The Columbia Guide to American Environmental History

The development of ecology as a science is an important theme in environmental history because the scientific analyses of human surroundings provide a basis for resource management and land-use development. Environmental historians have delineated a number of different approaches to the evolution of scientific ecology in twentieth-century America. They include human ecology, organismic ecology, economic ecology, and chaotic ecology. This chapter looks at the historical development of and implications for managing the human environment inherent in each of the four approaches.

Ecology derives from the Greek word oikos, meaning “household,” and is the study of the relationships among organisms and their surroundings. The science was named by German biologist Ernst Haeckel (1834–1919), who introduced the term in several works in the 1860s and 1870s, first in German and then in English, inspiring others to develop the science. In his Generelle Morphologie (General Morphology, 1866), Haeckel included a section entitled “Oecologie und Chorologie,” in which he defined ecology as the study of the organic and inorganic conditions on which life depends. “By ecology, we mean the whole science of the relations of the organism to the environment including, in the broad sense, all the ‘conditions of existence.’ These are partly organic, partly inorganic in nature; both, as we have shown, are of the greatest significance for the form of organisms, for they force them to become adapted.”¹

Haeckel further designated the inorganic conditions as the physical and chemical properties of the habitat, including climate, nutrients, and the nature of water and soil. The organic conditions included “the entire relations of the organism to all other organisms with which it comes into contact, and of which most contribute either to its advantage or its harm.” He noted that each organism had friends and enemies that favored or harmed its existence, but that science had so far mainly investigated the organism’s functions for preserving itself through nutrition and reproduction. Instead, a more comprehensive approach was needed. Haeckel employed the influential idea of nature as a household, stating that biologists had neglected “the relations of the organism to the environment, the place each organism takes in the household of nature, in the economy of all nature.…” Darwin’s theories of descent and natural selection, he argued, filled these gaps by showing “all the complicated relations in which each organism occurs in relation to the environment.”² In this, his first use of the term, Haeckel placed the new concept squarely within the framework of evolution introduced just a few years earlier by Charles Darwin in The Origin of Species by Means of Natural Selection (1859).

Haeckel presciently connected two words, both deriving from oikos—“ecology,” or the study of the household, and, “economy,” or the management of the household. Haeckel’s idea of ecology as the study of the household, or home, would inspire those who later developed the field of human ecology, chemist Ellen Swallow Richards (1842–1911) and ecologist Eugene Odum (1913–). His idea of ecology as investigating the economy of nature would inspire those who later developed an economic approach to ecology, such as Charles Elton (1900–91), Arthur Tansley (1871–1955), and Raymond Lindeman (1915–42).

In 1869, Haeckel elaborated on his definition of ecology in his inaugural lecture to the philosophical faculty of the University of Jena, Germany. Here he drew specifically on Darwin’s theory of the struggle for existence and again included the idea of nature’s economy in his definition. “By ecology we mean the body of knowledge concerning the economy of nature—the investigation of the total relations of the animal both to its inorganic and to its organic environment; … in a word, ecology is the study of all those complex interrelations referred to by Darwin as the conditions of the struggle for existence.”³ This definition is significant, because in English translation it was included in the introductory epigraph (dated 1870) of the Chicago school of ecology’s classic 1949 treatise, Principles of Animal Ecology, thereby validating Haeckel’s preeminence as founder of the science. The authors were zoologists Warder C. Allee, Alfred E. Emerson, Orlando Park, Thomas Park, and Karl P. Schmidt.

The term “ecology” found its way into English in the translation of Haeckel’s two-volume work, The History of Creation (1873), a popular rendition of his 1866 General Morphology. In the preface “oecology” is listed in a series of sciences that explicate Darwin’s theory of natural selection, but in volume two, he elaborated on it further as one of several “facts” proving Darwin’s Theory of Descent: “The oecology of organisms, the knowledge of the sum of the relations of organisms to the surrounding outer world, to organic and inorganic conditions of existence; the so-called ‘economy of nature,’ the correlations between all organisms living together in one and the same locality, their adaptation to their surroundings, their modification in the struggle for existence.…” Here Haeckel argued in opposition to the “unscientific” explanation based on “the wise arrangements of a creator acting for a definite purpose,” that phenomena could be explained as “the necessary results of mechanical causes.”⁴ The creationist versus evolutionary explanation of the origins of the natural world generated ongoing conflict in later years, sparking a debate over human origins that continues to the present.

