Choices in Ecology
Beyond the light of my desk lamp and computer screen, and the hum of my air conditioner, there exists a coastal hardwood swamp of great mystery. Though I live in the old settled East, not far from Providence and Boston, even closer to Fall River and New Bedford, my garden and lawn connect to a greenbelt teeming with wild life. Coyotes cry to the stars at night, hunt the deer in corridors of wet green, and raid sheep farms in town. Foxes visit my deck when it’s late and quiet, delicately feasting on sunflower seeds I’ve spilled for the birds. In daylight, red-tailed hawks float above the treetops, searching for rabbits and songbirds in the dense growth below. Sometimes eagles drift up there as well.
The life surrounding us appears as a matrix of information, presenting some events which fit our expectations, and others which do not. In order to focus on one set of relationships, we must exclude others. An ecological study of coyotes in my county must leave out earthworms; as a biologist friend wades the coastal waters collecting invading crabs, and examines their stomach contents to explore impacts on prey species, she ignores ospreys circling above, and mosquitoes grazing her ear. Choices must be made before the first hypothesis can be tested.
What then gets chosen? How are some species selected and highlighted? Why are others consigned to the background of scientific attention? These are aspects of ecology’s observer problem. We are used to such a concept in physics, where we understand that spatial and temporal measurements are relative to an observer’s position. And we may realize that in anthropology, the attitude of an ethnographer shapes interviewee responses. But we’re so accustomed to viewing familiar scenes of park or garden, or the turns of a local trail, as nature that exists with or without us, that we’re tempted to imagine all nature in such static pictures. What has this tableau to do with us? Wouldn’t it be the same whether we observe it or not? And shouldn’t it be possible to inventory all species present in such an elegant, well-ordered scene?
In their book, Toward a Unified Ecology, Timothy F.H. Allen and Thomas W. Hoekstra discuss what we might call an open secret at the heart of ecology. This is that a human observer determines what is recognized and studied, and in this sense valued. The same person who includes certain animals and plants within a frame of reference necessarily excludes other species from the framework.
In Physics, we recognize that measurements of the position and speed of subatomic particles are relative to the observer’s position. By contrast, Allen and Hoekstra write, “The things we study in ecology seem very real. Nevertheless, ecology is a science and is therefore about observation and measurement more than about nature independent of observation.”1
Even at the grossest level of decision making, when the ecologist chooses what to study, that act influences the outcome of the investigation. When one chooses to study shrews, there is an implicit decision not to study everything else. In that implicit decision most other things ecological, such as trees, rivers, or ants, are excluded from the data.
Allen and Hoekstra remind us of the story that the entire army of Alexander the Great slept beneath a single Banyan tree. Is this true? It depends upon the observer’s viewpoint: the Banyan extends thin rootlets which touch the ground and begin to thicken and spread roots. Eventually they appear as new trunks. Genetically identical to the original tree, they become either its spatial extensions or an entirely new forest, depending upon one’s perspective. Perhaps for a biologist they would be a single tree, while for the army being sheltered beneath the many trunks and branches, they would be a forest.
These examples show that the concept of the observer’s position includes more than spatiotemporal location. It encompasses interests, needs, and a way of focusing attention. This way implies a cultural matrix, a language, and a community of investigators.
Every project proposed by developers rests upon a framework which includes implicit claims about which species matter. To the timber corporations of the American northwest, pine, fir, and cedar are interesting, while spotted owls are a nuisance. All our activities take place within frames of ecological reference; by attending to how ecologists, developers, planners and others specify these, we may learn to see our role as decision-makers about the ecosystems around us. After all, while local nature is ‘out there’ in an objective sense, frames of ecological reference are the stage sets upon which environmental debates are dramatically enacted. Scale within the framework is determined by grain and extent of the data. Grain determines how small the observed data will be, while extent determines their largest possible size in time and space. Scale in this sense is not about ‘the world out there,’ but is about our measuring conventions. Scientific stories are limited in this way, as are all stories.
Allen and Hoekstra point out that definitions are primary. Before we can discuss change, we must identify static frames of reference within which change occurs. (For example, if we study change for one year on a farm, we must first draw a line at the edge of the farm property, and another at the end of the year, and pretend not to notice what happens outside this zone.) But as the example about shrews, ants, trees, and rivers shows, specifying an ecological frame of reference always leaves much out, and hence is relative to personal/cultural observer positions. These choices of what to focus upon are subjective in the sense that other options exist initially, but once the choices are made the observations which follow are objective.
