One of the thorny, and somewhat unexpected, problems facing modern society’s attempts to live more harmoniously with nature is recognizing what nature is. At a gut level we all think we know what we mean by nature. Perhaps, like art or pornography, nature is something that we can’t define but we know it when we see it. But do we? What is “natural”?
The fisheries biologist Daniel Pauly first coined the term “shifting baselines” to describe the phenomenon in which we unconsciously regard our own first experience of the world as its pristine or natural state. Because each successive generation experiences a new, changed vision of the world, society as a whole develops a sort of blind spot, in which we can’t see where we have come from or how far we’ve come. Pauly originally used the term to refer to the state of the world’s marine fish populations, which are believed to be at much lower abundances than the ocean can support. Randy Olson and Jeremy Jackson seized on the idea and created a web site dedicated to publicizing and working to reverse this phenomenon.
So how do we find the baseline against we which we should compare the modern state of things? Consider the forests of eastern North America. We can still find big trees in certain steep, rugged places inimical to farming or development. But are these remnants of the primeval forest? Hardly. The forest clothing eastern America when Columbus scraped his boat up on the beach at San Salvador would be utterly unrecognizable to us today. For one thing, it was dominated by American chestnut, a tree still common when my grandmother was born in 1900, but essentially gone by the time she reached marriagable age. As Donald Culross Peattie wrote in his incomparable book “A natural history of trees of eastern and central North America” (1948):
“All words about the American chestnut are now but an elegy for it. This once mighty tree, one of the grandest features of our sylva, has gone down like a slaughtered army before a foreign fungus disease, the Chestnut blight. In the youth of a man not yet old, native chestnut was still to be seen in glorious array, from the upper slopes of Mount Mitchell, the great forest below waving with creamy white Chestnut blossoms in the crowns of the ancient trees, so that it looked like a sea with white combers plowing across its surface. Gone forever is that day.”
Few alive today can imagine such a sight. Likewise,sycamore trees, now seen mostly as plantings along suburban streets, once populated the river bottomlands that have since been appropriated for agriculture and human settlement. Some still occur there. But in the olden days, these trees reached huge sizes in the rich soil and tended to rot out at the center. These hollow giants were common enough that settlers sometimes stabled livestock inside one. Peattie again:
“The men of Long’s great expedition to the Rockies noted, as they passed through, that ‘the fruit of the sycamore is the favorite food of the paroquet, and large flocks of these gaily-plumaged birds constantly enliven the gloomy forests of Ohio.’ The Carolina paroquet, only member of the parrot family native in the United States, is extinct now, and so are the gigantic sycamores of the virgin forest.”
Gloomy forests of Ohio? Filled with parakeets? Not to mention flocks of passenger pigeons so numerous that they literally blackened the skies. The mind struggles to grasp such scenes. That baseline has gone under, we can no longer even imagine it.
Clearly humans have fundamentally transformed the American landscape. But our keystone status is not just a recent phenomenon. Humans evidently have transformed the structure of terrestrial and nearshore ecosystems for thousands of years. It is now widely accepted that Pleistocene hunter-gatherers with rudimentary technology were largely responsible for extinguishing most of the large vertebrates on every major continent except Africa. Australia, for example, was home to wombats the size of bears, among many other bizarre creatures, until they disappeared in very short order about 40,000 years ago, around the same time that humans successfully crossed over from New Guinea and spread out over the continent, bringing their voracious appetites and fire with them. Much the same story has been played out in North America, New Zealand, Madagascar, and various oceanic islands numerous times since. The pre-human baselines for most of the continents evidently looked a lot more like Africa, with big herds of large animals, than they do now.
But America was still pristine in the frontier days when the west was wild, right? The majestic Plains Indian warriors on horseback are an iconic symbol of the untamed American West. But the horses arrived with the Spaniards only a couple hundred years earlier, before which Indians had only dogs as domestic draft animals.
What could be a more archetypal vision of pristine nature than the Amazon rain forest? As summarized in a recent article by Fred Pearce in Conservation magazine, new evidence has emerged that, for a thousand years prior to European contact, the dark heart of the Amazon rain forest supported an elaborate society with engineered earthworks, cultivated land, and roads 50 meters wide, and supported perhaps 100,000 people. When Francisco de Orellano traveled down the Amazon in 1542, these dense settlements were still thriving and he described fertile land, “very fine highways”, and “very large cities that glistened white” in his journal. Recent archeological evidence supports these historical records. But European diseases soon wiped these societies out, and the traumatized survivors fled into the forests, evidently devolving into the “primitive” hunter-gatherer societies of the Amazon more familiar to moderns. The large cities and highways were soon forgotten, and the Amazon became “wilderness”. As Stephen Pyne of Arizona State University put it, “Virgin forest was not encountered in the sixteenth and seventeenth centuries; it was invented in the late eighteenth and early nineteenth centuries.” Significant parts of the Amazon, like the woods around my home in Virginia, are second-growth forest on abandoned agricultural land.
So our conception of the “pristine” state of nature could use some adjustment. The shifting baseline extends farther back than most of us would have suspected. And the farther back we go, the more we realize that the landscape is always changing. Many stands of old-growth forest in America developed during the cooler climatic conditions of the Little Ice Age (~1350-1850 AD) and are thus “ecological legacies” of former conditions. Such vegetation could not have developed there today or even a hundred years ago.
Which brings us back to the question: what is “natural”? This is not merely an academic issue. Fundamental policies of resource management and conservation, costing real money and affecting real people, depend on how we define it. Natural clearly cannot mean the state of nature in the absence of humans, both because humans have been a part of nature for tens of thousands of years, and because growing evidence shows that we have profoundly affected earth’s ecosystems for at least tens of thousands of years. The pre-human baseline is long gone, and irrelevant to modern society in practice.
As a working definition, I suggest that a landscape can be considered “natural” if it supports some substantial fraction of the native biological diversity that is capable of living under those conditions of climate, soil, and so on. A “substantial fraction” is admittedly vague, but it is a start. Note that this definition does not exclude humans, and it does not explicitly refer to a past baseline. It does, however, require that we have some conception of what is native to an area (not always an easy diagnosis, to be sure), and that we know something about its natural history and ecology. Such a definition would exclude the typical urban landscape dominated by a small number of species, many of them non-native. But it does not, in principle, exclude urban landscapes entirely, much less rural and suburban ones. But it does require that human-dominated landscapes be designed with attention to their fit with the non-human environment. It is quite possible to envision human population centers designed to support both humans and other organisms. Michael Rosenzweig has given examples of such places in his book “Win-win ecology”.
The important point, in our rapidly changing world, is that we need an informed, adaptive concept of what nature is, and how we fit into it. Understanding how humans have interacted with nature in the past is key to doing so productively and sustainably in the future, and to stewarding a world that conserves as many as possible of our fellow travelers.