In the English translation of The Evolution of Man (1879), drawn from a set of lectures he gave at the University of Jena, Haeckel provided a more detailed discussion of ecology. Here again, he drew on the root of the term oikos as a household and argued that Darwin’s “Theory of Descent” would explain “all the remarkable phenomena which, in the ‘Household of Nature,’ we observe in the economy of the organisms.” He elaborated further on the role of adaptation in the new science of ecology, stating, “all the various relations of animals and plants, to one another and to the outer world, with which the Oekology of organisms has to do … admit of simple and natural explanation only by the Doctrine of Adaptation and Heredity.” Finally, he reiterated his own historically significant assessment that the older theory of creation by a benevolent deity was far weaker in explanatory power than was Darwin’s new scientifically derived theory of evolution. “While it was formerly usual to marvel at the beneficent plans of an omniscient and benevolent Creator, exhibited especially in these phenomena, we now find in them excellent support for the Theory of Descent; without which they are, in fact, incomprehensible.”⁵ In these books and articles, Haeckel defined and elaborated the concept of ecology, but did not explicate the science itself. A handful of followers, who read Haeckel’s work in its original German and later in English, began to use ecology as an explanation for the role played by the environment in maintaining biotic, including human, life and the ways humans could use the science to manage the economy of nature.

The first approach to ecology that developed in the United States was that of human ecology, put forward by chemist Ellen Swallow Richards in the 1890s. The second was the organismic approach developed by Frederic Clements (1874–1945) in 1916 and elaborated by scientists who worked on the Great Plains in the 1930s and 1940s. The third was the economic approach, emerging out of the nineteenth-century science of thermodynamics as elaborated by British ecologists Charles Elton and Arthur Tansley and many American ecologists during the 1940s through the 1960s. The fourth, or chaotic, approach rose out of work in population ecology as influenced by chaos theory in mathematics during the 1970s to 1990s, and was explicated by scientists such as Robert M. May, S.T.A. Pickett, and P.S. White. There are major differences in the assumptions that each of these approaches makes about nature itself, its management, and the human ethical relationship to it. In Swallow’s human ecology, people are part of nature and work within it. In the organismic approach, humans are separate from nature and should follow nature as a teacher. In the economic approach, humans are managers of nature and assume control over it, while the chaotic approach implies that humans need to relinquish the hubris implicit in attempts to control the natural world, accept the disorderly order of nature, and work within nature’s limits.

Chemist Ellen Swallow Richards (1842–1911) developed the concept of human ecology and applied it to the human home and its surroundings. In his 1973 book Ellen Swallow: The Woman Who Founded Ecology, Robert Clarke attributed the introduction of ecology in the United States to Swallow. “As early as the late 1860s, [Haeckel] is credited with suggesting a science be developed to study organisms in their environment.…Then leaving “Oekologie” for others to develop, he concentrated on other sciences.… Fluent in German, Swallow traced the German word Oekologie to its origin—the Greek word for house.”⁶ Following Clarke’s lead, ecologist Robert P. McIntosh, in The Background of Ecology (1985), wrote: “Ellen Swallow (Mrs. Richards) recognized many problems of the environment in an era when industrialization and modern technology were just developing some of the bases of air and water pollution and rural and urban decay which are the bane of modern environmentalists. She was a crusader for establishing a scientific basis for bettering human life.”⁷ In 1892, at a meeting of the Boston Boot and Shoe Club, she introduced the term to the United States as “oekology,” or the science of right living, “perhaps,” notes McIntosh, “the first appearance in the public press of Haeckel’s word.”⁸

For Swallow, ecology had its roots in the biology and chemistry of life. Chemistry, which had been her focus as a special student at the Massachusetts Institute of Technology, was the science of the environment. The human home, or community, was one point in a larger environmental framework. Water flowed into and out of that home, air surrounded it, and fertile soils within it produced nutritious food.