The Observer Problem in Conservation
Which species claim our attention determines what we see at a given place and time. The knowledge we eventually generate helps determine how others act there, and what environmental policies are adopted. A study of bears might bring hunters; a discovery of rare plants might halt development. If we ignore a species, its uniqueness may be lost in the ethos of change and transformation that grips our time.
Cultural and political interests are involved. Scientists often specialize in organisms which the wider society has blessed with funding: mountain lion, condor, elegant osprey. In these cases beauty and scarcity lead a biologist to describe a place, on a certain day, as the habitat of this creature alone. Selection of a few organisms from a rich matrix is necessary before ecological study can begin.
A parallelism holds in the field of conservation. Whether one looks at planet Earth from a satellite 40 miles high and sees exploding cities eating green space alive, or takes a drive around one’s own town and counts the white ends of plastic pipe (percolation tests for new house sites) it is evident that development continues rapidly. Conservationists can save less territory now because land prices have risen so dramatically. It has become critical to pick one’s battles. Out of the surrounding matrix of environmental problems, upon which shall I focus my energy and time?
Ecology and conservation arise within cultural and political situations. A complex weave of factors brings scientist or conservationist to subject and site. These factors will include society’s long-term interests in educating people one way rather than another, and local, shorter-term urgencies concerning bulldozers, chain saws, and the disappearance of species. Ecologist and conservationist, by professional custom, respond to slowly deteriorating conditions in the informational matrix. (Without this general situation their roles would hardly have arisen at all.) Within this framework, each project they undertake will address limited windows of opportunity for knowledge or protection. In short, they respond to dynamic, unstable situations, in which effective storytelling holds a key to success.
Both ecologist and conservation writer frame particular species within a limited region of time and space for a study. But whereas a scientist contrasts known factors (constants) with unknown ones (variables) in an effort to discover whether a specific relationship exists, a conservationist seeks to preserve or restore a status quo. This does not mean a no-change zone, where evolution is halted, but rather a slow-change zone, where humans interfere minimally with species relations.
Just what choices must be made before a slow-change zone can be responsibly defined? At a fairly abstract level, a common prime directive for conservation work is ‘protect diversity.’ This principle alone does not tell us what to do in a specific situation, because there are different kinds of diversity, and because reasonable people can disagree about strategy and tactics. But in its very generality, the principle ‘protect diversity’ may allow stakeholders in an environmental discussion to proceed toward an agreed goal. This convergence is part of the urgency conservationists feel about the world today; it is also connected to the words ‘conserve,’ ‘conservationist,’ and ‘conservative’: all arise in relation to a valued state of affairs in which diversity is threatened.
Proceeding from this common point, we must ask in any given case whether the best path is ‘hands off’ an ecosystem, or whether we ought to take actions to encourage some species and discourage others. Even small, unobtrusive actions, like filling a bird feeder with seed, or opening the door to release a cat for the day, have dramatic effects when combined with the similar actions of millions of people.
One way of describing this situation is to say that almost every part of the natural world is a landscape for somebody. And landscapes are cultural and political entities as well as ecological ones. As J.B. Jackson has put it, “A landscape is… a space deliberately created to speed up or slow down the process of nature. As Eliade expresses it, it represents man taking upon himself the role of time.”2
If we viewed Earth from the space shuttle we would be frightened by the spreading of cities. From an airplane over the American Midwest, one is amazed by vast fields of cropland — monocultures for food and profit. On foot, walking in parks or even wilderness areas, we respond emotionally to large trees with open vistas beneath — landscapes encouraged for their scale, which is to say our scale. Each approach to Earth reveals humans in control of nature, human time imposed upon, and altering the processes of, evolution.
When we think about what is happening to Earth as a whole, we recognize the need to plan conservation actions with several different timescales in mind. For example, ecologists distinguish three kinds of diversity: alpha, beta, and gamma. Alpha diversity means species diversity within a patch of land; beta diversity indicates diversity between several patches in the same area; gamma diversity indicates diversity on a regional scale, which includes many mosaics of land patches.
