Sanctioned trails tend to ramify with 鈥渦se trails,鈥� among other things. These branching outlaw trails, put in by hikers, mountain bikers, and off-roaders, have become a grave problem in the designated wilderness of many national forests, in many wilderness areas managed by the Bureau of Land Management, and in some national parks.

Advocates of more trails in wilderness always describe some transformative experience on the Appalachian Trail, or an epiphany on the Pacific Crest Trail, or how their kids discovered nature or self-reliance on the John Muir Trail. These are wonderful human stories. But it鈥檚 not all about us. This is what is difficult for many to grasp about the wilderness idea. Wilderness is not all about us.聽

At first, the national parks were all about us, expressly dedicated to recreational opportunities for humans. But in the century since the Park Service was established, there has been steady evolution toward a more generous idea: that wilderness exists for biodiversity, for the web of life, for all its plants and animals; and that, in fact, the interests of the original species here have priority over our own鈥攁 novel concept for Homo sapiens. Wilderness exists for itself. Today 80 percent of our national parklands are designated wilderness or are managed as such.聽

The Forest Service, for most of its 135-year existence, was all about timber production, but in the past few decades the agency has moved steadily (with some lapses) toward ecosystem management as the goal. The Forest Service 鈥淩oadless Rule鈥� prohibits timber harvest and construction or reconstruction of roads on nearly 60 million acres of inventoried roadlessness in the national forests. This rule recognizes, by its very name, the incompatibility of roads and wilderness. Earth 鈥� Roads = Wilderness虏, we might write the equation.聽

The wilderness trail is a wonderful convenience for us bipedal apes. But how is it for the creatures displaced along its route by aversion to us? And how are wilderness ecosystems distorted by those creatures drawn to our trails?聽

Clark鈥檚 nutcracker, a quick learner, was already nicknamed 鈥渃amp robber鈥� by the middle of the 19th century in the mountains of the West. This high-altitude relative of the crow has a phenomenal cartographic memory. It buries thousands of caches of pine seeds and remembers the locations of most. But not all; a portion of the forgotten seeds grow up into pines. In my home mountains, the Sierra Nevada, Clark鈥檚 nutcracker is key to propagation of the whitebark pine. That nutcracker, slyly easing the PowerBar out of your backpack, and not planting more whitebarks, as she should; what is the effect of her negligence on regeneration of that tree? I have read no studies on this. Just asking.聽

I do know that in the 1950s, when I was a boy in the High Sierra, we never carried bear barrels or roped our food over high branches. Black bears did not come into the high country back