In 1907, Swallow used the term “human ecology” in her book Sanitation in Daily Life. She stated: “Human ecology is the study of the surroundings of human beings in the effects they produce on the lives of men.”⁹ The features of the environment came both from climate, which was natural, and from human activity, which was artificial and superimposed on the environment. The sanitation movement of the post–Civil War era had raised public consciousness of problems caused by humans living in the cities—for example, garbage, noise, smoke, and water pollution. Swallow brought all this under the rubric of what she called municipal housekeeping. She argued that fresh air and clean water free of pollutants from factories were as necessary to human health as was good nutrition. Swallow’s approach was quite different from that of scientific ecology, which was developing about the same time. She viewed humans as part of nature, while scientific ecology, as it later developed, separated humans from nature in order to study the environment prior to human influence.

The history of scientific ecology and its various schools of thought in the United States have been described by environmental historian Donald Worster in his foundational work, Nature’s Economy (1978). Frederic Clements (1874–1945), a major founder of ecology, developed an organismic approach to the field. “Two interrelated themes dominated Clements’ writing,” states Worster, “the dynamics of ecological succession in the plant community and the organismic character of the plant formation.”¹⁰ Clements was influenced by the work of U.S. ornithologist C. Hart Merriam (1855–1942) and Danish botanist Eugenius Warming (1841–1924), both of whom looked at relationships among plants, animals, and their populations. Warming had written a treatise on the foundations of ecological plant geography in 1895 entitled Plantesamfund: Grundträk af den okologiske Plantegeografafi, and Clements followed in the footsteps of the evolving science of ecology by publishing “Research Methods in Ecology” in 1905 and “Plant Physiology and Ecology,” in 1907. Working on the Great Plains at the University of Nebraska, Clements approached the evolution of plant relationships in terms of plant communities. He investigated how those communities changed over time and were dependent on climatic factors, such as temperature, rainfall, and wind. If dry climate with little rainfall prevailed, deserts developed, whereas moderate rainfall produced grasslands, and heavier rainfall resulted in forests. The type of plant community in a particular locale developed through stages, initiated by soil formation. Soils determined which plants could thrive in a particular type of climate. Over time a stable equilibrium evolved through succession, a process he characterized in his 1916 book Plant Succession.

For Clements, the plant community developed like a living organism. As he stated in Plant Succession (1916): “The unit of vegetation, the climax formation, is an organic entity. As an organism, the formation arises, grows, matures, and dies.… The climax formation is the adult organism, the fully developed community.…”¹¹ The vegetative community found on the Great Plains was the mature grassland, developing from an early youthful period into a mature adult period and then finally dying back as the individual organisms died. In Bioecology (1939), Clements integrated animals into the plant community, using a concept he called the biome. Plants determined which animals could be supported in a given place and mediated between the habitat and animal populations. They provided a buffer against the extremes of climate and supplied food for animals that established themselves there.

Clements believed that there were several types of climax communities, but they evolved in two ways, both starting from bare areas denuded of vegetation. He differentiated between primary and secondary areas: “Primary areas, such as lakes, rocks, lava-flows, dunes, etc., contain no germules at the outset, or no viable ones other than those of pioneers. Secondary areas, on the contrary, such as burns, fallow fields, drained areas, etc., contain a large number of germules, often representing several successive stages.”¹² Primary succession was the process by which vegetation began to cover an area that had never before borne vegetation, proceeding from an initial stage to an intermediate stage and then to a mature climax formation. A pond or a lake would be invaded by the marshy lands around it as plants began to cover the waters. Then it would become muck, supporting herbaceous species that began to come in from the edges. Eventually an entire forest would cover the land, obscuring the water. Succession was thus the development of the life history of the climax formation. Terms such as “pioneers,” “invaders,” “migration,” “communities,” and “societies” recalled stages in the developmental history of the United States, from pioneering through farming and finally urbanization. Clements identified several types of mature climax formations in North America: the deciduous forest climax, the prairie-plains climax, the Cordilleran (or mountain range) climaxes of the Rocky Mountains, and the desert climaxes of the Southwest.