Clearly we need to know as much as possible about the gamma-diversity situation of species. Lacking this knowledge we might attempt to maximize diversity within a single patch, which might have reverse effects from the ones desired, because many species, such as deer, grouse, and crows, thrive on diversity within patches, and other species, such as the Florida Scrub Jay, can only thrive in relatively nondiverse plant communities, and then only in small numbers. So even though a patch of earth over which we have influence (like the woods and marsh behind my house) might be a tempting framework for a conservation plan, a wiser perspective would encompass my entire town and the watershed beyond.
Alpha, beta, and gamma diversity are concepts applicable to nature at many scales. Within these, choices must be made regarding grain and extent. Even then, once a region and its critical species are listed, the principle ‘protect diversity’ requires us to imagine different management strategies. In imagining policies for my wetland, differences appear depending whether I advocate for the deer or the coyotes, the rabbits or the foxes. From a logical point of view, an infinite number of perspectives on a single ecosystem are possible. This infinity of choices can seem bewildering, even debilitating. But this is true only if one clings to a simple model of nature and culture, or hopes for a simple metaphor like those which guided our ancestors, such as nature is divine order, nature is an organic creature, and nature is a great machine.
Every choice within ecology and conservation, just as those within development activities, requires creativity. Every action, and every restraint upon action, requires design decisions. This design ultimately includes physical treatment of land, but it begins with the writing process, where old metaphors are analyzed and new ones tried out.
Suppose I wish to make a narrow trail through the easternmost acre of my woods. Here the land is spongy and mossy, and the vegetation is dominated by Shad Blow, Haw, Holly, and shrub-sized bushes and trees growing in thickety profusion. A human can’t walk through most of this, and a deer doesn’t often choose to. If I cut a trail for my own exploring, and to draw the large mammals through, this will favor them but harm species which need shelter from them. Probably the deer, coyotes, foxes, raccoons, opossums, and neighborhood dogs have enough paths from which to invade tangles and swampy patches. In the past few years pheasant, quail, and woodcock have become scarce, and I’m sure members of these species would appreciate (if they could) my not cutting such a path. I reach for a new metaphor like home is foxless, to clarify a woodcock’s interests and to guide my action. Here I combine the connotations of home (the warm modern sense of which only arose in 18th Century Holland3), with ecological knowledge about a specific place.
Consider a habitat which includes ‘edge effects,’ as most do. This is a concept promoted in 1933 by Aldo Leopold as beneficial to wildlife, and widely adopted as a management strategy. Leopold thought junctures of fields and forests, streams and uplands, even trails and thickets, provide advantages to many species. This is true for some, but not for all. By defining ‘wildlife’ as ‘game species,’ managers often rationalized breaking up uniform habitats into diverse patches; more deer and grouse were frequently the predictable and desired result, but lost in this ‘edge effect’ planning were many unnoticed, non-game species.
If one imagines a boundary between habitat types, it may be tempting to think of this line as a ‘real’ feature of nature, but as biologists William S. Alverson, et al, point out, such a line can only be defined by the experiences of particular organisms. Nearness to the line will produce a range of events of varying intensity.
Ecological field studies sometimes record the number of times particular organisms approach such a line. From these data points, an ‘isoacme’ map can be drawn to show average intensities at the same average densities from the line. Such displays are different for each species considered. Perhaps this is a useful way of illustrating how differently each species ‘evaluates’ edge effects in its habitat. This underscores the critical importance of being chosen as a key species for a study. It’s unlikely that creatures omitted from study will have their interests considered in plans resulting from the study.
Species numbers are greater than we are accustomed to thinking. In the 43 year period from 1940-1983, five new bird species were discovered every two years.4 New species of mammals are now found at the rate of about five per year. Oceanic exploration for new life forms has just begun, bringing news of new whales and sharks, and deep-sea communities of sulfur- and methane-eating organisms. Biologist Terry Erwin and colleagues, working with associates in the 1970s studying rain forest trees, discovered each individual tree contained huge numbers of anthropod species, the spiders—and each tree contained unique species. Extrapolations from his data have led to estimates that the undiscovered anthropod species on Earth number from five to 30 million.
If we turn to smaller organisms the surprises are even greater. Studies of bacterial DNA in a single gram of beech-forest soil in Norway turned up between four and five thousand species. Examination of a gram of soil from the shallow seas off Norway’s coast revealed an equal number, but virtually all of them were different from those in the forest sample.
