Norman L. Christensen
My favorite Duke Forest walk begins at Gate 23 on Mt. Sinai Road and descends to the wooden bridge that crosses New Hope Creek. Seeing the large oaks and pines, many who walk this heavily traveled trail probably assume that the woods that surround them are truly ancient, maybe even primeval. But travelers on this road 150 years ago were surrounded by abandoned and eroded farm fields—a landscape reminiscent of some of the most deforested and impoverished places on our planet.
The history of change that produced that 1865 landscape and the one we see today has much to teach us about sustainable land stewardship.
A Mr. John Patterson was the first person to have formal title to this land (more than 1,000 acres), having received it as a grant from the colonial governor in 1758. But he was by no means the first person to manage this land. Native Americans were already hunting and gathering here 10,000 years ago, in the midst of post–Ice Age climate change. Their numbers may have been sparse, but they had already hunted many large mammals to extinction and altered much forest land with their deliberate use of fire.
Five thousand years later, larger populations of semi-nomadic people were hunting elk, woodland bison and deer in the uplands and cultivating crops such as squash and tomatoes in the floodplains along nearby creeks and rivers. The first Europeans explored this region nearly 500 years ago, and they encountered large numbers of Native Americans. Tens of thousands farmed land near permanent villages. Others hunted and gathered in large expanses of fire-maintained oak photos from Duke Forest Archives savanna. What Patterson and his kin saw when they first traversed their estate were forests and bottomlands shaped by the actions of hundreds of human generations.
Early on, Patterson and most of his neighbors employed a form of shifting agriculture in the context of a subsistence economy. They grew enough to meet their needs, with surplus to trade in nearby towns for the things they could not grow themselves. Small tracts, 3-5 acres perhaps, were cleared—an arduous process given limited human and technological resources. Crop production would be robust for a few years, but would decline after that as soil nutrients were depleted by erosion and harvest. That tract would then be abandoned, and another one cleared and put into production.
In this region fallow land is very quickly re-vegetated naturally by a succession of plant species. Over 2 to 3 years, annual weeds give way to perennial grasses and herbs and the seedlings of shrubs and trees. After 4 to 5 years, those shrubs and trees form a diverse and impenetrable thicket. During these 4 to 5 years, soil organic matter and stores of essential nutrients are restored. Left to its own devices, this thicket will soon develop into a young forest. But at this point in the succession, farmers intervened and replowed fallow land to begin another cycle of growth. Fallow farming systems of this kind were sustainable so long as the total amount of land in production was small and fallow cycles were sufficiently long to ensure restoration of soil fertility.
The Patterson family sold this property to William Robson in about 1790 during a major transition in land use in this region. Worldwide demand for agricultural products—most particularly cotton, tobacco and dye stuffs like indigo—was rapidly growing. Technologies such as the cotton gin and mechanized looms allowed the processing of these crops on very large scales. Farm families like the Robsons were likely selling their produce and buying their necessaries in fully monetized markets.
These developments vastly altered incentives for land use and stewardship, and they set in motion economic, social and ecological changes that would prove to be truly unsustainable. The fallow farming system was abandoned and declining productivity was countered by putting ever more land into production. The uncertainties associated with regional and global markets reinforced this pattern of deforestation. By 1830, many hundreds of acres of the Robson property were in cultivation. Given available technology, a single family, no matter how large, could not by itself farm that much land.
As we know too well, they accomplished this with slave labor. Slavery had been on the decline in the late 18th century, but this transition to market agriculture greatly increased the demand for and dependence on slave labor. We don’t know the specifics of the Robson’s holdings, but other ownerships of this size depended on the labor of scores of slaves.
By 1860, only 30 percent of the region’s forests remained, and these forest fragments had been severely degraded by livestock grazing and high-graded for fuel wood. An average of 1 to 2 feet of topsoil had been transported from exposed cropland to nearby streams and peracre productivity was severely reduced. Deep erosion gullies still scar the hillsides in many places along the path to the Wooden Bridge. The effects of this erosion extended well beyond individual farm fields as sediment polluted creeks and rivers, filled in mill ponds and caused the closure of water-driven mills on all but the largest streams.
Sustainability is often likened to a threelegged stool, with the legs representing social, economic and environmental systems and the seat representing the inescapable linkages among these systems. Surely, the changes for the Robsons and their contemporaries, the inexorable downward spiral of dependence on slavery, the diminished production and polluted waterways, and the ever increasing fragility of the economic system validate this tripartite metaphor.