Secondary succession resulted from either natural disturbances, such as hurricanes, tornadoes, fires, or floods, or from human activities, such as clearing land or draining swamps. In each case there was a reinvasion of vegetation through successional stages on the disturbed or abandoned land. For example, in the first stage of forest succession, weedy species, such as crabgrass, began to cover an abandoned field. In the second stage, after two or three years, grasses and herbaceous plants began to come in. After several more years, trees, such as the pines of the eastern forests, seeded themselves among the grasses, and in ten to thirty years, the pine forest matured. Finally, in about seventy years, hardwoods, which seeded themselves beneath the pine trees, produced the eastern climax forest.

In the context of the dry, windy conditions of the 1930s, known as the Dust Bowl, Clements brought humans into the equation. The grasslands of the Great Plains represented the climax community, or the vegetative organism. Humans were outsiders to that biome—disrupters of the naturally evolved grasslands. The eastern forests had been settled by Europeans, whose axes gave them victory over nature, but in the grasslands, nature began to get the upper hand, defeating human efforts to subdue the land. Clements wrote two papers, one on “Plant Succession and Human Problems” (1935) and the other on “Environment and Life in the Great Plains” (1937), in which he identified harvests of monocultures, such as wheat and corn, as the transformers of the natural grasslands of the Plains that produced the Dust Bowl.

The Dust Bowl of the 1930s influenced the organismic approach to ecology. In his book Deserts on the March (1935), ecologist Paul Sears (1891–1990) stated that the Great Plains were turning into a desert much like the Sahara. The pioneers had not appreciated or understood the grassland biome native to the Plains. A land-use policy modeled on the climax theories of ecology was needed. A resident ecologist on the Plains could promote ecological education for the benefit of the people and could advise farmers on how to conserve the soil.

Scientists working at the Universities of Kansas and Nebraska in entomology and soil science further developed the organismic approach during the Dust Bowl years. Entomologist Roger Smith of Kansas State University considered the ways in which insect pests began to increase and take over during periods of drought, again helping to upset the balance of nature. John Weaver and Evan Flory, ecologists at the University of Nebraska, proposed that the country should create a grassland conservation program based on Clements’ concept of the climax ideal. Clements himself began to look at regional management plans from an ecological point of view. He proposed saving relict prairies adjacent to areas where species had disappeared. Relicts remained in cemeteries, along railroad tracks, and along fencerows, where one could identify native species and then perhaps replant and restore them. Ecological historian Ronald Tobey writes: “Clements envisioned … that a plan to save the plains would require the federally regulated use of the midcontinental grasslands on scientific principles and the resettlement of the region’s rural population.… The ecologist was to be a social planner and manager, deriving his authority from the highest level of government.”¹³

Another branch of the organismic school of ecology developed at the University of Chicago after World War I through the collaboration of a group of animal ecologists: Warder C. Allee, Alfred E. Emerson, Orlando Park, Thomas Park, and Karl P. Schmidt. The group rejected Social Darwinist assumptions of a nature characterized by Thomas Henry Huxley as “red in tooth and claw,” for a nature of cooperation among individuals in animal and human communities. According to historian of science Gregg Mitman, this school of ecologists developed “a focus on the organism-environment relationship as an interactive process, in which the organism, through its behavior and activity, continually restructured its environment to meet new demands.… It was a developmental picture that was goal directed and progressive, lending credence to one of ecology’s earliest cherished principles—succession.”¹⁴ The group published a foundational volume in 1949 entitled Principles of Animal Ecology, in which they elaborated their theories of community organization, succession, and development. For Allee and Emerson, the ecologist functioned as a social healer, applying knowledge gained from the study of the natural world to repair the human social organism damaged by depression and war, aggression and competition. They believed, states Mitman, that “the task of the biologist was to discover nature’s moral prescriptions and thereby serve as savior of society.”¹⁵