These examples remind us that Earth’s biological diversity is largely unknown, and that we miss whole realms of life by operating within many of our ordinary frames of reference. It’s not only beetles and spiders that go extinct through massive rain forest burning — cases we hear about but may find emotionally distant. What about the newly discovered life forms around oceanic vents? Are these impacted by ocean dumping? What of the new bird species discovered every year? Are we destroying their habitats before we see them?
Birds are often omitted from our ecological planning considerations because of their migratory habits. We know that continued suburban development destroys habitats and encourages predatory species like Bluejays, Brown-Headed Cowbirds, and Seagulls. Small, beautiful warblers are often the losers as ‘edge effects’ spread across the planet. Yet birds receive little consideration in many planning decisions, simply because they ‘pass through’ and their relation to a particular site may be difficult to establish.
All this indicates that every choice of an observer’s position is fraught with consequences. And yet without such a choice there can be no observations, data-gathering, theorizing, or planning — for development or research or conservation. Once an ecological frame is chosen, and specified in both extent and grain, a discussion can begin about appropriate goals for this part of the natural world. And eventually diverse goals can find their way into a plan. But plans never spring from a void. They arise in response to threats and opportunities for conservation. Selecting a frame in space, including valued organisms within it, leads directly to concern with time — both the time of evolution past, which produced the place, and the cultural time which affects it now.
The next question is what target event the conservation writer has in mind. Sometimes this will be a vote (in a small community, a congress, a parliament, or another organization); at other times it will be an executive policy decision. Such pivotal moments determine whether ecosystems are protected or lost. Conservation work, like science, requires that a writer frame a region of space-time (extent), specify entities within that region (grain), and point to events projected into the future. For science, the effort is to observe these events; for the conservation writer, to influence them. (This is simplistic, of course: conservation biology as well as conservation writing require both descriptive and prescriptive components.)
The observer problem is a purely formal one: any story must begin with a specification of what is to be talked about, and with exclusions from the discussion. This means that conservation writers, like ecologists, must make choices before they can begin their work. Sometimes these involve ethical and aesthetic commitments, and always they involve practical and cultural commitments.
Choosing Landscape Values
In A Sand County Almanac, Aldo Leopold proposed that we extend ethical thinking and action from fellow human beings to nature. “An ethic, ecologically,” he wrote, “is a limitation on freedom of action in the struggle for existence.” Limiting our activities for the sake of other species, and their habitats, he called “a land ethic.” When Leopold wrote these words they sounded strange, but some sixty years later many people embrace the idea. In our wetlands and woods, in our gardens and ponds, we take pleasure in restraint to protect nature.
The land ethic is widely embraced, as is the land aesthetic — guiding our efforts to promote landscape beauty. Yet these are only the starting points of land protection activities. How do we make practical decisions about when to leave a site completely alone, and when to introduce mowing or planting, for example? And what happens when the needs of different species conflict — how can we choose between them?
When management strategies like mowing, thinning, and stream-clearing are undertaken for aesthetic goals, one must choose the historical moment whose ‘look’ is sought. Consider two brief cases which illustrate this:
On Cape Cod, state park rangers needed a policy and management plan to protect a new acquisition for the park system. The landscape included fields, woods, and several historic houses. Planners chose the date of origin of a single one of these houses, then sought to make the surrounding landscapes conform to the way they had looked in that period. It wasn’t possible to preserve the landscape aesthetics of all the houses; the attempt to do so would have resulted in a patchwork of views and ecological states lacking coherence. As Elizabeth R. Lehr has pointed out6 by selecting a single period for guidance in landscape practices, the rangers achieved a measure of ecological and aesthetic unity. This example shows how historic preservation is subtly entwined with, and often guides, nature conservation.
Consider the Boundary Waters Canoe Area Wilderness in Minnesota. Some areas of this park are maintained so that a canoeist may glide along beneath huge trees with an open understory. To the uninitiated, this experience seems to touch ‘true wilderness.’ But actually management practices have created and sustained the forest in this ‘climax stasis’ condition; it mimics the ecosystem and aesthetics of the historical moment when European fur trappers first contacted the indigenous people of the region. The forest is magnificent, visually satisfying, and offers the visitor a sense of travel back in time to an unspoiled day. Although reserve designers made a good choice in their historic date for landscape practices, their cleverness in erasing subsequent history — power lines and cleared fields, for example — might tempt the visitor to imagine there was no previous history. In other words, the canoeist might believe these park-like forest banks embody a natural ideal which persists indefinitely. In the 18th Century and before, they were probably shaped by Native Americans through seasonal burning.