The Civil War and the Reconstruction that followed brought new changes to the land and inaugurated a period of regional economic depression that would extend up to World War II. The Robson land, like that of so many neighbors, was put into foreclosure. Although tenant farming and sharecropping continued in some places, much land was simply abandoned.
Most of the land along the Wooden Bridge trail was abandoned between 1870 and 1910, and that fallow succession was repeated once again. Old field weeds were soon replaced with dog-hair thickets of pines. Through time, these pine thickets thinned to respectable forests. When Duke Forest was formally established in 1931, pine stands were about 40 to 60 years old and broadleaved trees—oaks, sweetgums, maples and hickories—were prominent beneath them.
The waters of New Hope Creek that flowed beneath the Wooden Bridge in 1870 were red with sediment, and flash floods were common. But within a couple decades, the roots of regrowing forest trees and shrubs stabilized fragile soils and mitigated flows. Today, at least at that location, New Hope Creek runs clear and supports a diverse array of aquatic life. The fact that ecosystem change has repaired some of the impacts of those many years of unsustainable land use is reason for hope; but it is also true that no vestige of old-growth forest remains and that it will take many more decades, even centuries, to restore soils to their former productivity.
Rapid change continues on this landscape. Once-rural land is rapidly becoming urban. Forest is being replaced by complex, impervious surfaces like roof tops, parking lots and roads that greatly alter local climate, the quality, quantity and timing of water flows, and wildlife habitat. Is all of this change sustainable?
The word “sustainability” is tricky. “To sustain” is defined in many dictionaries as “to keep in existence, to maintain.” To some this implies an idealistic sustainable endpoint—a destination. But if history tells us anything, it is that sustainability is a journey, not a destination, and that journey always occurs in the context of three kinds of change.
First, the world is changing. The capacity for ecosystems to change is essential to their persistence. Forested landscapes and watersheds are constantly being disturbed and constantly undergoing change. Over the long term, change is essential to adaptation and survival.
Second, we are changing. Each generation of human beings brings new technologies and values to the land. My interests and values are very different from those of my parents and grandparents, and the interests and values of my children and grandchildren are no less different from mine. And third, we are changing the world. This has always been true, but today there are more than 7 billion of us, and our individual effects on Earth’s ecosystems are disproportionately magnified by the power of the technologies we employ to garner the things we need or think we need.
We are today agents of unprecedented change. And we are hopeful that nature’s change processes will mitigate our impacts, too. But history provides no guarantee that that will be the case. Our human population has increased over eightfold since the Robsons abandoned their land, and each of us individually consumes 10 times more energy and resources than did the Robsons and their peers. Furthermore, many of our insults to our planet’s ecosystems have no precedent in either historic or prehistoric times.
Sustainability, I would argue, is an inherently anthropocentric concept. For millions and millions of years, Earth’s myriad ecosystems functioned wonderfully in our absence. It may be humbling, but it is good to remember that we are not an essential element to any of Earth’s ecosystems. No other single organism has changed our planet to the extent that we have. But, were we to disappear tomorrow, ecosystems would continue to change and life would continue to evolve. Eventually, our portion of Earth’s history would be reduced to a thin, albeit messy, layer in its geologic strata.
I have a favorite Gary Larson cartoon. A stegosaurus stands at a lectern before an audience of other dinosaurs and says, “Friends the picture is bleak; climates are changing, mammals are on the rise, and here we sit with brains the size of a walnut.” Dinosaurs are, unfairly I think, often depicted as the exemplar of unsustainability—unable to adapt, they were a cul de sac in the history of life. But, these remarkable beasts dominated Earth’s ecosystems for a remarkable span of time—150 million years.
Humankind has been around for about 1/1,000th of that amount of time, yet many seem to think that the entire history of life that preceded us occurred solely for our benefit. That view has encouraged the widespread belief that we cannot severely damage Earth’s capacity to sustain us or our children. But the history of our interactions with the land tells us otherwise.
We are fond of calling attention to two human features, intelligence and selfawareness, that set us apart from all the rest of creation; we have, after all, brains the size of a grapefruit. We are hopeful that these traits will lead us on a more sustainable path, although there is not much evidence in our history to support that hope. But I believe our future will hinge much more on two other traits—the empathy to care for the well-being of others living now and in the future, and the humility to understand our proper place in the world and our dependence on the health and diversity of its ecosystems.
Norman L. Christensen is founding dean of the Nicholas School and professor emeritus in the Division of Environmental Sciences and Policy.