While Allee and Emerson sought to use ecology to heal human society, ecologist Aldo Leopold (1887–1948) wanted to use society to heal the land. Leopold’s work became the basis for restoration ecology and for a new kind of ethical relationship between the human being and nature, one that derived from Clements’ organismic approach. By following nature as teacher, people could restore the land as doctors healed their patients. Leopold’s famous manifesto, “The Land Ethic,” written about 1948, was published posthumously in A Sand County Almanac (1949). Here, Leopold differentiated between two forms of ethics that he called the A-B cleavage, that is, the land used for human benefit, a homocentric view, versus the land as a biotic pyramid, an ecologically centered view. In the A portion of the A-B cleavage, forestry, wildlife, and agriculture were managed for human benefit; in the B portion, they were seen as parts of a larger ecological system. In Game Management (1933), Leopold had viewed game—such as deer or elk—as crops, just as trees or foods were crops. But by 1948, he was differentiating between the land as a managed system and the land seen as a natural process that reproduced and maintained itself. The organismic approach thus saw people as separate from nature, but capable of both disrupting its successional systems and having the scientific and ethical tools to follow nature and heal it.

Donald Worster contrasts the organismic approach to ecology with the competing economic approach, or “new ecology,” in which organisms are characterized as producers and consumers and nature maximizes efficiencies and yields, ultimately to the benefit of man, the consumer at the apex of the food chain. “The New Ecology,” Worster notes, was “an energy-economic model of the environment that began to emerge in the 1920s and was virtually complete by 1950.”¹⁶ The economic approach grew out of critiques of Clements’ organismic theories. Among the early critics of Clements was botanist Henry Gleason (1882–1975), who in 1926 published a paper entitled “The Individualistic Concept of the Plant Association.” Gleason argued that the type of vegetation that occurred in a particular place was more accidental than Clements’ theory allowed. “The vegetation of an area is merely the resultant of two factors, the fluctuating and fortuitous immigration of plants and an equally fluctuating and variable environment.” Plants migrated from one place to another as seeds, carried by winds, storms, and other disturbances. Some of those seeds took root and thrived. The environment itself was likewise more variable than Clements had held. Gleason believed that if two areas had the same vegetation, it was by chance alone. “Every species of plant is a law unto itself,” he wrote. “The species disappears from areas where the environment is no longer endurable.”¹⁷ Migration and environmental selection operated independently in each area, no matter how small. Clements’ climax community was not the result of a determinative law, but was a mere association or mosaic of plants. Succession was haphazard, not a harmoniously ordered developmental process.

Another critic of Clements, British ecologist Arthur Tansley (1871–1955), developed ideas that led directly to the economic approach to ecology. In a 1935 paper entitled, “The Use and Abuse of Vegetational Concepts and Terms,” he introduced the term “ecosystem” to the field. He challenged the use of anthropomorphic concepts from human development that Clements had imposed on nature when in the process of plant succession, nature developed as did a living organism. Tansley, schooled in the laws of thermodynamics developed in nineteenth-century studies of heat transfer in steam engines, began to apply those concepts to nature. Rather than considering a plant community as greater than the sum of its parts, as in organismic theory, Tansley held that the whole was simply the sum of its parts, as in Euclidean geometry. The ecosystem was made up of individual components that were physical entities, like the parts of a machine. The components were quantifiable and the method reductionist and analytic. Tansley applied terms from thermodynamics, such as “energy,” “systems,” and “fields.” He described the structure of the ecosystem in terms of abiotic factors—such as oxygen, nitrogen, carbon dioxide, calcium, and phosphorous—and biotic factors—such as plants, animals, and bacteria. With the ecosystem concept, ecology moved toward an economic or managerial approach, in which humans considered themselves above nature and able to control it. The goal was to manage nature, using utilitarian values to enhance human life. If nature was managed in a beneficial way, the productivity and yields of forests, soils, and crops could be increased.

The economic approach to ecology drew on such concepts as producers, consumers, efficiencies, and yields. As early as 1926, August Thieneman had begun to designate producers, consumers, and reducers. Producers are organisms, such as trees and grasses that collect energy from the sun by photosynthesis and create complex organic compounds from simple chemicals. Consumers, such as animals, use these chemicals for growth and for metabolism. In a terrestrial ecosystem, the primary consumers are herbivores, such as rabbits or deer, which eat the grasses. Then secondary consumers—predators, such as mountain lions or wolves—eat the herbivores. At the top of the scale are tertiary consumers, such as humans. Completing the cycle are reducers or decomposers—micro-organisms that break down animal dung and detritus, such as falling leaves and dying grasses—into simple chemicals to be taken up by the roots of trees. A pond ecosystem is similar to the terrestrial ecosystem. Here, the producers are aquatic plants, such as marsh grasses growing along the edge of the pond. Phytoplankton are plantlike producers in the water, while the primary consumers are zooplankton, or animal-like plankton. A fish is a secondary consumer and a turtle a tertiary consumer. In the pond’s sediment are Thieneman’s reducers, or what are now called decomposers.