When one first embarks on a land conservation project it is tempting to imagine one is saving nature ‘as it ought to be.’ But usually this goal includes an aesthetic component —nature ‘as it ought to look.’ And the first question is: When? Any answer involves cultural history. This, in turn, requires choices: not every moment of past succession, or landscape configuration, can be represented.
An important part of the conservation task is historic preservation; to achieve this consistently, one must choose a date and manage for the ‘correct look of that history.’ Such choices shouldn’t discourage us. They are part of the creative challenge of conservation, and they give us a meaningful role to play in the unfolding of nature.
Some conflicts cannot be evaded. For example, recently Massachusetts land managers had a painful choice between actions to support seagulls or piping plovers. A ‘no action’ policy would support the gulls.
Similarly, in western Massachusetts, managers had to face the fact that domestic dogs were killing numbers of deer. ‘No action’ would have supported the dogs.
With regard to any piece of property one can choose:
- to make the needs of a single species paramount (e.g., an endangered species);
- to craft policies which will favor several species, ranked in a particular order;
- one may attempt what is called ‘integrated management,’ in which one seeks a rough balance of (a limited number of) species needs, without selecting any one of these for special treatment;
- one may treat a parcel as a baseline in a scientific study, which means it must be left alone, no matter what happens. While this sounds attractive and appeals to our ‘pure wilderness’ desire, in reality it means never compensating for natural events we dislike, such as devastating invasions of exotic species, windstorm damage, and fire.
Just as in the case of cultural values, the stewardship of natural values requires choices.
States of Nature versus Rates of Change
Early in this century ecologists came to believe in the idea of forest succession: that every forest goes through stages until it reaches a grand ‘climax’ state. This idea was applied to all sorts of ecosystems, with the result that each one was believed to have a proper, final, long-lasting, and most favorable stage. It became the goal of conservation to identify and protect such climax states of nature.
Recently ecologists have realized that much of the focus on preserving climax states was really driven by aesthetics, as in the case of the Boundary Waters Canoe Area discussed above. In the real world, climax states change eventually, perhaps in response to hurricanes, fires, earthquakes, volcanoes, diseases, or invasion by exotics; they often shift dynamics, restarting the clock and beginning a new succession, in response to influences like bulldozers and chainsaws.
What this means for conservationists is that we should protect slow rates of change, rather than no change at all. We need an historical account of each parcel including intelligent guesses about where it will trend with, and without, our interventions. Our goal should be wise stewardship of slow rates of change. Toward this understanding, some land trusts have begun to compile histories for the places they protect.
The Grand and the Pretty
In her 1997 book Placing Nature, landscape ecologist Joan Iverson Nausauer discusses the need for conservationists to appeal to aesthetic tastes and principles shared by their audiences. Americans are deeply committed to two distinct ‘looks’ for the natural world, which Nausauer calls ‘grand’ and ‘pretty.’ Grand landscapes feature broad rolling green fields framed in the distance by tall trees. They mimic 18th Century English estates, the sort designed by Humphery Repton and Capability Brown. Such landscapes, beyond the financial reach of most citizens, grace campuses, parks, golf courses, and grounds of the wealthy.
The other ideal, ‘pretty,’ lies within everyone’s grasp. This is the look of a small but carefully tended lawn, garden, or window box. The pursuit of such landscapes often leads to faithful mowing, weed whacking, pruning and raking.
Two common features should be noted about these styles: first, they express care for nature, and signal that their owner is a careful person. We’ve all heard stories about people who ‘let their place go’ — refusing to mow, or make other concessions to a community’s customary look. Despite good intentions, say to provide habitat, in the end such people are regarded much like those who never cut their hair. They lose their place at the table of community conversation about how landscapes should be treated.5 In order to have standing to contribute to decisions about landscapes, people must signal, through their treatment of nature, key facts about themselves.
The other common feature of these two styles, grand and pretty, is that they can enhance, or destroy, environmental values. That is to say, neither style is inherently good or evil, from a conservation perspective. To decide whether our gardens, lawns and woodlots, in conforming to these aesthetic ideals, are helping or hurting species, and encouraging a particular balance of nature, requires careful attention to each site.
