In Half Earth, his latest book, renowned biologist Edward O. Wilson has written an impassioned plea to save Earth’s biological resources by reserving half of the earth for nature. He proposes to set aside areas where human impacts on ecosystems are deliberately minimized, in the model of large national parks and nature reserves—but on a scale of conservation vastly greater than what has ever before been imagined. He presents compelling evidence that much of the earth’s biological heritage, the product of four billion years of evolution, depends on conservation at that scale.
Dr. Wilson has erected a high goalpost. There are enormous political and economic barriers to scoring on his goal if the approach is a frontal one, attempting to directly set aside such huge areas. What Dr. Wilson’s book lacks is a realistic strategy; I surmise that he trusts others to figure out how to move towards his goal.
The need is compelling. Dr. Wilson reviews the extensive evidence that species extinctions, driven by human activities, are proceeding at rates that have rarely been exceeded in Earth’s history, and only then by great cosmic catastrophes known from the geologic record1. Among those would be the massive Chicxulub meteor impact 66 million years ago, which obscured the sun for years, removed roughly 75% of species, ended the age of dinosaurs, and inaugurated the age of mammals.
To humans living in developed economies, it is not immediately evident that we are, to the same degree as other species, dependent on ecosystems. Our ecological independence is, however, an illusion; we breath oxygen and eat food that is ultimately made by plants. But for those who do not live in hunter-gatherer mode, or in subsistence farming mode, it may seem that we are dependent on our grocery store and not on ecology. We humans have learned to cheat nature, using external energy rather than our innate energy—the limit for all other species—to control our immediate environment and to bring needed ecological products to us. This cheating of nature allows us to live in hostile places—I have myself spent many weeks on the Antarctic Ice Cap—and, therefore, allows us to invade any (all?) ecosystem(s).
In nature, ecosystem dependence is often immediate and compelling. Take away one species and another species that depends on that species dies, or perhaps ten others die. Ecological blindness to these realities fosters political and economic systems that focus on the short term; these systems ignore the large scale and the long term, and take no action on their behalf. Jobs and profits trump long term stewardship of the planet and its biota.
In considering conservation at this scale, I have to ask what has been overlooked. Are there unstated principles that might help the cause? I believe that two principles are overlooked in Half Earth and are generally overlooked by ecologists and conservationists:
- Healthy ecological functioning is supported by maintaining separation between ecological resources and human disturbance.
- Economic rules can be used to compensate for loss of separation in one place by protecting separation in another, nearby and ecologically similar, place.
The first point turns most ecological analysis on its head, although not in an oppositional way—it is just a difference of perspective. Ecologists, including Dr. Wilson, generally work to unravel the complex web of interactions—cause and effect—that describe operation of an ecosystem. If one uses this approach in an effort to understand human induced change, then complexity becomes overwhelming; Dr. Wilson himself makes this point. By thinking in terms of immunity to human influences rather than myriad individual influences, the problem can be seen perhaps less precisely, but also more tractably—one can see the forest of human influence rather than its separate trees. Distance from obvious human disturbances does not provide immunity from influence in a neat linear way—global climate change driven by human activity anywhere on the planet is a cogent demonstration (an influence that reaches everywhere)—but distance generally must diminish influence, because an influence that could increase with distance would overwhelm things far away, and we know that this is generally not true2. The relatively recent literature on road ecology, which describes myriad effects of roads on natural systems, documents wildly differing ranges of these influences. There is no defensible weighting system to add this ensemble of effects into a single summary metric of “total road effect.” It is time, however, to recognize that valuable conservation insight—and conservation action—can be based on the concept of immunity to this host of effects.
So, if we can provide separation from human disturbance, then we will improve ecological conditions. This observation validates the high goal expressed in Half Earth, and also offers an avenue for local action. What if we can, within an area of relative ecological uniformity (an ecoregion), provide protection based on distance from disturbance—recognizing that distance in a general way translates to immunity from ecological effects? That protection, locally implemented and applied over broad areas, certainly leads in the direction of Half Earth’s goal. This idea reflects back to a classic conservation slogan: “think globally, act locally.”
The second point is that, by employing a metric that counts both area and distance, and attaching financial consequences to changes in such a metric, profits that accrue from development can be harnessed to protect nearby and ecologically similar undisturbed space.Development can pay for conservation, a radical idea. In other words, development can pay for conservation, a radical idea. Such a system will be both fairer and more palatable if the payments are not based directly on dollars (or another currency), but on the metric itself. If a development will diminish the metric, and the immunity that it expresses, by a certain amount—then the developer, who will be making profit in some way from the development, must provide protections of an equal amount (or in some other ratio) nearby.
How might we construct an area-and-distance metric? With a geographic information system (GIS), we can take a map of human disturbances and from that generate a map that measures, on a regular grid, the distance to the nearest disturbance. For any land parcel, we multiply the area by the average distance to disturbance. This metric expresses space in a new and useful way. It can be applied to, for instance, a single farm, a county, or a state. As one would expect and desire, this space metric is additive; for example, the space in a state is the total of the spaces of its constituent counties. If one takes, for example, a square mile (or square kilometer) bounded by roads, then the space metric is 1/6 cubic mile (km)3. If one adds two roads that run parallel to the sides of the square, between the center points of the sides—thus creating four smaller squares—then the new metric is 1/12 cubic mile (km). In other words, bisecting an area in both directions without changing area will decrease the area-and-distance (space) metric by half. Experiments with various configurations of disturbances make the undelying principle clear: invasions into previously open space reduce the metric because invasions diminish mean distance to disturbance.
To see how this works, do an experiment in your home. Choose a room that has some furniture near the center of the room, then move all the furniture to the walls. Doing this, you will increase the room’s average distance to a piece of furniture (our surrogate for human disturbances) and you will leave a large open space in the center. It is no accident that furniture is often moved in this way for dances and parties; it provides unobstructed distance.
Large space, understood as the product of area × mean distance to human disturbance, ensures large separation between human disturbance and ecological resources—not everywhere, but in some parts of the measured area, else the mean distance to disturbance could not be large, nor could the metric formed from it be large because it incorporates mean distance as a multiplicative factor. Thus, large space ensures—in relative terms—some areas of high immunity to disturbances.
1 Dr. Wilson is one of many biologists and ecologists who have written about the irrecoverable loss of species in what is now often called the sixth extinction. An excellent summary of this extinction, written for the non-specialist, is The Sixth Extinction by Elizabeth Kolbert. Look here for a description of this book.
2 This is a general principle first articulated by geographer Waldo Tobler and known as Tobler’s First Law of Geography.
3 Within a square, the average distance to an edge is 1/6 of the length of the edge.