The economic approach to ecology uses other terms derived from agriculture, such as annual yields. The total organic structure formed per year at any one of the levels of producers—or primary, secondary, and tertiary consumers—can be calculated, along with the efficiency of energy transfer from one level to another.

In 1942, Raymond Lindeman (1915–42) introduced into ecology the idea of the food chain, or trophic levels, in a paper called “The Trophic-Dynamic Aspect of Ecology.” Trophic means nutrition, and the food chain represents the process of food metabolism at each trophic level. Metabolism produces energy, so that when one organism is eaten by one at the next level, its energy is transformed into food, and in turn into that organism’s own energy. Each organism thus converts energy from the trophic level below it for its own survival. From measurements of the energy expended at each level can be calculated the efficiency of energy transfer and hence the productivity of each level.

English ecologist Charles Elton (1900–91) of Cambridge University integrated animal populations into the system of trophic levels. He counted the numbers of various species in the ecosystem and studied the ways the numbers of those species changed, developing the concept of the pyramid of numbers. As he formulated it, the combined weight of predators must be less than that of all the food animals, and these in turn must be less than plant production. The Eltonian pyramid can be illustrated by the number of individuals at each trophic level. If at the bottom of the pyramid, there are a million producers, or phytoplankton, then at the next higher level, the number of primary consumers, or zooplankton, would be much smaller, for example 10,000. Secondary consumers, such as fish in the aquatic ecosystem, would then be 100, and the apex organism at the top, such as a human being who consumes the fish, would only be one. Thus one person might be supported by a million phytoplankton. If people are vegetarians, more people can eat at a lower level of the Eltonian pyramid, and therefore the plant community can support a larger human population than if they are consumers who eat beef.

According to Elton, at each level there is an inefficiency in energy transfer owing to the second law of thermodynamics. The energy available for work declines at each level of the energy-producing process. As in the case of the steam engine, one hundred percent efficiency of energy output is never possible. No steam engine can transform all its fuel into energy available to do work because it loses energy to the environment in the form of heat. That heat, or the energy unavailable to do work, is entropy, a quantity that is always increasing in the environment. At each step in the Eltonian pyramid, heat is lost, and therefore the calories, or usable energy available for the next level, keep declining. For example, 10,000 calories at the level of producers might decline to 1,000 at the level of primary consumers, to 100 calories at the level of secondary consumers, 10 calories for tertiary consumers, and one calorie for the apex organism, such as the human being.

The economic approach to ecology was epitomized in 1968 by ecologist Kenneth Watt (1929–) of the University of California at Davis, who stated that the goal of ecology was to “optimize the harvest of useful tissue.”¹⁸ In Watt’s Ecology and Resource Management: A Quantitative Approach (1968), the human being is seen as an economic animal, and economic ecology’s goal is to maximize the productivity of each type of ecosystem and each level of that ecosystem for human benefit.

During the 1960s, ecologist Eugene Odum (1913–) at the University of Georgia argued that maximizing the productivity of ecosystems, as advocated by the economic approach, led to their degradation. Odum’s concept of the balanced, homeostatic ecosystem integrated Clements’ ideas about the evolution of the biotic community through successional stages, with thermodynamic approaches that employed food chains and energy transfers. In nature, there was a homeostatic balance within a mature ecosystem. The primary disturbance came from human beings. If humans disrupted the system by cutting forests or plowing prairies, a degraded ecosystem resulted. Expanding human populations, increasing demands for food, and growing industrial wastes were upsetting the balance of nature by polluting lakes, rivers, and wetlands, and depleting natural resources. But Odum argued that if humans cared about nature and were conservers of its processes, we could restore those degraded systems. Following a line of thinking similar to that of Ellen Swallow, Odum focused on the idea of the oikos as the human home and, like Aldo Leopold, argued that we need to be wise managers of the landscapes in which we live. We need to conserve our resources and use our capabilities as human managers to restore the lost balance of nature. Odum’s synthesis of ideas from the organismic and economic approaches to ecology became the guideline for the environmental movement that emerged in the 1960s. Humanity might disrupt evolved ecosystems, but through scientific ecology and ethical principles, it could repair the damaged web of nature on which life depended for its continued existence.