When we appeal to our neighbors for a certain look for a conserved landscape, we will have deeply-rooted culture on our side if we cast our argument in terms of one of the dominant styles. If we can find a way to combine either, or both, with such practices as leaving some areas entirely alone, audiences will feel more comfortable.
These are some of the kinds of information one needs to form clear and consistent conservation goals, strategies, and management plans. Not to discuss such matters leads to ‘no action,’ which of course is an action — one which supports current trends, whatever they are.
We might approach each parcel in two stages: the first to gather information of these kinds, and the second to discuss and choose goals, strategies, and plans. Ideally, we need information from many sources, such as neighbors of the property, oral histories of the town, stories from hunters and fishers, and so forth. We also need the perspectives of professional ecologists, biologists, landscape planners, and others.
Initially, each stage might be approached thus:
- Describe the place at landscape scale (that is, the way it appears to humans):
- Include natural features, such as landform, species, and tree of life information;
- Include cultural features, such as agriculture, stone walls and buildings.
- Give the history of the place.
- Include human factors, such as farming uses;
- Include non-human factors, such as plant successions;
- Describe rates of change for species in the past.
- Describe conflicts:
- Between species;
- Between other species and the human species.
- List possible land stewardship goals, such as:
- Management for a certain stage of nature (through annual mowing or flooding, for example);
- Management to encourage a particular succession;
- Management to encourage a particular rate of succession;
- Prioritize goals, such as:
- Aesthetics for human pleasure;
- Single-species benefit;
- Multiple-species benefit in ranked order;
- Mixed-species integrated and equal benefit;
- ‘No action,’ as part of a scientific baseline study.
- Discuss the state of our knowledge; decide whether we need additional data, or can make provisional decisions. If we need data, plan for these with a timeline. Project the consequences of no action, and of several practical actions.
- Choose goals, strategies, and management plans. Set a date at which to revisit these decisions in the light of new data.
All this takes time, and many of us have to make decisions about our landscapes without the rich information we desire. But no matter how much information we have, creative decisions will be necessary. The process which leads to conversations and decisions must begin with a point of view from which a story is told. That point of view selects the grain (smallest units in space and time) and extent (largest units) of the part of nature in question. This is a purely formal requirement of both science and storytelling, and thus of ecology and conservation. Once the domain, or informational grid, of the place is specified, both science and storytelling about cultural values have roles in filling in detail. In order to rationally apply a land ethic or a land aesthetic to a particular place, historic and current patterns of species coexistence there, as well as historic and current patterns of cultural valuations there, must be specified. Much of this information, such as the alpha, beta, and gamma diversity, and the valuations expressed in historic land use patterns, is objective. Yet underlying the entire conversation, from the first description to the last vote, are issues of viewpoint and choice. ‘No action’ is a choice to favor current trends, so it isn’t really no action at all. Writers and other citizens can influence the outcomes of conservation decisions by gathering the science and cultural history of a place, then using appeals to values like the grand, the pretty, and the protection of diversity to influence actions and policies. Opposing cries of “sacred nature” versus “relative values” oversimplify matters. Writing and speaking from within one’s considered point of view, in a manner which celebrates what is there in both natural and cultural senses, can gently persuade others. That is how Henry David Thoreau, John Muir, Marjory Stoneman Douglas, and Rachel Carson changed the world.
This piece is adapted from Luke Wallin’s Conservation Writing: Essays at the Crossroads of Nature and Culture, published in 2006 by the Center for Policy Analysis; to download or order this book please see http://www.lukewallin.com/cwriting.htm. Wallin teaches in Spalding University’s brief-residency Master of Fine Arts in Writing program.
1 Allen, Timothy F.H., and Hoekstra, Thomas W., Toward a Unified Ecology, NY: Columbia University Press 1993.
2 Jackson, J.B., Discovering the Vernacular Landscape, New Haven: Yale University Press 1984.
3 Rybcinski, Withold, Home: A Short History of an Idea, New York: Viking Penguin, 1985.
4 Alverson, William S., Walter Kuhlmann, and Donald M. Waller, Wild Forests: Conservation Biology and Public Policy, Chicago: Island Press, 1994.
5 Pollan, Michael, Second Nature, New York: Grove Press 2003.
6 Private communbication wih the author.