The idea of the balance of nature was challenged by a fourth approach to ecology, which began to take shape in the 1970s and 1980s with the development of chaos theory. The new science, according to Worster, represented “a radical shifting away from the thinking of Eugene Odum’s generation, away from its assumptions of order and predictability, a shifting toward what we might call a new ecology of chaos.”¹⁹ Natural, rather than human disturbances, were viewed as playing a greater role in transforming nature than had previously been assumed by the balance of nature approach. Massachusetts biologists William Drury and Ian Nisbet, in a 1973 paper, “Succession,” revived Henry Gleason’s 1926 “individualistic” approach, arguing that succession leads neither to stability nor equilibrium. The following year, mathematical ecologist Robert May published “Biological Populations with Nonoverlapping Generations: Stable Points, Stable Cycles, and Chaos,” demonstrating that older mathematical models in ecology could not predict aperiodic ecological events such as pest outbreaks.

Other ecologists who challenged both Clements’ organismic approach and Odum’s balance of nature included ecologists S.T.A. Pickett and P.S. White, whose work on The Ecology of Natural Disturbance and Patch Dynamics (1985) argued that ecosystems should be described in terms of patch dynamics. “Patch dynamics includes not only such coarse-scale, infrequent events as hurricanes, but also such fine-scale events as the shifting mosaic of badger mounds in a prairie.” Ecosystems should be considered dynamic, fine-textured patches, rather than homogeneous stable systems. “Preservation of natural systems necessarily involves a paradox,” they noted, “we seek to preserve systems that change. Success in a conservation effort thus requires an understanding of landscape patch structure and dynamics.”²⁰

During the 1980s and 1990s, the idea that nature itself was a major disturber of ecosystems became more widely incorporated into ecology through the work of population biologists. Chaos theory lent credence to the idea that natural disturbances, such as hurricanes, tornadoes, and earthquakes, could within a few minutes completely destroy an ecosystem that might have taken centuries to evolve. Unpredictable, chaotic disturbances began to play a much more important role in ecosystem studies.

Influenced by the new work in chaos theory, Eugene Odum, his brother Howard T. Odum, and his son William Odum wrote a paper entitled, “Nature’s Pulsing Paradigm” (1995), in which they modified some of their earlier ideas about nature as a balanced ecosystem. A more realistic way to think about nature, they stated, is in terms of pulsing steady-state systems. A pulsing system is a repeating oscillation that is poised on the edge of chaos. Examples of pulsing ecosystems are tidal marshes and seasonally flooded wetlands. Ecosystem performance and species survival are enhanced when external and internal pulses are coupled together. They suggested that pulsing was a key to sustainability in ecosystems. In a similar vein, recent work in complexity theory characterizes a complex system as one that exists on the edge between order and chaos. Many ecosystems and human communities are examples of changing, perhaps pulsing, complex systems. Whereas an ethic based on the balance of nature grants humans the capacity and power to restore degraded systems, chaos and complexity theory challenge humanity to recognize nature as both predictable and unpredictable, orderly and disorderly. Both humans and nonhumans disrupt nature, and both can work in partnership to restore it.

The history of ecology can be seen as moving through several historical phases, each with differing assumptions about nature and the human ethical relationship toward it. Human ecology incorporates humans into nature and adapts to nature’s limits; organismic ecology views humans as separate from nature, but as followers of its balanced, homeostatic processes; economic ecology asserts humans as scientific managers of a nature that can be controlled for human benefit; finally, chaotic ecology sees nature as having unpredictable characteristics, leaving humans as only partially able to manage its systems. Nature is thus far more complex than previously considered, and is best described as a disorderly order, rather than a harmonious balance.